Energy Retrofit Field Study 

and Best Practices in a 

Hot-Humid Climate 

J. McIlvaine, K. Sutherland, and E. Martin

Building America Partnership for Improved 

Residential Construction 

March 2013
NOTICE

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iii

Energy Retrofit Field Study and Best Practices

in a Hot-Humid Climate

Prepared for:

The National Renewable Energy Laboratory 

On behalf of the U.S. Department of Energy’s Building America Program

Office of Energy Efficiency and Renewable Energy

15013 Denver West Parkway

Golden, CO 80401

NREL Contract No. DE-AC36-08GO28308

Prepared by: 

J. McIlvaine, K. Sutherland, and E. Martin

BA-PIRC/Florida Solar Energy Center

1679 Clearlake Road 

Cocoa, FL 32922

NREL Technical Monitor: Stacey Rothgeb

Prepared under Subcontract No. KNDJ-0-40339-00

March 2013
iv

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v

Contents

Acknowledgements ................................................................................................................................... xi

List of Figures ............................................................................................................................................ vi

List of Tables ............................................................................................................................................. vii

Definitions................................................................................................................................................. viii

Executive Summary................................................................................................................................... ix

1 Introduction........................................................................................................................................... 1

1.1 Background..........................................................................................................................3

1.2 Stakeholder Need.................................................................................................................4

1.3 Analysis Tools and Methods................................................................................................4

2 Dataset Characterization and Retrofit Trends................................................................................... 6

2.1 Dataset Overview.................................................................................................................6

2.2 Thermal Envelope Components...........................................................................................7

2.2.1 Exterior Wall Construction and Insulation ..............................................................7

2.2.2 Exterior Wall Solar Absorptance .............................................................................8

2.2.3 Windows..................................................................................................................9

2.2.4 Roof........................................................................................................................12

2.2.5 Ceiling Insulation...................................................................................................14

2.3 Building Infiltration ...........................................................................................................16

2.4 Mechanical Space Conditioning Systems..........................................................................19

2.4.1 Mechanical Equipment Efficiency, Pre-Retrofit....................................................20

2.4.2 Mechanical Equipment Size ..................................................................................24

2.4.3 Air Handler Unit Location and Configuration.......................................................24

2.4.4 Duct Heat Transfer.................................................................................................28

2.4.5 Duct Airtightness...................................................................................................29

2.4.6 Outside Air Ventilation..........................................................................................31

2.4.7 Thermostats............................................................................................................32

2.5 Domestic Hot Water ..........................................................................................................32

2.6 Appliances..........................................................................................................................33

2.7 Lighting and Ceiling Fans..................................................................................................34

2.8 Conditioned Area Reductions............................................................................................34

3 Whole-House Improvement and Cost Effectiveness ...................................................................... 36

3.1 HERS Index Improvement.................................................................................................36

3.2 Composition of Deep Energy Retrofit Improvement Packages.........................................38

3.3 Cost Effectiveness of Energy Retrofit Improvement Packages.........................................41

4 Gaps and Challenges ......................................................................................................................... 45

5 Best Practices..................................................................................................................................... 46

6 Conclusions ........................................................................................................................................ 51

References................................................................................................................................................. 52

Appendix A: 30% Energy Efficiency Solution Package ........................................................................ 54

Appendix B: Deep Energy Retrofit Packages ........................................................................................ 58

Appendix C: Draft Current Best Practices.............................................................................................. 65

Appendix D: Sarasota NSP Energy Conservation Standards .............................................................. 70
vi

List of Figures

Figure 1. Mean HERS Index at pre-and post-retrofit by decade vintage ............................................... x

Figure 2. U.S. Census Bureau historical housing starts by decade...................................................... 1

Figure 3. U.S. Census Bureau regions...................................................................................................... 1

Figure 4. Building America climate zone map ......................................................................................... 2

Figure 5. Study homes of typical character with ranch style floor plans, slab-on-grade 

foundations, concrete block exterior walls, low sloped roofs, and 8-ft ceiling heights ............... 3

Figure 6. Vintage of the 70 home dataset spanned 49 years.................................................................. 6

Figure 7. Conditioned floor area for the pre-retrofit dataset .................................................................. 7

Figure 8. Typical wall construction of light color paint on stucco finish over concrete block .......... 8

Figure 9. Typical awning-style window type ............................................................................................ 9

Figure 10. Pre-retrofit awning window in its most closed position is still slightly open as indicated 

by the pitch of the red line................................................................................................................. 12

Figure 11. Roof pitch plotted by vintage displays trend of older homes with shallower pitch 

n = 70.................................................................................................................................................... 12

Figure 12. Typical shallow roof pitch of Florida homes built before 1980.......................................... 13

Figure 13. Typical pre-retrofit ceiling insulation condition .................................................................. 14

Figure 14. Post-retrofit ducts buried by blown-in fiberglass................................................................ 15

Figure 15. Scatter plot for whole-house airtightness test results (ACH50) by vintage for homes 

tested pre-retrofit and post-retrofit (n = 59)..................................................................................... 17

Figure 16. Pre-retrofit drywall penetrations: Ceiling fixture has been removed, but penetration to 

attic was unsealed (left); plumbing access in wall covered with a return grille rather than a 

solid cover or patch (center); large opening beneath bathroom vanity where block and drywall 

were removed as part of an incomplete renovation (right)............................................................ 17

Figure 17. Gaps or holes at ceiling of air handler closet...................................................................... 19

Figure 18. Post-retrofit: Unsealed range hood penetration through top of cabinet into the attic.... 19

Figure 19. Looking up at pre-retrofit clogged, dirty cooling coils in air handler unit (AHU) (left); 

corroded and clogged cooling coil (right) ....................................................................................... 20

Figure 20. Pre-retrofit AC efficiency (SEER) by house vintage (n = 70).............................................. 21

Figure 21. Pre-retrofit heat pump heating efficiencies by house vintage (n = 70) ............................. 21

Figure 22. Mechanical system cooling efficiency at pre- and post-retrofit audit............................... 23

Figure 23. Pre-retrofit, the majority of homes had air handlers located in the conditioned space 

with greater prevalence in homes built before the 1990s (n = 70) ................................................ 25

Figure 24. Upflow air handler in conditioned space in a dedicated closet (left). Interior air handler 

closets with returns formed by platforms had wall mounted return grilles (right). .................... 26

Figure 25. Return plenums were formed by either unfinished, open framing (left) or sealed duct 

board (right) or drywall. ..................................................................................................................... 26

Figure 26. Interior closets that served as return plenums had louvered doors or door mounted 

return grilles........................................................................................................................................ 27

Figure 27. Upflow air handlers on framed platforms in garage with a wall mounted filter-back grille 

ducted directly into the platform cavity. .......................................................................................... 27

Figure 28. Horizontal flow air handlers mounted at ceiling of garage (left) and in the attic (right).. 27

Figure 29. Exterior package units with return air path through a wall mounted filter-back grille. The 

metal shroud houses return and supply ducts (left) and wall-hung package unit with atticmounted ducts (right). ....................................................................................................................... 28

Figure 30. Return air plenum lined with duct board without sealant at edges and seams (left). 

Narrow air handler closet functioning as return with uncontrolled air flow (center). Attempt to 

make a sealed return plenum around a metal air handler stand (right), with noticeable 

unsealed gap at bottom edge of duct board.................................................................................... 30

Figure 31. Crowded air handler closet with little room to access and seal duct connections to 

cabinet ................................................................................................................................................. 31

Figure 32. Typical pre-retrofit appliance condition for range (left) and refrigerator (right) .............. 33

Figure 33. Pre-retrofit exterior wall of porch converted into conditioned space ............................... 34
vii

Figure 34. Pre-retrofit HERS Indices (blue) in descending order paired with post-retrofit HERS 

Indices (green) .................................................................................................................................... 36

Figure 35. HERS Index improvement goal (30%, yellow line) was met in 46 deep retrofits.............. 37

Figure 36. Mean HERS Index at pre-and post-retrofit by decade vintage ........................................... 37

Figure 37. HERS Index improvement compared to the pre-retrofit HERS Index for the whole 70 

house dataset...................................................................................................................................... 38

Figure 38. Incremental costs by percent HERS Index improvement for 42 deep retrofits with cost 

data ...................................................................................................................................................... 43

Figure 39. Incremental annual cash flow by percent HERS Index improvement for 42 deep retrofits 

with cost data...................................................................................................................................... 44

Figure 40. BEopt screen shot of base house......................................................................................... 54

Unless otherwise noted, all figures were created by BA-PIRC.

List of Tables

Table 1. Building America Multiyear Energy Savings Goals for Existing Homes (2010) .................... 2

Table 2. Final Disposition of All 70 Study Houses, by Partner............................................................... 6

Table 3. Pre-Retrofit Exterior Wall Construction for 70-Home Dataset................................................. 8

Table 4. Exterior Wall Color Pre- Versus Post-Retrofit ........................................................................... 9

Table 5. SHGC of Replacement Windows............................................................................................... 10

Table 6. U-Values of Replacement Windows.......................................................................................... 11

Table 7. Roof Shingle Color..................................................................................................................... 13

Table 8. Ceiling Insulation R-Values ....................................................................................................... 14

Table 9. Pre- and Post-Retrofit Whole-House Airtightness (ACH50) and Improvement by 

Decade................................................................................................................................................. 18

Table 10. Pre-Renovation and Post-Renovation AC Efficiency............................................................ 22

Table 11. Change in Cooling Capacity Post-Retrofit............................................................................. 24

Table 12. Average Pre- and Post-Retrofit Duct Test Results (Qn,out) by Decade ............................. 30

Table 13. Pre-Retrofit Domestic Hot Water Efficiency by Fuel Type ................................................... 33

Table 14. Pre- and Post-Retrofit Conditioned Area and Removed Floor, Ceiling, and Window 

Area...................................................................................................................................................... 35

Table 15. Average HERS Index Improvement for Top Partners by Vintage........................................ 38

Table 16. Prevalence of 13 Key Efficiency Strategies Implemented.................................................... 40

Table 17. Summary of Current Best Practices (Appendix C) ............................................................... 48

Table 18. Basic House Characteristics................................................................................................... 55

Table 19. Prevalence of Key Efficiency Strategies in 70 Retrofit Field Study Homes ....................... 55

Table 20. Projected Energy Savings and Economics Calculations for 30% Improvement 

Package ............................................................................................................................................... 56

Table 21. Composition of Deep Energy Retrofit Packages................................................................... 59

Table 22. Energy Costs and Savings, Improvement Costs, and Cash Flow for Deep Retrofits (n = 

46)......................................................................................................................................................... 61

Unless otherwise noted, all tables were created by BA-PIRC.
viii

Definitions

AC Air conditioning

ACH, ach Air changes per hour

AHRI Air-Conditioning, Heating, and Refrigeration Institute

AHU Air handler unit

AFUE Annual fuel utilization efficiency

ASHRAE American Society of Heating, Refrigerating, and Air Conditioning 

Engineers

BA-PIRC Building America Partnership for Improved Residential Construction

BEopt Building Energy Optimization

CFL Compact fluorescent lamp

COP Coefficient of performance

CFM Cubic feet of air per minute

DOE U.S. Department of Energy

EF Energy factor

EGUSA Energy Gauge USA

FSEC Florida Solar Energy Center

HERS Home Energy Rating System

HSPF Heating seasonal performance factor

HUD U.S. Department of Housing and Urban Development

HVAC Heating, ventilation, and air conditioning

kWh Kilowatt per hour

NSP Neighborhood Stabilization Program

Pa Pascal

R-value Value denoting thermal resistance

RESNET Residential Energy Services Network

sd Standard deviation

SEER Seasonal energy efficiency ratio

SHGC Solar heat gain coefficient

U-value Value denoting thermal conductance
ix

Executive Summary

In the U.S. Census Bureau’s Southern region, housing starts ranged from 4.6 to 5.9 million per 

decade from the 1970s through the 2000s, nearly twice as many as any other region across all 

decades. The potential for energy savings in these homes is vast, perhaps our most available 

untapped resource for reducing energy needs. This study was conducted in central Florida, which 

forms part of the Census Bureau’s Southern region. It examines efficiency retrofit opportunities, 

typical renovation practices, and pathways for achieving U.S. Department of Energy (DOE) 

goals for existing homes in that region.

Researchers partnered with local government and nonprofit affordable housing entities 

conducting comprehensive renovations in foreclosed homes. Nearly all of the homes were 

renovated through the U.S. Department of Housing and Urban Development’s (HUD)

Neighborhood Stabilization Program (NSP). 

DOE’s Building America Partnership for Improved Residential Construction (BA-PIRC), based 

at the Florida Solar Energy Center (FSEC), led the research. Renovation activities were 

conducted in 70 foreclosed homes built from the 1950s through the 2000s.

Pre-retrofit Home Energy Rating System (HERS) Indices ranged from 95 to 184 (sd = 22), with 

an average of 129. Post-retrofit HERS Indices range from 65 to 135 (sd = 11), with an average of 

83. Projected annual energy savings ranged from $35 to $1,338. All but four homes achieved a 

HERS Index ≤ 95, which is similar to new Florida homes built in the early 2000s, a remarkable 

reversal. This may suggest that achieving a HERS Index of 95 is a reasonable goal for energy 

retrofits in homes with similar characteristics to those in the dataset, though the actual savings 

will vary depending on house-specific conditions. 

The average improvement for the 70-house dataset was a 34% decrease in HERS Index. Average 

projected annual energy cost savings were 25%. Forty-six of the 70 homes (66%) achieved a

30% reduction in HERS Index with an average projected energy cost savings of 31%. Nineteen 

fell between 15% and 29%, and only five fell below 15% improvement. A cost effectiveness 

discussion compares incremental cost for higher performance choices to projected annual energy 

cost savings for the retrofit meeting or exceeding the 30% improvement goal.

Despite widely disparate pre-retrofit HERS Indices and varying scopes of work, the mean of 

post-retrofit HERS Indices by decade ranged from 74 to 86, a range of only 12 points compared 

to a 56-point spread across the decades in pre-retrofit HERS Index (Figure 1).
x

Figure 1. Mean HERS Index at pre- and post-retrofit by decade vintage

To assess the feasibility of replicating these positive results in the general housing stock, 

researchers examined the mix of improvements associated with the 30% or greater improvement 

in HERS Index (n = 46). These “deep” retrofits had much in common and were the homes with 

the most room for improvement, as they all needed multiple energy-related replacements and 

improvements. Researchers identified 13 key efficiency measures related to equipment, 

appliance, and lighting efficiency and envelope components. These form the basis of a set of best 

practices for replacement and in-situ treatment. 

The best practices are intended to support program administrators and the general remodeling 

industry in efforts to enhance energy efficiency of the existing housing stock at the time of major 

renovation.
xi

Acknowledgments

This work was initially supported by the Florida Energy Systems Consortium (2009) and 

subsequently sponsored by DOE, Office of Energy Efficiency and Renewable Energy, Building 

America Program under cooperative agreement number DE-FC26-06NT42767 (2010) and 

Subcontract No. KNDJ-0-40339-00 (2011-12).

The support and encouragement of past DOE program managers, George James, Terry Logee, 

Ed Pollock, and William Haslebacher, as well as current DOE program managers, Stacey 

Rothgeb, Ren Anderson, Eric Werling Sam Rashkin, and David Lee, is gratefully acknowledged. 

This support does not constitute DOE endorsement of the views expressed in this paper. 

We thank Eric Martin, project director of BA-PIRC, for his direction and support. We also thank 

Rob Vieira and Philip Fairey, both of FSEC, for their advice and support in conducting many 

aspects of this work. This project would not have been possible without the leadership and vision 

of the late Subrato Chandra, project manager for the Building America Industrialized Housing 

Partnership.

Early partnership and participation of Sarasota County and the City of Sarasota were 

instrumental in launching this study, including collaboration with Nina Powers, Sustainability 

Outreach Coordinator at Sarasota County Government; Don Hadsell, Director of the Sarasota 

Office of Housing and Community Development, and Nan Summers (formerly, Director of the 

Florida House at Sarasota County Government). We are deeply grateful for their participation 

and that of other local governments who were also recipients of HUD NSP funding, and their 

partnering nonprofit housing entities, contractors, and home energy raters. Special thanks are 

also due to:

• Sarasota Office of Housing and Community Development NSP Partners, Sarasota 

County, Florida:

o Tanya Lukowiak and Sandy McKitterick of Community Housing Trust of 

Sarasota County, Inc.

o Che Barnett of Greater Newtown Community Redevelopment Corporation

o Dean Shelton of Habitat for Humanity of Sarasota, Inc.

o Laura Carter Taylor of Goodwill Industries, Manasota

• Ian Golden, Sam Detra, Roy Davis, and Tom Sullivan of Brevard County Housing and 

Human Services Department, Brevard County, Florida

• Dona DeMarsh, Paula Szabo, and Sue Redstone from Volusia County Community 

Assistance, Volusia County, Florida

• Mike Byerly, Alachua County Commission, Ken Fonorow, Florida H.E.R.O., and 

Thomas Webster and Karen Johnson of Alachua County Housing Programs, Alachua 

County, Florida

• Johnny Roberts of Habitat for Humanity of Greater Birmingham, Birmingham, Alabama

• Brenda Carson Lawless and Josh Shedeck of Habitat for Humanity of Southwest 

Alabama (formerly Mobile Habitat), Mobile, Alabama

• Mitchell Glasser, Lee Coulter, Dave Tarpley, and Barry Counts of Orange County 

Housing & Community Development, Orange County, Florida
xii

• Sue Hann, John Rodgers, and Robert Williams of the City of Palm Bay, Florida

• Judy Wilcox and Michael Stollito of Habitat for Humanity, South Sarasota County, Inc. 

and Dennis Stroer of CalcsPlus, Sarasota, Florida.

We wish to thank the certified home energy raters who, in addition to author Karen Sutherland, 

conducted the energy audits and analyses: Kevin Schleith and Patrick Gillis, both formerly of 

FSEC; David Beal of FSEC; and Tabatha Reyes of Energy Potential, Inc. 

We are grateful for the support of other FSEC staff, past and present, including Ian Lahiff, Oscar 

Toledo, David Hoak, Keith Abbott, Dave Chaser, Stephanie Thomas-Rees, and Jamie 

Cummings.

We also express great appreciation to FSEC’s Billy Bauman for programming expertise and 

Danielle Daniel and Wanda Dutton for their excellent editorial assistance.
1

1 Introduction

The U.S. Census Bureau has been collecting data on the construction industry for decades. 

Figure 2 shows single-family (1 unit) housing starts by decade (from 1960 through 2011) in total 

and in the four census regions (Figure 3). The potential for energy savings in these homes is vast, 

perhaps our most available untapped resource for reducing energy needs.

Figure 2. U.S. Census Bureau historical housing starts by decade

Figure 3. U.S. Census Bureau regions
2

Regional data collection is available beginning in 1964. Figure 2 shows that at least 1 million 

homes were built in each region in each full decade. From the 1970s through the 2000s, housing 

starts were strongest in the “South” census region and ranged from 4.6 to 5.9 million, nearly 

twice as many starts as any other region across all decades. The South census region covers 

several Building America climate zones (Best Practices Series 7.1: High Performance 

Technologies Guide to Determining Climate Regions by County 2010) (see Figure 4).

Figure 4. Building America climate zone map

(PNNL 2010)

This study was conducted in Florida, which falls in climate zone 2, commonly referred to as the 

“hot-humid” climate zone. Building America program goals for existing homes in the hot-humid 

climate are shown in Table 1 (“Summary of Prioritized Research Opportunities” 2011). 

Table 1. Building America Multiyear Energy Savings Goals for Existing Homes (2010)

(NREL and Newport Partners (2011)

Achieving these goals in any particular home is closely linked to the pre-retrofit condition of the 

home’s energy-related characteristics. Older homes that have been well maintained and upgraded 

over the years may have a higher whole-house efficiency level than newer homes in disrepair. 

There is no single solution for all existing homes, even within a given climate. However, this 

study did reveal trends among the improvement packages in houses that achieved these goals,
3

which are now proposed as a set of current best practices, meaning that they can be implemented 

by the labor force using off-the-shelf materials, components, and equipment. Not all the best 

practices will be applicable to all homes; however, the partners in this study implemented 

combinations of them in 70 homes and achieved an average projected energy cost savings of 

25%.

1.1 Background

Between the fall of 2009 and the end of 2011, BA-PIRC1 researchers at the Florida Solar Energy 

Center (FSEC) worked with affordable housing partners to identify pathways for meeting the 

goals in Table 2. Researchers participated in renovations of 70 homes in Florida, built between 

1957 and 2006 (examples shown in Figure 5). 

Figure 5. Study homes of typical character with ranch style floor plans, slab-on-grade 

foundations, concrete block exterior walls, low sloped roofs, and 8-ft ceiling heights

The nine partnering organizations consisted of local governments and nonprofit organizations.

Almost all the partners were awardees under the U.S. Department of Housing and Urban 

Development’s (HUD) Neighborhood Stabilization Program (NSP). NSP provides funds for the 

purchase and renovation of unoccupied foreclosed homes with the provision that they will be 

sold as affordable housing. Partners retained contractors to carry out the renovation work. The 70 

homes are located in central (66) and north (4) Florida in the hot-humid climate zone.

 1 BA-PIRC began this work under a previous Building America contract wherein the team name was the Building America 

Industrialized Housing Partnership.
4

Almost all the homes acquired by the partners were distressed, foreclosed homes that each 

needed comprehensive renovation. The scopes of work often included energy-related elements 

such as mechanical system and window replacements. However, the potential for additional costeffective efficiency improvements was evident early in the investigation. Nonenergy-related 

improvements such as new bathroom and kitchen fixtures, flooring, and rewiring were not 

included in the energy cost analysis. 

All improvements were implemented at once, before resale. Researchers posit that the foreclosed 

home retrofit findings are relevant to the home-owning public, who has the opportunity to 

address a package of energy-related improvements as part of a home resale or an equity-drawing 

home refinance. 

1.2 Stakeholder Need

Partners repeatedly requested a standardized approach or cost-effective improvement package 

that could be adopted program-wide. They preferred this path over conducting in-depth audits

and analyses of individual homes, because of the associated time and burdens and because 

professionals are not readily available in all communities for these activities. Before this study, 

BA-PIRC did not have such a resource. The best practices proposed in this report are meant to 

respond to this need and lay out strategies to reach the Building America 30% energy-saving 

renovation goal for the hot-humid climate.

1.3 Analysis Tools and Methods

Before each renovation, researchers conducted a pre-retrofit “test-in” energy audit, produced 

modeling analysis, and provided recommendations. Partners determined a scope of work and 

cost estimate needed to bring a home up to market standards before submitting an offer to 

purchase each home. The number of offers far exceeded the number of actual purchases; 

therefore, conducting audits and analyses before partners acquired the homes was not practical.

The test-in audit included a sketch of the home; envelope measurements; characteristics of all 

energy-related equipment, materials, and components; whole-house and duct airtightness testing; 

interzonal pressure measurements; and extensive photographs. 

The audit data were used to build a pre-retrofit simulation model. The partner’s scope of work 

was modeled parametrically to determine projected savings from each improvement. Then, 

incremental improvements to each specification and additions to the scope of work were 

modeled parametrically. Last, researchers calculated annual energy cost savings and cash flow 

for the partner’s package of improvements and the recommended package. All the modeling 

results were presented in a spreadsheet and discussed with the partner. Partners selected energy 

improvements based on what they deemed cost appropriate within the broader scope of 

renovation work and in the context of local market norms.

The Building America program has standardized methods for calculating projected energy 

savings which are delineated in the Building America House Simulation Protocols2 (Hendron 

and Engebrecht 2010) and the 2012 Addendum (Engebrecht Metzger et al. 2012). For existing 

homes, comparison of actual energy use before and after renovation would be preferable; 

however, these homes were unoccupied. In such cases, the protocol calls for comparing whole-

 2 The Building America benchmark home is used to characterize savings in new construction only.
5

house annual energy use simulations for the pre- and post-retrofit characteristics using Building 

Energy Optimization (BEopt) modeling software. At the time this study was conducted, 

however, BEopt could not model the mechanical equipment frequently present in the subject 

homes. Therefore, it could not be used for analysis and partner decision making. However, 

BEopt analysis shows that a package of the eight most common improvements produced 34% 

source energy savings in a base house that reasonably represents the dataset (with seasonal 

energy efficiency ratio [SEER] 10 air conditioning [AC]). Results are included in Appendix A. 

Because heating, ventilation, and air conditioning (HVAC) equipment efficiency improvement 

was a central element of whole-house energy savings, researchers used an alternate simulation 

program, EGUSA, with the same modeling protocols. One caveat to this substitution is that 

EGUSA does not have detailed occupancy input called for in the protocols. To maintain 

standardization across multiple analysts, the occupancy, appliance, lighting, and thermostat 

settings for the 2006 Home Energy Rating System (HERS) Reference home were used. 

In addition to annual energy savings targets, researchers targeted a 30% improvement in wholehouse energy efficiency using the HERS Index. This metric accounts for differences in fuel mix 

among the homes, normalizes the effect of conditioned house size, and uses a standardized 

reference house. It was familiar to many partners because they had already worked with the 

metric in new construction activities. These characteristics are helpful for interpreting changes 

across a set of homes. Researchers also promoted the health, durability, and comfort guidelines 

outlined in DOE’s Builders Challenge Program (Version 1) Quality Criteria (DOE 2009). 

To reiterate, the research objectives were to document typical characteristics and retrofit 

practices and to identify cost-effective best practices for reaching Building America goals. 

Typical characteristics and retrofit practices are presented in Section 2. Analysis of homes that 

achieved 30% improvement follows in Section 3.
6

2 Dataset Characterization and Retrofit Trends

2.1 Dataset Overview

The final dataset of 70 homes included homes in Alachua, Brevard, Orange, Sarasota, and 

Volusia Counties, all in Florida (Table 2). 

Table 2. Final Disposition of All 70 Study Houses, by Partner

Partner Homes in Final 

Dataset

Alachua County Housing Programs 4

City of Palm Bay Housing and Neighborhood Development Services 2

Brevard County Housing and Human Services Department 20

Orange County Housing and Community Development 2

Sarasota Office of Housing and Community Development including: 22

Community Housing Trust of Sarasota County, Inc. (12)

Greater Newtown Community Redevelopment Corporation (4)

Habitat for Humanity of Sarasota, Inc. (6)

Volusia County Community Assistance 20

Total 70

The typical configuration was a three-bedroom, two-bath, concrete block, ranch-style floor plan 

with shingle roof, and almost exclusively, a slab-on-grade foundation. The dataset is composed

of 64 single-family detached homes (91%) and six multifamily dwellings (9%). Two of the 

multifamily dwellings were single-story duplex units. Two were two-story duplex units, and two 

were condominiums. Figure 6 and Figure 7 show the year of construction and conditioned area 

for the dataset.

Figure 6. Vintage of the 70 home dataset spanned 49 years
7

Figure 7. Conditioned floor area for the pre-retrofit dataset

The oldest home was built in 1957 and the most recent in 2006 (Figure 6). The mean year of 

construction was 1982, with a standard deviation (sd) of 13.8 years. Home size ranged from 792 

to 2,408 ft2, with an average of 1,365 ft2 (Figure 7). 

Pre-retrofit HERS Indices ranged from 95 to 184. There is a general trend for newer homes to 

have lower (better) HERS Indices because of improvements in the Florida Energy Code, 

appliance standards, and installation practices. However, some older homes in the study had 

lower HERS Index scores because of previous efficiency improvements. This is reflected also in 

the estimated annual energy cost, which ranged from $1,253 to $3,101 for the 70-home dataset. 

2.2 Thermal Envelope Components

2.2.1 Exterior Wall Construction and Insulation

Painted stucco over wood frame or concrete block describes the exterior wall finish of nearly 

every study home, a style typical of the Florida housing stock (Figure 8). A few older study 

homes were painted concrete block with no stucco, and a few had vinyl siding. Forty-one homes 

(59%) were constructed entirely with concrete block walls and 22 (31%) were all frame. The 

remaining seven (10%) were a combination of block and frame (Table 3).
8

Figure 8. Typical wall construction of light color paint on stucco finish over concrete block

Table 3. Pre-Retrofit Exterior Wall Construction for 70-Home Dataset

Vintage Concrete 

Block

2 × 4 Wood 

Frame

Combination of 

Block and Frame Total

1950s 1 1 2

1960s 13 1 1 15

1970s 10 3 1 14

1980s 4 16 2 22

1990s 6 2 1 9

2000s 7 1 8

Total 41 22 7 70

Percent of Total 59% 31% 10%

Because none of the retrofits in this study was a gut rehab, the wall insulation values could not 

be assessed visually. Given that conductive wall heat gain is relatively low in this climate, 

auditors chose to make assumptions about the insulation values based on convention at the time 

of construction rather than take invasive action.

Older concrete block walls were assumed to be uninsulated; newer ones were assumed to be 

consistent with the conventional practice of installing a radiant barrier product on furring strips 

between the block and the drywall. The frame construction homes (predominantly of 1980s or 

newer vintage) were assumed to have a conventional wall insulation value of R-11. These 

assumptions were applied respectively in homes with a combination of block and frame, which 

were primarily block homes with an addition or enclosure of a porch or garage. 

Wall R-values were unchanged at post-retrofit for all the homes where the conditioned area was 

unchanged, except in one home where two uninsulated frame walls were opened and insulated 

with R-13 fiberglass batts. The latter was included in the best practices for gut rehab or other 

situations that expose frame wall cavities.

2.2.2 Exterior Wall Solar Absorptance

Solar absorptance values of exterior wall color were not measured at either pre- or post-retrofit. 

Researchers used the EGUSA default values in the modeling software, which are based on a 

compilation of sources. The default solar absorptance was 0.8 for dark exterior walls, 0.6–0.7 for 
9

medium, 0.5 for light, and 0.4 for white. Exterior wall color at pre-retrofit was judged to be dark 

on 16 houses, medium on 24 houses, light on 27 houses, and white on 3 houses.

For houses being painted, many partners allowed buyer input. Choices included a mixture of 

buyer and partner preferences. Light or white finishes for exterior walls provide only a modest 

annual energy savings over medium and dark colors; however, there is no cost associated when a

home is slated to be painted. In 20 of the 30 homes that were repainted or received new vinyl 

siding, a white or light color was selected (Table 4). Light exterior wall finish was chosen for 

inclusion in the best practices.

Table 4. Exterior Wall Color Pre- Versus Post-Retrofit

Post-Retrofit

Pre-Retrofit Dark Medium Light White

Dark 3 2 4

Medium 2 5 2

Light 2 7 1

White 1 1

Total Repainted/Resided (n = 30) 3 7 17 3

2.2.3 Windows

Windows were characterized by window type, number of panes (single or double), frame 

material (wood, metal, insulated metal, or vinyl), window area, horizontal depth of overhang, 

and vertical separation from overhang. Only six homes had double-pane windows, all with clear 

glass. Eleven homes had single-pane tinted windows, which were either original or had applied 

film. The remaining 53 homes had single-pane clear windows. Pre-retrofit windows were almost 

exclusively metal frame units. Typically, older homes had awning-style operation (Figure 9) or, 

less frequently, jalousie. Homes built during or since the 1980s were typically single-hung or 

horizontal slider operation. 

Figure 9. Typical awning-style window type
10

In the hot-humid climate, thermal conduction through windows has much less impact on energy 

consumption than does the radiant solar heat gain. The solar heat gain coefficient (SHGC) and 

U-values were unknown in all pre-retrofit cases. Defaults in the modeling software were applied

based on the number of panes, presence of tinting, and frame material. For example, a singlepane window with clear glass and a metal frame (the typical pre-retrofit scenario) was assigned 

an SHGC of 0.80 and a U-value of 1.20. In contrast, post-retrofit window specifications were 

nearly always known from National Fenestration Rating Council labels. In a few cases, partners 

did not leave the labels adhered to windows for researchers’ post-retrofit observations; in those 

cases, assumptions were made. 

Based on these assumptions, the SHGC was reduced in 49 homes (70%). In 43 homes (61%), the 

SHGC improvements were achieved with window replacement. In the other six homes with 

improved SHGC, window film was applied on the glass surface facing the interior of the home.

A reduction of 0.42 in SHGC was the overall average for homes with window improvement 

measures. Generally, all windows in a given home would be upgraded. All newly installed 

windows would typically have the same—or nearly the same—specifications. In eight cases, the 

total window area was reduced. In one home, the total window area increased. 

Windows were replaced, first and foremost, because they were no longer functional or were not 

acceptable for some other reason (such as aesthetics) in the current market. Partners could have 

elected to replace them with new, minimum performance windows. However, they typically 

chose higher performance units, which reduced heat gain and associated cooling energy use.

In 27 homes, the windows were in good working order or needed only minor repairs. For singleor double-pane clear windows left in place, researchers always recommended installing window 

film to reduce the solar heat gain. Partners elected not to do so in 21 homes where they deemed 

the windows to be acceptable in current market conditions. In some cases, site shading reduced 

the potential benefit of film application. Researchers also found, anecdotally, that the decision 

was based on use of funds for higher priority elements of the renovation, not necessarily energyrelated improvements. 

The most common replacement window type was double-pane, low-e, vinyl frame, single-hung 

with an SHGC of 0.20–0.40 (Table 5). These windows also feature a lower U-value that comes 

from the insulative quality of double-pane glazing and vinyl frame. The U-value of replacement 

windows ranged from 0.55 to 0.8 (Table 6). Although the conductive heat gain through windows 

is largely eclipsed by radiant gain in the hot-humid climate, double-pane windows have 

nonetheless become the norm in central Florida. 

Table 5. SHGC of Replacement Windows

SHGC Ranges* Houses (Total of 43) % of Houses

0.40–0.63 11 26%

0.2–0.4 32 74%

*Based on the primary replacement window type in each house (excludes window film)
11

Table 6. U-Values of Replacement Windows

U-Value* Houses (Total of 43) % of Houses Description

> 0.80 2 5% Single pane, metal

0.55–0.80 8 19% Double pane, metal

< 0.55 33 77% Double pane, vinyl

*Based on the primary replacement in each house (excludes window film)

Many partners specified ENERGY STAR® windows in their work orders. This is easier for the 

partners and the contractors than numeric specifications for SHGC and U-value. In the early 

stages of the project, Version 4 of the ENERGY STAR Window Standard was in effect, 

supplanted by Version 5 in 2010. For the central Florida region, Version 4 set a maximum 

allowable SHGC of 0.4 and U-value of 0.65. Replacement windows in 28 homes met the Version 

4 requirements. Of the 28, replacement windows in 14 homes met the more stringent

requirements of Version 5 that set a maximum SHGC of 0.27 and U-value of 0.60. ENERGY 

STAR-qualified windows (Version 5) were incorporated into the best practices for replacement 

windows and application of window film with low SHGC and high visible transmittance to clear 

windows being left in place.

Based on reported costs, window replacements cannot be justified on payback from annual 

energy savings. However, if windows need to be replaced for cosmetic or functionality reasons, 

the incrementally higher cost for double-pane, low-e windows (over minimum replacement) may 

be justifiable based on projected annual energy cost savings. This depends on the actual 

incremental cost in the local market and warrants careful consideration aided by projected 

savings modeling. Regardless of annual cash flow implications, a missed opportunity to choose 

higher performance replacement windows will likely not arise again for two or more decades. 

The cost of a high performance window film with a low SHGC or shading coefficient can be 

justified for clear windows left in place.

As a final note on window replacements, the window type sometimes had great impact on wholehouse airtightness. Jalousie and awning windows often did not close completely at pre-retrofit, 

creating extensive air infiltration paths (see Figure 10). The window in its most closed position is 

still slightly open. The red line indicates the pitch of the closed pane. If the window closed 

completely, the frame edge and red line would be vertical rather than pitched. In addition to 

efficiency gains from reducing solar heat gain and thermal conductance, replacing such poorly 

closing windows has the added benefit of large infiltration reductions. Air sealing between the

window frame and rough opening likewise enhances the infiltration reduction. This third 

airtightening benefit of window replacement is reflected in the whole-house airtightness testing 

at the test-out audit (see Section 2.3); however, it is not accounted for in the cost associated with 

the infiltration reduction measure.
12

Figure 10. Pre-retrofit awning window in its most closed position is still slightly open,

as indicated by the pitch of the red line.

2.2.4 Roof

Florida does not have a snow load that requires the steeper roof pitches found in mixed and cold 

climates. However, homes in the dataset built in the 1980s or later had steeper roof pitches 

consistent with changing design preferences (Figure 11). Twenty-six (37%) homes had a shallow 

roof pitch of ≤ 3.5:12 (Figure 12), 24 (34%) had a roof pitch of 4:12, and the remaining 20 

homes had a mixture of steeper pitches (Figure 11).

Figure 11. Roof pitch plotted by vintage displays trend of older homes with shallower pitch n = 70
13

Figure 12. Typical shallow roof pitch of Florida homes built before 1980

The prevalence of shallow roof pitch has implications for potential roof and attic energy 

improvements. In 58 of the 70 homes, partners elected to add ceiling insulation, and blown-in 

fiberglass was by far the predominant choice. Attaining the desired R-value throughout the entire 

attic space was often not possible, given the confined space of shallow roof pitches, presence of 

air distribution ducts, and truss framing (see Section 2.2.5). The shallow roof pitch and cramped 

attic also ruled out retrofitting an attic radiant barrier, which was not included in any of the 

homes. If complete roof deck replacement had been needed, radiant barrier-backed decking 

would have been recommended; however, the need to replace damaged sheathing would have 

been determined by the roofing contractor after the exterior roofing material was removed (after

the pre-retrofit analysis was completed), rather than specified in the scope of work.

Sixty-eight of the 70 houses had asphalt shingle roof coverings.

3 The solar absorptance was not 

measured as part of the energy audits. Simulation software defaults were used based on the 

researchers’ observations of shingle color. A qualitative assessment of pre-retrofit roof color 

reveals that medium colors were predominant in the dataset, followed by dark colors (Table 7). 

Table 7. Roof Shingle Color

Post-Retrofit Color

Pre-Retrofit Color Dark Medium Light White

Dark 1 6 2 2

Medium 1 12 3 4

Light 1 2 1 0

White 0 0 0 1

Total Replaced (n = 36) 3 20 6 7

Replacement of roof finish was a common part of the retrofits. For the 36 renovations calling for 

shingle replacement, researchers recommended a light or white color. Compared to the homes’

 3 One house had a metal roof. It was not replaced. One house had a white tile roof that was replaced with light 

shingles.
14

original shingle colors, partners selected a lighter shade for 17 homes, the same shade for 14 

homes, and a darker shade for 5 homes. Medium was the predominant choice. The recommended 

light or white (Table 7) shingles were installed on only 13 homes. Anecdotally, researchers 

learned this was driven by partner or buyer preference. 

There is not a large difference in solar absorptance between dark and white shingles; therefore, 

this choice does not make a major impact on the simulated cooling load. However, the modest 

improvement (approximately 1% annual energy cost) from a lighter shade comes at no additional 

cost when shingles are being replaced. For this reason, researchers elected to retain the 

recommendation of light or white replacement shingles in the current best practices rather than 

the color chosen most often.

2.2.5 Ceiling Insulation

With few exceptions, homes had vented attics with some level of batt or blown insulation (Figure 

13) applied to the attic floor, except in two cases that had no insulation. The pre-retrofit R-value 

was not precisely known and had to be estimated based on visual inspection. Typically, a section 

of the ceiling insulation depth could be measured. Researchers’ estimates of pre-retrofit ceiling 

insulation values ranged from R-0 to R-34 (average R-16), with about 75% between R-9 and R25. Improving the ceiling insulation level was among the most common retrofit measures 

included in 58 retrofits (83%) (Table 8).

Figure 13. Typical pre-retrofit ceiling insulation condition

Table 8. Ceiling Insulation R-Values

< R-19 R-19 R-25 R-30 R-38 > R-38

Did Not Add Insulation (n = 12) 2 4 3 3 0

Added Insulation To Achieve (n = 58) 21 36 1

Achieving R-30 or greater ceiling insulation was recommended for all homes. Over 60% of 

homes with added insulation achieved R-38, which was incorporated into the best practices. 

In 12 homes, however, the partners elected not to add ceiling insulation. Six were built between 

2004 and 2006; their insulation values were estimated at R-25–R-30. The expense of adding an 

insulation was deemed not justifiable for the projected energy savings. The two homes with 

insulation below R-19 had no accessible attic space. The ceiling finish was formed or attached to 
15

single assembly roof or very shallow cathedral style trusses. Of the four R-19 homes, the scope 

of work in one was limited to equipment replacement and window repair. In the other three, 

partners prioritized other work over ceiling insulation, but achieved 13%–22% annual energy 

cost savings and 21%–28% HERS Index improvement through a combination of equipment and 

window measures.

Typically, ceiling insulation retrofit consisted of blown-in fiberglass on top of existing insulation 

of various types to achieve the total desired insulation value, rather than removal of existing 

insulation. Often, researchers observed forced-air ductwork that was not strapped in place above 

the insulation and was partially buried after insulation was blown into the attic. Although 

strapping is required by the Florida Residential Mechanical Code for new construction, it is not 

required for mechanical system change-outs. Where ducts are partially or completely buried 

under insulation (Figure 14), moisture may condense on the outer surface of the duct if the 

insulation causes the surface temperature to drop below the dew point of the humid attic air.

Duct leakage can increase this risk. Based on these durability concerns, researchers included the 

mechanical code guidelines for supporting flexible ducts above attic insulation that are required 

for new construction in the best practices. In other research, the Building America program is 

investigating the effects and benefits of covering attic-mounted ducts with insulation.

Figure 14. Post-retrofit ducts buried by blown-in fiberglass

Another concern that warrants follow-up investigation concerns attic ventilation. Though 

recommended, researchers encountered only one contractor who made it standard practice to 

install ventilation baffles and dams over the exterior wall top plates before blowing in insulation. 

Other contractors cited roof pitch and attic access issues as the reasons this was not done. No 

doubt, the labor to install these materials would have increased the ceiling insulation expense,

which would need to be factored into the cost analysis. The resulting attic airflow dynamics were 

pointed out to the partners as an area of concern with potential moisture and thermal 

performance implications; however, direct investigation was outside the scope of the study. 

Post-retrofit, insulation thickness usually varied throughout the attic space. The shallow roof 

pitch and typical truss configuration of older homes often limit access in the attic and restrict 

space for insulation over the exterior wall top plates to only a few inches. Insulation was 

generally deeper under the ridges of the attics. Rather than estimating an effective insulation 

level, the full purchased insulation value was used in the simulations. For example, if the partner 

paid the contractor to bring the insulation up to R-30, this value was used in the post-retrofit 
16

simulations based on the assumption that the deep and shallow portions averaged out to the 

specified R-value. Steeper pitched roofs typically afforded adequate room for the desired depth 

of insulation throughout the attic, extending to the exterior wall top plates.

Attic access was typically through a hatch in a central hallway, closet, or garage ceiling. 

Researchers recommended gluing rigid insulation or stapling a fiberglass batt to the back of the 

hatch cover. The audit procedure did not specifically track this detail; however, auditors agree 

that it was rarely, if ever, executed. When contractors are primarily or exclusively installing 

blown-in insulation, neither rigid nor batt insulation is commonly on hand. 

2.3 Building Infiltration

Even though reducing infiltration is not a major savings for homes in the hot-humid climate, 

(because of the low temperature difference between indoors and out) gaining control over 

airflow is essential for achieving good indoor air quality, controlling air-transported moisture, 

and enhancing comfort. Cummings et al. (1990; 2012) showed that mechanically induced 

infiltration introduces heat and moisture, even when the drivers of natural infiltration are weak. 

The ceiling plane tends to be the primary infiltration path in slab-on-grade, concrete block 

homes. 

The pre- and post-retrofit retrofit audits included a standard test for estimating whole-house 

airtightness and infiltration (RESNET 2006). Whole-house airtightness (ACH50) is calculated as 

air changes per hour measured at a test pressure of negative 50 Pa with respect to the outside, 

divided by the building volume. By using a measurement that is normalized by conditioned 

volume, the relative airtightness of different size homes can be compared. Researchers

recommended a target maximum ACH50 of 6, which is similar to minimum code, new 

construction homes in Florida. 

Researchers were able to conduct whole-house airtightness tests in 60 homes at pre-retrofit and 

in 69 homes at post-retrofit. In 10 homes, it was not possible to conduct pre-retrofit whole-house 

testing because of health concerns or large missing sections of drywall. The overlap of pre- and 

post-retrofit testing created a set of 59 homes. Whole-house airtightness test results are plotted in 

Figure 15 by vintage for pre- and post-retrofit.
17

Figure 15. Scatter plot for whole-house airtightness test results (ACH50) 

by vintage for homes tested pre- and post-retrofit (n = 59)

For the 59 homes, pre-retrofit ACH50 ranged from 3.6 to 41.8 with an average of 10.5. All but 

one home had ACH50 < 25. When test-in results were high, auditors identified airflow pathways 

and provided that information to the partner. In Florida’s hot-humid climate, high infiltration

rates are less detrimental than they are in climates with larger temperature differentials between 

outside and conditioned spaces. It is less beneficial and less cost effective to expend labor on 

extensive air sealing efforts in the hot-humid climate. Air sealing efforts necessary to achieve the 

target ACH50 test result include sealing around drywall penetrations (for supply and return 

registers, dryer vents, wiring, lighting and fan fixtures, and plumbing), replacing missing 

plumbing access panels, correcting poor window and door closure, eliminating recessed lighting, 

and installing gaskets at attic access panels in the conditioned space (Figure 10 and Figure 16).

Figure 16. Pre-retrofit drywall penetrations: The ceiling fixture was removed, but penetration to the 

attic was unsealed (left); plumbing access in the wall covered with a return grille rather than a

solid cover or patch (center); large opening beneath the bathroom vanity where block and drywall 

were removed as part of an incomplete renovation (right).
18

A list of important infiltration points to investigate was developed for the pre-retrofit audit 

process. Identified problem areas were provided to partners to ensure air sealing efforts 

addressed the highest priorities. Researchers found that these leakage points were not common 

knowledge to partners. Therefore, a list of the most important air sealing sites is included in the 

best practices (see Appendix C) to guide air sealing efforts to the most likely sources of 

uncontrolled airflow.

Whole-house airtightness was improved in 51 cases by 35% on average (Table 9). Post-retrofit 

ACH50 ranged from 3.5 to 11.5. All but five homes achieved ACH50 < 10.0, and 30 achieved 

the target ACH50 of 6.0. The highest reductions were seen in the 13 homes built in the 1950s

and 1960s (Table 9), in which the mean ACH50 was reduced by more than half but still tended 

to be higher at post-retrofit than houses of newer vintage. Whether looking at pre- or postretrofit, newer homes tend to be more airtight, though the tendency is much more subtle postretrofit. Note the low post-retrofit sd within each decade and the similarity of post-retrofit 

ACH50 across the decades. This suggests that, with this building type, whole-house airtightness 

levels similar to new construction (ACH50 ≤ 6.0) can be achieved in vintages newer than the 

1960s, regardless of pre-retrofit degree of airtightness. Among the 1960s homes (and one 1958 

home), ACH50 ranged from 5.8 to 11.5, suggesting that the target ACH50 is possible but may 

require more diligence for homes of this age. Based on these finding, a target ACH50 ≤ 6.0 is 

included in the best practices.

Table 9. Pre- and Post-Retrofit Whole-House Airtightness (ACH50) and Improvement by Decade

59 Homes Tested at 

Pre- and Post-Retrofit

Pre-Retrofit 

ACH50

Post-Retrofit 

ACH50

Airtightness

Improvement

Decade Number of 

Houses Average sd Average sd Average Percent

1950s 1 15.6 – 5.8 – 9.8 63%

1960s 12 18.2 8.5 8.7 1.6 9.5 52%

1970s 13 10.1 2.4 7.9 1.7 2.2 22%

1980s 18 8.2 2.1 6.2 1.3 2.0 24%

1990s 8 7.7 3.6 5.8 1.7 1.9 25%

2000+ 7 6.3 3.4 4.5 1.3 1.8 29%

Average 10.5 6.0 6.8 2.0 3.7 35%

The home with pre-retrofit ACH50 of 41.8 was built in 1967 and had severe window closure and 

drywall penetration issues (Figure 10). After a window change-out and other improvements, the 

ACH50 dropped to 8.1. 

A common infiltration path that sometimes remained post-retrofit was located at the ceiling of 

the air handler unit (AHU) closet (Figure 17). Contractors often did not seal the gap around the 

supply plenum at the ceiling drywall. Access to this gap is complicated by closets that were 

designed for smaller AHUs. 
19

Figure 17. Gaps or holes at ceiling of AHU closet

In two cases where whole-house airtightness was not improved it was virtually unchanged. In 

five cases, the leakage was marginally increased (≤ 6%); however, in one home the leakage 

nearly doubled. The airflow paths included unsealed penetrations near the new bathroom vanity 

and the kitchen exhaust hood (Figure 18).

Figure 18. Post-retrofit: Unsealed range hood penetration through top of cabinet into the attic

Although post-retrofit airtightness could not be precisely predicted, researchers anticipated that 

ACH50 test results might be very low given that duct and air barrier sealing measures were 

likely in all homes. Therefore, whole-house, outside air ventilation was recommended for every 

house (see Section 2.4.6) and included in the best practices. 

2.4 Mechanical Space Conditioning Systems

At pre-retrofit, all 70 homes in the dataset had forced-air, central AC systems with single, 

centrally located returns. The heating fuel in 64 of the homes was electricity, either heat pump or 

an electric resistance coil integrated into the central AHU. The remainder had naturally aspirated

gas furnaces. AHUs were located in the main living space in 40 (57%) homes, the garage in 21 

(30%) homes, the attic in 6 (9%) homes, and outside in 3 homes (4%). None of the homes had 

more than one mechanical system. Mechanical equipment efficiency and size, AHU

Supply 

duct 

(with 

mastic)

Closet ceiling

Closet 

wall
20

configuration, duct heat transfer, duct airtightness, outside air ventilation, and thermostats are 

detailed in Sections 2.4.1–2.4.7.

2.4.1 Mechanical Equipment Efficiency, Pre-Retrofit

With few exceptions, the mechanical systems’ rated heating and cooling efficiencies were 

identifiable at pre-retrofit by looking up model numbers in the Air-Conditioning, Heating, and 

Refrigeration Institute (AHRI) Directory of Certified Product Performance. However, 

occasionally name plate labels were too worn to read, and in a few cases the compressor had 

been stolen. In those cases, researchers made assumptions based on the rated efficiencies of the 

AHUs or furnaces, partially identifiable model numbers, and estimating the age of the systems

and using the minimum efficiencies available at that time. 

The Building America House Simulation protocols call for adjusting rated efficiency for 

equipment age and maintenance level. Neither was known for these homes. Rather than make 

assumptions, researchers did not derate equipment efficiencies. The rated cooling and heating 

efficiencies, when known, were consistently modeled in all 70 homes. 

By assuming rated efficiency for pre-retrofit simulations, we ensure that savings projections 

from equipment replacement are conservative and that savings across the dataset are not 

influenced by variance in auditor assessment. Researches commonly observed conditioning 

equipment with combinations of significant corrosion, rust, clogged coils, crimped or punctured 

condensate lines, missing access panels, and tangled wiring (Figure 19). Pre-retrofit cooling and 

heating efficiencies for the 70-home dataset are plotted in Figure 20 and Figure 21.

Figure 19. Looking up at pre-retrofit clogged, dirty cooling coils in the AHU (left); 

corroded and clogged cooling coil (right)
21

Figure 20. Pre-retrofit AC efficiencies (SEER) by house vintage (n = 70)

Figure 21. Pre-retrofit heat pump heating efficiencies by house vintage (n = 70)

The pre-retrofit cooling efficiencies, including some estimates as described above, ranged from

SEER 7.8 to 15, with a mean of SEER 10.6, and an sd of 1.6 (Figure 20). Only 10% met or 
22

exceeded SEER 13, the current federal minimum efficiency allowed for AC manufacture and 

sale, denoted by the red line in Figure 20. Over 60% of the AC equipment (43 units) was SEER 

10 or lower efficiency. For many of these homes, installing an air conditioner with a SEER of 13 

would have been a dramatic improvement. Note that savings (and costs) for higher SEER AC 

replacements are quantified in comparison to this federal minimum, because nothing lower could 

have been installed. For example, annual energy cost for a SEER 15 replacement was compared 

to the annual energy cost for a SEER 13 replacement, rather than the original SEER 8 equipment. 

For more detailed discussion of this concept, see Appendix B.

Heating systems were predominantly electric. Twenty homes had central electric resistance 

heating systems (coefficient of performance [COP] of 1), which is sometimes referred to as an 

electric furnace. The remaining 44 homes had air source electric heat pumps. Figure 21 shows 

that pre-retrofit heat pump heating efficiencies ranged from 6.6 to 8.2 heating seasonal

performance factor (HSPF), with a mean of 7.4 (sd = 0.48). Six homes had gas furnaces at preretrofit with efficiencies ranging from 0.76 to 0.80 annual fuel utilization efficiency (AFUE).

Mechanical equipment was replaced in 61 homes (87%). In 40 cases, a central air source electric 

heat pump was replaced with one of higher efficiency. Partners replaced 18 of the 20 electric 

resistance systems with heat pumps. In three homes, a naturally aspirated gas furnace with 

straight AC was replaced with like equipment. Post-retrofit, the mechanical systems’ rated 

efficiencies were always determined using the AHRI directory. Table 10 and Figure 22 show 

pre- and post-cooling efficiency.

Table 10. Pre-Renovation and Post-Renovation AC Efficiencies

Replacement SEER Rating

13–13.9 14–14.9 15–15.9 16–16.2

Pre-Retrofit 

SEER 

Rating

<10 1 7 4

10–10.9 4 2 16 9

11–11.9 1

12–12.9 2 4 4

13–13.9 4 2

14–14.9 1

Total Replaced (n = 61) 5 4 32 20
23

Figure 22. Mechanical system cooling efficiency at pre- and post-retrofit audit

Average SEER improvement was 49%. All the SEER 10 and lower units were replaced. One 

home had its compressor replaced with a like kind. Only five of the 61 replacements were SEER 

13 units, the current federal minimum efficiency. Only two others fell below 14.5, the current 

specification for ENERGY STAR-labeled air conditioners (dashed purple line on Figure 22). 

The rest were SEER 15 or higher with a maximum of 16.2. In two cases, cooling efficiency 

doubled from SEER 8 to SEER 16. 

Replacement heat pump heating efficiencies ranged from 7.7 to 9.5 HSPF with an average of 8.6. 

Only five fell below the ENERGY STAR equipment HSPF requirement of 8.2. HSPF ratings are 

tied directly to heat pump cooling efficiency, which is the primary equipment selection driver in 

the hot-humid climate. As heat pump cooling efficiency rises, so does heating efficiency.

The best practices call for ENERGY STAR-labeled replacement equipment.

For the nine homes where equipment was not replaced, researchers recommended that it be 

serviced and that other HVAC system improvements such as duct tightening be implemented. In 

six of these cases, the equipment left in place had a SEER of 13 or higher. Five were heat pumps;

one was electric resistance. In three homes, equipment with a SEER slightly over 10 was left in 

place (two heat pumps and one electric resistance). In each of these homes, the equipment was 

functional and deemed by partners as acceptable for market conditions. 
24

2.4.2 Mechanical Equipment Size

During the course of this study, mechanical equipment sizing calculations were required for new 

construction in Florida but not for replacements. In 2012, the Florida Energy Code changed to 

require sizing calculations for replacements. Regardless of requirements, researchers 

recommended that conditioning equipment be sized using ACCA Manual J calculations or 

equivalent. Matching equipment size to load improves humidity control compared to oversized 

equipment. Table 11 shows change in cooling capacity.

Table 11. Change in Cooling Capacity Post-Retrofit

Number of Systems 

(Total = 61)

24 kBtu Smaller (12 kBtu = 1 ton) 1

~12 kBtu Smaller 5

~6 kBtu Smaller 11

No or Minor Change (± 2 kBtu) 30

~6 kBtu Larger 11

~12 kBtu Larger 3

The test-out audit procedure did not include collecting sizing calculations. Anecdotally, it did not 

appear that mechanical contractors were providing them to the partners, whether or not they were 

doing calculations. AHRI data, when available, were used to determine equipment capacity preand post-retrofit. Half the replacement cooling equipment (30 homes) was within ±2 kBtu of the 

original equipment capacity. Twenty-two systems were approximately ±6 kBtu (0.5 tons) smaller

or larger. Three systems were essentially 12 kBtu (1 ton) larger and five were one ton smaller. 

One replacement system was 24 kBtu (2 tons) smaller than the original equipment. 

2.4.3 Air Handler Unit Location and Configuration

The AHU, the heart of the air distribution system, was located in the conditioned space 

(“interior”) in 40 cases (57%), in the garage in 21 cases (30%), in the attic in six cases (9%), and 

outdoors in three cases (4%). The dataset shows a clear trend toward interior AHU closets in 

homes built before the 1990s (Figure 23). In only four retrofits were the AHUs relocated; all four 

were moved to locations with lower heat gain. In three houses, the AHU was moved into 

conditioned space, and in the other, it was moved from the attic into the garage. 
25

Figure 23. Pre-retrofit, 40 homes had AHUs in the conditioned space,

with greater prevalence in homes built before the 1990s (n = 70)

Researchers observed five basic air distribution system configurations:

• Forty homes. Upflow AHU in conditioned space, usually in a dedicated closet (Figure 

24), mounted on either:

o A framed AHU platform with a wall-mounted filter-back return grille (Figure 24) 

and a central return plenum formed by a cavity under the platform. In many 

homes, the cavity was unfinished (Figure 25, left). Finished cavities were formed 

by sealed duct board (Figure 25, right) or drywall.

o A metal AHU stand or framed platform with the filter at the bottom of the AHU

and the whole closet constituting the return plenum. The return air path was 

usually through a louvered door or a grille in the closet door (Figure 26).

• Nineteen homes. Upflow AHU on a framed platform in the garage (Figure 27) with 

plywood or drywall exterior finish and duct board or open framing inside platform 

forming a return plenum underneath. This is the typical configuration for new Florida 

homes with garages (except the return plenum must have a sealed interior finish). The 

return air path is through:

o A wall-mounted filter-back grille ducted directly into the platform cavity.

o A ceiling-mounted filter-back grille connected to a flex duct running through the 

attic to the top of framed platform in the garage.

• Two homes. Horizontal flow AHU in the garage (Figure 28, left) with duct board supply 

and return plenums. The return air path is through a wall- or ceiling-mounted filter-back 

grille.
26

• Six homes. Attic-mounted horizontal flow AHU (Figure 28, right) with duct board 

supply and return plenums. The return air path is through a ceiling-mounted filter-back 

grille. 

• Three homes. Package unit exterior to house with return air path through a wall-mounted 

filter-back grille. Two were units typical of manufactured housing (Figure 29, left) and 

one unit was typical of portable classrooms (Figure 29, right). In all three homes, systems 

were put together haphazardly with ill-fitting parts, which makes airtight assembly 

challenging.

Figure 24. Upflow AHUs in conditioned space in a dedicated closet. Interior AHU closets 

with returns formed by platforms had wall-mounted return grilles with a 

full door on an adjacent wall (left) or a partial door above (right).

Figure 25. Return plenums were formed by either unfinished, 

open framing (left) or sealed duct board (right) or drywall.
27

Figure 26. Interior closets that served as return plenums had louvered doors 

or door-mounted return grilles.

Figure 27. Upflow AHUs on framed platforms in garage with a wall-mounted filter-back grille

were ducted directly into the platform cavity.

Figure 28. Horizontal flow AHUs mounted at ceiling of garage (left) and in the attic (right)
28

Figure 29. Exterior package units with return air path through a wall-mounted filter-back grille. 

Ground mounted unit with metal shroud housing main return and supply ducts (left) and wallhung unit with attic-mounted ducts (right).

The best practices related to AHU replacement are modeled after the Florida Residential 

Mechanical Code requirements for new homes. These include finished and sealed return air 

plenum, mechanically fastened and sealed supply plenum connection to the AHU, finished closet 

walls and ceiling (when applicable), provision of 4-in. clearance around the AHU. Additional 

best practices not related to new construction code include ACCA Manual D return sizing, 

sealing the gap between the supply plenum and ceiling drywall, and sealing the gap between the 

return plenum and the AHU platform.

2.4.4 Duct Heat Transfer

Only two houses had supply ducts in the conditioned space, which is the most desirable location 

because it minimizes duct heat gain and loss and keeps any duct leakage in the conditioned 

space. One was a two-story home with a single assembly roof; the supply ducts were located in 

the floor cavity. The other was a one-story home with exposed roof rafters. It had a supply trunk 

in a soffit above the central hallway. The remaining 68 homes had attic-mounted supply ducts. 

Typically, supply duct runs (flex) branch off the main supply plenum (duct board) or a smaller 

junction box (duct board). In addition to this “spider” style system, which is very common in 

Florida new construction, researchers observed a smaller number of systems where supply ducts 

branched off a central supply trunk. Some metal ductwork was observed.

The audit procedure did not specifically track it, but few, if any, homes had fully ducted return 

air systems that served bedrooms or passive return air pathways from bedrooms. The Florida 

Residential Mechanical Code has required passive return air pathways for new construction since 

the 2001 edition; however, the requirement does not apply to replacement systems.

Researchers made efforts to determine the rated insulation value for the mechanical distribution 

systems pre-retrofit. However, access to duct systems was limited by the shallow, crowded attic 

conditions described in Sections 2.2.4 and 2.2.5. In some cases where ducts were accessible, 
29

material degradation had obscured insulation value labeling. When the insulation value could not 

be determined, auditors assumed a value based on the estimated age of the material and the 

convention at that time. The same insulation value was assumed for the entire distribution 

system. 

Supply duct insulation was improved in 21 homes with R-6 duct insulation replacing insulation 

ranging from R-2 to R-4.3. In the remaining 49 houses, the pre- and post-retrofit duct insulation 

was the same with 24 at R-6 and 25 lower than that. Florida residential mechanical code has 

required R-6 duct insulation for new homes since 1991. Although the code does not mandate R-6 

for replacement ducts, R-6 has become the norm driven by product availability and was adopted 

as part of the best practices.

2.4.5 Duct Airtightness

Even without replacing the duct system, duct airtightness improved significantly when the 

typical return plenum configuration was addressed. This consists of a wood frame platform 

formed in the lower portion of an AHU closet that supports an upflow AHU. The space below 

the platform forms a central return plenum. Often the plenum is open to adjacent wall cavities

that form the closet. By finishing and sealing the wall cavities or constructing a ducted return air 

path instead, much of the total duct leakage as well as the duct leakage to the outside can be 

eliminated. For example, open framing under the AHU platform creates an unintentional airflow

path between the attic (via surrounding wall cavities) and the return air plenum. This dynamic is 

taken to an extreme when the upper portion of the closet is partially or completely open to the 

attic. This was observed in closets with the above platform configuration as well as in closets 

where the AHU was mounted on a metal stand instead of a wood platform. In the latter, the 

whole closet functions as the return plenum, usually connected to the house by through a 

louvered door. 

Pre- and post-retrofit duct airtightness was measured by depressurizing the duct system using a 

calibrated “duct blaster” fan in accordance with a standard test procedure (RESNET 2006). Duct 

tightness is expressed in terms of airflow required to achieve a standard test pressure (25 Pa) in 

the duct system, measured in cubic feet per minute or CFM25. 

The test procedure measured both the total leakage (CFM25,total) and leakage involving air 

outside the conditioned space (CFM25,out). For comparison among different size houses, the 

CFM25 results are normalized by conditioned floor area of the house yielding Qn,total and 

Qn,out. 

The target maximum Qn,out for the retrofits was 0.06 or 6 CFM/100 ft2 of conditioned floor area 

at the standard test pressure. Researchers chose the target as a practical expectation based on 

extensive experience in both new construction (McIlvaine et. al 2003; Chandra 2004) and in 

repair of existing houses (Moyer et al. 2001).

A pre-retrofit duct leakage test was conducted in 54 of the homes (77%); it was not performed in 

14 homes, generally because the ductwork was visually assessed to be too leaky to test or where 

depressurization posed health risks. In one case, the AC coils were coated with paint ingested 

into the system during spray painting (apparently with the AHU running), which blocked 

airflow. Two homes had problems with the whole-house air barriers, which prevented 
30

depressurizing of the whole house and precluded testing for leakage to the outside. Post-retrofit 

auditing included duct testing in 69 homes. The overlap created a set of 53 homes tested before 

and after renovation.

Pre-retrofit Qn,out ranged from 0.015 to 0.398 with an average of 0.123 (sd = 0.098). At preretrofit, 16 homes met the duct airtightness target of Qn,out ≤ 0.06, ranging in vintage from 1958 

to 2004. At the post-retrofit audit, two of those were found to be leakier, but an additional 24

homes met the target, including 18 with Qn,out ≤ 0.03. This level of duct tightness is exemplary. 

It meets the requirements of new construction above-code programs such as ENERGY STAR

and the Builders Challenge. Table 12 presents average duct airtightness results by decade for the 

set of 53 homes tested before and after renovation.

Table 12. Average Pre- and Post-Retrofit Duct Test Results (Qn,out) by Decade

Pre-Retrofit Post-Retrofit 

Decade n Qn,out sd Qn,out sd

1950s 1 0.04 NA 0.07 NA

1960s 11 0.15 0.10 0.06 0.03

1970s 12 0.20 0.13 0.11 0.09

1980s 15 0.09 0.04 0.07 0.04

1990s 7 0.09 0.07 0.06 0.04

2000+ 7 0.07 0.05 0.03 0.03

Overall 53 0.12 0.10 0.07 0.06

Of the 53 houses tested before and after retrofit, duct leakage was reduced in 42 (79%) and 

stayed the same in one (2%). In 10 homes, ducts were leakier after renovation. In three of those, 

new ductwork had been installed. Six had a noticeable lack of return plenum sealing (Figure 30, 

left). Five had no dedicated return plenum; rather, the whole AHU closet with a louvered door 

(Figure 30, center) or door-mounted return grille served as the return plenum surrounding an 

AHU mounted on a metal stand (Figure 30, right). 

Figure 30. Return air plenum lined with duct board without sealant at edges and seams (left). 

Narrow AHU closet functioning as return with uncontrolled airflow (center). Attempt to make a 

sealed return plenum around a metal AHU stand (right), with noticeable unsealed gap at bottom 

edge of duct board.

Contractors were often challenged by existing conditions. Figure 30, right, shows an attempt to

create a sealed return air plenum around a metal stand supporting an AHU. The contractor had 
31

good intent, as evidenced by the extensive use of mastic sealant; however, the bottom edge of the 

material is notably unsealed and constitutes a major leakage point. To address some of the 

concerns related to air distribution system leakage, the best practices call for ducted return 

plenums, sealed with mesh and mastic, with a wall-mounted, filter-back return grilles. As of 

March 2012, the Florida Residential Energy Code requires contractors to seal accessible ducts, 

defined as 30 in. of work space. Building America has produced a relevant guideline titled 

“Sealing and Insulating Ducts in Existing Homes,” which provides guidance and drawings for a 

number of typical scenarios (Aldrich and Puttagunta 2011).

Four houses were retested after additional duct repairs were made. In one, duct leakage was 

reduced from 0.13 to 0.05, and was negligibly improved in the other three. Given the number of 

retrofits that resulted in higher duct leakage, we recommended that partners define a clear chain 

of action and responsibility as part of the scope of work to measure and correct duct leakage that 

exceeds the target, including establishing financially responsibility for repairs and retesting. We 

also added a list of typical duct leakage points to the best practices to draw attention to common 

problem areas contractors can address to improve odds of achieving the target.

One problem encountered in many homes was that an AHU was being replaced with a larger one 

in a relatively small AHU closet (Figure 31). The larger AHUs are coincident with higher 

efficiency equipment, even within the same or smaller capacity. Contractors had a difficult time 

reaching the areas that needed to be sealed, including the return plenum (construction joints and 

connection to the AHU), the supply plenum connection to the AHU, and the gap around the 

supply plenum in the closet ceiling.

Figure 31. Crowded AHU closet with little room to access and seal duct connections to cabinet

2.4.6 Outside Air Ventilation

As discussed in Section 2.3, the target infiltration post-retrofit was an ACH50 of 6.0. Although 

partners did not plan extensive air sealing to achieve the target, some of the homes were already 

below the target pre-retrofit and researchers anticipated others would be at post-retrofit. 

Infiltration was reduced primarily by replacing windows and doors and repairing drywall, but 
32

partners did not include special measures (such as gasketed electrical cover plates) to achieve

super tight homes.

Because the eventual level of whole-house airtightness was impossible to predict, researchers 

recommended a passive, supply-only outside air ventilation strategy. This approach provides

additional air exchange and controls the outside air pathway. Supply-only ventilation induces a 

small positive air pressure (< 1 Pa positive with respect to outside) in the house that reduces 

infiltration through unintended paths.

The strategy includes an outside air duct with a filtered intake and balancing damper to allow 

adjustment of outside airflow. The duct terminates in the return plenum. The recommended duct 

sizing is based on ASHRAE Standard 62.2-2010 flow rate for continuous ventilation. However, 

the outside air flows during normal AHU operation only. The recommended passive system 

design has been successfully implemented in hundreds of BA-PIRC research homes in central 

and northern Florida with no reports of adverse moisture impacts (Fonorow et al. 2007).

Researchers successfully worked with a partner to incorporate the recommended passive outside 

air ventilation approach in one retrofit of the 70. Partners who did not include ventilation

reported factors such as lack of room to accommodate the outside air duct in already cramped 

AHU closets, difficulty of accommodating an outside air inlet in small soffits (typically 1-in.

overhangs), skepticism about occupant/owner awareness of maintenance requirements, and 

skepticism about the likelihood of post-retrofit need for ventilation. The measure was never 

included in any scope of work. It was incorporated into the one house using a change order. 

Clearly, more education and outreach are required for partners to understand implications related 

to mechanical ventilation.

2.4.7 Thermostats

Only nine homes (13%) had programmable thermostats during the pre-retrofit audit. Five were 

either unchanged or replaced with similar units; however, four (6%) were replaced with nonprogrammable models. Programmable thermostats were installed in 32 (46%) of the 51 homes 

that did not previously have them. Although the expense of upgrading to a programmable control 

was minimal (typically around $100), partners who did not incorporate this recommended 

measure cited unlikely occupant use because of programming complexity.

2.5 Domestic Hot Water

The fuel type for the water heaters at test-in was electric in 62 cases (89%), natural gas in seven 

cases (10%), and propane in one case. All the gas systems were 40-gal tank-type units. Electric 

tank sizes ranged from 28 to 80 gal, averaging 43 gal. There were five 40-gal and ten 50-gal 

units.

Researchers determined the energy factor (EF) using model numbers and manufacturers’

published technical specifications. In a few cases, the pre-retrofit rated efficiency could not be 

determined, and researchers made assumptions based on rated efficiencies of similar equipment. 

The average EF, including a few assumed values, at test-in was 0.88 for electric units and 0.59 

for combustion units. Table 13 provides a summary of the pre-retrofit EFs by fuel type.
33

Table 13. Pre-Retrofit Domestic Hot Water Efficiency by Fuel Type

Fuel Type Number of Homes Efficiency

EF Mean EF Range EF sd

Electric 62 0.88 0.80 – 0.92 0.03

Natural Gas/Propane 8 0.59 n/a n/a

Twenty-eight electric tank-type units were replaced with more efficient units of the same type;

many were only marginally better. In total, the electric tank units at the post-retrofit audits

(including units that were not replaced) had an average EF of 0.91. Four of the electric tank-type 

units were replaced with heat pump water heaters units with average COP of 2.3, and two were 

replaced with tankless electric systems (EF 0.99). 

Two of the eight gas water heaters were replaced with tankless gas units (EF 0.82), and the 

remaining six combustion units were replaced with electric tank units. All these replacement 

units had an EF of 0.92.

2.6 Appliances

Before renovation, appliances were typically missing, old, or in poor condition (Figure 32). 

Many of the homes were not equipped with dishwashers. Researchers attempted to use 

manufacturers’ rated efficiencies; however, often model numbers were illegible or the equipment 

had been removed before the pre-retrofit audit. Thus, to define efficiencies for the appliances at 

pre-retrofit, researchers relied almost exclusively on estimates which likely overestimated the 

efficiencies, making improvement projections conservative. 

Figure 32. Typical pre-retrofit appliance condition for range (left) and refrigerator (right)

Refrigerator replacement was the only appliance change-out that had meaningful impact on 

modeled energy savings. Three refrigerators found at the pre-retrofit audits were equivalent to 

ENERGY STAR efficiency (at or below 479 kWh/yr). Under the program guidelines for NSP 

funds, when replacing refrigerators, partners were encouraged by HUD to install ENERGY 

STAR equipment. Fifty-two homes (74%) were retrofitted with more efficient ENERGY STAR

refrigerators, with an average rating of 451 kWh/yr. 
34

2.7 Lighting and Ceiling Fans

Lighting characteristics were audited for the pre- and the post-retrofit homes using a count of 

fluorescent tube and compact fluorescent lamp (CFL)-equipped fixtures compared to the total 

fixture count. Forty-four homes (63%) had no fluorescent lighting at test-in. The other 26 homes 

had on average 13% of their fixtures fitted with CFLs or fluorescent tubes. In 46 cases (66%),

the retrofit included the addition of fluorescent lighting with an average 53% increase in the 

number of fixtures using fluorescent bulbs. In 22 cases (31%) there was no change in lighting,

and in two cases there was a decrease in fluorescent lighting at post retrofit.

Ceiling fans are very common in Florida homes. At least one fan was present pre-retrofit in 59

homes; however, model numbers were never available at the pre-retrofit audit. Researchers relied 

exclusively on estimates for fan efficiency. As with the appliances, the fans, often old, were 

probably less efficient than the estimates; hence, researchers deemed this to be a conservative 

approach. In 10 cases (14%), ENERGY STAR ceiling fans were installed as part of the retrofit.

The typical efficient unit was rated at 130 cfm/Watt at medium speed. In several cases new units 

were installed but the partner was unable to provide documentation specifying the efficiency of 

the new equipment. In such cases, no efficiency gains were assumed.

2.8 Conditioned Area Reductions

During pre-retrofit audits, researchers found that many homes had porches and garages enclosed 

and made part of the conditioned space (Figure 33). These were retained as part of the 

conditioned space in all but five homes. Returning those spaces to their original use reduced 

conditioned floor area, volume, and thermal envelope area. Conditioned floor area reductions 

ranged from 140 ft2 to 696 ft2 and were, with one exception, coincident with a reduced window 

area (Table 14). Rather than include this envelope change in every energy-saving measure, 

researchers adjusted the pre-retrofit simulation model to reflect the change. This effectively 

focuses savings on efficiency improvements rather than on size adjustments that are relevant to a 

small number of renovations. The analysis reflects the savings from the package of 

improvements if the house had been the same size at pre-retrofit. From a homeowner 

perspective, though, reducing the size of a home would likely produce annual savings.

Figure 33. Pre-retrofit exterior wall of porch converted into conditioned space
35

Table 14. Pre- and Post-Retrofit Conditioned Area and Removed Floor, Ceiling, and Window Area

Removed 

Enclosure 

Type

Pre-Retrofit 

House 

Conditioned Area 

(ft

2

)

Post-Retrofit 

House 

Conditioned Area 

(ft

2

)

Resulting 

Reduction in 

Floor

Area (ft

2

)

Change in 

Window

Area (ft

2

)

Garage 1,499 1,145 354 -9

Porch 1,275 952 323 +12

Porch 1,158 1,018 140 –98

Porch 2,178 1,482 696 –75

Porch 1,944 1,683 261 –57
36

3 Whole-House Improvement and Cost Effectiveness

3.1 HERS Index Improvement

The primary metric researchers used in partner communications, and to evaluate whole-house 

improvements, was percent change in HERS Index pre- and post-retrofit. This is similar to a 

percent change in projected annual energy use and cost. Nuances in the HERS Index calculation 

procedure account for differences among the homes in fuel mix and conditioned area. Most 

partners were familiar with the metric from new construction activities. In all cases, researchers 

also provided partners with projected annual energy cost savings and cash flow analysis for each 

efficiency improvement when measure cost was provided. Additionally, BEopt analysis 

description and results are included in Appendix A.

Pre-retrofit HERS Indices ranged from 95 to 184 (sd = 22), with an average of 129. Post-retrofit 

HERS Indices range from 65 to 135 (sd = 11), with an average of 83 (Figure 34). Projected 

annual energy savings ranged from $35 to $1,338. All but four homes achieved a HERS Index ≤

95, which is similar to new Florida homes built in the early 2000s, a remarkable reversal. This 

may suggest that achieving a HERS Index of 95 is a reasonable goal for energy retrofits in 

homes with similar characteristics to those in the dataset, though the actual savings achieved will 

vary depending on house specific conditions. 

Figure 34. Pre-retrofit HERS Indices (blue) by vintage

paired with post-retrofit HERS Indices (green)

The average improvement in HERS Index for the 70-house dataset was 34%. Average projected 

annual energy cost savings were 25%. Forty-six homes (66%) achieved a 30% improvement in 
37

HERS Index (above the yellow line in Figure 35) with an average projected energy cost savings 

of 31%. Nineteen had 15% and 29% HERS Index improvement and only five fell below 15%.

Figure 35. HERS Index improvement goal (30%, yellow line) was met in 46 deep retrofits. 

Mean HERS Index improvement among houses built in the same decade ranged from 21% to 

55% with a trend of higher improvement levels in older homes (Figure 36). Despite widely 

disparate pre-retrofit HERS Indices and varying scopes of work, the mean of post-retrofit HERS 

Indices by decade ranged from 74 to 86, a range of only 12 points compared to a 56-point spread 

across the decades in pre-retrofit HERS Index (Figure 36).

Figure 36. Mean HERS Index at pre-and post-retrofit by decade vintage
38

Researchers investigated the relationship among these comprehensive renovations between the 

HERS Index improvement and numerous other factors. Beyond a few slight trends detected, 

there is a correlation between pre-retrofit HERS Index and HERS Index improvement (r = 0.7, P 

< 0.001). The linear regression line in Figure 37 displays the fit between these variables for the 

whole 70-house dataset (R2 = 0.4994). All but two homes (red diamonds) with pre-retrofit 

HERS Indices above 124 met the 30% improvement threshold. 

Figure 37. HERS Index improvement compared to the pre-retrofit 

HERS Index for the whole 70-house dataset

Table 15 shows that among the three most active partners similar average improvement levels 

were achieved in homes of similar age. The overall average savings (bottom row) among the 

partners was consistent (34%–36%). 

Table 15. Average HERS Index Improvement for Top Partners by Vintage

Vintage

Partner A

(n = 20)

Partner B

(n = 22)

Partner C

(n = 20)

Overall Mean

(n = 70)

1950s 48% 60% 54%

1960s 40% 48% 42% 42%

1970s 38% 28% 37% 34%

1980s 36% 36% 33% 35%

1990s 25% 29% 33% 28%

2000s 18% 9% 26% 20%

Overall Mean 36% 34% 34% 34%

3.2 Composition of Deep Energy Retrofit Improvement Packages

To assess the feasibility of replicating these positive results in housing of similar pre-retrofit 

character, researchers looked more closely at the mix of improvements associated with the 

houses that had ≥ 30% improvement in HERS Index (n = 46), hereafter referred to as “deep” 
39

retrofits. The deep retrofits had much in common and were the homes with the most room for 

improvement, as they all needed multiple energy-related replacements and improvements.

Table 16 shows the prevalence of 13 key efficiency measures in three groups: deep retrofits (n = 

46, 66%), less than deep retrofits (n = 24, 34%), and the whole dataset (n = 70). 
40

Table 16. Prevalence of 13 Key Efficiency Strategies Implemented

Category 13 Key Efficiency Strategies

≥ 30% HERS 

Improvement 

(n = 46)

< 30% HERS 

Improvement

(n = 24)

All Houses

(n = 70)

Mechanical System Equipment 1. Installed equipment with higher 

cooling and/or heating efficiency 96% 71% 87%

Thermal Envelope, Ceiling 2. Added ceiling insulation 93% 63% 83%

Whole-House Airtightness 3. Improved ACH50 test results 92% 77% 88%

Air Distribution System 

Airtightness 4. Improved Qn,out test results 86% 68% 80%

Windows

5. Applied window film or installed 

replacement windows with lower 

SHGC and/or U-value (based on 

primary retrofit window type in 

each home)

80% 46% 67%

Appliances 6. ENERGY STAR-labeled 

refrigerator 76% 71% 74%

Water Heating 7. Replaced existing with higher 

efficiency unit 70% 38% 59%

Lighting

8. Efficient lighting increase by at 

least 30% (number of fluorescent 

fixtures) 

52% 42% 49%

Mechanical System Controls

9. Replaced non-programmable 

thermostat with programmable 

thermostat

48% 42% 46%

Air Distribution System, 

Thermal Barrier 10. New ducts with higher R-value 39% 13% 30%

Thermal Envelope, Exterior 

Wall

11. Lighter color exterior wall paint 

(lower solar absorptance) 30% 8% 23%

Thermal Envelope, Roof 12. Lighter shingle color (lower solar 

absorptance) 30% 13% 24%

Ceiling Fans 13. Fan(s) with improved efficiency 15% 13% 14%
41

As shown in Table 16, 96% of deep retrofits included a mechanical system replacement, 93% 

included additional ceiling insulation, and 92% included infiltration reduction. Most also 

included duct tightening (86%) and window replacement or film (80%). All these measures are 

related to cooling energy savings with additional heating season benefits. Additional cooling 

load reduction strategies were less prevalent. They include R-6 replacement ductwork (39% of 

deep retrofits), light color exterior paint (30%), and light color shingles (30%). Although the

latter two improvements provide relatively small energy savings, they are usually free at the time 

of replacement as long as choices are made within the same line of paint or shingles.

In addition to measures chosen to reduce space conditioning energy use, partners incorporated 

appliance, water heating, and lighting improvements: 67% of the deep retrofits included an 

ENERGY STAR refrigerator and 70% included a higher efficiency water heater. Typically, the 

water heating efficiency gains were modest (e.g., 0.88–0.92). 

About half the retrofits increased the number of fluorescent lighting fixtures by 30% or more and 

a similar number added programmable thermostats. ENERGY STAR-labeled ceiling fans were 

incorporated into only 15% of the deep retrofits. 

These key efficiency measures were also present in large percentages of the non-deep retrofits

(Table 16). Window improvements were nearly twice as prevalent in the deep retrofits as in the 

non-deep. If any given one of the non-deep houses had needed a window replacement, it would 

likely have resulted in another deep retrofit. The important conclusion is that the deep retrofits 

included a combination of major improvements supplemented with multiple minor 

improvements. The mechanical system efficiency improvement was particularly important; 

however, two homes without conditioning equipment replacement did achieve a deep retrofit 

through an expanded package of other improvements. The retrofit package for one of these 

homes included nine of the 13 key strategies, including significant improvement in ceiling 

insulation, duct leakage, and numbers of CFLs. The second home realized significant savings 

from a heat pump water heater.

These trends taken together with the cost data discussed in the next section formed the basis for 

developing the best practices document for Part 2 of the research. Reference Appendix B for a 

detailed look at the 13 key energy efficiency strategies incorporated into each deep retrofit.

3.3 Cost Effectiveness of Energy Retrofit Improvement Packages

To assess cost effectiveness, projected annual energy cost savings were weighed against the 

reported cost of improvements. Projected annual cost savings are used in lieu of actual utility 

bills or monitored data because these were unoccupied, foreclosed homes. All references to 

annual energy cost and cost savings are based on simulation projections. A more detailed 

discussion of cost-effectiveness calculations is provided in Appendix B.

Partners did not, and in some cases could not, provide complete cost information in all 70 retrofit 

cases. Habitat for Humanity affiliates, for instance, often received donated time and materials 

and were not able to submit the true costs associated with a particular measure and therefore the 

complete retrofit package. Similarly, mechanical contractors generally billed for the whole job 

without showing line item costs. Costs for all work, for instance to replace a heat pump and seal 

ductwork, were combined into one invoice. A final challenge in collecting cost data related to 
42

retrofits that had multiple benefits. Typically the costs identified for whole-house leakage were 

often under-reported, because they fell into other measures. A classic example of this is a 

window replacement; it improves the efficiency of the window and typically reduces the wholehouse leakage.

Preference for one cost-effectiveness metric over another may vary depending on the finance 

mechanisms and interests of the owner. Almost all the homes in this research were being sold to 

qualifying affordable housing buyers after renovation. In this scenario, the cost associated with 

the deep retrofit package is assumed to be rolled into a mortgage, slightly increasing the 

homeowner’s annual mortgage burden. When the annual savings exceed this incrementally 

higher annual debt burden, it creates a net positive annual cash flow for the owner. 

Researchers used financing terms of 7% for a 30-year mortgage as delineated in the House 

Simulation Protocols—high compared to current rates, but typical of a number of years ago 

when this research began. The cost-effectiveness calculation does not consider life cycle cost, 

return on investment, or other metrics that may be important in some situations; however, it is a 

simple metric that provides partners with a snapshot of the immediate projected cash flow, which 

is extremely important to sustainable ownership in affordable housing. This metric provides a 

concrete, though hypothetical, indication of the financial difference between making and not 

making the energy improvements. And although the annual cost of the debt will remain the same 

year after year, the utility cost (and consequently savings) will likely rise, creating greater cash 

flow in future years. 

In some cases, cost-effectiveness calculations used the full cost of a measure; others used the 

incremental cost, which is defined as the cost premium for higher performance or efficiency at 

replacement. When the incremental cost was used, it was compared to the incremental energy 

cost savings beyond replacement with an item of like performance. In the case of mechanical 

equipment replacement, however, a like efficiency unit is not always available because of federal 

minimum efficiency standards. Then, incremental savings are calculated in comparison to 

savings achieved beyond a SEER 13 replacement. For example, if SEER 8 cooling equipment 

were being replaced for functional reasons, the minimum efficiency replacement would be a 

SEER 13 unit, which would certainly produce savings. However, if a higher efficiency SEER 15 

unit were selected instead, the cost effectiveness of that choice would be calculated using 

incremental cost (over the SEER 13) compared to the incremental savings (over the SEER 13). 

For some measures, the incremental cost was deemed to be zero. No cost premium was 

associated with a higher performance choice at the time of replacement. These include:

• When roof was replaced, a lighter color was chosen.

• When exterior walls were painted, a lighter color was chosen.

• When electric tank type water heaters were replaced, a slightly more efficient unit of the 

same type was chosen.

For other measures, the full cost was compared to the full energy savings in cost analysis 

because they were implemented in absence of functionality needs, purely for energy efficiency 

improvement. These include:
43

• Whole-house air sealing measures that were not part of other measures (caulk, foam, etc., 

estimated by partners)

• Servicing or sealing HVAC equipment and air distribution system components (in the 

absence of HVAC replacement)

• CFLs

• Outside air runtime vent for indoor air quality and durability (one house)

• Programmable thermostat

• Ceiling insulation.

In a perfect world, partners would have provided the cost for the higher performance 

replacement item as well as the cost for replacing an item with an item of the same (or minimum 

available) efficiency. However, partners do not usually catalog prices for items they do not buy,

so researchers typically had to estimate the incremental costs for these measures based on other 

partner activity, price checking, and other research.

In the 42 deep retrofits for which we have cost information, total retrofit cost, including 

incremental cost over replacement with like efficiency where applied, ranged from $780 to 

$8,382 and averaged $3,854 (sd = 1,687). The scatter plot in Figure 38 displays incremental 

costs compared to percentage improvement in the HERS Index for the 42 houses. 

Figure 38. Incremental costs by percent HERS Index improvement for 

42 deep retrofits with cost data
44

To allow comparison among the retrofits, the annual energy cost calculations were made using a 

standard utility rate of $0.13/kWh, $1.72/therm of natural gas, and $1.40/gal of propane (one 

home). This is a known bias in the study, in that local utility rates may be higher or lower; 

however, in the interest of studying the whole dataset, utility rates needed to be standardized. 

Although using the annual energy use rather than the annual energy cost would have allowed 

comparability without this complication, it would not have provided a path for the costeffectiveness calculations. Where utility rates were higher or lower than the standardized rate, 

resulting annual cash flow would have been higher or lower, respectively.

A scatter plot of the incremental annual cash flow compared to HERS Index improvement is 

provided in Figure 39. Incremental annual cash flow ranged from –$79 to $626 and averaged 

$169 (sd = 158). Cash flow was positive in all but six cases (86% were positive).

Figure 39. Incremental annual cash flow by percent HERS Index 

improvement for 42 deep retrofits with cost data

Five of the six negative cash flow retrofits were marginal, –$7 to –$26 annually, which might 

have been positive under less conservative financing terms or local utility rates. In two cases,

expensive window retrofits had a major impact on incremental costs. In one home the window 

specifications were unknown and, to be conservative, software program defaults were used to 

calculate savings even though the actual specifications were likely better. In two other cases very 

high efficiency mechanical systems were installed that generated only modestly higher 

incremental savings that were heavily outweighed by incremental cost. In the one remaining case 

with an annual cash flow of –$79, the retrofit included an expensive electric tankless water 

heater (which researchers recommended against) that saved little energy. For a more detailed 

discussion on energy costs and savings, improvement costs, and cash flow for deep retrofits, see 

Appendix B.
45

4 Gaps and Challenges

Similar to researchers’ experience in new construction, a major barrier to widespread 

implementation of high efficiency, high performance specifications is lack of building science 

and energy efficiency awareness among contractors, buyers, code officials, and subcontractors. 

The best practices include retaining a certified home energy rater or other building science 

support to provide the guidance, analysis, and quality assurance that researchers provided to the 

partners during the study. 

We have also included specific material to help contractors meet the targets in three areas where 

problems occurred: duct and whole-house airtightness and passive return air pathways. In 

addition to target metrics, the best practices include checklists of typical leakage points to seal 

and direct contractors to sections of the Florida Residential Mechanical Code that apply to new 

construction for further information. These criteria are particularly important in renovation

projects to identify unanticipated pressure differentials that can have a negative impact on health 

and building durability, including moisture degradation and back drafting combustion exhaust 

into the conditioned space. These serious potential risks are addressed in multiple elements of the 

best practices, including post-retrofit testing and assessment by a Class I certified home energy 

rater, regardless of rater involvement before or during renovation. After partnering on this study, 

the Sarasota Office of Housing and Community Development integrated this practice into the 

standard specifications for all NSP renovations (Appendix D) with successful implementation in 

many homes. 

In addition to these criteria, other parts of the best practices cover items required by the Florida 

Residential Mechanical Code for new construction but not for existing homes. These items 

specifically address system design, quality installation, duct integrity, durability issues, and 

system accessibility:

• Mechanical system sizing using ACCA Manual J 

• Matching indoor and outdoor mechanical system components

• Duct system components mechanically attached and sealed with fiberglass mesh and 

mastic or code approved alternative

• Sealed return air plenums

• Abandonment of building cavities used as ducts

• 4-in. allowance between AHUs and surrounding walls

• Flexible ductwork to be supported above attic insulation.
46

5 Best Practices

Researchers evaluated trends in the 46 deep retrofits to identify the most commonly implemented 

measures. They developed a standardized set of best practices to be used in combination as a 

viable approach to achieving 30%–50% HERS Index improvement in homes similar to those in 

the study. 

The best practices are intended as general guidance for organizations that want to develop 

consistent energy-related specifications for a standard “Community Wide Improvement 

Package.” The overall best practices list is expected to be customized by organizations, and a 

subset of the overall list will be implemented. The best practice includes health and safety 

criteria, which are greatly influenced by Building America new construction research and the 

Quality Criteria for DOE’s Builders Challenge (Version 1).

4 Some of these criteria, such as 

moisture control and combustion safety, are mandatory measures that apply to every home 

regardless of specific replacements. Others, such as performing room-by-room ACCA Manual D 

calculations to size ducts, are recommended 

The measures incorporated into the best practices were regularly implemented in the deep 

retrofits. In some cases, a less common specification was chosen. For example, the best practice 

for shingle color is “white” even though “light” was more prevalent in the dataset based on 

partners’ aesthetic preferences. 

The best practices include measures that address house characteristics such as recessed lighting, 

crawlspaces, and pools, that are not well represented in the study. Other measures are included 

that were recommended but not widely implemented. These known opportunities included 

ducted kitchen and bath exhaust fans to the outside, more thorough return plenum sealing, 

Residential Energy Services Network (RESNET) Class I knee wall insulation, maximum CFL 

installation, and ENERGY STAR ceiling fans.

Depending on initial conditions, replacement specifications in the best practices may not be 

applicable in a given house. In those cases, the best practices often include improvements that 

can be made in-situ to existing equipment and components. This dynamic means that not every 

home will achieve deep energy savings with a standard approach; however, homes that need a 

combination of replacements will likely reach the 30% improvement mark and across a 

community an average of 30% improvement can probably be reached (Table 15).

The best practices are divided into in the following 16 categories:

• Combustion safety

• Mechanical equipment and air distribution

• Ventilation

• Infiltration

• Roof

• Ceiling insulation

 4 This program is now called the DOE Challenge Home and has many more required elements than the Builders 

Challenge, Version 1.
47

• Knee walls 

• Windows

• Exterior walls

• Floors

• Water heating

• Appliances

• Lighting

• Fans

• Moisture

• Pool.

Even if a home needs no replacements, the in-situ strategies should improve its overall 

performance at some level. In addition to replacement specifications, there are a variety of 

performance criteria to raise awareness about whole-house and duct airtightness. Researchers 

provide a list of typical locations that often need to be sealed. This is not a comprehensive 

prescriptive approach, but it will help contractors meet the performance targets. A simplified 

version of the best practices is presented in Table 17. An expanded version is included in 

Appendix C. 
48

Table 17. Summary of Current Best Practices (Appendix C)

Components and 

Strategies Replacement Measure Specifications

Additional Requirements and 

Recommendations for All Projects and 

Maintenance/Repair Measures for 

Components Not Being Replaced

Combustion Safety

Locate combustion appliances in unconditioned space when feasible; if combustion appliances are in 

conditioned space or attached unconditioned space, perform combustion zone safety procedures to 

ensure an adequate supply of combustion air and install carbon monoxide detectors.

Mechanical 

Equipment and Air 

Distribution

A three-part guideline details specifications for 

replacing mechanical equipment. The guideline is 

segmented into the following sections:

1. HVAC Assessment, Design, and 

Specifications

2. HVAC Installation

3. Post-retrofit HVAC Testing and Verification

Key components addressed within the sections of 

the guideline include:

• ENERGY STAR (minimum SEER 14.5) 

qualified conditioning equipment

• Ensure ducted returns

• Ensure flex duct collars are fully insulated

• Seal off all joints and edges (preferably with 

mastic) in supply ducts, return plenum, and 

connections to air handler

• Ensure duct leakage to the outside ≤ 6% 

(Qn,out ≤ 0.06)

• Ensure new ductwork is strapped to trusses to 

achieve clearance over anticipated ceiling 

insulation

• Ensure any new ducts are insulated to R-value 

≥ 6

• Perform ACCA Manual J load calculation and 

A four-part guideline details specifications when

keeping an existing mechanical system. The 

guideline is segmented into the following 

sections:

1. HVAC Return Plenum and Passive Return 

Air Pathways

2. HVAC Service Mechanical Equipment

3. HVAC Test Duct System Airtightness Preretrofit

4. Post-retrofit HVAC Duct Testing and 

Verification

Key components addressed within the sections of 

the guideline include:

• For existing atmospheric combustion 

furnaces, provide adequate supply of 

combustion air 

• When feasible, retrofit a duct board plenum 

into platform returns, otherwise fully seal 

platform return

• When feasible, replace louvered doors on 

AHU closets with a correctly sized central 

return grille mounted in the wall (if adjacent 

to a living space) or in a solid door. 

• When feasible, replace AHU stands with 
49

Components and 

Strategies Replacement Measure Specifications

Additional Requirements and 

Recommendations for All Projects and 

Maintenance/Repair Measures for 

Components Not Being Replaced

size the system accordingly

• When feasible, install a dampered, passive 

mechanical ventilation duct to provide outside 

air to return plenum

• Ensure pressure balance between main body of 

the house and each bedroom

ducted return plenum

• Ensure servicing by HVAC contractor

• If measured duct leakage exceeds 6% (Qn,out 

≥ 0.06), identify and seal leakage points

• Ensure pressure balance between main body 

of the house and each bedroom

Ventilation

In addition to the passive mechanical ventilation 

system in the HVAC section, install kitchen and 

bathroom exhaust fan ducted to outdoors.

Install kitchen and bathroom exhaust fans ducted 

to outdoors.

Infiltration

Conduct pre- and post-retrofit blower door test to assess whole-house airtightness and identify leakage 

points. Target test result is ACH50 ≤ 6.0. Measure combustion zone pressure differences. Identify and 

repair duct and/or whole-house infiltration points if necessary to achieve proper balance. A list of 

common infiltration points is provided.

Roof

Achieve solar reflectance ≥ 0.25 with asphalt 

shingles, ensure proper installation of flashing, and 

install drip edge.

Ceiling Insulation

Before installing insulation, complete mechanical, electrical, and plumbing rough-in and replace “can” 

lights and fluorescent tube figures with insulation contact and airtight rated units. Support ducts above 

ceiling insulation. Insulate vented ceiling to achieve RESNET Grade I R-38. Insulate any interior attic 

hatch.

Knee Walls Ensure RESNET Grade I installation to R-13 or greater insulation.

Windows

Install ENERGY STAR-labeled windows with Uvalue ≤ 0.6 and SHGC ≤ 0.27. Ensure proper 

flashing installation, ensure proper cutting and 

wrapping of any house wrap, replace any rotted 

materials, air seal around opening, and caulk 

edges.

Ensure proper flashing installation, replace any 

rotted materials, air seal around opening, and 

caulk edges.

Exterior Walls If replacing drywall in frame construction, install 

RESNET Grade I R-13 insulation. Select light or 
50

Components and 

Strategies Replacement Measure Specifications

Additional Requirements and 

Recommendations for All Projects and 

Maintenance/Repair Measures for 

Components Not Being Replaced

white paint.

Floors If crawlspace, repair or install ground cover for vented areas, lapping joints 6 in., and continuing up 

stem wall 2 ft.

Water Heating Wrap tank with R-5 blanket and insulate accessible hot water pipes.

Appliances

Install ENERGY STAR-rated refrigerator, 

dishwasher, washing machine, and vent dryer to 

outdoors.

Vent clothes dryer to outdoors.

Lighting Install screw-in or pin-based CFLs where feasible.

Fans Select ENERGY STAR ceiling fans.

Moisture Remove moisture loading at walls and foundation.

Pool Add pool cover to existing or newly installed pool.
51

6 Conclusions

Based on the incremental cash flow available for 42 of the 46 deep retrofits in the hot-humid 

climate zone, the study fundamentally finds that cost-neutral deep energy retrofits of 30% or 

more improvement can be done, even under the more conservative finance terms described 

above. The emphasis here is that most of the key efficiency improvement strategies were applied 

at the time of replacement when higher performance items can be implemented for a relatively 

low incremental cost.

In general terms, this means that the incremental cost of higher performance components, 

equipment, and materials can often be justified at the time of natural replacement, based on the 

incremental savings over a comparable item of minimum performance. This is true also for the 

improvements made for energy efficiency reasons alone, such as ceiling insulation and duct 

sealing when existing conditions are poor. However, considering the renovation projects in this 

study, we find no evidence to suggest that the total cost of replacing equipment, components, 

materials, and systems in good working condition can be justified on the sole basis of anticipated 

energy savings, with the possible exception of CFLs. 

As expected, there was not a one-size, or one-package, fits-all solution for deep energy retrofits. 

The diversity of packages manifest in the 46 deep retrofits (Appendix B) plainly illustrates 

multiple paths to 30% savings within a core group of key strategies, depending on the condition 

of the house. In essence, the cost effectiveness (and therefore applicability) of any one of the key 

efficiency strategies in a particular house will depend on whether the existing condition justifies 

replacement.

Revisiting Table 15, we are reminded that an average savings of more than 30% was achieved by 

the most active partners in samples of houses with widely diverging characteristics producing a 

great range of post-retrofit HERS Indices. This bodes well for the concept of applying a common 

set of best practices across a community-wide renovation program where each house receives the 

best practice treatment in all replacement selections as well as a number of universally applicable 

measures such as combustion safety, duct and whole-house air sealing, and high efficiency 

lighting. Further research is needed to refine the best practices and research their implementation 

on a community scale.
52

References

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Homes. Steven Winter Associates, Inc., Norwalk, CT. Norwalk, CT: Consortium for Advanced 

Residential Buildings (CARB). Accessed 2013: http://apps1.eere.energy.gov/buildings/ 

publications/pdfs/building_america/meas_guide_seal_ducts.pdf.

Chandra, S. (2004). Standards for Clean Air Florida Homes. Cocoa, FL: FSEC. Accessed 2013: 

http://www.fsec.ucf.edu/en/publications/pdf/FSEC-GP-254-04.pdf.

Cummings, J. B.; Tooley, J. J.; Moyer, N. A.; Dunsmore, R. (1990). Proceedings of the ACEEE 

1990 Summer Study Impacts of Duct Leakage on Infiltration Rates. Space Conditioning Energy 

Use, and Peak Electrical Demand in Florida Homes. Pacific Grove, CA.

Cummings, J.; Withers, C.; Martin, E.; Moyer, N. (2012). Managing the Drivers of Airflow and 

Water Vapor Transport in Existing Single-Family Homes. Cocoa, FL: FSEC. Accessed 2012: 

http://www.fsec.ucf.edu/en/publications/pdf/FSEC-RR-384-12.pdf.

DOE. (2009). Builders Challenge Quality Criteria Support Document. Building America Best 

Practices Series Volume 8 Version 1.2. Richland, WA: Pacific Northwest National Laboratory.

Engebrecht Metzger, C.; Wilson, E.; Horowitz, S. (2012). Addendum to the Building America 

House Simulation Protocols. NREL/DE-AC36-08GO28308. Golden, CO: National Renewable 

Energy Laboratory. Accessed 2013: http://apps1.eere.energy.gov/buildings/publications/pdfs/ 

building_america/hsp_addendum_2012.pdf

Fonorow, K.; Chandra, S.; McIlvaine, J.; Colon, C. (2007). Proceedings from the 7th 

International Conference for Enhanced Building Operations. Commissioning High Performance 

Residences in Hot, Humid Climates. San Francisco, CA.

FSEC. (1996-2005). Energy Gauge USA, http://www.energygauge.com/usares/.

Hendron, R.; Engebrecht, C. (2010). Building America House Simulation Protocols. NREL/TP550-49426. Golden, CO: National Renewable Energy Laboratory. Accessed 2013: 

http://www.nrel.gov/docs/fy11osti/49246.pdf.

McIlvaine, J.; Beal, D.; Moyer, N.; Chasar, D.; Chandra, S. (2003). Achieving Airtight Ducts in 

Manufactured Housing. Cocoa, FL: FSEC. Accessed 2013: 

http://www.fsec.ucf.edu/en/publications/pdf/fsec-gp-234-03.pdf.

Moyer, N.; Beal, D.; Chasar, D.; McIlvaine, J.; Wither, C.; Chandra, S. (2001). Reprinted by 

permission from ASHRAE, Conference Proceedings IAQ2001. Moisture Problems in 

Manufactured Housing: Probable Cause and Cures. Accessed 2013: 

http://www.fsec.ucf.edu/en/publications/pdf/FSEC-GP-212-01.pdf

PNNL. (2010). Best Practices Series 7.1: High Performance Technologies Guide to Determining 

Climate Regions by County.PNNL-17211. Richland, WA: Pacific Northwest National 
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Laboratory; Oak Ridge, TN: Oak Ridge National Laboratory. Accessed 2013: 

http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/ba_climateguide_7_1.

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RESNET (2006). 2006 Mortgage Industry National Home Energy Rating Systems Standards. 

Chapter 8, Section 805: Work Scope and Combustion Safety Procedures. Oceanside, CA: 

RESNET.

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publications/pdfs/building_america/meeting_summary_50675.pdf.
54

Appendix A: 30% Energy Efficiency Solution Package

The 30% energy efficiency solution package described results from data collected from the 

retrofits of more than 70 homes studied under BA-PIRC. The study was conducted in central and 

north Florida, in the hot-humid climate zone. The characteristics of the base house were either 

the average (where appropriate) or most frequently occurring in the dataset.

Although the base house represents the typical characteristics found in the BA-PIRC research, it 

does not necessarily represent the average building in the hot-humid climate region. Most

buildings analyzed in the study group were previously foreclosed properties that were purchased 

and placed in community rehabilitation programs. In most cases, HUD NSP funds were used to 

purchase and renovate the homes. Community partners provided cost data based on actual 

expenditures; however, these costs could not be broken down into labor and materials categories.

A model of the base house was created in BEopt version 1.1 (Figure 40), an annual energy use 

simulation and optimization software. Envelope and equipment characteristics are shown in 

Table 18.

Figure 40. BEopt screen shot of base house
55

Table 18. Basic House Characteristics

House Characteristics Base House Improved House

Foundation Type Slab on grade Same

Exterior Wall Type Concrete block, R-0 Same

Attic/Roof/Ceiling 

Insulation Vented/shingle/R-19 Vented/shingle/R-38

Location of Ducts/Air 

Handler Attic/interior same

Window Type Single pane, metal frame, 

awning

Double pane, low-e, vinyl 

frame

Lighting/Appliances 10% fluorescent/standard

reference

80% fluorescent/ENERGY 

STAR reference

Heating Electric resistance Heat pump HSPF = 8.8

Conditioned area of the base house is 1,424 ft2

. This single-story, concrete block, single-family 

home has three bedrooms and two bathrooms. It is located in Orlando, Florida and is 

approximately 30 years old. 

The 30% improvement package includes equipment, appliance, lighting, and envelope elements 

consistent with the trends in the 70 retrofits in the BA-PIRC field study. The package is 

composed of the eight most prevalent improvements in the field study data (Table 19). 

Table 19. Prevalence of Key Efficiency Strategies in 70 Retrofit Field Study Homes

13 Key Efficiency Strategies All Houses

(n = 70)

1. Higher efficiency cooling and/or heating equipment 87%

2. Added ceiling insulation 83%

3. Reduced infiltration (ACH50 test results) 88%

4. Improved duct airtightness (Qn,out test results) 80%

5. Window film or windows with lower SHGC and/or U-value 67%

6. ENERGY STAR labeled refrigerator 74%

7. Higher efficiency water heater 59%

8. 30% more fluorescent lighting 49%

9. Programmable thermostat 46%

10. New ducts with higher R-value 30%

11. Lighter color exterior wall finish 23%

12. Lighter color roof finish 24%

13. Efficient ceiling fans 14%

Table 20 shows the “as found” and “replacement” characteristics for individual components of 

the package, as well as estimated costs, projected cost savings, and projected annual cash flow. 
56

Table 20. Projected Energy Savings and Economics Calculations for 30% Improvement Package 

191

$2,929

Home 

Component As Found 

Replacement or 

Improvement

Full First 

Cost

Incremental First 

Cost for Higher 

Efficiency at 

Replacement

Cost Used 

for 

Economic 

Calcs8

Annual 

Source 

Energy 

Savings 

(MBtu)1,4

Annual 

Energy 

Cost 

Savings 

($)1,2,4

Simple 

Payback 

(years)4

Annual 

Finance 

Cost for 

Retrofit at 

Resale ($) 3 

Annual 

Cash 

Flow if 

Financed 

($)3,4 

Heating and 

Cooling 

Straight Central AC, SEER 10, 

Electric Resistance Heating, 3 

Ton, Non Programmable 

Thermostat

Central Heat Pump, 

SEER 15, HSPF 8.8, 

3 Ton, Programmable 

Thermostat

$4,252 $4,252 44 $637 6.7 $343 $294

Windows (21) Single, clear, metal frame 

(U = 1.20; SHGC = 0.80)

Double Pane, Low-E, 

Vinyl frame, U value 

<= 0.5, SHGC <= 

0.35

$6,825 $3,150 $3,150 11 $154 20.5 $254 ($100)

Air Distribution 

System5

Older R-4 rigid ducts with 

leakage of 15%, central return

New R-6 ducts with 

leakage of 7.5%, 

central return

$1,196 -- $1,196 11 $157 7.6 $96 $61

Infiltration6,7 ACH50 = 12 ACH50 <= 6.0 $459 -- $459 8 $116 4.0 $37 $79

Lighting 20 fixtures; 2 CFL's (10%) 80% CFL's $56 -- $56 9 $132 0.4 $5 $127

Ceiling 

Insulation R-19 Fiberglass Batt

Add Blown-In 

Fiberglass to achieve 

R-38

$1,082 -- $1,082 7 $92 11.8 $87 $5

Refrigerator Default, 18.5 cubic inch Energy Star, 18.5 

cubic inch $750 $0 $0 4 $56 0.0 $0 $56

Water Heating 50 Gallon, electric (EF=0.88) 50 Gallon, electric 

(EF=0.92) $750 $0 $0 2 $31 0.0 $0 $31

Total for Package of Energy Improvements and Higher Efficiency Replacement Specifications4 $10,195 64 $928 11 $822 $106

Annual Savings (%) 34% 32%

1

 Annual energy use and energy cost calculations made with BEOpt version 1.1. Remaining economic analysis completed outside of BEopt. 

2

 Utility rate used for annual energy cost calculations was $0.1165 per kWh chosen from the BEopt utility library, Florida average.

3

 Finance terms at time of resale assumed to be 30 year mortgage at 7% interest.

5

 Air distribution system leakage is shown as a percentage of air handler flow.

6

 Whole house air tightness testing results shown in air changes per hour at a test pressure in the house of 50 pascals with respect to the outdoors.

7

 A portion of the infiltration improvement results from the window replacement. The cost associated with that improvement is included in the incremental window cost.

8

 The economic calculations use the Full First Cost when a measure is chosen strictly for efficiency improvement (e.g. ceiling insulation). Total first cost was used for Heating and Cooling system 

because we are counting total savings. The Incremental First Cost for Higher Efficiency at Replacement is used when a component is in need of replacement. For example, for Windows, incremental 

cost over replacement with single clear is used.

4

 Values in some columns can not be added to arrive at a total because of interaction among the measures. Values in the "Total for Package..." row are for the package of 

improvements considered all together.

As Found Annual Source Energy Use (MBtu)1

As Found Annual Energy Cost ($)1,2
57

The base home had an annual source energy use of 191 MBtu. At a utility rate of $0.1165/kWh 

(BEopt library Florida average), the estimated annual energy cost was $2,929.

The annual finance cost (column 10) for financing the cost of these efficiency improvements is 

compared to annual energy cost savings (column 8) to estimate annual cash flow (last column). 

Positive cash flow indicates that energy cost savings exceed the finance costs. For the whole 

improvement package, the modeling showed annual source energy savings of 34% (64 MBtu) 

and annual energy cost savings of 32% ($928).

The cost estimate for the improvement package was $10,195. Financed over a 30-year period at 

7% interest, the annual finance cost was estimated to be $822. This results in a calculated $106 

of annual positive cash flow. 

The economic calculations use the full first cost when a measure is chosen strictly for efficiency 

improvement (e.g., ceiling insulation). The incremental first cost is used for a higher efficiency 

or performance choice at the time of replacement. Replacement might be needed for 

functionality or to meet market standards. For example, when windows are replaced for 

functionality or market standards, higher than minimum performance windows could be chosen. 

Those would likely carry a cost premium. The economic calculations in Table 20 show a $3,150 

premium for choosing double-pane, low-e, vinyl frame windows instead of single-pane clear 

windows.

In this example, all individual improvements created positive annual cash flow except for the 

high performance windows, which were the second largest improvement package expense. The 

annual finance cost of $254 for the window retrofit exceeded the projected annual energy cost 

savings of $154, for a negative annual cash flow of $100. Note that the energy cost savings 

associated with the reduced infiltration of new windows are not captured in this measure’s 

savings. Also, the estimated incremental cost of the windows is purposely on the high side of the 

cost range to avoid overstating potential annual cash flow. During the field study, partners were 

given analysis showing the projected annual energy savings from higher performance 

replacement windows. Then the partner decided whether to make that upgrade. In some cases, 

the higher cost of more efficient windows may have created negative cash flow (for that single 

measure, not the whole package). Despite this, they installed the higher performance units in 41 

homes. They generally selected double-pane, low-e windows, even though they could have 

chosen basic replacement windows at a significantly lower cost. Anecdotally, partners point out, 

and researchers agree, that a missed opportunity for window replacement might not arise again 

for two or more decades. The higher performance window makes a significant contribution to 

overall energy savings, and there was net positive annual cash flow from the combined effect of 

the other improvements of $106.

Equipment and envelope conditions in existing homes vary widely, as do the costs for some of 

these components. Rather than a specific set of improvements, the 30% package proposed here 

should be considered as an example. In general, the field study showed that a combination of 

measures that address the efficiency of major end-use equipment and conditioning loads is 

needed to reach the 30% target. 
58

Appendix B: Deep Energy Retrofit Packages

Composition of Improvement Packages

Table 21 provides more detail for all 46 deep retrofits, including HERS Index and a 

representation of which of the 13 key energy efficiency strategies are incorporated in each deep 

retrofit. The houses are ranked in descending order of improvement (column 4). Each of the 13 

key strategies is shown as a column heading. A green cell with a “Y” for “yes” indicates 

inclusion of that measure in that house. “N” indicates “no” for measures not included. Because 

airtightness improvements are variable, ranges indicate improvement level in percentage 

reduction in ACH50 and Qn,out using the ranges 1%–25%, 26%–50%, 51%–75%, and > 75%. 

As discussed in Section 2.3 and Section 2.4.5 of this report, airtightness testing results were 

worse post-retrofit in some houses. This is indicated by the term “worse” in those columns. The 

term “untested” indicates that the house was not tested prior to renovation or in one case after 

renovation for reasons described in Section 3 and Section 2.4.5, respectively. In the domestic hot 

water column, the brighter green cells indicate much greater efficiency gains realized with a heat 

pump water heater (4) or tankless gas (1) over the much smaller efficiency improvement seen 

with tank-type and electric tankless units. The bottom row shows the prevalence of each key 

strategy in the deep retrofit dataset in descending order, exactly as shown in Table 19.
59

Table 21. Composition of Deep Energy Retrofit Packages

TestInTestOut

% 

Chan

ge

1 172 68 60% Y Y UntestedUntested Y N HP Y Y Y N Y N

2 165 74 55% Y Y >75% 51-75% Y Y Y Y N N Y N N

3 177 81 54% Y Y 51-75% 51-75% Y Y Y N N Y N N N

4 148 72 51% Y Y UntestedUntested Y Y Y Y Y Y Y Y N

5 160 78 51% Y Y UntestedUntested Y Y Y Y N N Y N N

6 164 84 49% Y Y 26-50% >75% Y N N N Y N N Y N

7 153 79 48% Y Y 51-75% Worse Y Y Y Y N N N Y N

8 160 83 48% Y Y 51-75% >75% Y Y TG N N Y N N N

9 151 79 48% Y Y 51-75% 51-75% Y Y N Y N N Y N N

10 142 76 46% Y Y UntestedUntested Y Y Y N Y N Y N N

11 164 88 46% Y Y 1-25% 26-50% N Y N N N N N Y N

12 121 65 46% Y Y Untested >75% Y Y Y Y Y Y N Y Y

13 130 70 46% Y Y UntestedUntested Y Y Y Y Y Y Y N N

14 131 71 46% Y Y 51-75% 51-75% N Y HP Y Y N N N Y

15 166 91 45% Y Y 26-50% Worse Y N Y N Y N N Y N

16 168 93 45% Y N 51-75% 51-75% Y Y N N N N Y Y N

17 136 76 44% Y Y 26-50% 26-50% Y N Y Y Y Y N N Y

18 131 74 44% Y Y 1-25% Untested Y Y N Y Y Y N N N

19 118 70 41% Y Y 1-25% Worse Y Y Y Y Y Y N N Y

20 116 69 41% Y Y 1-25% 26-50% Y Y Y Y N N Y N N

21 178 106 40% Y Y 26-50% 26-50% Y N N N N Y N N N

22 140 84 40% Y Y 26-50% 26-50% Y Y Y Y N N N N N

23 132 80 39% N Y 26-50% 51-75% Y Y Y Y Y N Y N N

24 142 87 39% Y Y 26-50% 26-50% Y N N N N N N N N

25 138 85 38% Y Y 51-75% >75% Y Y Y N N Y Y N N

26 106 66 38% Y Y 26-50% 51-75% Y Y HP Y N N N Y N

27 130 81 38% Y Y Untested >75% N N Y Y Y N Y N N

28 130 81 38% Y Y 26-50% Untested N N Y N N Y N Y N

29 132 83 37% Y Y 1-25% 1-25% Y Y Y N N Y Y N N

30 137 87 37% Y Y 1-25% 1-25% Y Y N N Y N N N N

31 118 75 36% Y Y 26-50% 1-25% Y Y Y Y Y Y Y N N

32 116 74 36% Y Y 1-25% Worse Y Y Y Y N N N N Y

33 140 90 36% Y Y 26-50% 51-75% Y Y Y N Y N N N N

34 130 84 35% Y Y Worse 26-50% N Y N N N N N Y N

35 184 120 35% Y N 26-50% 26-50% Y N N N N Y N N N

36 127 83 35% Y Y 26-50% 51-75% Y Y Y Y N Y N N N

37 120 79 34% Y Y UntestedUntested Y N Y N Y N N N N

38 111 74 33% Y Y UntestedUntested Y Y N Y N N N N N

39 120 81 33% Y Y 26-50% 51-75% Y Y Y Y N Y N N Y

40 117 79 32% Y Y Worse 26-50% Y Y N N N N N Y N

41 99 67 32% N Y 1-25% 26-50% N Y HP Y Y N Y Y Y

42 122 83 32% Y N 26-50% 51-75% N N Y Y Y Y N N N

43 125 86 31% Y Y Worse 26-50% Y Y N N Y N N N N

44 126 88 30% Y Y 1-25% Worse N Y Y N Y N N N N

45 114 80 30% Y Y 26-50% 26-50% Y Y N N Y N N Y N

46 122 86 30% Y Y 1-25% Untested N Y Y N N N N N N

96% 93% 92% 86% 80% 76% 70% 52% 48% 39% 30% 30% 15%

 13 Key Efficiency Strategies

Improvement

#1 

HVAC

#2 

Ceiling 

Insulation

#3 

House 

Leakage

#4 

Duct 

Leakage

#5 

Window

#6 

Refrigerator

#7 

Domestic 

Hot 

Water

#8 

30% + 

More 

CFLs

#9 

Programable Tstat

#10 

Duct RValue

#11 

Exterior 

Wall 

Color

#13 

Efficient 

Fans

% Deep Retrofits w/Measure: House Count

#12 

Roof 

Color
60

Energy Costs and Savings, Improvement Costs, and Cash Flow for Deep Retrofits

Cost-effectiveness information for each of the 46 deep retrofits is presented in Table 22. The first 

four columns show house count, HERS Index pre- and post-retrofit, and the improvements 

percentage. The table is sorted by HERS Index improvement (column 4) in descending order. 

The remaining columns show factors involved in the cost-effectiveness calculations, specifically:

• House count (column 1)

• HERS Index improvement (columns 2–4)

• Test-in projected annual energy cost (column 5)

• Test-out projected annual energy cost savings (column 6)

• Test-out projected annual energy cost savings over minimum (column 7)

• Total improvement costs (column 8)

• Incremental improvement costs (column 9)

• Incremental annual cash flow (column 10).

Columns 2 through 4 related to HERS Index improvement are discussed in Section 3.1. The 

factors in columns 5 through 10 are discussed after the table.
61

Table 22. Energy Costs and Savings, Improvement Costs, and 

Cash Flow for Deep Retrofits (n = 46)

Column 1 Column 5 Column 6 Column 7 Column 8 Column 9 Column 10

Test-In Test-Out % Change

1 172 68 60% $2,036 $1,087 $764 $31,882 $7,433 $165

2 165 74 55% $1,983 $863 $719 $18,571 $5,181 $301

3 177 81 54% $2,445 $999 $999 n/a n/a n/a

4 148 72 51% $2,669 $1,338 $525 $25,975 $4,520 $161

5 160 78 51% $2,020 $980 $420 $18,488 $4,326 $71

6 164 84 49% $2,030 $697 $697 $16,250 $3,204 $439

7 153 79 48% $1,817 $659 $530 $18,955 $5,167 $114

8 160 83 48% $1,880 $728 $728 $17,595 $3,011 $485

9 151 79 48% $2,561 $1,092 $902 n/a n/a n/a

10 142 76 46% $1,981 $674 $511 $11,496 $3,171 $255

11 164 88 46% $2,854 $814 $468 $22,648 $3,793 $162

12 121 65 46% $1,666 $595 $590 $24,384 $5,013 $186

13 130 70 46% $2,179 $785 $626 $45,326 $7,856 $7

14 131 71 46% $2,331 $702 $702 $13,103 $4,891 $308

15 166 91 45% $3,101 $1,055 $1,021 $19,152 $5,321 $592

16 168 93 45% $1,939 $639 $401 $19,146 $2,271 $218

17 136 76 44% $1,894 $578 $455 $21,430 $4,080 $126

18 131 74 44% $1,887 $599 $465 $9,570 $3,759 $162

19 118 70 41% $1,637 $536 $428 $8,385 $3,072 $180

20 116 69 41% $1,600 $475 $366 $22,623 $4,633 $7

21 178 106 40% $2,761 $955 $955 $21,200 $4,088 $626

22 140 84 40% $1,811 $567 $567 n/a n/a n/a

23 132 80 39% $1,746 $555 $555 $9,835 $3,386 $282

24 142 87 39% $1,923 $514 $266 $8,394 $781 $203

25 138 85 38% $2,106 $477 $477 $22,210 $4,693 $99

26 106 66 38% $1,946 $662 $662 $36,905 $8,382 $13

27 130 81 38% $1,739 $488 $487 $11,165 $4,040 $161

28 130 81 38% $1,592 $396 $400 $14,500 $3,400 $126

29 132 83 37% $1,558 $414 $386 $17,535 $4,623 $13

30 137 87 37% $1,727 $436 $414 $10,300 $3,821 $106

31 118 75 36% $1,617 $387 $387 n/a n/a n/a

32 116 74 36% $2,296 $711 $419 $39,308 $6,180 $79

33 140 90 36% $1,783 $509 $481 $8,974 $3,155 $227

34 130 84 35% $1,712 $414 $283 $14,029 $2,418 $88

35 184 120 35% $2,289 $593 $324 $7,580 $1,399 $211

36 127 83 35% $1,746 $364 $364 $14,835 $4,470 $4

37 120 79 34% $1,614 $316 $234 $8,085 $2,822 $7

38 111 74 33% $1,721 $410 $380 $14,325 $5,042 $26

39 120 81 33% $1,624 $312 $312 $11,600 $3,468 $33

40 117 79 32% $1,826 $399 $399 $4,536 $780 $336

41 99 67 32% $1,496 $495 $495 $12,156 $3,506 $212

42 122 83 32% $1,688 $462 $345 $9,055 $2,780 $121

43 125 86 31% $1,642 $349 $315 $6,195 $1,800 $170

44 126 88 30% $1,963 $453 $302 $5,053 $1,813 $156

45 114 80 30% $1,437 $277 $177 $11,573 $2,448 $20

46 122 86 30% $1,766 $359 $287 $5,488 $1,868 $136

Min: 99 65 30% $1,437 $277 $177 $4,536 $780 -$79

Max: 184 120 60% $3,101 $1,338 $1,021 $45,326 $8,382 $626

Average: 138 81 41% $1,949 $612 $500 $16,424 $3,854 $169

Test-Out 

Projected 

Annual 

Energy Cost 

Savings Over 

Minimum2

Total 

Improvement 

Costs

Incremental 

Improvement 

Costs

Incremental 

Annual Cash 

Flow

1

The change in HERS Index is not necessarily equivalent to the change in projected annual energy cost . This relates to the calculation procedures 

outlined in the RESNET Home Energy Rating System Standard.

 HERS Index Improvement

House Count

Test-In 

Projected 

Annual 

Energy Cost

Test-Out 

Projected 

Annual 

Energy Cost 

Savings1

 Deep Retrofits (30% HERS Reduction or more): Energy Costs, Savings, Improvement Costs, & Incremental Cash Flow

2

The "Minimum" is a revision to the 'test-in' scenario to include: 1) the federal minimum efficiency standard for air conditioner replacement (SEER 

13), if the system was replaced, and 2) test-out house envelope size alterations (with normalized test-in leakage results). Associated improvement 

costs and energy cost savings for both have been removed from the cash flow calculation.

Columns 2-4 
62

Test-In Projected Annual Energy Cost (column 5)

Projected annual energy cost for the pre-retrofit homes ranged from $1,437 to $3,101, and 

averaged $1,949 (sd = $376).

Projected annual energy calculations were produced using EGUSA with the operating and 

thermostat schedules designated by the 2006 HERS Standard (RESNET 2006). Because of 

calculation procedures in the HERS Rating Standard, the percent change in HERS Index does 

not match the percent change in projected energy costs. To allow comparison among the 

retrofits, the annual energy cost calculations were made using a standard utility rate of 

$0.13/kWh, $1.72/therm of natural gas, and $1.40/gal of propane (one home). This is a known 

bias in the study in that local utility rates may be higher or lower; however, in the interest of 

studying the whole dataset, utility rates needed to be standardized. Although using the annual 

energy use rather than the annual energy cost would have allowed comparability without this 

complication, it would not have provided a path for the cost-effectiveness calculations. Where 

utility rates were higher or lower than the standardized rate, resulting annual cash flow would 

have been higher or lower, respectively.

Test-Out Projected Annual Energy Cost Savings and Savings Over Minimum

(columns 6 and 7)

Projected annual energy cost savings for each deep retrofit are presented in two ways. The first 

(column 6) is a straightforward difference between projected pre- and post-retrofit annual energy 

costs. Projected annual savings over the as-found condition ranged from $277 to $1,338, with an 

average of $612 (sd = $244, column 6). 

The second (column 7, Test-Out Projected Annual Energy Cost Saving Over Minimum) 

addresses a nuance of retrofit savings calculations that is important in relation to calculating 

incremental cost.

In some cases, an item could not be replaced with one of equal efficiency or specification. This 

complicates calculating incremental cost in some scenarios, such as when a SEER 10 heat pump 

is being replaced with a SEER 15 unit, because SEER 10 units cannot be purchased. In these 

cases, cost cannot be obtained for an “apples to apples” replacement. Incremental savings and 

costs are calculated instead in comparison to the pre-retrofit house with a SEER 13 central, split 

system air conditioner paired with either an integral electric resistance heating element (COP = 

1) or a naturally aspirated gas furnace (0.78 AFUE) depending on the pre-retrofit heating fuel. 

One exception to this is when an as-found unit with SEER 12 heat pump would have lower 

annual energy cost than SEER 13 with electric resistance heating. To create a less efficient basis 

of comparison would effectively overstate the savings; thus, comparisons in these cases are made 

to the original system.

These issues arise also when conditioned area is reduced. For example, comparing R-38 over a 

1,500 ft2 (post-retrofit area) to R-9 over 2,000 ft2 (pre-retrofit area) would exaggerate the project 

cost energy savings.

These few items are combined into a modified version of the pre-retrofit house called “Minimum 

Improvement,” which represents the pre-retrofit house with adjusted size (five houses) and 

minimum efficiency or specification replacements. Annual savings compared to this scenario are 
63

shown as “Projected Annual Energy Cost Savings Over Minimum” (column 7). Excluding the 

savings from any reduction in conditioned area and cooling efficiency improvement up to SEER 

13, the savings over minimum ranged from $177 to $1,092, with an average of $500 (sd = 

$201).In retrofits where there was no change to the conditioned area and the air conditioner was 

not replaced or was replaced with a SEER 13, there is no difference between column 6 and 

column 7. For examples, see houses 6 and 8.

Total and Incremental Improvement Costs (columns 8 and 9)

Improvement costs are characterized in two ways: total cost and incremental cost. Many of these 

homes needed extensive repair to bring them up to local market standards, costing tens of 

thousands of dollars. Only costs associated with energy-related elements of the renovation are 

being reported here in Total Improvement Costs (column 8). For example, costs for cabinets, 

interior painting, electrical system repairs, and other nonenergy-related items are not reported.

Researchers requested that partners provide costs for individual energy-related improvements in 

each house. Partners provided costs for 42 of the 46 deep retrofits (as well as 21 of the other 

homes). Total improvement costs (column 8) ranged from $4,536 to $45,326 and averaged 

$16,424 (sd = $9,262). 

When labor and materials were donated or heavily discounted, partners were unable to provide 

meaningful costs. In several cases, the partner was unable to provide cost information for all the 

elements of the improvement package. In these cases, researchers estimated costs, relying on 

reported costs for the same or similar items in a different home or bid documents, which are 

often identical to actual invoices in these projects. There are four deep retrofits for which 

researchers received no cost information. Accounting for the costs associated with improving the 

envelope leakage measure was also not possible in any of the houses. Typically, this 

improvement was simultaneous with other improvements such as window replacement, drywall 

repair, and lighting and plumbing fixture replacements, rather than an extensive air sealing 

campaign.

Researchers found no evidence that the total cost for replacing functional equipment and 

components in good condition could be offset by projected annual energy cost savings. However, 

when an energy-related item needs to be replaced, the incremental cost of choosing higher 

performance options can often be offset by the incremental savings. Incremental cost (column 9) 

is the portion of total cost related to higher performance specifications when energy-related items 

needed to be replaced. For example, when a water heater is worn out and must be replaced, it 

could be replaced with a unit of the same (or nearly the same) efficiency; a higher performance 

unit can be purchased for a slightly higher cost. That cost difference is the incremental cost that 

would be added to the mortgage for higher performance. This accounting strategy parallels the 

decision-making process. It responds to the question, “If the water heater needs to be replaced, is 

a higher performance specification worth the money?” As described previously incremental costs 

and savings were sometimes calculated in comparison to a modified version of the pre-retrofit 

home when equipment cannot be replaced with models of like efficiency.

In the 42 deep retrofits for which we have cost information, total incremental cost, or cost over 

replacement with like efficiency, ranged from $780 to $8,382 and averaged $3,854 (sd = 1,687).
64

Incremental Annual Cash Flow (column 10)

In all cases, the incremental mortgage burden is compared to the “Projected Energy Savings 

Over Minimum” scenario (column 7) for the whole package of improvements to generate the 

Incremental Annual Cash Flow (column 10). Numbers in black indicate positive cash flow in 36 

of the 42 deep retrofits with improvement cost data. “n/a” indicates that the partner did not 

provide cost data. Incremental annual cash flow ranged from –$79 to $626 and averaged $169 

(sd = 158). Cash flow was positive in all but six cases (86% were positive).

The six retrofits with negative cash flow are discussed in Section 3.3.
65

Appendix C: Draft Current Best Practices

Preliminary Standard Building Science and Energy Efficiency Guidelines

Items italicized and in red indicate required measures.
66
67
68
69
70

Appendix D: Sarasota NSP Energy Conservation Standards

After participating in Part 1 of this Building America research, the Sarasota Office of Housing 

and Community Development (Sarasota County and City of Sarasota, Florida) developed this set 

of standard specifications in consultation with BA-PIRC, HERS raters in the Sarasota region, 

non-profit housing providers in the community, and staff. 

NEIGHBORHOOD STABILIZATION PROGRAM 2

ENERGY CONSERVATION STANDARDS

Exterior Standards

Exterior Siding and Trim – All siding and trim must be intact, waterproof and free of 

deterioration. Replacement of damaged sections may include up to 25% of sound surfaces. If 

more than 25% of the section is damaged, the entire section must be replaced. All exterior 

surfaces must have a continuous coat of paint or bonded finish with an expected life of at least 5 

years.

Replacement standard – All siding that is replaced must be sensitive to the historic nature 

of the home. All exterior painting must be light color or white with low or no Volatile 

Organic Compounds (VOCs).

Roofs – All roofs must be weather tight. Shingles must be in good shape and show no signs of 

blistering or curling. Missing shingles and flashing must be repaired or replaced. Broken 

antennas must be removed. All roofs must have at least a ten-year minimum expected useful life 

and be installed after March 1, 2001.

Replacement standard – Flat roofs will be replaced with 10-year rated material and any 

roof coating must be ENERGY STAR qualified. Pitched roofs will be replaced with an 

ENERGY STAR minimum 25 year rated shingle. If an ENERGY STAR shingle is not 

available, the shingle must be a light color. The entire roof deck must be re-nailed in 

compliance with the hurricane mitigation manual section 201.1 and a secondary water 

barrier shall be provided as required by section 201.2. Roof to wall connections will be 

installed and facilitated as deemed appropriate by OHCD inspector.

Insulation – Attics must be insulated to R-30. Exterior walls only need to be insulated if the 

plaster or drywall is removed. 

Replacement standard – All new insulation must use formaldehyde-free recycled content 

materials such as fiberglass or cellulose and if new or additional insulation is being 

installed, it must be brought to R-38.

Windows – Each habitable room, excluding the kitchen, bathroom and interior rooms must have 

at least one window. All windows must be weather tight and those accessible from the ground 

must have locking hardware. If the existing windows will remain, the OHCD inspector is to 

consider the use of solar window film on windows facing the south or west. 
71

Replacement standard – Replacement windows will be dual pane ENERGY STAR

insulated window for our climate zone with impact glass. Bathrooms windows must be 

opaque or have a window covering if viewable from the outside.

Window protection – All openings must have hurricane protection by either having hurricane 

resistant glass or shutters.

Replacement standard – If windows are not being replaced, each opening must have 

shutters installed that meet the Florida Building Code for newly constructed housing in 

the area. 

Caulking and weather stripping – All windows and doors must be caulked and/or weather striped 

and in an excellent condition.

Replacement standard - Caulk and weather-strip doors and windows, using foam sealant 

for larger gaps. Install foam gaskets behind outlet and switch plates on walls. Replace 

leaky door thresholds with ones that have pliable sealing gaskets.

WeatherizationWhere accessible all areas where plumbing, ducting, or electrical penetrates through 

walls, floors, ceiling must be sealed. All attic leaks where walls meet attic floor, dropped 

soffits, behind kneewalls, attic hatch or door, etc must be sealed.

HVAC

Heating plant – Each unit must have a heating system capable of heating the unit to 68 

degrees when the outside temperature is 40 degrees. All HVAC systems must have a 

SEER rating of at least 13 and be less than 8 years old. If the existing HVAC unit is not 

replaced, the following services must be performed: inspect condensate drain while in 

cooling mode; Inspect, clean, and/ or change air filter; clean indoor and outdoor coils; 

check central AC refrigerant charge and charge if needed.

Replacement standard – An ENERGY STAR unit with a SEER rating of 16 or greater 

will be installed. In cases where the existing space does not permit the installation of a 16

SEER rated unit, an ENERGY STAR unit with a minimum SEER rating of 15 may be 

installed. A Manual J form must be submitted to OHCD prior to specification and 

purchase of unit.

Ducts –All ducts must be deemed to be in an excellent condition. If the ducts are not 

being replaced, a Duct Test must be all and all joints and connections must be sealed with 

duct mastic with a goal of 6% or less leakage. Where the duct meets floor, wall, or 

ceiling, the gaps must be sealed.

Replacement standard –All ductboard must have a minimum insulation of R-6. Flexible 

Ducts shall be class 1. All systems shall be designed to minimize ductboard lengths and 
72

all plenums shall be sealed and constructed in accordance with the Florida Mechanical 

Code.

Thermostats – All units must have a programmable thermostat controlling the HVAC 

unit.

Replacement standard – An ENERGY STAR 7-day programmable thermostat that 

controls each zone must be installed.

Vent Fans

Replacement Standard- All newly installed kitchen and bathroom fans must be ENERGY STAR.

Appliances and Equipment

Hot Water Heater – All units must have a water heater capable of producing 100 degree F 

at the faucet and must not be more than 8 years old.

Replacement Standard – All new hot water heaters must be an ENERGY STAR qualified 

model.

Refrigerators – All units must have a working refrigerator that is less than 10 years old 

that is appropriately sized for the home and capable of keeping food cold.

Replacement standard – An ENERGY STAR labeled model.

Dishwasher - Units are not required, but may have dishwashers.

Replacement standard – An ENERGYSTAR unit must be installed The unit must be a 

CEE tier 2 with a minimum energy factor of 0.68 or greater, have a maximum annual 

energy use of 325 kWh or less and have a water factor of 6.5 or less.

Ceiling fansReplacement Standard – All new ceiling fans must be ENERGY STAR labeled. New 

ceiling fan light kits must be ENERGY STAR.

Lighting 

Fixtures – Eighty Percent of all light fixtures must have ENERGY STAR LED or CFL or 

fluorescent light bulbs installed in the fixtures.

Replacement standard – All replaced lighting and lightning fixtures must use ENERGY 

STAR LED or CFL light bulbs.
73

Plumbing

Toilet – All units must have a working toilet with a maximum 1.6 gallons.

Replacement standard – All units must be WaterSense labeled (1.28 gallons or less per 

flush).

Shower heads – All shower heads must be WaterSense labeled (2 gallons or less per 

minute)

Bathroom Faucets – All bathroom faucets must be WaterSense labeled (1.5 gallons or 

less per minute) or retrofitted with a WaterSense labeled faucet aerator.

Kitchen Faucets – All kitchen faucets must have flows of 2.2 gallons or less per minute

Landscaping – All exterior downspouts that are not on the front of the home must be 

connected to a rain barrel or cistern to reduce runoff and provide rainwater harvesting for 

landscape purposes. All renovated landscaping shall follow the guidelines of the 

SWFWMD Florida Water Star Program for existing homes to conserve water.

Shut off valves 

Replacement Standard- All shut off valves shall be replaced with quarter turn or 

push/pull turn offs. All supply lines shall be reinforced or armored.

Well – All wells will be inspected to insure that they are safe.

Indoor Environmental Quality (IEQ)

The existing specifications will be changed to only use LOW OR NO VOC paints, glues, 

adhesives, solvents, cleaners and finishes to minimize occupant exposure to chemicals.
DOE/GO-102013-3896 ▪ March 2013

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