Cost Effectiveness of 

Home Energy Retrofits in 

Pre-Code Vintage Homes 

in the United States

Philip Fairey and Danny Parker

BA-PIRC

November 2012
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iii

Cost-Effectiveness of Home Energy Retrofits in 

Pre-Code Vintage Homes in the United States

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:

Philip Fairey and Danny Parker

BA-PIRC/Florida Solar Energy Center

1679 Clearlake Road, Cocoa, FL 32922

NREL Technical Monitor: Stacey Rothgeb

Prepared under Subcontract No. KNDJ-0-40339-02

October 2012
iv

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v

Contents

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

List of Tables .............................................................................................................................................. vi

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

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

2 Methodology ......................................................................................................................................... 3

2.1 Archetypes...........................................................................................................................3

3 Simulation Modeling ............................................................................................................................ 6

4 Other Considerations in the Optimizations ....................................................................................... 7

5 Economic Model ................................................................................................................................... 8

5.1 General Inflation Rate and Discount Rate ...........................................................................8

5.2 Optimization Method...........................................................................................................9

5.3 Equipment Replacement ......................................................................................................9

6 Energy Price Rates............................................................................................................................. 11

7 Retrofit Improvement Measures........................................................................................................ 12

8 Improvement Cost Model................................................................................................................... 16

9 Results................................................................................................................................................. 24

9.1 Archetype Baseline Energy................................................................................................24

10 Cost Optimization Results................................................................................................................. 28

10.1 Optimization Scenario 1 ........................................................................................28

10.2 Optimization Scenario 2: Homeowner Financing..................................................31

10.3 Optimization Scenario 3: HVAC Contractor Financing........................................32

10.4 Optimization Scenario 4: Home Remodel Refinancing.........................................38

10.5 Method in Action: Optimization Results for a Specific Home..............................40

11 Conclusions ........................................................................................................................................ 43

References................................................................................................................................................. 46

Appendix A. Calculation of Economic Cost Effectiveness Section of RESNET Standards........ 48

Appendix B. Determination of HVAC Equipment Costs.................................................................. 53

Appendix C. Optimization Scenario 1— Default Economic Parameter Model.............................. 57

Appendix D. Optimization Scenario 2— Homeowner Financing Home Improvement Loan Model69

Appendix E. Optimization Scenario 3— HVAC Contractor Financing Business Model .............. 79

Appendix F. Optimization Scenario 4— Home Remodel/Refinance.............................................. 89
vi

List of Figures

Figure 1. Histogram of achievable source energy reductions in 14 climates using four different 

financing alternatives........................................................................................................................... x

Figure 2. U.S. Census Bureau data on existing housing unit construction vintage by decade........ 1

Figure 3. Median U.S. home size from U.S. Census Bureau data: 1973–2010...................................... 3

Figure 4. Starting screen for CostOpt..................................................................................................... 22

Figure 5. Ft. Worth analysis using full costs for all measures and outright replacement ................ 34

Figure 6. Ft. Worth analysis using incremental costs (natural replacement costs) for all measures34

Figure 7. Source energy savings bins for the four optimization scenarios........................................ 40

Figure 8. Optimization results for a specific home in Ft. Worth, Texas .............................................. 42

Figure 9. Results from regression analysis of CostOpt HVAC cost estimates .................................. 54

Figure 10. Comparison of CostOpt HVAC cost estimates and NREL HVAC cost estimates ............ 56

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

List of Tables

Table 1. Pre-Code Vintage Existing Archetype Home Characteristics by IECC Climate Zone........... 4

Table 2. Economic Parameter Values ....................................................................................................... 8

Table 3. Household Energy Cost Index .................................................................................................... 9

Table 4. Statewide Revenue-Based Energy Rates................................................................................. 11

Table 5. Description of Retrofit Improvement Measures ...................................................................... 12

Table 6. Example Cost Calculations for 1600 ft2, Slab-on-Grade, Wood-Frame Archetype Home... 18

Table 7. Calculation of Annual Maintenance Costs f8 or Specific Items ............................................ 21

Table 8. Comparison of Baseline Home Energy Uses With 2005 RECS Data..................................... 24

Table 9. Archetype Descriptions, Locations, and Baseline Energy Uses and Costs ........................ 26

Table 10. Optimization Scenario 1—Default Economic Parameter Optimizations............................. 29

Table 11. Optimization Scenario 2—Home Improvement Mortgage Optimizations........................... 31

Table 12. Optimization Scenario 3—HVAC Replacement Optimizations ............................................ 37

Table 13. Optimization Scenario 4—Home Refinance Optimizations.................................................. 38

Table 14. Weighted Average Source Energy Savings and Average NPV for Four Optimization 

Scenarios............................................................................................................................................. 39

Table 15. NREL Cost Estimates for Heat Pumps ................................................................................... 55

Table 16. NREL Cost Estimates for Air Conditioners............................................................................ 55

Table 17. NREL Cost Estimates for Gas Furnaces ................................................................................ 55

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

Definitions

ACH50 Air changes per hour

AEU Average source energy use

AFUE Annual fuel utilization efficiency

AHU Air handling unit

ASHRAE American Society of Heating, Refrigerating and Air Conditioning 

Engineers

BEopt Building Energy Optimization

CF Cubic feet

cfm Cubic feet per minute

CFL Compact fluorescent lamp

CMU Concrete masonry wall system

Crwl Crawlspace foundation

CZ Climate zone

DnPmt Down payment rate

DR Discount rate

EA Number of each

EAC Equivalent annual cost

EF Energy factor

EIA Energy Information Administration

ER Energy inflation rate

FMC Fixed measure cost

Frm Frame wall system

GF Gas furnace archetype (natural gas space and water heating)

GR General inflation rate

GSF Gross square feet

HEM Home energy management

HP Heat pump archetype (electric space and water heating)

HSPF Heating seasonal performance factor

HVAC Heating, ventilation, and air conditioning

HW Hot water

IECC International Energy Conservation Code
viii

kBtu One thousand British thermal units

kWh Kilowatts per hour

LED Light-emitting diode

LF Linear feet

MBtu One million British thermal units

MMC Minimum measure cost

MR Mortgage interest rate

MURS Minimum upgrade reference ratio

NPV Net present value

NSF Net square feet

pEA Unit cost per each item (normally appliances, etc)

pCF Unit cost per cubic foot (normally the house volume)

pGSF Unit cost per gross square foot (normally for skin finish cost)

pLF Unit cost per linear foot (normally the perimeter)

pNSF Unit cost per net square foot (normally applied to walls only)

pSFpR Unit cost per square foot per ΔR (normally blown insulation applied

to GSF)

PV Photovoltaics

ΔR R-value difference between existing home and improvement 

measure

RECS Residential Energy Consumption Survey

ReFi Refinance

RESNET Residential Energy Services Network

SEER Seasonal energy efficiency ratio

SHGC Solar heat gain coefficient

SIR Savings-to-investment ratio

SOG Slab-on-grade

StDev Standard deviation

Sty Story

TMC Total measure cost

UC Bsmt Unconditioned, unfinished basement foundation
ix

Executive Summary

This analytical study examined the opportunities for cost-effective energy efficiency and 

renewable energy retrofits in residential archetypes constructed before 1980 (Pre-Code) in 14 

U.S. cities. These cities represent each International Energy Conservation Code climate zone in 

the contiguous United States.

The analysis was conducted using an in-house version of EnergyGauge USA v.2.8.05 named 

CostOpt that was programmed to perform iterative, incremental economic optimization on a long 

list of residential energy efficiency and renewable energy retrofit measures. The principal 

objectives were to:

• Determine the opportunities for cost-effective source energy reductions in this large 

cohort of existing residential building stock as a function of local climate and energy 

costs.

• Examine how retrofit financing alternatives impact the source energy reductions that are 

cost-effectively achievable.

A key finding was that the energy efficiency of even older, poorly insulated homes across U.S. 

climates can be dramatically improved. Moreover, with favorable economics, they can reach 

performance levels close to zero energy when evaluated on an annual source energy basis.

Findings indicated that retrofit financing alternatives and whether equipment requires 

replacement had considerable impact on the achievable source energy reduction in this cohort of 

residential building archetypes. 

Figure 1 shows the study results. The four optimization scenarios examined are:

1. Default 30-yr. 30-year mortgage at 6.15% interest using full replacement cost

2. Home Improve 7-yr. 7-year mortgage at 6.15% interest using full replacement cost

3. incHVAC 7-yr. 7-year mortgage at 6.15% interest using incremental HVAC costs

4. ReFi 30-yr. 30-year refinance mortgage at 4.0% interest using full replacement costs.
x

Figure 1. Histogram of achievable source energy reductions in 14 climates 

using four different financing alternatives

The figure shows that the standard short-term home improvement mortgage option seriously 

restricts cost effectiveness. However, at the same time, if only the incremental costs of 

replacement for heating, ventilation, and air-conditioning (HVAC) equipment are used in the 

analysis (the HVAC equipment is no longer operational), a short term mortgage can result in 

significant energy reductions. And, as expected, the home refinance option results in the largest 

potential for source energy savings in this residential cohort.

If home energy retrofits and their attendant energy cost and environmental emission reductions 

are considered advantageous to society as a whole, these results also have general policy 

implications:

• HVAC contractors should be encouraged to take advantage of low incremental 

replacement costs to substantially improve homes using short-term financing.

• Home refinance and resale opportunities offer a significant advantage to dramatically 

improve home energy efficiency.

• The foreclosure marketplace and 30-yr mortgages should be a focus for home 

improvement opportunities.

The findings relative to specific measures and how they perform across climates, utility costs,

and financing scenarios are:

• What works everywhere. Compact fluorescent lamps, duct sealing, ceiling insulation, 

hot water tank wraps, low-flow fixtures.
xi

• What works in some places. Frame wall insulation, crawlspace wall insulation, solar 

water heating, heat pump water heaters, photovoltaic systems, appliances that need 

replacement and have low incremental costs.

• What does not work anywhere. Outright replacement of windows; most expensive

HVAC systems, and roof replacement.
1

1 Introduction

Many U.S. homes were constructed before the advent of building energy codes. In 1975, the 

American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 

promulgated Standard 90-75, which is widely regarded as the first U.S. residential energy code. 

Since that time, housing energy efficiency has significantly improved in many states. However, 

pre-code housing remains a significant fraction of the nation’s housing stock.

According to the U.S. Census Bureau, almost 25 million of the nation’s 130 million existing 

housing units were built in the 1970s. The data comprising Figure 2 also show that more than 

62% of existing housing was constructed before 1980, when building energy codes first began to 

be adopted. A significant fraction of this stock includes components that have never been 

improved since their original construction. Many comprise subdivisions and neighborhoods with 

similar home designs and construction types. These neighborhoods provide significant 

opportunities for targeted delivery of community-scale retrofit programs and projects.

Figure 2. U.S. Census Bureau data on existing 

housing unit construction vintage by decade

This study investigates the cost effectiveness of a large number of potential home energy retrofit 

measures using pre-code home archetypes that can be considered typical in a range of climates 

throughout the United States. The analysis is conducted using an in-house optimization version 

of EnergyGauge USA v.2.8.05 (EnergyGauge CostOpt) that has been configured to perform 

economic cost-effectiveness analysis in accordance with recent standards (RESNET 2012).

Similar cost-effectiveness analysis was conducted by Casey and Booten (2011) using BEopt 

software (Christensen et al. 2006; Polly et al. 2011). This investigation parallels this previous 

work, using a somewhat different economic model specified by a recent RESNET Standard 

(RESNET 2012). This study also uses home archetypes that vary from those used in the previous 

analyses. For example, the previous study did not evaluate housing archetypes with concrete 

masonry wall construction that is prevalent in the southeastern United States. This study also 
2

allows fuel switching (changing from electric equipment to gas equipment and vice versa) and 

examines how this can impact cost effectiveness under local climate and utility rate structures. 

This investigation also directly analyzes solar hot water and solar photovoltaics (PV). Also, 

contrary to the BEopt optimization scheme, the CostOpt method focuses on reductions to site 

energy cost rather than source energy use, as this is what consumers pay.
3

2 Methodology

2.1 Archetypes

The archetype home characteristics used in this investigation are presented in Table 1. They are 

largely characterized by the International Energy Conservation Code (IECC) climate zone in 

which the archetype is located. At 1,600 ft2, the conditioned floor area is significantly smaller 

than current practice but, according to the U.S. Census Bureau, this is consistent with homes 

constructed before 1980 (see Figure 3).1

Figure 3. Median U.S. home size from U.S. Census Bureau data: 1973–2010

These archetypes are similar to those used by Casey and Booten (2011) and by Parker et al. 

(1998), but they differ in some important ways. In climate zone 1 (southern Florida), only 

concrete masonry walls are considered and in climate zone 2 concrete masonry and frame wall 

system are considered. Additionally, the assumed archetype envelope and duct air leakage 

characteristics differ from those used by Casey and Booten. For example, Casey and Booten used 

envelope air leakage of 19 ACH50 in all locations; this investigation uses 12, 9, and 7 ACH50 in 

climate zones 1–2, 3–4, and 5–6, respectively. These much lower envelope leakage rates are 

supported in part by data collected in Florida on a large number of existing homes (McIlvaine 

2011) and are reasoned to more accurately characterize air leakage rates in other climates where 

a significant cost penalty is incurred for very leaky homes, inducing homeowners to caulk and 

weather strip their homes as matter of common do-it-yourself practice. That homes are somewhat 

tighter in colder climates has also been observed in evaluations of large databases with tested fan 

pressurization data (Sherman et al. 1986).

 1 U.S. Census Bureau. http://www.census.gov/const/C25Ann/sftotalmedavgsqft.pdf
4

Table 1. Pre-Code Vintage Existing Archetype Home Characteristics by IECC Climate Zone

Archetype Characteristics CZ 1-2 CZ 3-4 CZ 5-6

Conditioned floor area (ft2) 1,600 1,600 1,600

Foundation type SOG Crwl UC Bsmt

AHU location Garage Crwl UC Bsmt

Duct location Attic Crwl UC Bsmt

Duct insulation R-value 4.2 4.2 4.2

Duct leakage (cfm25/ft2 floor area) 0.11 0.11 0.08

Envelope ACH50 12 9 7

Roof solar absorptance 0.85 0.85 0.85

Wall solar absorptance 0.55 0.55 0.55

Ceiling R-value 10 15 20

Frame wall insulation R-value 1.5 5 7

Block wall insulation R-value none n/a n/a

SOG perimeter R-value none n/a n/a

Crawlspace floor R-value n/a 5 n/a

Basement ceiling (house floor) R-value n/a n/a none

Basement wall R-value n/a n/a none

Window U-factor 1.2 0.75 0.6

Window SHGC 0.8 0.7 0.6

Door U-factor 0.5 0.4 0.3

HP HSPF (y2004; standard; degraded) 6.5 6.5 6.5

HP SEER (y2004; standard; degraded) 9.6 9.6 9.6

AC SEER (y2004; standard; degraded) 9.6 9.6 9.6

Furnace AFUE (y2004; standard; degraded) 76% 76% 76%

Gas HW EF (y2004; 40 gal; standard) 0.59 0.59 0.59

Elec HW EF (y2004; 40 gal; standard) 0.92 0.92 0.92

HW pipe insulation R-value none none none

Lighting % fluorescent or equivalent 10% 10% 10%

Lighting kWh/yr 1,736 1,736 1,736

Refrigerator kWh/yr (y2004; 20 cf; SS/TDI) 717 717 717

Range/oven kWh/yr 447 447 447

Dishwasher kWh/yr (y2004; standard) 171 171 171

Clothes Washer kWh/yr (y2004; standard) 69 69 69

Clothes Dryer kWh/yr (y2004; standard) 970 970 970

Miscellaneous kWh/yr 2,000 2,000 2,000

Key to Table 1 abbreviations:

ACH 50: air changes per hour at a 50 Pascal pressure difference

AFUE: Annual fuel utilization efficiency

AHU: Air handling unit

CFM: Cubic feet per minute

Crwl: Crawlspace foundation

EF: Energy factor

HSPF: Heating seasonal performance factor

HW: Hot water

SEER: Seasonal energy efficiency ratio

SHGC: Solar heat gain coefficient

SS/TDI: Side-by-side, through the door ice

SOG: Slab-on-grade foundation

UC Bsmt: Unconditioned, unfinished basement foundation
5

Air distribution system leakage values are also supported by Walker (1998) and reinforced by 

recent measured Florida data (McIlvaine 2011; Walker 1998). These rates are expected to be 

consistent across a wide swath of the country. However, for the unconditioned basement 

archetypes (climate zones 5 and 6) it is reduced to account for leakage in basements, which 

results in significant regain and much less loss to the outdoors compared to cases where ducts are 

located in vented attics or crawlspaces. For instance, recent work in Wisconsin in unconditioned 

basement homes found that average tested duct leakage to the outside was only about 5% (Pigg 

and Francisco 2006)—one third the typical leakage rate in homes with attic ducts.

Equipment efficiencies for the archetypes are based on the assumption that all equipment is 2004 

vintage (currently 8 years old and halfway through its life expectancy) and is slightly degraded 

using a maintenance factor of 0.005 (see Hendron 2006). Lighting and appliance energy uses are 

based on the default values provided by RESNET (2012).
6

3 Simulation Modeling

The simulation analysis is conducted using EnergyGauge CostOpt, an implementation of 

EnergyGauge USA v.2.8.05 with cost optimization capability. CostOpt uses an enhanced version 

of DOE-2.1E to conduct detailed hourly simulations, including air distribution system leakage, 

duct system heat transfer, improved HVAC systems modeling that includes improved relative 

humidity (RH) and part load characterization as well as solar hot water and PV systems 

performance prediction.

CostOpt performs cost optimization using an iterative incremental assessment method. The 

analysis is “incremental” in that within any given category of improvement, such as insulation or 

equipment efficiency, a number of options are presented to the software such that various 

insulation values for each component, equipment efficiency, and their associated costs are 

evaluated against each other simultaneously during each iteration. An iteration comprises a 

simulation of each available improvement case on a measure-by-measure basis. At the 

conclusion of each iteration, the improvement measure with the largest present value savings to 

investment ratio (SIR; also known as the benefit to cost ratio) is incorporated into the home and 

the remaining improvement measures are evaluated again on an incremental measure-bymeasure basis for the next iteration. This iterative process is continued until all available 

measures that meet the user-specified SIR lower limit have been incorporated into the home.

CostOpt has been configured to “rank” measures within each iteration by net present value 

(NPV). Although this option is not used in this investigation, it is often considered the economic 

indicator of choice and, because it incorporates the improvement measures with the largest NPV 

first, it passes over many measures that are incorporated incrementally and later improved by the 

SIR ranking method. Thus, the NPV ranking method runs many fewer simulations (finishes 

faster). Nonetheless, the SIR ranking method is chosen for this investigation for two reasons: 

• It provides the incremental cost effectiveness of multiple options within a category of 

measures (e.g., it will select R-19 ceiling insulation and then later replace it with R-30 

insulation, usually installing other improvement measures). 

• It provides an opportunity to answer an important question: What are the most costeffective improvement measures to select if one has only a limited budget? This is a 

frequent constraint in many retrofit projects.
7

4 Other Considerations in the Optimizations

Other noteworthy simulation considerations:

• Optimization simulations generally allow fuel switching. The exception is in climate zone 

1, where there is little, if any, reasonable access to residential natural gas.

• Gas furnaces (without an air conditioning component) were not allowed to compete in the 

simulations if the baseline archetype did not contain a gas furnace. However, gas furnaceair conditioner combinations were always allowed to compete in the simulations, 

regardless of the equipment used for the baseline archetype.

• For the unconditioned basement homes, floor insulation (in the basement ceiling) was 

limited to climate zone 5, where house floor insulation measures were allowed to 

compete with basement wall insulation measures. For the coldest climate zone 6, floor 

insulation was not allowed to compete out of concern that it could lower basement space 

temperatures enough to allow freezing. In climate zone 6 archetypes, only basement wall 

insulation was allowed as a basement thermal improvement.

• PV systems are evaluated assuming full net metering such that each kilowatt-hour the PV 

system displaces is valued at the retail cost of electricity. This is true even when the PV 

system produces more electricity than the home actually uses. This situation is seldom 

encountered

• HVAC system sizing is dynamic in CostOpt. The building loads are calculated at the 

beginning of each iteration using the building configuration resulting from previous 

iterations. As a result, the building loads and required system capacity will decrease as 

improvements are made. This, in turn, reduces HVAC improvement costs commensurate 

with the reduction in building load and HVAC system capacity. HVAC measures are 

much more likely to become cost effective following improvements than they are at the 

start of the optimization.
8

5 Economic Model

CostOpt incorporates an economic model based on the Duffie and Beckman (1980) P1-P2 

methodology. This procedure calculates two factors (P1 and P2) that can be applied 

comprehensively to understand the cost effectiveness of energy-saving measures.

P1 is the ratio of the present value of the energy savings over the analysis period to the first year 

energy cost savings. P2 is the ratio of the present value of the improvement costs over the 

analysis period to the first cost of the improvement. In addition to standard rate parameters 

(general inflation, fuel inflation, mortgage interest, and discount rate), both P1 and P2 

incorporate the full range of applicable economic factors, including measure life, replacement 

cost, maintenance cost, property tax cost, salvage value, and income tax benefit into their 

calculation. As a result, if one knows the first cost of an energy improvement and the first year 

energy saving of the improvement, the present value SIR of the improvement is simply P1 times 

savings divided by P2 times cost. Likewise the NPV of the improvement is simply P1 times 

savings minus P2 times cost. Furthermore, one can also calculate the break-even cost (the cost at 

which SIR = 1) of an improvement given only the energy cost savings. This cost is simply P1 

divided by P2 times the first year energy cost savings.

A large part of this model (except income tax benefit and property tax cost) has recently been 

adopted by RESNET as part of its national consensus standard (RESNET 2012). In addition to 

the economic model, the RESNET standard specifies a standard methodology of determining the 

economic parameters values used in the model. The standard also dictates an economic analysis 

period of 30 years. A full description of the RESNET implementation, which is used in this 

investigation, is provided in Appendix A. In accordance with its standards, RESNET also 

publishes the economic parameter values2 that are intended for use in determining cost 

effectiveness (see Table 2).

Table 2. Economic Parameter Values

General Inflation Rate (GR) 2.39%

Discount Rate (DR) 4.39%

Mortgage Interest Rate (MR) 6.15%

Down Payment Rate (DnPmt) 10.00%

Energy Inflation Rate (ER) 4.42%

The economic model used here differs from that proposed by Casey and Booten (2011) in 

several important ways. 

5.1 General Inflation Rate and Discount Rate

The model used in this investigation differentiates between the general inflation rate and the 

discount rate; the model used by Casey and Booten sets them equal. The impact of setting these 

two economic parameters equal is to say that the investor expects no return on investment. 

However, it is not clear from Casey and Booten (2011) whether the discount rate they specify is 

 2 See http://www.resnet.us/standards/mortgage
9

the nominal discount rate or the real discount rate. For clarification, the discount rate provided in 

Table 2 is taken as the nominal discount rate, making the real discount rate for the analysis 

reported here equal to 1.95%. 

The Casey and Booten analysis also appears to set the energy inflation rate equal to the general 

inflation rate. The history of household energy costs during the past 10 years seems to contradict 

this assumption. Table 3 presents U.S. Bureau of Labor Statistics data on the household energy 

cost index since 2000.3 These data show that household energy costs rose at an annual compound 

rate of 4.42% between 2000 and 2010.

Table 3. Household Energy Cost Index4

Year 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

HHeI 122.8 135.4 127.2 138.2 144.4 161.6 171.1 181.7 200.8 188.1 189.3

HHeI = household energy cost index

Further evidence from the U.S. Energy Information Administration (EIA) shows that U.S. 

average revenue-based residential electricity rate rose from $0.0824/kWh in 2000 to 

$0.11.54/kWh in 2010. The annual compound rate for this rate change is 4.09%.

5.2 Optimization Method

The optimization method and philosophy used by BEopt (Polly et al. 2011) differ from that used 

by CostOpt. BEopt ranks available improvement measures based on the least equivalent annual 

cost (EAC) per percentage savings of annual average source energy use (AEU). Measures are 

thus selected that emphasize source energy use savings. On the other hand, CostOpt uses 

consumer-borne site energy costs, ranking available improvement measures based solely on the 

life cycle present value SIR of the improvement measure over the analysis period. This results in 

a different order of measure ranking and selection. Although source energy savings may be a 

good societal objective, the methodology employed here reflects energy costs that will be best 

appreciated by consumers.

5.3 Equipment Replacement

Another important methodological difference in the two methods is that BEopt assumes future 

costs and energy savings for replacing equipment on burnout for the baseline home (Minimum 

Upgrade Reference Scenario or MURS); CostOpt does not. Philosophically, the BEopt method 

can be justified from the perspective that these costs and savings will occur at some time in the 

future because equipment fails and minimum equipment standards may exceed those of the 

equipment in the home. The BEopt cash flow analysis assumes that these future payments will be 

in monies spent at the time of replacement and includes these payments (as well as the energy 

savings they induce) in the equivalent annual energy cost calculation for the upgrade. As a result, 

in the BEopt scenario, the equivalent annual cost for the MURS is higher than what consumers 

would normally consider when they shop for the lowest cost improvement or the lowest 

proposed bid.

 3 These data used in determining economic parameter values in RESNET (2012). 4 U.S. Bureau of Labor Statistics, Table 3A. Consumer Price Index for all Urban Consumers (CPI-U): U.S. city 

average, detailed expenditure categories http://www.bls.gov/cpi/cpi_dr.htm
10

The BEopt optimization analysis also allows this equipment to be replaced in the retrofit home in 

year 1 using a finance mechanism (5 years at 7% in the case of the Casey and Booten analysis). 

Thus, the cost of the year 1 replacement is effectively reduced by the difference between the 

present value of the future equipment replacement cost in the MURS and the year 1 replacement 

cost (including financing) in the retrofit case. Thus, older equipment will often be considered as 

having a lower retrofit cost than the out-of-pocket expense for its replacement. The impact of this 

assumption is large in the NREL assessment, as equipment and appliances are assumed to be 

halfway through their useful service life.

This approach makes a credible academic argument (and a reasonable way to consider financing 

from a societal perspective); however, in reality the full cost of any retrofit must be borne by the 

homeowner at the time of replacement. Thus, discounting year 1 retrofit costs using the present 

value of an anticipated future replacement cost does not bear on how much the home retrofit will 

actually cost the consumer. On the contrary, consumers are often fixated on the out-of-pocket 

costs of energy-related improvements, such that the CostOpt scheme better reflects homeowner 

decision making.

CostOpt does not incorporate future upgrade costs and energy savings in the reference case. 

Thus, the full improvement cost the consumer will face for the retrofit is used to calculate the 

SIR for measure ranking and optimization. As a result, CostOpt is typically more conservative in 

measure selection (especially for equipment upgrades) and is significantly more sensitive to the 

financing term than BEopt, and longer term financing is significantly more productive than 

short-term financing. We believe this better reflects the real constraints that most consumers 

consider in choosing efficiency-related home improvement options.
11

6 Energy Price Rates

The CostOpt investigation uses statewide, revenue-based energy price rates derived from the 

latest annual EIA databases5,6 for residential electricity and natural gas, respectively. In some 

instances (notably New York, California, and Maryland for electricity and New York, Arizona, 

and Florida for natural gas) the EIA residential energy price rates differ substantially from those 

used by Casey and Booten (2011). The energy price rates used for the 14 cities included in this 

investigation are given in Table 4. These may differ from the specific utility costs in the various 

locations, which could have a large impact on results. Further, the EIA utility revenue-based 

rates do not include state, local, and municipality utility taxes, which are typically 5%–15%.

Thus, these rates are very conservative for our initial optimization assessment.

Table 4. Statewide Revenue-Based Energy Rates

City State CZ $/kWh $/therm

Miami Florida 1 $0.1144 $1.844

Houston Texas 2 $0.1160 $1.115

Atlanta Georgia 3 $0.1007 $1.564

Los Angeles California 3 $0.1475 $1.023

Seattle Washington 4 $0.0804 $1.262

Phoenix Arizona 2 $0.1097 $1.636

Minneapolis Minnesota 6 $0.1059 $0.903

Detroit Michigan 5 $0.1246 $1.167

New York New York 4 $0.1874 $1.448

Ft. Worth Texas 3 $0.1160 $1.115

San Francisco California 3 $0.1475 $1.023

Denver Colorado 5 $0.1104 $0.838

Baltimore Maryland 4 $0.1432 $1.283

St. Louis Missouri 4 $0.0908 $1.202

U.S. Average $0.1154 $1.174

 5 http://www.eia.gov/electricity/data.cfm#sales

6 http://www.eia.gov/dnav/ng/ng_pri_sum_dcu_STX_a.htm
12

7 Retrofit Improvement Measures

Ninety retrofit improvement measures are included in the analysis. Table 5 shows the acronyms 

used for these measures and their descriptions. The category names in the second column are 

used to affect the incremental analysis such that if two measures have the same category name, 

they are effectively compared against one another on a cost differential basis. For example, if R19 ceiling insulation is accepted as the most cost-effective measure during the first iteration of 

the optimization, the cost for all other ceiling insulation options during subsequent iterations is 

equal to the difference in cost between the R-19 ceiling insulation that has already been accepted 

and the cost of the other ceiling insulation options that remain on the list of potential 

improvements. In this way, the various efficiency levels within a given category of measures are 

incorporated only as they become cost effective, often with intervening measures from another 

category incorporated in between.

Table 5. Description of Retrofit Improvement Measures

Acronym Category Description

SEER13HP AC-HP Minimum efficiency heat pump (SEER-13; HSPF-7.7)

SEER15HP AC-HP Improved efficiency heat pump (SEER-15; HSPF-9.0)

SEER18HP AC-HP High efficiency heat pump (SEER-18; HSPF-9.5)

SEER21HP AC-HP Very high efficiency heat pump (SEER-21; HSPF-10)

Mini-Split AC-HP Best efficiency mini-split heat pump (SEER-26; HSPF12)

SEER13AC AC-SH Minimum efficiency air conditioner with strip heat 

(SEER-13; COP-1.0)

SEER15AC AC-SH Improved efficiency air conditioner w/ strip heat 

(SEER-15; COP-1.0)

SEER18AC AC-SH High efficiency air conditioner with strip heat 

(SEER-18; COP-1.0)

SEER21AC AC-SH Very high efficiency air conditioner with strip heat 

(SEER-21; COP-1.0)

SEER13GF80 AC-GF Minimum efficiency gas furnace/minimum efficiency air 

conditioner (SEER-13; AFUE-80)

SEER13GF90 AC-GF Improved efficiency gas furnace/minimum efficiency air 

conditioner (SEER-13; AFUE-90)

SEER13GF96 AC-GF High-efficiency gas furnace/minimum efficiency air 

conditioner (SEER-13; AFUE-96)

SEER15GF90 AC-GF Improved efficiency gas furnace/improved efficiency air 

conditioner (SEER-15; AFUE-90)

SEER15GF96 AC-GF High efficiency gas furnace/improved efficiency air 

conditioner (SEER-15; AFUE-96)

SEER18GF96 AC-GF High efficiency gas furnace/high efficiency air conditioner

(SEER-18; AFUE-96)

AFUE-80 GF Minimum efficiency gas furnace (AFUE-80)

AFUE-90 GF Improved efficiency gas furnace (AFUE-90)

AFUE-96 GF High efficiency gas furnace (AFUE-96)

SealDucts Ducts Seal ducts to 6 cfm25-out per 100 ft2 conditioned floor 
13

Acronym Category Description

area

LeakFree Ducts Substantially leak free ducts at 3 cfm25-out per 100 ft2

conditioned floor area

IntDucts Ducts Install substantially leak-fee ducts inside the conditioned 

space

IntAHU Move air handler unit to inside the conditioned space

Ceil_R11 Ceiling_Ins Insulate ceiling to R-11

Ceil_R16 Ceiling_Ins Insulate ceiling to R-16

Ceil_R19 Ceiling_Ins Insulate ceiling to R-19

Ceil_R30 Ceiling_Ins Insulate ceiling to R-30

Ceil_R38 Ceiling_Ins Insulate ceiling to R-38

Ceil_R49 Ceiling_Ins Insulate ceiling to R-49

Ceil_R60 Ceiling_Ins Insulate ceiling to R-60

WhShngl Roof Replace roof shingles with white shingles (solar 

absorptance = 0.75)

DrkShngl Roof Replace roof shingles with dark shingles 

(solar absorptance = 0.92)

Wht Roof Roof Install a white metal roof (solar absorptance = 0.30)

RBS Install an attic radiant barrier system

CrwlFl_R11 CrwlFloor_ins Insulate floor between crawlspace and conditioned space 

to R-11

CrwlFl_R19 CrwlFloor_ins Insulate floor between crawlspace and conditioned space 

to R-19

CrwlFl_R30 CrwlFloor_ins Insulate floor between crawlspace and conditioned space 

to R-30

SOG_R5-2h SOG_ins Insulate slab perimeter edge to R-5; 2 ft deep

SOG_R5-4h SOG_ins Insulate slab perimeter edge to R-5; 4 ft deep

Tile Floor SOG_Floors Install tile floors on slab

Carpet SOG_Floors Install carpet floors on slab

Wood Floor SOG_Floors Install wood floors on slab

BsmtFl_R11 BsmtFloor_ins Insulate floor between unconditioned basement and 

conditioned space to R-11

BsmtFl_R19 BsmtFloor_ins Insulate floor between unconditioned basement and 

conditioned space to R-19

BsmtFl_R30 BsmtFloor_ins Insulate floor between unconditioned basement and 

conditioned space to R-30

CMU_R5 CMU_Ins Add R-5 exterior insulation to concrete masonry walls

CMU_R10 CMU_Ins Add R-10 exterior insulation to concrete masonry walls

FrmW_R13 FrameWall_ins Insulate exterior frame walls to R-13 (drill and fill)

FrmW_R18 FrameWall_ins Insulate exterior frame walls to R-18 (drill and fill + 

insulation sheathing + skin)

CrwlW_R5 CrwlWall_ins Insulate crawlspace walls to R-5 (includes sealing 

crawlspace)

CrwlW_R10 CrwlWall_ins Insulate crawlspace walls to R-10 (includes sealing 

crawlspace)
14

Acronym Category Description

CrwlW_R15 CrwlWall_ins Insulate crawlspace walls to R-15 (includes sealing 

crawlspace)

Crwl_noVnt CrwlWall_ins Seal vented crawlspace (includes required ground cover)

BsmtW_R11 BsmtWall_ins Insulate unconditioned basement walls to R-11

BsmtW_R19 BsmtWall_ins Insulate unconditioned basement walls to R-19

BsmtW_R30 BsmtWall_ins Insulate unconditioned basement walls to R-30

Lgtwalls Paint exterior walls light color (solar absorptance = 0.40)

Darkwalls Paint exterior walls dark color (solar absorptance = 0.70)

Tight Infiltration Air seal to ACH50 = 7

Tighter Infiltration Air seal to ACH50 = 5

VTight Infiltration Air seal to ACH50 = 3

StrmWin Windows Add storm windows

WinTint Windows Add window tint film to windows

SGreflect Windows Replace with single-pane reflective windows 

(U = 0.78; SHGC = 0.24)

DGLES Windows Replace with double-pane low-e solar windows 

(U = 0.39; SHGC = 0.28)

DGLEH Windows Replace with double-pane low-e heating windows 

(U = 0.39; SHGC = 0.52)

DGLEArH Windows Replace with double-pane low-e, argon heating windows 

(U = 0.29; SHGC = 0.48)

DGLEArS Windows Replace with double-pane low-e, argon solar windows (U 

= 0.29; SHGC = 0.24)

TGLEArH Windows Replace with triple-pane low-e, argon heating windows (U 

= 0.20; SHGC = 0.43)

Lgts_50% Lighting Install 50% high efficiency lighting

Lgts_75% Lighting Install 75% high efficiency lighting

Lgts_100% Lighting Install 100% high efficiency lighting

HWwrap Add R-10 hot water tank wrap

LowFloSh Replace shower heads with low-flow shower heads

Std_EHW Water_Heater Replace with minimum standard electric hot water system 

(EF = 0.92)

Std_GHW Water_Heater Replace with minimum standard gas hot water system (EF 

= 0.59)

ES_GHW Water_Heater Replace with ENERGY STAR gas hot water system (EF 

= 0.62)

TGWH Water_Heater Replace with tankless gas hot water system (EF = 0.82)

SHW_40/80PV SolarHW Replace with 40-ft2, 80-gal, PV-pumped solar hot water 

system

SHW_ICS40 SolarHW Replace with 40-gal, integrated collector storage solar hot 

water system

SHW_ICS-HP SolarHW Replace with 40-gal ICS solar hot water system with 

HPWH backup

HRUnit Install hot water heat recovery unit on HVAC system

HPWH HPWH Install heat pump hot water heater (COP = 2.0)
15

Acronym Category Description

Dryer Dryer Replace with high efficiency clothes dryer 

(809 kWh/yr)

ES_Fridge Replace with ENERGY STAR refrigerator 

(460 kWh/yr)

ES_dWash Replace with ENERGY STAR dishwasher (EF = 0.68)

ES_Washer Replace with ENERGY STAR washer 

(washer = 123 kWh/yr; dryer = 618 kWh/yr)

Misc/HEM Misc Home energy management (reduces lighting and 

appliance use by 480 kWh/yr)

WHFan Install whole-house ventilation fan (produces 2.5 ACH

ventilation when running)

PipeIns Add R-2 Insulation to exposed hot water piping

Ins_Door Replace exterior doors with insulated doors (U = 0.29)

5kW-PV PV Install 5-kW PV system
16

8 Improvement Cost Model

In most cases, improvement costs used in this investigation parallel those available from the

National Renewable Energy Laboratory’s (NREL) National Residential Efficiency Measure 

Database.7 However, this study includes measures for which costs are not available in the NREL 

database (such as solar water heating and PV). 

For heating and air conditioning equipment, costs were incorporated based on a separate study 

whereby the costs are expressed in an equation as a function of the equipment capacity and 

efficiency along with an offset. The data and analysis that underlie these heating and cooling 

equipment cost equations are presented in Appendix B. For certain other costs, the NREL cost 

data were reduced to equations based on component areas and incremental improvement 

changes. For example, examination of the NREL data on fibrous insulation reveals that the cost 

of fibrous insulation is approximately $0.035/ft2 per R-value. For these types of improvements 

these costs were cast in such terms. For most other costs, the costs contained in the NREL 

database were adopted.

For HVAC equipment, CostOpt uses the following equations to calculate installed retrofit costs 

(see also Appendix B for derivations).

• Heat pumps: –5539 + 604*SEER + 699*tons

• Air conditioners (with strip heat): –1409 + 292*SEER + 520*tons

• Gas furnace/air conditioner: –6067 + 568*SEER + 517*tons + 4.04*kBtu + 1468*AFUE

• Gas furnace only: –3936 + 14.95*kBtu + 5865*AFUE

where:

tons = air conditioning capacity

kBtu = gas furnace capacity, which is limited to a minimum value of 45

The estimating equations are valid for heat pump and cooling system sizes of 1.5–5 tons and 

multiples thereof. Similarly, the costs of gas heating equipment are based on capacities of 40–

120 kBtu/h.

For other options, costs depend on either the building configuration or the quantity of items 

required. We generally use the following equation to define measure costs as a function of the 

home geometry or number of items required.

TMC = FMC + (pSFpR*ΔR*GSF) + (pNSF*NSF) + (pGSF*GSF) + (pLF*LF) + (pCF*CF) + (pEA*EA)

or MMC, whichever is less

where:

TMC = Total measure cost ($)

FMC = Fixed measure cost (coming out charge, etc.)

MMC = Minimum measure cost (cost below which the measure will not be implemented)

pSFpR = Unit cost per square foot per ΔR (normally blown insulation applied to GSF)

 7 www.nrel.gov/ap/retrofits/index.cfm
17

ΔR = R-value difference between existing home and improvement measure

GSF = Gross square feet

pNSF = Unit cost per net square foot (normally applied to walls only)

NSF = Net square feet

pGSF = Unit cost per gross square foot (normally for skin finish cost)

pLF = Unit cost per linear foot (normally the perimeter)

LF = Linear feet

pCF = Unit cost per cubic foot (normally the house volume)

CF = Cubic feet

pEA = Unit cost per each item (normally appliances, etc.)

EA = Number of each

Table 6 presents an example of the measure cost determination used by CostOpt. Where the 

measure cost is shown as $0, there is no construction component for the specific home being 

modeled.
18

Table 6. Example Cost Calculations for 1600 ft

2

, SOG, Wood-Frame Archetype Home

RunNameMeasureCostMeasureLifeIncentiveIncrementalCostMaintFracIncBasis(fullCost - IncBasis = incCost)MMC (min measure cost)FMC (fixed measure cost)pSFpR (per sq.ft. per ΔR)units of pSFpRΔR-valuepNSF (per net sq.ft.)units of pNSFpGSF (per gross sq.ft.)units of pGSFpLF (per linear ft.)units of pLFpCF(per cu.ft.)units of PCFpEA(per each item)units of EAdescription of EA

SealDucts $500 20 $0 $5000 $1.25 400

LeakFree $900 20 $0 $9000 $2.25 400

IntDucts $6,400 50 $0 $6,4000 $4.00 1600

IntAHU $1,600 15 $0 $1,6000 $1.00 1600

Ceil_R11 $300 50 $0 $3000 $300 $0.035 16001

Ceil_R16 $336 50 $0 $3360 $300 $0.035 16006

Ceil_R19 $504 50 $0 $5040 $300 $0.035 16009

Ceil_R30 $1,120 50 $0 $1,1200 $300 $0.035 1600 20

Ceil_R38 $1,568 50 $0 $1,5680 $300 $0.035 1600 28

Ceil_R49 $2,184 50 $0 $2,1840 $300 $0.035 1600 39

Ceil_R60 $2,800 50 $0 $2,8000 $300 $0.035 1600 50

KneeW_R11 $0 50 $0 $00 $300 $0.0350 11 $0.750

KneeW_R19 $0 50 $0 $00 $300 $0.0350 19 $0.750

KneeW_R30 $0 50 $0 $00 $300 $0.0350 30 $0.750

KneeW_R38 $0 50 $0 $00 $300 $0.0350 38 $0.750

CathC_R11 $0 50 $0 $00 $300 $0.0350 11 $2.000

CathC_R19 $0 50 $0 $00 $300 $0.0350 19 $2.000

CathC_R30$0 50 $0 $00 $300 $0.0350 30 $2.000

CathC_R38 $0 50 $0 $00 $300 $0.0350 38 $2.000

CathC_R49 $0 50 $0 $00 $300 $0.0350 49 $2.000

WhShngl $3,200 15 $0 $10 3,190 $2.00 1600

DrkShngl $3,200 15 $0 $10 3,190 $2.00 1600

Wht Roof $11,200 30 $0 $8,000 3,200 $7.00 1600

RBS $2,400 30 $0 $800 1,600 $1.50 1600

CrwlFl_R11 $0 50 $0 $00 $0.0350 11 $0.750

CrwlFl_R19 $0 50 $0 $00 $0.0350 19 $0.750

CrwlFl_R30 $0 50 $0 $00 $0.0350 30 $0.750

RasdFl_R11 $0 50 $0 $00 $0.0350 11 $2.500

RasdFl_R19 $0 50 $0 $00 $0.0350 19 $2.500

RasdFl_R30 $0 50 $0 $00 $0.0350 30 $2.500

FOGar_R11 $0 50 $0 $00 $0.0350 11 $2.500

FOGar_R19 $0 50 $0 $00 $0.0350 19 $2.500

FOGar_R30 $0 50 $0 $00 $0.0350 30 $2.500

SOG_R5-2h $820 50 $0 $8200 $5.00 164

SOG_R5-4h $1,148 50 $0 $1,1480 $7.00 164

Tile Floor $4,480 50 $0 $4,4800 $4.00 1120

Carpet $3,520 50 $0 $3,5200 $2.75 1280
19

RunNameMeasureCostMeasureLifeIncentiveIncrementalCostMaintFracIncBasis(fullCost - IncBasis = incCost)MMC (min measure cost)FMC (fixed measure cost)pSFpR (per sq.ft. per ΔR)units of pSFpRΔR-valuepNSF (per net sq.ft.)units of pNSFpGSF (per gross sq.ft.)units of pGSFpLF (per linear ft.)units of pLFpCF(per cu.ft.)units of PCFpEA(per each item)units of EAdescription of EA

Wood Floor $5,320 50 $0 $5,3200 $4.75 1120

BsmtFl_R11 $0 50 $0 $00 $300 $0.0550 11

BsmtFl_R19 $0 50 $0 $00 $300 $0.0550 19

BsmtFl_R30 $0 50 $0 $00 $300 $0.0550 30

CMU_R5 $0 50 $0 $00 0.960 $5.500

CMU_R10 $0 50 $0 $00 1.100 $5.500

FrmW_R13 $3,225 50 $0 $3,2250 $0.035 1032 13 $2.10 1312

FrmW_R18 $6,177 50 $0 $6,1770 $0.035 1032 13 $4.35 1312

CrwlW_R5 $0 50 $0 $00 1.710 $1.000

CrwlW_R10 $0 50 $0 $00 1.850 $1.000

CrwlW_R15 $0 50 $0 $00 2.250 $1.000

Crwl_noVnt $0 50 $0 $00 $1.000

BsmtW_R11 $0 50 $0 $00 $0.0350 11 $2.000

BsmtW_R19 $0 50 $0 $00 $0.0350 19 $2.000

BsmtW_R30 $0 50 $0 $00 $0.0350 30 $2.000

Lgtwalls $656 15 $0 $10 646 $0.50 1312

Darkwalls $656 15 $0 $10 646 $0.50 1312

Tight $320 20 $0 $3200 $300 $0.025 12,800

Tighter $1,280 20 $0 $1,2800 $0.100 12,800

VTight $2,560 20 $0 $2,5600 $0.200 12,800

StrmWin $2,400 20 $0 $2,4000 $10.00 240

WinTint $1,500 10 $0 $1,5000 $6.25 240

SGreflect $6,720 50 $0 $240 6,480 $28.00 240

DGLES $7,200 50 $0 $720 6,480 $30.00 240

DGLEH $7,200 50 $0 $720 6,480 $30.00 240

DGLEArH $8,160 50 $0 $1,680 6,480 $34.00 240

DGLEArS $8,160 50 $0 $1,680 6,480 $34.00 240

TGLEArH $14,400 50 $0 $7,920 6,480 $60.00 240

Lgts_50% $1205 $0 $1200 $0.08 1600

Lgts_75% $2405 $0 $2400 $0.15 1600

Lgts_100% $4005 $0 $4000 $0.25 1600

HWwrap $50 12 $0 $500 $501 HWtank

LowFloSh $70 15 $0 $700 $352 shower

Std_EHW $408 12 $0 $10 398 $4081 system

Std_GHW $700 12 $0 $292 408 $7001 system

ES_GHW $750 12 $0 $342 408 $7501 system

TGWH $950 12 $0 $542 2.41% 408 $9501 system

SHW_40/80

PV $6,000 40 $1,800 $5,592

1.13%

408 $6,0001 system

SHW_ICS40 $4,500 40 $1,350 $4,092 0.42% 408 $4,5001 system
20

RunNameMeasureCostMeasureLifeIncentiveIncrementalCostMaintFracIncBasis(fullCost - IncBasis = incCost)MMC (min measure cost)FMC (fixed measure cost)pSFpR (per sq.ft. per ΔR)units of pSFpRΔR-valuepNSF (per net sq.ft.)units of pNSFpGSF (per gross sq.ft.)units of pGSFpLF (per linear ft.)units of pLFpCF(per cu.ft.)units of PCFpEA(per each item)units of EAdescription of EA

SHW_ICS-

HP $6,000 40 $1,800 $5,592

1.44%

408 $6,0001 system

HRUnit $1,500 15 $0 $1,5000 $1,5001 HRU

HPWH $1,900 15 $300 $1,492 1.05% 408 $1,9001 HPWH

Pstat $150 15 $0 $1500 $1501 stat

cFan $1,080 20 $0 $400 680 $2704 Nbr+1

Dryer $800 15 $0 $100 700 $8001 dryer

ES_Fridge $1,000 15 $0 $100 900 $1,0001 fridge

ES_dWash $400 15 $0 $75 325 $4001 dWash

ES_Washer $1,200 15 $0 $200 1,000 $1,2001 cWash

Misc/HEM $600 10 $0 $6000 $6001 system

WHFan $2,350 10 $0 $2,3500 $1,1752 fan

PoolPump $0 15 $0 $00 $3200 pump

WellPump $0 15 $0 $00 $1500 pump

Cln_FrigCoil $303 $0 $300 $301 fridge

PipeIns $40 15 $0 $400 $401 pipe ins

Ins_Door $600 40 $0 $250 350 $3002 door

5kW-PV $32,500 40 $9,750 $32,500 1.58%0 $6.50 5,000 wattsPV
21

The maintenance fractions given as a percent in Table 6 are equal to the annual maintenance cost 

divided by the measure cost. Maintenance fractions are useful for describing differential 

maintenance costs as compared with the standard practice and are also a good way to include 

added costs for items in a system that do not last the full life of the longest lasting components of 

the system, such as solar systems where pumps and tanks need replacement much more often 

than the collector. They also allow for incorporation of performance degradation factors such as 

those that occur in PV systems. The maintenance fractions used by CostOpt in this investigation 

are shown in Table 7.

Table 7. Calculation of Annual Maintenance Costs for Specific Items

RunNamemaint$/yearmaint$_#1maintPeriod_#1maint$_#2maintPeriod_#2maint$_#3maintPeriod_#3

Comments/Notes

TGWH $22.92 $25 1 $25/yr for cleaning

SHW_40/80PV $67.50 $150 5 $300 10 $750 20

$150 every 5 yrs for 

pump + $300 every 10 yrs 

for tank + $750 every 20 

yrs for reroofing

SHW_ICS40 $18.75 $750 20

$750 every 20 yrs to 

remove and replace for 

reroofing

SHW_ICS-HP $86.67 $750 20 $1,000 15 $150 5

$750 every 20 yrs to 

remove and replace for

reroofing + replace 

HPWH every 15 yrs + 

150 every 5 yrs for 

HPWH

HPWH $20 $150 5 $150 every 5 yrs

5kW-PV $350 $4,000 10 $2,000 20

$0.80/W for new inverter 

every 10 yrs + $0.40/W 

every 20 yrs for reroofing 

+ 0.5% PV degradation
22

CostOpt also provides two operational “flags” for each measure that control the simulations. One 

is a simulation flag controlling whether a given measure is included in the list of measures to be 

simulated. If the measure cost evaluates to $0 (see Table 6 for examples), this flag is 

automatically set to false and the measure is not included in the list of measures evaluated. 

However, users can manipulate the simulation flag to reduce the number of simulations 

performed when they know that a measure is highly unlikely to be cost effective or if they do not 

want to consider the measure for aesthetic or practical reasons. 

The second flag is the incremental cost flag, which indicates that incremental cost should be used 

to evaluate the measure because the option is at the end of its service life and must be replaced. 

This flag defaults to false for all measures. However, users can set this flag to true on a measure 

by measure basis, allowing measures to be evaluated on an incremental cost basis rather than a 

full cost basis. For example, if the HVAC equipment is no longer operational and will be 

replaced, the incremental flag for HVAC equipment can be set to true and the incremental cost 

rather than the full cost will be used by CostOpt in the optimization. 

Optimization is initiated with the economic parameter and optimization control screen shown in 

Figure 4. Unless otherwise stated, the values shown on this screen are those used for the 

optimization analysis reported in this investigation. There are two notable exceptions: 

• The mortgage period was set to 7 years for a selection of evaluations to study the impact 

of this important economic variable.

• For at least one set of optimizations the interest rate was changed to 4% to reflect rates 

that are available currently as a refinance (ReFi) option.

Figure 4. Starting screen for CostOpt
23

The Cost Optimization screen allows users to control the economic parameters as well as other 

factors affecting the analysis. The Run Type option allows either a simple rank ordering of the 

measures or a full optimization to be run. The Spending Limit will stop the optimization when 

the specified expenditure limit has been reached. Optimization iterations can be ranked by either 

SIR or NPV; NPV usually produces significantly fewer total simulations. An SIR limit can be 

set, whereby only measures that exceed this limit are accepted. CostOpt also simulates solar 

electric PV systems (Menicucci and Fernandez 1988).8 If a PV system is included in the list of 

measures to be considered, CostOpt will automatically set the optimization SIR Limit to either 

the value entered on the startup screen or to the SIR for the PV system, whichever is less. A 5-

kWp(dc) PV system was included in all optimizations conducted for this investigation to

investigate geographic and economic impacts of its competition with efficiency improvements.

 8 PVFORM, developed by Sandia National Laboratory, is used for PV simulations.
24

9 Results

9.1 Archetype Baseline Energy

How well the baseline energy consumption represents the housing stock is relevant to the 

investigation. The U.S. EIA Residential Energy Consumption Survey (RECS) database provides 

detailed microdata for the four largest states that can be used for this purpose. Table 8 presents a 

comparison of the archetype baseline energy uses with the 2005 RECS data in these large states.

Table 8. Comparison of Baseline Home Energy Uses With 2005 RECS Data

New York Baseline Homes 2005 RECS Data

Mixed Fuel Homes Simulation

Proto 

error Mean StDev n

kWh 8,364 –1.19% 8,465 5,331 47

Therms 1,180 3.78% 1,137 452 47

All-Electric Homes

kWh n/a n/a n/a n/a n/a

California Baseline Homes 2005 RECS Data

Mixed Fuel Homes Simulation

Proto 

error Mean StDev n

kWh 6,306

–

21.88% 8,072 5,153 217

Therms 418

–

26.76% 570 335 217

All-Electric Homes

kWh 11,290

–

19.24% 13,980 7,323 13

Texas Baseline Homes 2005 RECS Data

Mixed Fuel Homes Simulation Mean StDev n

kWh 12,282

–

21.13% 15,572 9,183 109

Therms 500 –0.71% 504 257 109

All-Electric Homes

kWh 18,830 –0.80% 18,981 7,127 56

Florida Baseline Homes 2005 RECS Data

Mixed Fuel Homes Simulation

Proto 

error Mean StDev n

kWh n/a n/a n/a n/a n/a

Therms n/a n/a n/a n/a n/a

All-Electric Homes

kWh 17,651 –2.86% 18,171 6,890 86

Generally agreement was fairly good given the geographically coarse nature of the RECS data. 

State RECS data are available for only the four most populous states, so these data do not 

provide comparison for the other climates included in this investigation or for the specific 

simulated locations—particularly important for a state such as California, where local climates 

vary significantly. Thus, the fact that the archetype energy uses are from 4% larger to 26% 
25

smaller than the mean values derived from the RECS data is not particularly problematic. The 

fact that the archetype energy uses are smaller than the RECS averages probably tends to bias 

optimization results toward conservative energy savings estimates.

Fourteen cities with a representative range of U.S. climates were included (hot humid, mixed, 

cold, and marine) in the investigation. However, some cities have multiple archetype 

expressions. For example, climate zone 2 has a significant number of homes with concrete 

masonry wall systems and many with wood frame wall systems. Multiple space and water 

heating fuels were often considered in many locations as commonly encountered. Thus, 22 

archetypes were created in the 14 cities investigated, such that differing common alternatives 

could be evaluated.

All-electric and mixed-fuel archetypes were created in a number of cities, and the optimization 

analysis for each archetype allowed these fuels to be switched when the cost effectiveness 

economics favored such a change.

Table 9 presents the baseline energy uses and costs for each archetype configuration. Source 

energy use was calculated using the Building America fuel multipliers of 3.365 for electricity use 

and 1.092 for natural gas use. Baseline source energy use across all archetypes varied from a 

high of 247 MBtu for the concrete masonry wall archetype home with a heat pump and electric 

water heating in Phoenix, Arizona to a low of 102 MBtu for the frame wall archetype home with 

gas furnace and gas water heating in Los Angeles, California.
26

Table 9. Archetype Descriptions, Locations, and Baseline Energy Uses and Costs

Prototype Building 

Description

Location Cooling Heating Hot Water L&A Total Total Cost

City CZ kWh kWh Therms kWh Therms kWh kWh Therms Source 

MBtu $/year

1600sf-1sty-SOG-CMU-HP Miami 1 9,264 84 2,193 6110 17,651 203 $2,021

1600sf-1sty-SOG-CMU-HP Houston 2 5,904 2,827 2,615 6110 17,456 200 $2,025

1600sf-1sty-SOG-Frm-GF Houston 2 6,077 156 241 152 6110 12,343 393 185 $1,870

1600sf-1sty-SOG-Frm-HP Houston 2 6,048 2,839 2,615 6110 17,612 202 $2,042

1600sf-1sty-SOG-CMU-HP Phoenix 2 12,000 1,146 2,257 6110 21,513 247 $2,359

1600sf-1sty-SOG-Frm-GF Phoenix 2 11,298 57 86 132 6110 17,465 217 224 $2,272

1600sf-1sty-SOG-Frm-HP Phoenix 2 10,945 947 2,256 6110 20,258 233 $2,261

1600sf-1sty-Crwl-Frm-HP Atlanta 3 3,389 5,747 2,999 6110 18,245 210 $1,837

1600sf-1sty-Crwl-Frm-GF Atlanta 3 3,337 299 480 173 6110 9,746 653 183 $2,003

1600sf-1sty-Crwl-Frm-HP Ft Worth 3 5,826 5,270 2,842 6110 20,048 230 $2,327

1600sf-1sty-Crwl-Frm-GF Ft Worth 3 5,824 286 442 165 6110 12,220 607 207 $2,095

1600sf-1sty-Crwl-Frm-GF Los Angeles 3 45 70 111 173 6110 6,225 283 102 $1,209

1600sf-1sty-Crwl-Frm-HP Los Angeles 3 115 853 2,985 6110 10,063 116 $1,483

1600sf-1sty-Crwl-Frm-GF San Francisco 3 49 227 361 191 6110 6,386 552 134 $1,504

1600sf-1sty-Crwl-Frm-HP San Francisco 3 62 3,045 3,300 6110 12,517 144 $1,846

1600sf-1sty-Crwl-Frm-GF Baltimore 4 2,108 531 845 194 6110 8,749 1,038 214 $2,586

1600sf-1sty-Crwl-Frm-GF New York 4 1,640 614 982 198 6110 8,364 1,180 225 $3,276

1600sf-1sty-Crwl-Frm-HP Seattle 4 233 9,571 3,562 6110 19,476 224 $1,568

1600sf-1sty-Crwl-Frm-GF Seattle 4 189 537 878 205 6110 6,836 1,083 197 $1,918

1600sf-1sty-Crwl-Frm-GF St Louis 4 2,768 572 904 192 6110 9,450 1,096 228 $2,178

1600sf-1sty-Bsmt-Frm-GF Denver 5 607 491 732 207 6110 7,208 939 185 $1,581

1600sf-1sty-Bsmt-Frm-GF Detroit 5 733 629 938 211 6110 7,472 1,149 211 $2,271

1600sf-1sty-Bsmt-Frm-GF Minneapolis 6 423 805 1187 225 6110 7,338 1,412 238 $2,051

Building Description Key: 

1600sf: Square feet of conditioned space

1sty: One story

SOG: Slab-on-grade foundation

Crwl: Crawlspace foundation

Bsmt: Unconditioned, unfinished basement foundation

CMU: Concrete masonry wall system

Frm: Frame wall system

HP: Heat pump archetype (electric space and water heating)

GF: Gas furnace archetype (natural gas space and water heating)

CZ: IECC Climate Zone
27

The annual energy costs for the archetypes varied by climate severity, but also by local energy 

costs. The lowest annual energy cost of $1,209 was shown for the archetype in the mild weather 

of Los Angeles, also with the lowest source energy use. By way of contrast, the archetype 

located in the most severe cold climate, Minneapolis, Minnesota, had an annual energy cost of 

$2,051. While the Minneapolis archetype’s source energy use was slightly greater than the New 

York archetype, the annual energy cost for the New York archetype was $1,225 greater given the 

much higher utility costs. Thus, while climate severity definitely made a significant difference to 

source energy use, utility rates for electricity and natural gas had a much greater impact on 

annual energy costs.
28

10 Cost Optimization Results

Four sets of optimization scenarios were conducted for this investigation, each with a different 

scenario of financing assumptions and a relevant retrofit business model. The four scenarios are:

1. Default. A 30-year mortgage at 6.15% interest at full replacement cost

2. Homeowner finance. A 7-year mortgage at 6.15% interest at full replacement cost

3. HVAC contractor finance. A 7-year mortgage at 6.15% interest; incremental HVAC 

costs

4. Remodel with refinancing. A refinanced 30-year mortgage at 4.0% interest rate at full 

replacement costs.

The analysis period is 30 years for all four scenarios. Optimization Scenario 1 represents the 

“default” economic cost-effectiveness optimization case as specified in Table 2 and in 

accordance with the standards promulgated by RESNET (2012). Optimization Scenarios 2–4 are 

designed to represent alternative business models or financing opportunities.

Optimization Scenario 2 represents the general home improvement model, where long-term 

financing is unavailable and either a second mortgage or an unsecured loan is used to finance the 

improvements over a 7-year term.

Optimization Scenario 3 represents the HVAC contractor business model, where long-term 

financing is not available but the HVAC system has ceased to operate and must be replaced. For 

Scenario 3, the cost of the replacement HVAC equipment is reduced to the incremental cost 

difference between the minimum standard equipment and the improved efficiency equipment.

Optimization Scenario 4 represents the home mortgage refinance case where the homeowner or 

homebuyer can take advantage of a reduced mortgage interest rate concurrent with a 

comprehensive home energy improvement as part of a general house remodel.

10.1 Optimization Scenario 1

Optimization Scenario 1, the economic parameter default case, examines 23 archetypes in 14 

cities comprising six IECC climate zones ranging from climate zone 1 to climate zone 6. 

Summary results from this scenario of optimization runs are shown in Table 10. Six of the 

archetypes shown in Optimization Scenario 1 were evaluated for this scenario only. These are 

shaded light gray in Table 10. The remaining 17 archetypes were evaluated in each of the other 

Optimization Scenarios. Standard CostOpt plots for each archetype are given in Appendix C. 

These graphical results are useful in understanding the order in which improvement measures are 

selected and their relative performance in reducing energy use and influencing homeowner 

annual energy costs.
29

Table 10. Optimization Scenario 1—Default Economic Parameter 

Optimizations

Seven instances of fuel switching are shown via yellow highlighting in Table 10. Five show fuel 

switching from electricity to natural gas and two show switching from natural gas to electricity. 

Fuel switching is largely attributed to water heating systems (five cases), where tankless gas 

water heating systems are selected to replace electric hot water systems. However, one instance 

(Ft. Worth) shows switching from electricity to natural gas for both the HVAC system and the 

hot water system. And in Atlanta and Seattle we see HVAC fuel switching from a gas furnace to 

an electric heat pump. Examination of the fuel costs provides ready explanation for these 

choices. In Houston and Ft. Worth electricity is more than three times the cost of natural gas and 

in Los Angeles and San Francisco electricity is more than four times the cost of natural gas. On 

the other hand, in Atlanta and Seattle, where the fuel switching is in the opposite direction, 

electricity is less than twice the cost of natural gas. In Baltimore, New York, Denver, Detroit, 

and Minneapolis, we did not run all-electric cases as this is not common, so we do not see fuel 

switching occurring in these climates even though it would not likely occur because electricity is 

more than three times the cost of natural gas in these locations.
30

The two Phoenix all-electric cases are quite interesting. Electricity costs in Phoenix are less than 

twice the cost of natural gas, but natural gas water heating is not selected for the all-electric 

homes in Phoenix. Rather, because of the advantageous solar potential, a solar hot water system 

is selected for both all-electric cases. Conversely, solar hot water is not selected in Phoenix for 

the gas home archetype. Instead, the hot water pipes and the hot water tank are insulated—

measures that are not selected for the all-electric homes in Phoenix, where solar hot water 

systems are selected instead.

This illustrates the importance of the relationship between electricity and gas prices to the 

specific results. However, the absolute prices of gas and electricity are also very important to the 

selection of improvement measures and the potential to cut source energy use through retrofit 

measures. This is particularly true for PV, which is selected as cost effective in eight archetypes.

The five archetypes in California and New York all select 5-kW PV systems as cost effective 

because of the high price of electricity in those states ($0.1475/kWh and $0.1874/kWh, 

respectively). A 5-kW PV system is also selected as cost effective in Phoenix, where electricity 

prices are much lower ($0.1097/kWh), but where the solar resource is the greatest of all the 

climates studied. There, the generic 5-kW PV system produces 9,375 kWh/yr. In New York, San 

Francisco, and Los Angeles, the 5-kW PV systems produce 6,971, 8,080, and 8,424 kWh/yr, 

respectively. In New York, high electricity prices drive the selection of PV and in San Francisco 

and Los Angeles, the combination of a good solar resource plus high electricity prices enhance 

the desirability of the PV systems.

Utility prices also drive cost optimization from another important perspective. If utility prices are 

low, fewer improvement measures are selected as cost effective and smaller savings percentages 

are achieved. Denver, where electricity is $0.11/kWh and natural gas is $0.838/therm, offers 

perhaps the best example of this fact. Denver has the lowest natural gas price of all 14 cities. 

Thus, the cost-effective savings for the Denver natural gas archetype are only 18%, even though

the weather is fairly severe. In fact, because of the price of natural gas, it is not even cost 

effective to improve the efficiency of the archetype 76% AFUE gas furnace in Denver, 

something that was done in the other cold climate archetypes (Detroit and Minneapolis).

Table 10 also illustrates the sensitivity of improvement measures to their specific performance 

and cost characteristics. For example, replacing 100% of the incandescent lighting with CFLs or 

equivalent light-emitting diodes (LEDs) is cost effective in every location and circumstance. 

Thus, this measure does not appear to be sensitive to either climate or utility price. Home energy 

management (HEM) systems also appear to be cost effective across a large variety of climates 

and archetypes. They are selected in all archetypes except four located in Atlanta, Seattle, St. 

Louis, and Denver. Electricity prices are $0.10, $0.08, $0.09, and $0.11/kWh, respectively, in 

these cities. We also see that for most climates, addressing duct leakage is cost effective. The 

notable exceptions are Los Angeles, where the cooling and heating loads are very small, and in 

most of the unconditioned basement archetypes, where the archetype distribution system leakage 

is much less substantive.
31

In 13 of the 23 archetypes, the hot water system is also improved. And in all cases where the hot 

water system is not replaced, pipe insulation, hot water tank wrap, low-flow shower heads, or 

some combination of these options are selected.

Ceiling insulation is also improved in all archetypes except those in Los Angeles, again 

illustrating how benign this climate is with respect to heating and cooling loads. In fact, these

loads are so limited in Los Angeles that up to 34% source energy savings are achievable through 

lighting, HEM, and water heating retrofits. However, this savings level is achievable only if the 

archetype is all-electric. If the archetype has a gas space and water heating, only 18% efficiency 

savings are cost effective. Against that limitation, however, >100% source energy savings are 

cost effective in both Los Angeles archetypes with 5-kW PV systems that are indicated.

Optimization Scenario 1 achieves weighted average source energy savings or 37.4% without the 

selected PV systems. If the five cases where PV is selected are included, the weighted average 

source energy savings increase to 51.2%. Weighted average source energy savings are calculated 

as the sum of the source energy savings for all archetypes divided by the sum of the base home 

source energy use for all archetypes.

10.2 Optimization Scenario 2: Homeowner Financing

Optimization Scenario 2 is designed to study the cost effectiveness of a standard home 

improvement mortgage, typically financed by the homeowner over a short 7-year period. A total 

of 17 archetypes in 14 cities are evaluated. The mortgage period is set to 7 years and all other 

economic parameter values are as in Scenario 1. The summary results are presented in Table 11. 

Standard CostOpt plots for each archetype are given in Appendix D. These graphical results are 

useful in understanding the order in which improvement measures are selected.

Table 11. Optimization Scenario 2—Home Improvement Mortgage Optimizations
32

The average source energy savings for these same archetypes in Optimization Scenario 1 is 36%. 

For Optimization Scenario 2, the average is 21%—a 15% reduction in average source energy 

savings from the reduced mortgage period. Reducing the mortgage term from 30 years to 7 years 

means that monthly mortgage payments will be greater. This increase in short-term payments is 

offset some by the fact that the analysis period remains 30 years and the energy cost benefits 

continue to accrue after the mortgage is paid. However, the earlier and larger mortgage payments 

result in less out-year discounting of the improvement costs while the future energy benefits are 

discounted for the full period of the analysis. As a result, fewer measures are cost effective and 

overall source energy savings are reduced.

Source energy savings of 30% are achievable in only three archetypes (Houston, Phoenix, and 

New York) where tankless gas water heaters are cost effective. Two archetypes result in only 

single-digit savings. The heat pump archetype in Seattle shows savings of only 7% and the 

Minneapolis archetype shows savings of only 8%. This is explained by the fact that Seattle has 

an electricity cost of only $0.08/kWh and Minneapolis has a gas cost of only $0.90/therm. Once 

again, the strong influence of utility costs becomes evident in the level of improvements that can 

be economically justified. For example, in New York where both electricity and natural gas costs 

are relatively much greater ($0.18/kWh and $1.45/therm), the cost-effective energy savings are 

34%.

The savings (and the installed measures) for Denver are almost identical for Optimization 

Scenarios 1 and 2. The sole difference is that ceiling insulation goes to R-38 for Optimization 

Scenario 1 but only R-30 for Optimization Scenario 2. Thus, again the very low cost of natural 

gas in Colorado significantly reduces the cost effectiveness of improvement measures, nearly 

irrespective of mortgage period.

Optimization Scenario 2 achieves weighted average source energy savings across all archetypes 

and all climates of 21.5%. This is almost 16% less than the default scenario without PV and 

almost 30% less than the default scenario with PV included in the average. The 5-kW PV system 

is not cost effective for any location when the mortgage period is reduced to 7 years. On the 

other hand, the 5-kW PV system proved cost effective for five archetypes when the mortgage 

period was 30 years (Optimization Scenario 1).

10.3 Optimization Scenario 3: HVAC Contractor Financing

Many energy-using components in a home will eventually need replacement. A key ability of the 

economic methods used in our evaluation has been to account for replacement—sometimes 

multiple times—over the analysis time horizon. However, a less considered issue concerns how 

components and equipment are considered that need replacement at the time, or very close to the 

time, the retrofits are contemplated.

This circumstance is important because the incremental cost of choosing more efficient 

equipment is often quite low at the time of replacement. For instance, in our base analysis, which 

considers only outright replacement of functional equipment and components at full cost, 

changing to a more efficient electric heat pump and more efficient windows will seldom be 

selected in the optimization process. This is because replacing a working heat pump will often 

cost $5,000 or more and replacing functional windows can cost easily cost twice that.
33

If the heat pump is no longer working and is at the end of its useful life, the incremental cost of 

changing to a SEER-15/ HSPF-10 heat pump will often be only $500 after considering the $300 

federal tax credit. The same is true for windows that need replacing, where the cost of replacing 

standard double-glazed units with well-insulated, solar control low-e ones will only be a few 

thousand dollars as opposed to $10,000 or more for outright replacement. On the other hand, 

options such as PV systems or whole-house fans have incremental replacement costs that are the 

same as those for outright replacement, because they are not otherwise necessary for a functional 

household.

In the CostOpt analysis, it is possible to designate that certain items or equipment needs 

replacement at the time of the retrofits. This causes the analysis to use the “incremental cost” 

over the same less efficient minimum efficiency component to evaluate cost effectiveness. This 

often results in options being selected that are otherwise not selected in the outright replacement 

paradigm. Based on our evaluation, this often includes ENERGY STAR appliances, HVAC 

systems, windows, changes to wall and roof color. These items are often cost effective, but only 

at the time of natural replacement when a conventional replacement must be purchased anyway.

Figure 5 and Figure 6 reproduce two sets of optimization results for Ft. Worth, Texas. The 

figures are in a standard CostOpt format that plots the cumulative investment costs and the 

cumulative NPV of the investments on the left-hand vertical axis and the cumulative source 

energy savings percentage on the right-hand axis. Thus, if an individual improvement measure 

has an SIR greater than unity, cumulative NPV will increase. However, if an individual measure 

has an SIR less than unity, cumulative NPV will decrease. Therefore, the point at which the NPV 

is largest is the optimum cost effectiveness from the consumer’s perspective. However, measures 

often come in at the end of the optimization that have an individual measure SIR less than unity 

but that do not cause the cumulative NPV to drop below zero. These measures are also cost 

effective from a societal perspective in that they are “paid for” by the earlier highly costeffective measures. Thus, the neutral cost point from the CostOpt perspective is the line where 

the cumulative NPV equals zero. Because the optimization method is incremental, a number of 

measures are selected and then later replaced by higher efficiency measures in the same 

category. For ease of understanding, the final selections in each category are highlighted in light 

green on the plots.
34

Figure 5. Ft. Worth analysis using full costs for all measures and outright replacement

Figure 6. Ft. Worth analysis using incremental costs (natural replacement costs) for all measures

Figure 5 shows results from the conventional “outright replacement” paradigm (Optimization 

Scenario 1) where things are changed only if it is cost effective to pay full cost for removing and 

replacing them with more efficient equipment and components. As the heat pump is still good, 
35

its duct system is sealed and lighting is changed to CFLs or equivalent LEDs over the entire 

home. Other parts of the building envelope are further improved—notably ceiling insulation goes 

to R-38 and the crawlspace is sealed and insulated to R-15 on the exterior crawlspace walls. 

Because of the cost advantage of natural gas in Texas, the optimization decides to replace the 

standard electric water heater with a tankless gas model. The last installed measure with an SIR 

greater than unity is the R-15 crawlspace wall insulation. At that point in the analysis, the NPV 

of the improvements is maximized at $9,613 and an overall source energy savings of 32% is 

achieved. This includes a reduction in electricity use of 7,514 kWh/yr and adds 115 therms/yr of 

natural gas to cover water heating.

If the homeowner wants to install PV, the analysis indicates that other measures are cost 

effective before that point—notably energy feedback with a HEM system, a fully condensing gas 

furnace with a SEER-15 air conditioner, and leak-free ducts. The combination of all the 

measures with a 5 kW PV system is able to bring the building to a net annual electricity use of 

less than zero over the year (–188 kWh) and a source energy savings of 84%. The cumulative 

package SIR to achieve a near zero energy building is slightly less than unity (0.964).

Figure 6 shows the results where all available items in the retrofit library are indicated as needing 

replacement. The clothes washer and refrigerators are now cost effective to replace with 

ENERGY STAR models and the heat pump is changed to a SEER-15 air conditioner with a 96% 

efficient fully condensing natural gas furnace. The higher efficiency of the replaced HVAC 

system has the impact of only justifying R-30 ceiling insulation and making the sealed 

crawlspace with R-15 walls just outside the cost effectiveness limit (SIR = 1.0).

As before, fuel switching is also seen for water heating, where the optimization eventually 

chooses a tankless gas water heater. Other observed differences include the call for replacing the 

roofing with white shingles and choosing a light color for the house exterior walls when they

need repainting. Double-glazed, argon-filled low-e solar control windows are on the edge of cost 

effectiveness when their replacement is required. Practically, this would be the indicated choice 

for consumers needing to replace windows in Ft. Worth. A 41% source energy savings is 

achieved at the last measure with an SIR greater than unity (tightening house leakage). This 

comprises a reduction in electricity use of 12,478 kWh and adds 434 therms of natural gas use 

for space and water heating.

The measures installed to this point of maximum cost effectiveness are sufficient to “pay for” 

additional improvements before the “neutral cost point” for this home is reached. Figure 5 shows

that the 5-kW PV system drives NPV below zero; in Figure 6, the cost effectiveness of the 

improvements (because they are all evaluated at their incremental cost rather than their full cost 

of replacement) is large enough to “pay for” a number of additional improvement measures, 

including the 5-kW PV system, still leaving a cumulative NPV for the cumulative improvement 

investments of $10,176.

When the 5-kW PV system is added within the incremental analysis, three additional measures 

are cost justified before PV: an unvented crawlspace, high efficiency windows and an energy 
36

feedback system. Total annual electricity use is then –1,101 kWh and source energy savings over 

the year are >87%.9

A practical interpretation of the results of the incremental optimization in each location is that 

while the outright replacement selection identifies robust measures that will always be included, 

the incremental measures should be added to the package , if any of the chosen items in the 

incremental analysis are in need of replacement at the time of retrofit.

For consumers, the results of the incremental optimization analysis indicates that even after the 

retrofits are undertaken, the additional efficiency upgrade options indicated in the incremental 

optimization should be considered to improve household efficiency over time as equipment and 

components need replacement.

Generally the full incremental cost evaluation in higher electricity cost locations tended to call 

for every means of reducing appliance electricity (particularly in cooling-dominated climates); 

analysis in low-cost gas locations with gas appliances tends to justify lower potential savings 

from selected retrofits.

One component of incremental cost analysis is of particular interest to this study—the 

replacement of nonfunctioning HVAC systems. This is the focus of Optimization Scenario 3: 

HVAC Contractor Financing. Optimization Scenario 3 is designed to study the cost effectiveness 

of home improvements when the HVAC system requires replacement—the enlightened HVAC 

contractor business model. HVAC systems have a useful lifetime of 12–18 years. Thus, 

approximately 6% of all HVAC systems will be replaced each year. According to U.S. Census 

data, there are approximately 82 million existing single-family homes. This means that 

approximately 5 million HVAC replacements occur in American homes each year. From a 

retrofit business model perspective, this represents a particularly intriguing opportunity to 

influence energy efficiency decision making by homeowners. It is unlikely that the minimum 

efficiency HVAC system will ever be the most cost-effective option for the homeowner when the 

incremental cost of an upgrade is the economic cost effectiveness consideration. In addition, as 

shown in Figure 6, such upgrades provide significant economic benefits that will effectively “pay 

for” additional energy improvements to the home.

Seventeen archetypes in 14 cities are evaluated. The incremental cost of HVAC systems is used 

in the analysis and the mortgage period is set to 7 years. All other economic parameter values are 

as in Optimization Scenario 1. The summary results for Optimization Scenario 3 are presented in 

Table 12. Standard CostOpt plots for each archetype are given in Appendix E. These graphical 

results are useful in understanding the order in which improvement measures are selected.

 9 This analysis does not consider utility pricing schemes for PV-powered homes that generate more than they use. 

Some utilities will not pay anything for excess power produced annually beyond personal use. Others will pay the 

customer for the power at the end of the year at the wholesale rate. A few will reimburse the homeowner at the retail 

rate. Except in the latter case, an economically rational approach for the consumer would be to not change over 

appliances to natural gas so that what would be an excess with gas appliances can be applied to reducing homeowner 

costs to an absolute minimum. This can be accomplished simply in CostOpt by turning off the simulation flags that 

allow fuel switching.
37

Table 12. Optimization Scenario 3—HVAC Replacement Optimizations

Table 12 clearly illustrates how incremental HVAC costs impact optimization results compared 

with full HVAC costs. Save mild Los Angeles, every archetype installs an improved HVAC 

system versus a minimum efficiency system. Fuel switching occurs from electric to gas space 

heating in both Houston and Ft. Worth, where natural gas prices are relatively low compared to 

electricity prices. Gas space heating switches to electric space heating in Seattle, where 

electricity prices are relatively low compared to natural gas prices. There is also fuel switching 

for tankless gas hot water systems where gas prices are advantageous. 10 A heat pump hot water 

heater is selected only in Miami where gas was not available, although it would likely have been 

chosen in other locations had there been a fixed cost associated with switching from electricity to 

natural gas.

 10 The identified level of fuel switching to gas may be lower in cases where gas service is not already available at the 

home site as this cost is often $200–$500, depending on distances involved.
38

Weighted source energy savings for Optimization Scenario 3 are almost the same as for 

Scenario 1. However, again if the 5-kW PV systems are included, Scenario 3 achieves 13.6% 

less source energy savings than Scenario 1—again because a 7-year mortgage will not support 

the relatively large first cost for the 5-kW PV system.

10.4 Optimization Scenario 4: Home Remodel Refinancing

Scenario 4 represents the home refinance model. The summary results for Optimization 

Scenario 4 are presented in Table 13. Standard CostOpt plots for each archetype are given in 

Appendix F. These graphical results are useful in understanding the order in which improvement 

measures are selected.

Table 13. Optimization Scenario 4—Home Refinance Optimizations

Table 13 illustrates the much larger number of retrofit measures that qualify as cost effective

when the 30-year mortgage rate is reduced from 6.15% to 4.0%. Under the Remodel Refinance 
39

scenario, the 5-kW PV system is cost effective in 13 of the 17 archetypes—eight more than 

under Scenario 1. It is also apparent that the lower mortgage rate allows a larger fraction of high 

first cost measures to qualify that did not qualify in Scenario 1. For example, HVAC systems are 

improved in 10 archetypes under Scenario 4; only eight qualify under Scenario 1. High-cost 

window replacements occur in two archetypes under Scenario 4; none occur in Scenario 1.

Weighted average source energy savings for Scenario 4 are 74% (41.3% without PV systems). 

This is 23% larger than Scenario 1 with PV included.

Table 14 summarizes the achieved weighted average source energy savings and average NPV for 

each of the four Optimization Scenarios. Weighted averages are calculated by taking the sum of 

the source energy savings for all 17 archetypes in the sample set and dividing by the sum of the 

original source energy use for all 17 archetypes. Average NPV is the simple average, calculated 

as the sum of all seventeen individual NPVs divided by 17. Some business models are shown to 

be more productive than others.

Table 14. Weighted Average Source Energy Savings and 

Average NPV for Four Optimization Scenarios

Optimization Scenario

Source Savings NPV

Measures

Without Selected

PV

With 

PV

Without

PV

With 

PV

Scenario 1: Default 37.4% 51.2% $5,463 $5,586 27

Scenario 2: Homeowner Finance 21.5% – $1,019 – 18

Scenario 3: HVAC Finance 37.6% – $3,853 – 23

Scenario 4: Remodel Refinance 41.3% 74.0% $6,631 $6,904 31

The smallest weighted average source energy savings and average NPV are achieved by 

Scenario 2, the homeowner-financed improvement mortgage with a 7-year term. Likewise, the 

largest weighted average source energy savings and average NPV are achieved by Scenario 4, 

the home refinance model. Because PV is cost effective in a number of locations examined by 

this study, weighted average source energy savings and average NPV are both increased when 

PV savings are included in the averages. For Scenario 1, the inclusion of cost-effective PV 

systems raises the weighted average source energy savings from 37.4% to 51.2%. And for the 

remodel refinance scenario, the weighted average source energy savings climbs from 41.3% to 

74%—a 33% increase. A similar pattern can be observed in the number of selected measures in 

each scenario. The smallest number is selected for Scenario 2, where financing is poorest and the 

largest number is selected for Scenario 4, where financing is optimized.

Examination of the source energy savings bins achieved in each Optimization Scenario provides 

additional insight into the results. Figure 7 presents the achieved source energy savings 

(excluding any PV savings) for the 17 archetypes common to all Optimization Scenarios in the 

study. This figure shows that homeowner financing (Scenario 2) offers the smallest potential for 

cost effective home improvement with more than 75% of the archetypes achieving less than 30% 

source energy savings. At the other extreme, the remodel/refinance (Scenario 4) usually produces 

>30% source energy savings. The largest fraction of deep retrofit savings are also achieved 
40

through the home refinancing in Scenario 4 with average savings of 74% (41% if PV is 

excluded) ( a 5-kW PV system was cost effective in 13 of the 17 archetypes).

Figure 7. Source energy savings bins for the four optimization scenarios

A summary of the findings relative to specific measures and how they perform across climates, 

utility costs, and financing scenarios follows:

• What works everywhere. CFLs, duct sealing, ceiling insulation, hot water tank wraps, 

low-flow fixtures.

• What works in some places. Frame wall insulation, crawlspace wall insulation, solar 

water heating, heat pump water heaters, PV systems, appliances that need replacement 

and have low incremental costs.

• What does not work anywhere. Outright replacement of windows; most expensive 

HVAC systems, and roof replacement.

10.5 Method in Action: Optimization Results for a Specific Home

In real-world use, the retrofit optimization method would not use averages, but specifics for an 

individual house. This would include the pre-existing insulation and construction specifics, 

relevant appliances and equipment efficiencies, and a list of the appliances and equipment in 

likely need of replacement. House-specific thermostat preference and water consumption 

intensity should likely be considered. Further, the specific utility costs and financing 

arrangements would need to be realistically applied.

To illustrate how the described method would work in application, we show a case where a home 

is audited in order to be retrofitted based on its particular situation. This home is exactly the 

same as the standard building used in our analysis, but a number of differences are used to 
41

illustrate how the starting efficiency and equipment, utility rates, and replacement status can 

influence results. We used the default financing arrangements that are appropriate to a 30-year 

re-mortgage associated with a remodeling effort, coordinated by an HVAC contractor to replace 

an aging electric heat pump. The HVAC contractor works with auditors to perform a top-tobottom evaluation of the home’s energy upgrade needs and then recommends a comprehensive 

series of measures targeted for the specific circumstances.

In our scenario, the home has just been purchased by a family of four in Ft. Worth, Texas. The 

home has no natural gas access, the providing utility is TXU Energy, and the residential

electricity rate is $0.134/kWh. The home is 1974 vintage with a dark gray exterior. It needs

painting; the windows are leaking and need to be replaced. There are dense shade trees on the 

east and west sides. The frame walls have no insulation, but there is R-19 blown insulation in the 

attic. The crawlspace floors have no insulation. The heat pump needing replacement is assumed 

to have an equivalent SEER of 9 Btu/Wh, although the owners had a utility duct sealing program 

performed with the measured leakage to represent of Qn of 0.05. The new homeowners aim to 

replace the heat pump and the aging dishwasher, and to purchase a new washing machine. The 

household likes cool inside temperatures: 75°F in summer and 65°F in winter. The electric 

resistance hot water tank is 10 years old and has an EF of 0.86. This family has two teenagers, so 

the tank is set to 130°F to accommodate a large amount of hot water used each day (60 gal). The 

original 25-ft3 side-by-side refrigerator was audited and measured to use more than 4 kWh/day.

In the analysis, the equipment, settings, and insulation levels were adjusted and the following 

items on the upgrade list were set to have incremental replacement costs: heating and air 

conditioning, windows, dishwasher, clothes washer, and house paint. All natural gas options 

were eliminated because access was lacking, and the prevailing utility costs were input. The 

chosen objective for the home was to reach zero net annual source energy given the inputs.

Figure 8 shows that the specification of high higher utility rates and the incremental costs for 

some measures have a dramatic impact on measure selection. The no-cost choice of a lighter 

exterior color is made first; a SEER 15 heat pump and ENERGY STAR washer and dishwasher 

soon follow. Low-e double glazed windows with argon fill are then selected. Some measures, 

such as CFLs, airtightness, and ceiling insulation, are always chosen, although higher levels of 

ceiling insulation are called for. Wall and floor insulation is selected for the uninsulated parts of 

the structure and an ENERGY STAR refrigerator is specified along with an ICS solar water 

heater supplying a heat pump water heater. Interestingly, the last measure selected was to change 

the ducted central system for room-based mini-split heat pumps to eliminate duct losses.
42

Figure 8. Optimization results for a specific home in Ft. Worth, Texas

The indicated source energy savings were just over 100% at an installed cost of $45,000 and a 

first-year energy savings of $3,100. Even considering the added mortgage, the homeowners still 

save $200/yr. The combination of higher utility prices, a more intensive use of cooling and hot 

water, and replacement pricing for some options allows a greater justified level of energy 

savings. The example also illustrates how modeling specific circumstances allows for a rational 

method of selecting retrofit measures for specific homes.
43

11 Conclusions

We describe the results of using a comprehensive cost optimization model (EnergyGauge 

CostOpt) across a range of representative climates in the United States. Similar to BEopt, the 

model uses an iterative evaluation of all available measures, selecting the best performing option 

before then reassessing all remaining options for future selection. The optimization process 

typically takes 300–500 simulations before reaching the best performing package of 6–20 retrofit 

measures that are most cost effective.

The purpose of the exercise was to critically evaluate a large library of potential retrofit options 

with representative costs and performance and examine the various influences on potentials to 

cost-effectively reduce energy use in existing U.S. housing. The predicted energy uses of 

developed archetypes for the 14 locations simulated were favorably indexed where possible to 

available RECS data. For the most part, cost data came from the NREL National Residential 

Efficiencies Database, although augmented for estimating HVAC costs and those for renewable 

energy systems. Energy costs were the revenue-based EIA utility averages in each state, 

averaging $0.115/kWh and $1.174/therm. These are considered conservative in that they are now 

two years old and do not include relevant utility state, local, and municipality taxes that are often 

5%–15% greater than the EIA based numbers. The evaluation was carried out over a 30-year 

time horizon with documented economic parameters used for the assessment.

BA-PIRC evaluated measures appropriate to addressing poorly insulated and equipped housing 

stock 20 years or older. This located greatest opportunities, but the same approach can apply to 

newer existing housing, although with often many fewer options chosen. Thus, the starting point 

for an individual home will be important to its realistic savings potential. Still, many homes will 

also be worse than the average starting point such that the savings potentials will remain very 

large.

A key finding was that the energy efficiency levels of even older, inefficient homes can be 

dramatically improved such that they can reach performance levels associated with zero energy 

homes when evaluated on an annual source energy basis.

The results shown in the report can be considered conservative given that a small error in the P2 

parameter was discovered at the end of report preparation which would tend to improve the costeffectiveness results for options with no maintenance and a long service life (e.g., insulation). 

Also, two recent major studies (Hohen et al. 2011; Kok and Kahn 2012) reveal that the real

estate valuation of efficiency and PV measures is much higher than anticipated (approaching 

90% of the investment cost at 5 year resale). Addressing this in the established economic 

structure would entail reducing the rate at which resale/salvage values are discounted. This will 

tend to improve cost effectiveness determinations, particularly for short-term financing. We 

propose that the report eventually be reissued with the P2 error addressed as well as further 

evaluation of the sensitivity to the rate of discounting of the salvage/resale value.

Source energy savings were greatest for the most extreme climates, but chosen measures were 

very sensitive to measure cost and to prevailing utility costs. Where multiple fuels were 

considered, some fuel switching was observed where the ratios of natural gas to electricity costs 
44

were favorable. The analysis found a series of generic measures that were cost effective in nearly 

all locations (such as greater ceiling insulation, lighting, low-cost hot water measures, and duct 

sealing), whereas other options such as wall insulation and high-efficiency hot water systems 

depend on relative climate severity and/or utility costs.

A number of measures (such as all ENERGY STAR appliances) were highly cost effective, but 

only at the time of natural replacement. Some measures, such as high performance windows, 

were cost effective only in the most severe climates. This finding indicates that in a real program, 

the audited performance of each home, along with the remaining life of appliances and 

equipment, and operational related characteristics could be favorably used with a tool such as 

CostOpt to tailor a series of measures that are appropriate for that case so maximum savings are 

achieved in the most cost-effective manner possible.

Relative to results from the optimization analysis, the highest nonrenewable energy savings were 

achieved in hotter locations where more expensive electricity is used for cooling and potential 

savings are large. Across locations, the lowest achievable savings tended to be in milder 

climates, but in particular in locations with low natural gas prices.

The average achieved optimization savings were highly sensitive to the financing scheme and 

interest rates used to pay for the retrofits. Using the default 6.15% financing over a 30-year 

period, 51% source energy savings were indicated when including PV. Excluding PV, the 

savings were 37%, indicating the increasing relevance to solar electric generation to the retrofit 

approach now available.

Financing schemes were quite important—a fact with direct relevance to policy decisions 

relative to energy savings programs for existing U.S. housing. Homeowner-financed energy 

retrofits failed to achieve average savings >21% because of the higher annual costs incurred by 

the short finance period.

A financing model where retrofits are installed along with replacement of the HVAC system was 

superior to homeowner financing. In this scenario, the incremental HVAC costs were applicable, 

resulting in higher achieved source energy savings (37%), although many potential measures 

with high savings are still ignored because of the short financing terms.

The greatest energy savings—averaging 74% when PV was included—were based on a 30-year 

home remodel/refinancing scheme for which the interest rate was 4%. Programmatically, such a 

program might focus on home remodeling and refinancing and/or on the same at the time of 

resale. Another possibility would be to improve homes in the foreclosure market prior to resale.

Interestingly, this scenario showed solar electricity to be cost effective or near cost effective in 

most U.S. locations at $6.50/W installed. At a cost of $5/W installed, such systems would be cost 

effective across the United States, as long as the federal tax credit remains applicable. In 

particular, the results of the home refinance scenario results indicated that near zero source 

energy (>80% savings) was cost effective in eight of the 14 U.S. climates. These tended to be 

those with sunnier conditions and higher applicable electricity prices.
45

Observing the very large identified energy savings in older housing stock in the United States, 

implementation concerns become central—particularly given the lack of homeowner knowledge 

and motivation. Accordingly, the results suggest that:

• Efforts should be made to create a national retrofit program that seeks to match long-term 

financing with multiple retrofit options that are effectively bundled together. 

• Program participation could be matched to replacement of major HVAC system or hot 

water system improvements. These could be contracted at once with tailored retrofit 

measures chosen by a customized computerized evaluation that considers the starting 

point of home features and equipment along with local utility pricing.

• Participating households should have an evaluation of appliance age and functionality to 

take advantage of cost-effective opportunities for appliance replacement during the 

retrofit process.
46

References

Casey, S.; Booten C. (2011). Energy Savings Measure Packages: Existing Homes. Golden, CO: 

National Renewable Energy Laboratory. NREL/TP-5500-53023. 

www.nrel.gov/docs/fy12osti/53023.pdf.

Christensen, C.; Anderson, R. Horowitz, S; Courtney A.; Spencer, J. (2006). BEopt Software for 

Building Energy Optimization: Features and Capabilities. Golden, CO: National Renewable 

Energy Laboratory. NREL/TP-550-39929. www.nrel.gov/buildings/pdfs/39929.pdf.

Duffie, J.A.; Beckman, W.A. (1980). Solar Engineering of Thermal Processes, pp. 381-406, 

New York: John Wylie & Sons, Inc.

Hendron, R. (2006). Building America Performance Analysis Procedures for Existing Homes. 

Golden, CO: National Renewable Energy Laboratory. NREL/TP-550-38238. 

http://www.nrel.gov/docs/fy06osti/38238.pdf

Hohen, B.; Wisser, R.; Cappers, P.; Thayer, M. (2011). An Analysis of the Effects of Residential 

Photovoltaic Energy Systems on Home Sales Prices in the California Market, Berkeley, CA: 

Lawrence Berkeley National Laboratory, LBNL-4476e, April 2011.

Kok, N.; Kahn, M.E. (2012). The Value of Green Labels in the California Housing Market, UC 

Berkeley and UCLA.

McIlvaine, J.R. (2011). “NREL Submission Work,” unpublished test results spreadsheet and 

email to D. Parker, dated 9 June 2011.

Menicucci, D.F.; Fernandez, J.P. (1988). User’s Manual for PVFORM: A Photovoltaic System 

Simulation Program for Stand-Alone and Grid-interactive Applications. Albuquerque, NM: 

Sandia National Laboratories. Report 85-0375. http://prod.sandia.gov/techlib/accesscontrol.cgi/1985/850376.pdf.

Parker, D.; Huang, Y.; Konopacki, S.; Gartland, L.; Sherwin J.; Gu, L. (1998). “Measured and 

Simulated Performance of Reflective Roofing Systems in Residential Buildings.” ASHRAE 

Transactions, Vol. 104, Pt. 1, Atlanta, GA: American Society of Heating, Refrigerating and Air 

Conditioning Engineers.

Pigg, S.; Francisco, P. (2006). A Field Study of Exterior Duct Leakage in New Wisconsin 

Homes, ECW.

Polly, B.; Gestwick, M.; Bianchi, M.; Anderson, R.; Horowitz, S.; Christensen, C.; Judkoff, R.

(2011). Method for Determining Optimal Residential Energy Efficiency Retrofit Packages.

Golden, CO: National Renewable Energy Laboratory. TP-5500-50572; DOE/GO-102011-3261. 

www.nrel.gov/docs/fy11osti/50572.pdf.

RESNET. (2012). Mortgage Industry National Home Energy Rating Systems Standards, Section 

303.3.3 Economic Cost Effectiveness. Oceanside, CA: Residential Energy Services Network. 

www.resnet.us/standards/mortgage. 
47

Sherman, M.H.; Wilson, D.J.; Kiel, D.E. (1986). “Variability in Residential Air Leakage,” in 

Measured Air Leakage in Buildings, ASTM Special Publication 904, Philadelphia, PA.

Walker, I.S. (1998). Technical Background for Default Values used for Forced Air Systems in 

Proposed ASHRAE standard 152P. ASHRAE Trans. Vol.104 Part 1. Presented at ASHRAE TC 

6.3 Symposium, January 1998. LBNL 40588.
48

Appendix A. Calculation of Economic Cost Effectiveness 

Section of RESNET Standards 

303.3.3 Economic Cost Effectiveness. If ratings are conducted to evaluate energy 

saving improvements to the home for the purpose of an energy improvement 

loan or energy efficient mortgage, indicators of economic cost effectiveness shall 

use present value costs and benefits, which shall be calculated as follows:

LCCE = P1*(1st Year Energy Costs) (Eq 303.3.3-1)

LCCI = P2*(1st Cost of Improvements) (Eq 303.3.3-2)

where:

LCCE = Present Value Life Cycle Cost of Energy

LCCI = Present Value Life Cycle Cost of Improvements

P1 = Ratio of Life Cycle energy costs to the 1st year energy costs

P2 = Ratio of Life Cycle Improvement costs to the first cost of improvements

Present value life cycle energy cost savings shall be calculated as follows:

LCCS = LCCE,b – LCCE,i (Eq 303.3.3-3)

where:

LCCS = Present Value Life Cycle Energy Cost Savings

LCCE,b = Present Value LCC of energy for baseline home configuration

LCCE,i = Present Value LCC of energy for improved home configuration

Standard economic cost effectiveness indicators shall be calculated as follows:

SIR = (LCCS) / (LCCI) (Eq 303.3.3-4)

NPV = LCCS - LCCI (Eq 303.3.3-5)

where:

SIR = Present Value Savings to Investment Ratio

NPV = Net Present Value of Improvements

303.3.3.1 Calculation of P1 and P2. The ratios represented by P1 and P2 shall be calculated 

in accordance with the following methodology11:

P1 = 1/(DR-ER)*(1-((1+ER)/(1+DR))^nAP) (Eq 303.3.3-6a)

or if DR = ER then

P1 = nAP / (1+DR) (Eq 303.3.3-6b)

 11 Duffie, J.A. and W.A. Beckman, 1980. Solar Engineering of Thermal Processes, pp. 381-406, John Wylie &

Sons, Inc., New York, NY.
49

where:

P1 = Ratio of Present Value Life Cycle Energy Costs to the 1st year Energy Costs

DR = Discount Rate as prescribed in section 303.3.3.2

ER = Energy Inflation Rate as prescribed in section 303.3.3.2

nAP = number of years in Analysis Period as prescribed in section 303.3.3.2

P2 = DnPmt + P2A + P2B + P2C - P2D (Eq 303.3.3-7)

where:

P2 = Ratio of Life Cycle Improvement costs to the first cost of improvements

DnPmt = Mortgage down payment rate as prescribed in section 303.3.3.2

P2A = Mortgage cost parameter

P2B = Operation & Maintenance cost parameter

P2C = Replacement cost parameter

P2D = Salvage value cost parameter

P2A = (1-DnPmt)*(PWFd/PWFi) (Eq 303.3.3-8a)

where:

PWFd = Present Worth Factor for the discount rate = 1/DR*(1-(1/(1+DR)^nAP))

PWFi = Present Worth Factor for the mortgage rate = 1/MR*(1-(1/(1+MR)^nMP))

DR = Discount Rate as prescribed in section 303.3.3.2

MR = Mortgage interest Rate as prescribed in section 303.3.3.2

nAP = number of years of the Analysis Period as prescribed in section 303.3.3.2

nMP = number of years of the Mortgage Period

P2B = MFrac*PWinf (Eq 303.3.3-8b)

where:

MFrac = annual O&M costs as a fraction of first cost of improvements12

PWinf = ratio of present worth discount rate to present worth general inflation rate

= 1/(DR-GR)*(1-(((1+GR)/(1+DR))^nAP))

or if DR = GR then

= nAP/(1+DR)

GR = General Inflation Rate as prescribed in section 303.3.3.2

P2C = Sum {1/((1+(DR-GR))^(Life*i))} for i=1, n (Eq 303.3.3-8c)

where:

i = the ith replacement of the improvement

 12 The maintenance fraction includes all incremental costs over and above the operating and maintenance cost of the 

“standard” measure. Where components of a system have various lifetimes, the longest lifetime may be used and the 

components with shorter lifetimes may be included as a maintenance cost at the present value of their future 

maintenance cost. The maintenance fraction may also be used to represent the degradation in performance of a given 

system. For example, photovoltaic (PV) systems have a performance degradation of about 0.5% per year and this 

value can be added to the maintenance fraction for PV systems to accurately represent this phenomenon in this cost 

calculation procedure.
50

Life = the expected service life of the improvement

P2D = RLFrac / ((1+DR)^nAP) 13 (Eq 303.3.3-8d)

where:

RLFrac = Remaining Life Fraction following the end of the analysis period

303.3.3.2 Determination of Economic Parameters. The following economic parameter 

values shall be determined by RESNET in accordance with this Section each January using the 

latest available specified data and published on the RESNET website.

• General Inflation Rate (GR)

• Discount Rate (DR)

• Mortgage Interest Rate (MR)

• Down Payment Rate (DnPmt)

• Energy Inflation Rate (ER)

The economic parameter values used in the cost effectiveness calculations specified in Section 

303.3.3.1 shall be determined as follows:

303.3.3.2.1 General Inflation Rate (GR) shall be the greater of the 5-year and the 10-year 

Annual Compound Rate (ACR) of change in the Consumer Price Index for Urban Dwellers 

(CPI-U) as reported by the U.S. Bureau of Labor Statistics,14 where ACR shall be calculated as 

follows:

ACR = ((endVal)/(startVal))^(1.0/((endYr)-(startYr)))-1.0 (Eq 303.3.3-9)

where:

ACR = Annual Compound Rate of change

endVal = Value of parameter at end of period

startVal = Value of parameter at start of period

endYr = Year number at end of period

startYr = Year number at start of period

303.3.3.2.2 Discount Rate (DR) shall be equal to the General Inflation Rate plus 2%.

303.3.3.2.3 Mortgage Interest Rate (MR) shall be defaulted to the greater of the 5-year and 

the 10-year average of simple interest rate for fixed rate, 30-year mortgages computed from the 

Primary Mortgage Market Survey (PMMS) as reported by Freddie Mac unless the mortgage 

interest rate is specified by a program or mortgage lender, in which case the specified mortgage 

 13 Based on recent research by Kok and Kahn (2012) and Hohen et al. (2011), energy efficiency and PV system 

improvements are strongly valued by the public at resale—up to 90% of original value at the time of resale at five 

years. This would indicate that the salvage/resale value parameter should be only very lightly discounted—perhaps 

half the conventional discount rate. Although this was not evaluated in this study, sensitivity might be investigated 

in the future. In any case, not incorporating this real market influence represents conservatism in this study.

14 http://www.bls.gov/CPI/#tables
51

interest rate shall be used. The mortgage interest rate used in the cost effectiveness calculation 

shall be disclosed in reporting results.

303.3.3.2.4 Down Payment Rate (DnPmt) shall be defaulted to 10% of 1st cost of 

improvements unless the down payment rate is specified by a program or mortgage lender, in 

which case the specified down payment rate shall be used. The down payment rate used in the 

cost effectiveness calculation shall be disclosed in reporting results.

303.3.3.2.5 Energy Inflation Rate (ER) shall be the greater of the 5-year and the 10-year 

Annual Compound Rate (ACR) of change in the Bureau of Labor Statistics, Table 3A, Housing, 

Fuels and Utilities, Household Energy Index15 as calculated using Equation 303.3.3-9.

303.3.3.2.6 Mortgage Period (nMP) shall be defaulted to 30 years unless a mortgage finance 

period is specified by a program or mortgage lender, in which case the specified mortgage period 

shall be used. The mortgage period used in the cost effectiveness calculation shall be disclosed in 

reporting results.

303.3.3.2.7 Analysis Period (nAP) shall be 30 years.

303.3.3.2.8 Remaining Life Fraction (RLFrac) shall be calculated as follows:

RLFrac = (nAP/Life) – (Integer (nAP/Life)) Eqn. 303.3.3-10

or if Life > nAP

RLFrac = (Life-nAP) / nAP

where:

Life = useful service life of the improvement(s)

303.3.3.2.9 Improvement Costs. The improvement cost for Energy Conservation Measures 

(ECMs) shall be included on the Economic Cost Effectiveness Report.

303.3.3.2.9.1 For New Homes the improvement costs shall be the full installed cost of the 

improvement(s) less the full installed cost of the minimum standard or code option less any 

financial incentives that accrue to the home purchaser.

303.3.3.2.9.2 For Existing Homes the improvement costs shall be the full installed cost of the 

improvement(s) less any financial incentives that accrue to the home purchaser.

303.3.3.2.10 Measure Lifetimes. The ECM service life shall be included on the Economic Cost 

Effectiveness Report. Appendix C of this standard provides informative guidelines for service 

lifetimes of a number of general categories of ECMs.

303.3.3.3 The annual energy cost savings for the Rated home shall be estimated by comparing the 

projected annual energy cost of the Rated home to the projected annual energy cost of a baseline 

home. For new homes, the most recent HERS Reference home shall be the baseline, except when an 

 15 http://www.bls.gov/cpi/cpi_dr.htm
52

alternative reference home is specified by the lender or program underwriter. For existing homes, the 

unimproved home shall be used as the baseline.

303.3.3.4 The estimated monthly energy cost savings for the Rated home shall be equal to the annual 

energy cost savings divided by 12.

303.3.3.5 For FHA and Freddie Mac energy mortgages, the present value of energy savings 

shall be calculated in accordance with Equation 303.3.3-3 where the baseline home is as 

specified by the most current HUD Mortgage Letter. 
53

Appendix B. Determination of HVAC Equipment Costs

NREL maintains a very useful online National Residential Efficiency Measure Database 

(http://www.nrel.gov/ap/retrofits/index.cfm) containing estimated retrofit costs for HVAC 

equipment. 

The HVAC cost data are cast in terms of only the equipment capacity as Cost = a*CAP. The 

database provides the value of ‘a’ for each listed efficiency. Although it would likely be possible 

to use the listed efficiencies to develop a formulation cast in terms of both efficiency and 

capacity (e.g. Cost = a*CAP + b*EFF), this likely does not adequately characterize costs. 

Conventional pricing logic implies that fixed and variable costs are associated with HVAC 

installation. This can be empirically verified by regressing on collected cost data where fixed and 

variable cost components are clearly revealed. For example, fixed costs are associated with 

selling the new equipment, dispatching a vehicle and service personnel to the installation site, 

removing the old equipment, and hooking up the new equipment that are not tied directly to the 

efficiency or the size of the new equipment. Thus, the characterization of HVAC costs as 

stemming solely from equipment efficiency and capacity tends to underestimate costs for small 

capacity equipment (which will incur a larger percentage of fixed costs relative to total cost) and

overstate costs for large capacity equipment (which will incur a smaller percentage of fixed costs 

relative to total cost).

BA-PIRC attempted to characterize the fixed costs associated with HVAC replacements using an 

empirical approach. Available online retail costs from available manufacturers were used to

determine the, uninstalled retail cost of a variety of HVAC equipment. One clear advantage of 

this method is that the cost data, unlike those collected from installers are very consistent in their

origin with less statistical variation. To these online values were added fixed costs that make up 

the total price similar to those observed in the NREL database. The resulting total cost data are 

then regressed in terms of equipment efficiency and capacity for four categories of commonly 

available HVAC equipment. The four categories are:

• Heat pumps

• Air conditioners (with strip resistance heating)

• Gas furnaces (with no air conditioning)

• Gas furnace-air conditioner combinations

For each equipment category, an 8% tax was applied to the online retail cost plus a fixed 

“service” cost plus 35% overhead and profit, such that

Total Cost = Retail*1.08 + $750 + Retail*0.35

The fixed “service” cost is calculated based on 4 man-hours of sales time at $28.00 per hour and 

16 hours of installation time at $22.50 per hour with a 10% fringe and 30% overhead added to 

these salary rates. In addition, a daily average truck charge of $100 is added to this total salary 

charge to arrive at the fixed service charge.
54

The resulting total cost estimates are then regressed against the equipment capacity and 

efficiency from online data sources to arrive at generalized equations that can be used to 

calculate the HVAC costs used in the CostOpt optimizations. The resulting equations are as 

follows.

Heat Pumps: -5539 + 604*SEER + 699*tons

Air Conditioners (with strip heat): –1409 + 292*SEER + 520*tons

Gas Furnace/air conditioner: –6067 + 568*SEER + 517*tons + 4.04*kBtu + 1468*AFUE

Gas Furnace only: –3936 + 14.95*kBtu + 5865*AFUE

Results from the regressions showing the sample size (n) and correlation coefficient (R2

) for each 

equipment category are shown in Figure 9.

Figure 9. Results from regression analysis of CostOpt HVAC cost estimates

Considering the variability of the marketplace, the correlation coefficients are reasonable for 

these regressions. For comparison, Tables 15 through Table 17 show the range of costs provided 

by the NREL database for replacement heat pumps, air conditioners, and gas furnaces.
55

Table 15. NREL Cost Estimates for Heat Pumps

NREL Heat Pump Replacement Costs

SEER

Low

$/kBtu

High

$/kBtu

Average

$/kBtu ± %

13 97 170 140 26%

14 110 180 140 25%

15 110 190 150 27%

16 120 200 160 25%

17 130 210 170 24%

18 140 220 180 22%

19 140 230 180 25%

20 150 230 190 21%

21 160 240 200 20%

Table 16. NREL Cost Estimates for Air Conditioners

NREL Air Conditioner Replacement Costs

SEER

Low

$/kBtu

High

$/kBtu

Average

$/kBtu ± %

13 59 190 130 50%

14 66 200 130 52%

15 73 210 140 49%

16 80 210 150 43%

17 87 220 150 44%

18 94 230 160 43%

19 100 230 170 38%

20 110 240 170 38%

21 110 250 180 39%

Table 17. NREL Cost Estimates for Gas Furnaces

NREL Gas Furnace Replacement Costs

AFUE

Low

$/kBtu

High

$/kBtu

Average

$/kBtu ± %

78% 8.7 33.3 15 82%

80% 8.7 35.3 18 74%

82% 8.7 38.3 21 70%

90% 14.7 49.3 32 54%

92% 17.7 52.3 35 49%

94% 20.7 55.3 38 46%

96% 23.7 58.3 41 42%

These estimates indicate significant variations in the marketplace with respect to HVAC costs 

and to a certain degree mirror the variations in costs represented in Figure 9, with gas furnaces 

showing the largest variance. 
56

BA-PIRC evaluated the CostOpt estimates against those provided by the NREL database average 

cost estimates for heat pumps and gas furnaces. Figure 10 presents the results of this comparison.

Figure 10. Comparison of CostOpt HVAC cost estimates and NREL HVAC cost estimates

In Figure 10 the individual plot points represent different efficiencies, with SEERs of 13, 14, 15, 

16, 18, and 21 represented on the heat pump chart. The right-hand panel shows data for furnaces: 

with representative AFUEs of 78%, 80%, 82%, 90%, 92%, 94%, and 96%. Each chart also 

distinguishes between different capacities, with 1.5-, 2-, 3-, 4-, and 5-ton equipment on the heat 

pump chart and 45, 60, 75, 90, and 105 kBtu/h equipment on the gas furnace chart. 

Both charts show that the CostOpt estimates are larger for the lower capacity and smaller for the 

larger capacity equipment. The charts also show that, on average, the CostOpt estimates are 

consistent with the NREL estimates. However, the fact that the CostOpt estimates treat fixed 

costs more explicitly is evident on both charts. In a practical sense, the CostOpt estimates

generally show that monetary savings in the capacity of installed equipment coming from more 

efficient envelope measures are slightly less important than the original values in the NREL 

database.
57

Appendix C. Optimization Scenario 1—

Default Economic Parameter Model

The figures shown on the following pages are in a standard CostOpt format that plots the 

cumulative investment costs and the cumulative NPV of the investments on the left-hand vertical 

axis and the cumulative source energy savings percentage on the right-hand axis. Thus, if an 

individual improvement measure has an SIR greater than unity, cumulative NPV will increase. 

However, if an individual measure has an SIR less than unity, cumulative NPV will decrease. 

Therefore, the point at which the NPV is largest is the optimum cost effectiveness from the 

consumer’s perspective. However, often measures come in at the end of the optimization that

have an individual measure SIR less than unity but that do not cause the cumulative NPV to drop 

below zero. These measures are also cost effective from a societal perspective in that they are 

“paid for” by the earlier highly cost-effective measures. Thus, the neutral cost point from the 

CostOpt perspective is the line where the cumulative NPV equals zero. Because the optimization 

method is incremental, a number of measures are selected and then later replaced by higher 

efficiency measures in the same category. Thus, for ease of understanding, the final selections in 

each category are highlighted in light green on the plots.

Key to acronyms:

1600sf: Archetype home size in square feet

1sty: One-story abov- grade home

SOG: Slab-on-grade foundation

Crwl: Crawlspace foundation

Bsmt: Unconditioned basement foundation

HP: Electric space and water heating in base archetype

GF: Natural gas space and water heating in base archetype

7-yr: Seven year mortgage period (used in Scenarios 2 and 3)

incHVAC: Incremental costs used for HVAC systems (used in Scenario 3)

ReFi: Refinance scenario using 4% mortgage interest (used in Scenario 4)
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Appendix D. Optimization Scenario 2—

Homeowner Financing Home Improvement Loan 

Model

The figures shown on the following pages are in a standard CostOpt format that plots the 

cumulative investment costs and the cumulative NPV of the investments on the left-hand vertical 

axis and the cumulative source energy savings percentage on the right-hand axis. Thus, if an 

individual improvement measure has an SIR greater than unity, cumulative NPV will increase. 

However, if an individual measure has an SIR less than unity, cumulative NPV will decrease. 

Therefore, the point at which the NPV is largest is the optimum cost effectiveness from the 

consumer’s perspective. However, often measures come in at the end of the optimization that

have an individual measure SIR less than unity but that do not cause the cumulative NPV to drop 

below zero. These measures are also cost effective from a societal perspective in that they are 

“paid for” by the earlier highly cost-effective measures. Thus, the neutral cost point from the 

CostOpt perspective is the line where the cumulative NPV equals zero. Because the optimization 

method is incremental, a number of measures are selected and then later replaced by higher 

efficiency measures in the same category. Thus, for ease of understanding, the final selections in 

each category are highlighted in light green on the plots.

Key to acronyms:

1600sf: Archetype home size in square feet

1sty: One-story above grade home

SOG: Slab-on-grade foundation

Crwl: Crawlspace foundation

Bsmt: Unconditioned basement foundation

HP: Electric space and water heating in base archetype

GF: Natural gas space and water heating in base archetype

7-yr: Seven year mortgage period (used in Scenarios 2 and 3)

incHVAC: Incremental costs used for HVAC systems (used in Scenario 3)

ReFi: Refinance scenario using 4% mortgage interest (used in Scenario 4)
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71
72
73
74
75
76
77
78
79

Appendix E. Optimization Scenario 3—

HVAC Contractor Financing Business Model

The figures shown on the following pages are in a standard CostOpt format that plots the 

cumulative investment costs and the cumulative NPV of the investments on the left-hand vertical 

axis and the cumulative source energy savings percentage on the right-hand axis. Thus, if an 

individual improvement measure has an SIR greater than unity, cumulative NPV will increase. 

However, if an individual measure has an SIR less than unity, cumulative NPV will decrease. 

Therefore, the point at which the NPV is largest is the optimum cost effectiveness from the 

consumer’s perspective. However, often measures come in at the end of the optimization that

have an individual measure SIR less than unity but that do not cause the cumulative NPV to drop 

below zero. These measures are also cost effective from a societal perspective in that they are 

“paid for” by the earlier highly cost-effective measures. Thus, the neutral cost point from the 

CostOpt perspective is the line where the cumulative NPV equals zero. Because the optimization 

method is incremental, a number of measures are selected and then later replaced by higher 

efficiency measures in the same category. Thus, for ease of understanding, the final selections in 

each category are highlighted in light green on the plots.

Key to acronyms:

1600sf: Archetype home size in square feet

1sty: One-story above grade home

SOG: Slab-on-grade foundation

Crwl: Crawlspace foundation

Bsmt: Unconditioned basement foundation

HP: Electric space and water heating in base archetype

GF: Natural gas space and water heating in base archetype

7-yr: Seven year mortgage period (used in Scenarios 2 and 3)

incHVAC: Incremental costs used for HVAC systems (used in Scenario 3)

ReFi: Refinance scenario using 4% mortgage interest (used in Scenario 4)
80
81
82
83
84
85
86
87
88
89

Appendix F. Optimization Scenario 4—

Home Remodel/Refinance

The figures shown on the following pages are in a standard CostOpt format that plots the 

cumulative investment costs and the cumulative Net Present Value (NPV) of the investments on 

the left-hand vertical axis and the cumulative source energy savings percentage on the right-hand 

axis. Thus, if an individual improvement measure has a Saving-to-Investment Ratio (SIR) greater 

than unity, cumulative NPV will increase. However, if an individual measure has an SIR less 

than unity, cumulative NPV will decrease. Therefore, the point at which the NPV is largest is the 

optimum cost effectiveness from the consumer’s perspective. However, often there are measures 

that come in at the end of the optimization which have an individual measure SIR less than unity 

but which do not cause the cumulative NPV to drop below zero. These measures are also cost 

effective from a societal perspective in that they are “paid for” by the earlier highly cost effective 

measures. Thus, the neutral cost point from the CostOpt perspective is the line where the 

cumulative NPV equals zero. Since the optimization method is incremental there also are a 

number of measures that are selected and then later replaced by measures in the same category 

with greater levels of efficiency. Thus, for ease of understanding, the final selections in each 

category are highlighted in light green on the plots.

Key to acronyms:

1600sf: Archetype home size in square feet

1sty: One-story above grade home

SOG: Slab-on-grade foundation

Crwl: Crawlspace foundation

Bsmt: Unconditioned basement foundation

HP: Electric space and water heating in base archetype

GF: Natural gas space and water heating in base archetype

7-yr: Seven year mortgage period (used in Scenarios 2 and 3)

incHVAC: Incremental costs used for HVAC systems (used in Scenario 3)

ReFi: Refinance scenario using 4% mortgage interest (used in Scenario 4)
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DOE/GO-102012-3786 ▪ November 2012

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