A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

National Renewable Energy Laboratory 

Innovation for Our Energy Future 

Whole-House Energy Analysis 

Procedures for Existing Homes 

Preprint 

R. Hendron 

To be presented at SimBuild 2006 Conference 

Cambridge, Massachusetts 

August 2–4, 2006 

Conference Paper 

NREL/CP-550-39560 

August 2006 

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 
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WHOLE-HOUSE ENERGY ANALYSIS PROCEDURES FOR EXISTING HOMES 

Robert Hendron1

1

National Renewable Energy Laboratory, Golden, CO 

ABSTRACT

This paper describes a proposed set of guidelines for 

analyzing the energy savings achieved by a package of 

retrofits or an extensive rehabilitation of an existing 

home. It also describes certain field test and audit 

methods that can help establish accurate building 

system performance characteristics that are needed for a 

meaningful simulation of whole-house energy use. 

Several sets of default efficiency values have been 

developed for older appliances that cannot be easily 

tested and for which published specifications are not 

readily available. These proposed analysis procedures 

are documented more comprehensively in NREL 

Technical Report TP-550-38238 (Hendron 2006). 

INTRODUCTION

Because there are more than 101 million residential 

households in the United States today, it is not 

surprising that existing residential buildings represent 

an extremely large source of potential energy savings. 

Building America (BA) is investigating the best ways to 

make existing homes more energy-efficient, based on 

lessons learned from research on new homes. The 

research goals for BA include developing retrofit 

packages that can achieve a 20% reduction in energy 

use in existing homes by 2015 and a 30% reduction by 

2025. Research activities include a combination of 

computer modeling, field demonstrations, and long-term 

monitoring to support the development of integrated 

approaches to reduce energy use in existing residential 

buildings. Also, DOE partners with the U.S. 

Environmental Protection Agency to increase energy 

efficiency in existing homes through Home 

Performance with ENERGY STAR®. 

GENERAL ANALYSIS APPROACH

The general approach to modeling whole house energy 

savings for retrofits of existing homes is intended to 

complement similar guidelines developed by BA for 

new home construction, including the Building America 

Research Benchmark (Hendron 2005), more commonly 

referred to simply as the Benchmark. Most of the 

simulation tools that are useful for residential new 

construction are also applicable to residential retrofit 

analysis. Certain tools such as TREAT offer additional 

features such as side-by-side comparisons, automated 

efficiency package recommendations, and utility bill 

analysis/reconciliation. Further information about 

TREAT and a number of other useful tools for retrofit 

analysis of residential buildings can be found in the 

DOE Energy Software Tools Directory 

(www.eere.energy.gov/buildings/tools_directory/). 

It is not recommended that utility bills be heavily relied 

upon as a tool for model calibration, except as an 

approximate check of model accuracy. There are two 

important reasons for this position: 

• It is extremely difficult to accurately determine 

occupant behavior during the time period reflected 

in the utility bills. 

• The large number of uncertain input parameters 

allows multiple ways to reconcile the model with 

the small number of utility bills, and no reliable 

methodology exists for performing this calibration 

because the problem is fundamentally 

mathematically undetermined. 

Instead, detailed inspections, short-term testing, and 

long-term monitoring should be utilized to the greatest 

extent possible to minimize the uncertainty in model 

inputs. Default values may be used when certain 

building features are inaccessible (wall insulation) or 

efficiency characteristics cannot be readily determined 

through inspection or short-term testing (furnace 

AFUE). The effects of maintenance and repairs should 

always be considered when using default values for 

equipment efficiency or the amount of insulation. 

Throughout the remainder of this paper, the term “PreRetrofit Case” refers to the state of an existing house 

immediately before it undergoes a series of upgrades, 

repairs, additions, or renovations. These measures may 

be limited to a focused set of energy efficiency 

improvements to the house or may be part of a larger 

1
remodeling or gut rehabilitation effort. The term “PostRetrofit Case” refers to the same existing house after 

the package of improvements is complete. 

MODELING THE PRE-RETROFIT CASE 

Any element of the Pre-Retrofit Case that is not 

specifically addressed in the following sections, or is 

not changed as part of the package of energy efficiency 

measures, is assumed to be the same as the Post-Retrofit 

Case. To the extent possible, all building envelope 

components (including walls, windows, foundation, 

roof, and floors) for the Pre-Retrofit Case are based on 

physical inspections, audits, design specifications or 

measured data. Co-heating tests (Judkoff et al. 2000) or 

infrared imaging during cold weather may provide some 

useful information about the insulation quality without 

damaging the building envelope, but in most retrofit 

scenarios these tests are overly expensive and would not 

provide data that could be easily factored into a 

building simulation. 

If detailed envelope characteristics cannot be obtained, 

the following default specifications may be used: 

• R-values for cavity insulation in exterior 2x4 or 

2x6 wood frame walls from Table 1. 

• R-values for cavity insulation in floors over 

unconditioned space from Table 2. 

• Insulation thickness in all other locations is 

measured, and the default R-values per inch in 

Table 3 are applied. 

Table 1 Default R-values for wall cavity insulation 

(based in part on Huang and Gu 2002) 

Wall Year of Construction 

Construction 

Type 

Post 

1990 

1980-

89 

1950-

79 

Pre 

1950 

2x4, 16-in. o.c. 13 11 9 7 

2x6, 24-in. o.c. 19 17 15 13 

Table 2 Default R-values for floors above 

unconditioned space (based in part on Huang and Gu 

2002) 

Year of Construction 

Building America 

Climate Region Post 

1990 

1980

-89 

1950-

79 

Pre 

1950 

Cold, Very Cold, 

Subarctic, Marine 19 17 15 13 

All Others 0 0 0 0 

Table 3 Default R-value for common insulation types 

(DOE 2003, E-Star Colorado 2005) 

Year of 

Construction Insulation Material 1990 or 

after 

Before 

1990 

High density fiberglass batt 3.8/in. 3.0/in. 

Low density fiberglass batt 2.7/in. 2.0/in. 

Loose fill fiberglass 3.2/in. 2.5/in. 

Cellulose (blown, wet or dry) 3.7/in. 3.4/in. 

Expanded polystyrene (EPS) 4.0/in. 3.8/in. 

Extruded polystyrene (XPS) 5.0/in. 4.8/in. 

Open cell polyurethane foam 3.6/in. 3.3/in. 

Closed cell polyurethane foam 6.5/in. 5.9/in. 

Rigid polyisocyanurate 7.2/in. 5.8/in. 

• Default U-values for vertical fenestration, including 

windows and sliding glass doors, from Table 4 in 

Chapter 31 of the 2005 American Society of 

Heating, Refrigerating, and Air-Conditioning 

Engineers Handbook of Fundamentals (ASHRAE 

2005). 

• Total assembly solar heat gain coefficient (SHGC) 

for vertical fenestration from Table 13 in Chapter 

31 of the 2005 ASHRAE Handbook of 

Fundamentals (ASHRAE 2005). 

• Default solar absorptivity equal to 0.50 for opaque 

areas of exterior walls and 0.75 for opaque areas of 

roofs. 

• Default infrared emittance of exterior walls and 

roofs equal to 0.90. 

• The default framing factors in Table 4 may be used 

for houses using wood construction. 

Table 4 Default wood-framing factors 

To the extent possible, the performance characteristics 

(efficiency and capacity) of all space-conditioning 

components (including heating system, cooling system, 

dehumidification, air handler, and ducts) for the PreEnclosure Element 

Frame 

Spacing 

(inches o.c.)

Framing 

Fraction 

(% area)

Walls 16 23% 

Floors 16 13% 

Ceilings 24 11% 

2
Retrofit Case are based on physical inspections, audits, 

design specifications, and measured data. An estimate 

of Annual Fuel Utilization Efficiency (AFUE) for a 

furnace or Heating Seasonal Performance Factor 

(HSPF) for a heat pump can be obtained with 

reasonable accuracy by performing a co-heating test to 

determine the building loss coefficient (Judkoff et al. 

2000), then measuring the gas or electricity input over a 

period of time with known inside and outside 

temperatures. Field-audit procedures for heating 

equipment have also been developed by LBNL 

(Szydlowski and Cleary 1988). Cooling efficiency is 

much more difficult to measure directly as part of a 

short-term test, and in most cases the manufacturer’s 

published data should be used. 

If Pre-Retrofit space-conditioning system characteristics 

are unknown or unavailable, default specifications may 

be used. The tables of defaults provided in this paper 

are abridged versions of more complete tables included 

in the full NREL report (Hendron 2006) and include 

some of the more common types of equipment. 

Default furnace or boiler system efficiency may be 

calculated using Equation 1 in conjunction with the 

parameters in Table 5 if the actual efficiency of the 

equipment is unknown and cannot be readily obtained 

through field-testing (for example if the audit is 

conducted in the summer, the heating system is broken, 

or testing would be cost-prohibitive). Typical base 

values for AFUE were obtained from the ASHRAE 

HVAC Systems and Equipment Handbook (ASHRAE 

2004a), the 1987 EPRI Technical Assessment Guide 

(EPRI 1987), and the Technical Support Documents for 

the National Appliance Energy Conservation Act 

(NAECA) appliance standards (DOE 2004a). Estimates 

of degradation rates are partly based on the E-Source 

Space Heating Technology Atlas (E-Source 1993). 

AFUE = (Base AFUE) * (1-M)age (1)

Where: Base AFUE = Typical efficiency of PreRetrofit equipment when purchased

 M = Maintenance Factor 

 Age = Age of equipment in years. 

For example, the default AFUE for a 10-year-old, 

poorly maintained oil furnace with a conventional 

burner would be calculated as follows: 

AFUE = (71) * (1-0.025)10 = 55%. 

Auxiliary electricity use for furnaces and boilers, 

including blowers and controls, is measured directly if 

possible. If accurate measurements cannot be made, the 

default values of auxiliary electricity use in Table 6 may 

be used. 

The default air conditioner and heat pump efficiencies 

in Table 7 may be used if the actual efficiency cannot 

be calculated or measured. Base values for Seasonal 

Energy Efficiency Ratio (SEER), Energy Efficiency 

Ratio (EER), and Heating Seasonal Performance Factor 

(HSPF) were obtained from the engineering analysis of 

appliance standards for air conditioners and heat pumps 

(DOE 2002), and from the LBNL Energy Data 

Sourcebook (Wenzel et al. 1997). Adjustments to 

efficiency related to age and quality of maintenance are 

applied in accordance with Equation 2. Performance 

degradation rates for cooling systems are based in part 

on a study done by LBNL for the California Energy 

Commission (Matson et al. 2002). 

EFF = (Base EFF) * (1-M)age (2) 

Where: Base EFF = Typical efficiency of Pre- 

 Retrofit equipment when purchased 

 (SEER, EER, or HSPF) 

 M = Maintenance Factor 

 Age = Age of equipment in years. 

For houses with air ducts, the Pre-Retrofit Case is 

modeled using data collected through visual 

inspections, physical measurements, and duct leakage 

testing. Default values for duct leakage are not used. 

Duct-blaster testing is conducted in accordance with 

American Society for Testing of Materials (ASTM) 

Standard E1554 (ASTM 1994). Tracer-gas testing of 

the air-distribution system is encouraged when possible 

and is conducted in accordance with NREL 

Performance Test Practices for duct systems (Hancock 

et al. 2002). 

3
Table 5 Example default furnace and boiler system efficiencies (data excerpted from Hendron 2006). “Gas” refers 

to either natural gas or propane. 

Maintenance Factor (M) 

Type of Space Heating Equipment 

Base 

AFUE1 Annual 

Professional 

Maintenance 

Seldom or 

Never 

Maintained 

Condensing gas furnace 90 0.005 0.015 

Gas furnace, direct vent or forced draft combustion, electronic ignition, in 

conditioned space 80 0.005 0.015 

Gas furnace, natural draft combustion, standing pilot light, no vent 

damper, in unconditioned space 64 0.005 0.015 

Gas hot water boiler, natural draft combustion, standing pilot light 80 0.005 0.015 

Gas hot water / fan coil combo system 80 0.005 0.015 

Gas space heater, fan type 73 0.005 0.015 

Oil furnace, flame retention burner, vent dampers, in conditioned space 81 0.01 0.025 

Oil furnace, conventional burner, no vent dampers, in conditioned space 71 0.01 0.025 

Oil steam boiler 82 0.01 0.025 

Electric resistance furnace or boiler, conditioned space 100 0 0 

 

1 Combined Appliance AFUE (CAAFUE) for combo systems 

Table 6 Example default electricity consumption for heating-system blowers and other auxiliary heating 

equipment (data excerpted from Hendron 2006). 

Type of Heating Equipment Electricity/ Capacity 

Gas furnace (including mobile home furnace) 9.2 (kWh/yr)/ (kBtu/hr) 

Gas hot water boiler with hydronic distribution 1.1 (kWh/yr)/ (kBtu/hr) 

Oil furnace 8.0 (kWh/yr)/ (kBtu/hr) 

Electric furnace Included in AFUE 

Table 7 Example default air-conditioning and heat-pump efficiencies (data excerpted from Hendron 2006). 

Maintenance Factor (M) 

Type of Air Conditioning (A/C) or Heat Pump Equipment Base 

SEER

Base

EER

Base 

HSPF

Annual 

Professional 

Maintenance 

Seldom or 

Never 

Maintained

Split central A/C, two-speed reciprocating compressor, ECM 

blower motor, thermostatic expansion valve (TXV), fan coil 14 10.5 0.01 0.02 

Split central A/C, single-speed reciprocating compressor, 

PSC blower motor, cased coil, pre-1981 6.5 6.4 0.01 0.03 

Split heat pump, single-speed scroll compressor, ECM 

blower motor, TXV valve 14 10.5 8.0 0.01 0.03 

Split heat pump, single-speed reciprocating compressor, PSC 

blower motor, pre-1981 6.5 6.4 6.0 0.01 0.03 

Packaged central A/C, single-speed reciprocating 

compressor, PSC blower motor 10 9.1 0.01 0.03 

Room A/C, louvered sides, cooling only, single-speed 

compressor, PSC fan motor, pre-1981 6.5 0.01 0.03 

Direct evaporative cooling 25 0.02 0.05 

4
To the extent possible, the specifications of the 

domestic hot water (DHW) system in the Pre-Retrofit 

Case are based on audits, design specifications, physical 

measurements, and test data. Published data from the 

manufacturer provides the most reliable estimate of 

energy factor (EF), because in-situ testing introduces 

several variables (such as water-use profile and ambient 

temperature) that usually make a reliable measurement 

of standby losses impossible. The procedures to 

measure recovery efficiency and standby losses 

described by LBNL (Szydlowski and Cleary 1988) may 

be used in conjunction with the NREL tank loss 

spreadsheet to give a rough estimate of the EF 

(www.eere.energy.gov/buildings/building_america/docs

/tankloss.xls). If the EF of the equipment cannot be 

determined through measurement or examination of the 

published performance data, the default specifications 

in Table 8 may be used, with age and maintenance 

adjustments in accordance with Equation 3. These 

defaults were largely derived from technical support 

documents for the Federal appliance standard for water 

heaters (DOE 2000a). 

 EF = (Base EF) * (1-M)age (3) 

Where: Base EF = Typical energy factor of Pre-

 Retrofit equipment when purchased 

 M = Maintenance Factor 

 Age = Age of equipment in years 

Table 8 Default DHW energy factors. “Gas” refers to either natural gas or propane. 

Maintenance Factor (M)

Type of Water Heating Equipment 

Base 

Energy 

Factor 

(EF)

Annual 

Professional 

Maintenance 

Seldom or 

Never 

Maintained

Gas water heater, 40-gal tank, pilot light, natural draft combustion, poorly 

insulated, no heat traps, poor heat recovery from flue 0.45 0.005 0.01 

Gas water heater, 40-gal tank, intermittent ignition, forced draft combustion, 3-

in. insulation, heat traps, enhanced flue baffling, flue/vent dampers 0.64 0.005 0.01 

Gas instantaneous water heater 0.80 0.005 0.01 

Oil water heater, 32-gal tank, intermittent ignition, forced-draft combustion, 

poorly insulated, no heat traps, poor heat recovery from flue 0.53 0.005 0.01 

Oil water heater, 32-gal tank, interrupted ignition, forced-draft combustion, 3-

in. insulation, heat traps, enhanced flue baffling 0.61 0.005 0.01 

Electric water heater, 50-gal tank, poorly insulated, no heat traps 0.79 0.001 0.002 

Electric water heater, 50-gal tank, 3-in. insulation, heat traps 0.90 0.001 0.002 

Electric instantaneous water heater 1.00 0 0 

Four major end uses have been identified for domestic 

hot water: showers, sinks, dishwasher, and clothes 

washer. For showers and sinks, the daily volume is the 

same as the value defined for the Benchmark and 

represents the combined volume of hot and cold water. 

For clothes washers and dishwashers, the BA Analysis 

Spreadsheet developed by NREL is used to estimate 

the Pre- and Post-Retrofit hot-water consumption based 

on standard operating conditions and information listed 

on the EnergyGuide label. If no EnergyGuide label is 

available, then the default values of energy factor (EF) 

for dishwashers (see Table 13) or modified energy 

factor (MEF) for clothes washers (see Table 10) may 

be used for the Pre-Retrofit Case. The profiles for 

hourly hot water use and mains water temperature are 

the same as the Benchmark (Hendron 2005). 

The effective leakage area for the Pre-Retrofit Case is 

calculated based on blower-door testing conducted in 

accordance with ASTM E779-03 (ASTM 2003). It is 

recommended that blower door measurements be 

supplemented with tracer-gas testing when time and 

resources permit. 

Additional air exchange as a result of mechanical 

ventilation is assumed for the model of the Pre-Retrofit 

Case if it does not meet the ventilation guidelines of 

ASHRAE Standard 62.2-2004 (ASHRAE 2004b) 

based on natural infiltration alone. Supplemental 

mechanical ventilation is calculated using Equation 4, 

which is based on a simple continuous exhaust fan 

designed to raise the total ventilation rate to the 

minimum values specified in Equation 4.1a of 

ASHRAE Standard 62.2-2004, taking into account any 

infiltration credit allowed under Section 4.1.3. 

Supplemental mechanical ventilation is combined with 

the actual ventilation and natural infiltration in 

accordance with Section 4.4 of ASHRAE Standard 136 

5
(ASHRAE 1993) to determine an approximate 

combined effective air change rate. The fan energy use 

associated with supplemental mechanical ventilation 

for the Pre-Retrofit case is calculated by multiplying 

the supplemental ventilation rate by 3.942 kWh/cfm. 

This energy is added to the energy used by any 

ventilation fan present in the house. 

 Qsup = [0.01xFFA+7.5x(Nbr+1)] – 

 [AIxCFAxH/60 – 2xFFA/100]/2 

(4) 

Where: 

Qsup = supplemental mechanical ventilation 

assumed for the Pre-Retrofit Case 

(cfm) 

FFA = finished floor area (ft2

) 

CFA = conditioned floor area, including 

directly or indirectly conditioned 

basements (ft2

) 

H = average height of one story (ft) 

AI = annual average air changes per hour as a 

result of natural infiltration (ACH) 

Nbr = number of bedrooms. 

The total annual lighting budget for the Pre-Retrofit 

case is determined by conducting a detailed audit of 

light fixtures and lamps inside and outside the house. 

Operating hours may be determined through long-term 

monitoring or by conducting occupant interviews or 

surveys. If reliable estimates of operating hours cannot 

be obtained or calculated, then the default operating 

hours developed by Navigant based on a Tacoma 

Public Utilities lighting study (Navigant 2002) may be 

used (Table 9). The annual average normalized daily 

load shape for interior lighting is the same profile used 

by Building America in the context of new construction 

(Hendron 2005). 

Table 9 Default lighting operating hours for common 

room types (Navigant 2002) 

Room Type Hrs/day/ 

room Room Type Hrs/day/ room 

Bathroom 1.8 Kitchen 3.0 

Bedroom 1.1 Living Room 2.5 

Closet 1.1 Office 1.7 

Dining Room 2.5 Outdoor 2.1 

Family Room 1.8 Utility Room 2.0 

Garage 1.5 Other 0.8 

Hall 1.5 

To the extent possible, actual specifications for all 

major appliances should be based on manufacturer’s 

literature or an EnergyGuide label. Spot electricity 

measurements may be performed for loads that are 

relatively constant when operating, such as 

refrigerators and freezers. A more standardized 

procedure for calculating average daily electricity use 

for refrigerators was developed by Lawrence Berkeley 

National Laboratory (Szydlowski 1988). 

If EnergyGuide labels are available for dishwashers 

and clothes washers, then the BA Analysis Spreadsheet 

can be used to estimate annual energy use. If 

EnergyGuide labels cannot be located or do not exist 

for certain major appliances (e.g., ovens and clothes 

dryers), the default energy factors in Tables 10 through 

15 may be used. These defaults were derived from 

historical appliance efficiency studies (Wenzel et al. 

1997, DOE 2004b, EPRI 1986) and technical support 

documents for recent changes to Federal appliance 

standards (DOE 1993, DOE 2000b). 

Table 10 Default standard size (~2.5 ft3

) clothes 

washer characteristics 

Equipment Characteristics MEF 

(ft3/kWh) 

Horizontal axis, cold-rinse option, 

automatic fill, thermostatically 

controlled mixing valve, improved 

water extraction 

1.62 

Vertical axis, cold-rinse option, 

automatic fill, thermostatically 

controlled mixing valve, improved 

water extraction 

1.02 

Vertical axis, cold-rinse option, waterlevel option, standard mixing valve 0.64 

Vertical axis, no cold-rinse option, no 

water-level option 0.47 

Table 11 Default gas clothes dryer characteristics 

(assumes typical 1990 clothes washer capacity and 

remaining moisture content) 

Equipment Characteristics EF 

(lb/kWh) 

Cool-down mode, intermittent ignition, 

automatic termination control, improved 

door seal, well insulated 

2.67 

Cool-down mode, intermittent ignition, 

timer control, improved door seal, well 

insulated 

2.40 

No cool-down mode, pilot light, timer 

control, poor door seal, poorly insulated 2.00 

6
Table 12 Default electric clothes dryer characteristics 

(assumes typical 1990 clothes washer capacity and 

remaining moisture content) 

Equipment Characteristics EF 

(lb/kWh) 

Cool-down mode, automatic 

termination control, improved door 

seal, well insulated 

2.75 

No cool-down mode, timer control, 

poor door seal, poorly insulated 2.60 

Table 13 Default dishwasher characteristics 

Equipment Characteristics EF 

(load/kWh)

Power dry optional, multi-tier spray 

device, load size and soil level controls 0.6 

Power dry optional, multi-tier spray 

device, no load size or soil level controls 0.43 

Power dry always, single-tier spray 

device, no load size or soil level controls 0.24 

Table 14 Default gas oven / cooktop characteristics 

Equipment Characteristics EF 

Annual 

Energy 

(therms/yr)

Cooktop: intermittent 

ignition, sealed burner 

Oven: spark ignition, not 

self cleaning, improved 

door seals, reduced vent 

rate, high-density insulation 

Cooktop: 

42.0%

Oven: 

6.2%

Cooktop: 17

Oven: 18 

Cooktop: intermittent 

ignition, open burner 

Oven: electric glo-bar 

ignition, self cleaning 

Cooktop: 

40.0%

Oven: 

5.8%

Cooktop: 18

Oven: 19 

(+80 kWh)

Cooktop: pilot lights 

Oven: pilot light, not selfcleaning, standard door 

seals, standard vent rate, 

standard insulation 

Cooktop: 

18.8%

Oven: 

3.5%

Cooktop: 39

Oven: 36 

Table 15 Default electric oven / cooktop characteristics 

Equipment Characteristics Energy 

Factor 

Annual 

Energy 

(kWh/yr) 

Cooktop: reflective pans, flat 

coil elements 

Oven: self-cleaning, improved 

door seals 

Cooktop: 

77.7%

Oven: 

10.2%

Cooktop: 270

Oven: 349 

Cooktop: solid disc elements 

Oven: not self-cleaning, 

improved door seals, reduced 

vent rate, high density 

insulation 

Cooktop: 

74.2%

Oven: 

12.1%

Cooktop: 282

Oven: 293 

Cooktop: non-reflective pans, 

rounded coil elements 

Oven: not self-cleaning, 

standard door seals, standard 

vent rate, standard insulation 

Cooktop: 

73.7%

Oven: 

10.9%

Cooktop: 284

Oven: 326 

In most cases, Miscellaneous Electric Loads (MELs) 

are treated as a constant function of finished floor area, 

regardless of the actual MELs present in the PreRetrofit Case (Equation 5). Alternatively, if MEL 

improvements are included in the retrofit package, 

analysts may use the more detailed methodology 

developed for new construction, which allows energy 

savings credit for replacement of small appliances and 

reduction of standby losses. This methodology is 

documented in the BA MEL Analysis Spreadsheet 

(http://www.eere.energy.gov/buildings/building_americ

a/pa_resources.html). 

MEL = 1.49 x FFA x Fs (5) 

Where: MEL = miscellaneous electric loads for the 

Pre-Retrofit Case (kWh/yr) 

 FFA = finished floor area (ft2

) 

 Fs = state multiplier (NY=0.82, CA=0.77, 

 FL=0.94, TX=1.11, all others=1.00). 

Operating hours estimated through occupant surveys or 

interviews may be useful for determining the costeffectiveness of replacing certain appliances and 

electronic equipment for a particular homeowner. 

However, the standard operating conditions specified 

for the Benchmark are used for the purpose of 

calculating and reporting whole-house energy savings 

for existing homes in the context of Building America. 

In addition, the hourly load shapes for appliances and 

MELs and the fraction of end-use energy converted 

into internal sensible and latent load are the same as the 

Benchmark used for new construction (Hendron 2005). 

7
MODELING THE POST-RETROFIT CASE

The Post-Retrofit Case is modeled either as-designed 

or as-built, depending on the status of the project. All 

parameters for the Post-Retrofit model are based on 

final design specifications or measured data, with the 

following exceptions and clarifications: 

• House characteristics that are unknown or not part 

of the package of energy efficiency improvements 

should be the same as the Pre-Retrofit Case. 

• The effective leakage area for the Post-Retrofit 

Case is calculated based on blower-door testing 

conducted in accordance with ASTM E779. It is 

recommended that blower-door measurements be 

supplemented with tracer-gas testing if possible. 

• Additional air exchange resulting from mechanical 

ventilation is assumed if the Post-Retrofit Case 

does not meet the ventilation guidelines of 

ASHRAE Standard 62.2-2004 based on natural 

infiltration alone. Supplemental mechanical 

ventilation is calculated using the same 

methodology discussed earlier in the context of the 

Pre-Retrofit Case. 

• The installation of energy-saving appliances or 

other equipment may reduce hot water 

consumption for certain end uses, reduce the 

internal sensible and latent loads, or affect the 

hourly operating profiles. Energy savings 

calculations for the Post-Retrofit Case should take 

these effects into account. The number of cycles 

per year specified in the appliance standard for 

clothes washers is adjusted according to the 

number of bedrooms and the clothes washer 

capacity, using Equation 6: 

Clothes washer cycles per year = (392) x 

 (1⁄2+Nbr/6) x 12.5 lb / Wtest (6) 

Where: Wtest = maximum clothes washer test 

load weight found in 10 CFR 

part 430, Subpt B, Appendix 

J1, as a function of the washer 

capacity in ft3

. 

A dryer usage factor (DUF) is applied to the 

clothes washer cycles to determine the number of 

annual dryer cycles, using Equation 7: 

Clothes dryer cycles per year = DUF x Clothes 

 washer cycles per year (7) 

Where: DUF = 0.84. 

The dishwasher (DW) annual operating cycles are 

similarly calculated using Equation 8: 

DW cycles per year = (215) x (1⁄2 + Nbr/6) (8) 

The BA Analysis Spreadsheet posted on the BA 

web site automates these calculations and is 

strongly recommended for the analysis of waterconsuming appliances. It calculates the split 

between hot water and machine energy based on 

the EnergyGuide label, estimates dryer energy 

savings for clothes washers that reduce remaining 

moisture content, adjusts energy use for hot water 

and cold water temperatures that are different than 

the test values (140oF and 60oF/50oF), and adjusts 

for the type of controls present (thermostatic 

control valves, boost heating, cold water only). 

• Energy savings for a new range/oven may only be 

credited if an energy factor has been determined in 

accordance with the DOE test procedures for 

cooking appliances (DOE 1993). Annual energy 

consumption is then estimated as the product of the 

energy factor and the annual useful cooking energy 

output as defined in the same test procedure. If the 

energy factor is unknown for a new range/oven, 

then it is assumed that the Post-Retrofit energy use 

for cooking is the same as the Pre-Retrofit case. 

• Modifications to the Pre-Retrofit lighting profile 

and operating hours because of occupancy sensors 

or other controls may be considered for the PostRetrofit Case, but negative and/or positive effects 

on space conditioning load must also be 

calculated, assuming 100% of interior lighting 

energy contributes to the internal sensible load. 

• For the Post-Retrofit Case, all site electricity 

generation is credited regardless of energy source. 

Residential-scale photovoltaic systems, wind 

turbines, fuel cells, and micro-cogeneration 

systems are all potential sources of electricity 

generated on the site. An offset must be applied to 

this electricity credit equal to the amount of 

purchased energy used in the on-site generation 

process. 

OPERATING CONDITIONS

The same operating conditions are applied to both the 

Pre- and Post-Retrofit Cases. They are intended to 

represent the behavior of a typical set of occupants, not 

the current occupants of the house, because Building 

America is interested in estimating long-term energy 

savings of improvements to existing homes. The same 

operating conditions used for new construction are also 

8
used for existing homes. These operating conditions 

are documented in the BA Benchmark Definition 

(Hendron 2005) and are based on the cumulative 

experience of the authors through their work on 

Building America, HERS, Codes and Standards, and 

other residential energy efficiency programs. 

CONCLUSION 

This paper provides an overview of a proposed set of 

guidelines for analyzing the whole-house energy 

savings of retrofits and renovations of existing 

residential buildings. These guidelines are intended to 

complement the procedures developed for analyzing 

new homes (Hendron et al. 2004), and the two sets of 

guidelines share many of the same elements. We 

expect these procedures to evolve to some extent as 

existing homes become a higher priority for residential 

buildings research, and more aggressive energy savings 

targets are achieved. NREL also plans to evaluate the 

usefulness and accuracy of these procedures as part of 

a community-scale retrofit project by providing support 

for pre-retrofit audits, energy savings calculations, and 

post-retrofit monitoring. 

ACKNOWLEDGMENTS 

The author thanks the NREL staff for their ideas and 

inputs on this project, especially Ren Anderson, Paul 

Torcellini, Ali Jalalzedah, and Mark Eastment. The 

author also acknowledges the resources and guidance 

provided by Ed Pollock and George James of the U.S. 

Department of Energy Building America Program. 

NOMENCLATURE

AFUE annual fuel utilization efficiency for 

heating systems 

CAAFUE combined appliance AFUE 

EER energy efficiency ratio for cooling systems 

EF energy factor for water heaters, 

dishwashers, ranges, and clothes dryers 

HSPF heating seasonal performance factor 

M maintenance factor 

MEF modified energy factor for clothes washers 

SEER seasonal energy efficiency ratio for cooling 

systems 

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Leakage Rate by Fan Pressurization. ASTM 

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by Fan Pressurization. ASTM E1554-94. 

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ASHRAE (American Society of Heating, Refrigerating, 

and Air-Conditioning Engineers). 1993. A 

Method of Determining Air Change Rates in 

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1993, Atlanta, GA. 

ASHRAE (American Society of Heating, Refrigerating, 

and Air-Conditioning Engineers). 2004a. HVAC 

Systems and Equipment Handbook. Atlanta, GA. 

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E-Source. 1993. Space Heating Technology Atlas. 

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http://www.e-star.com/ecalcs/table_rvalues.html

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Hancock, E., Norton, P., and Hendron, R. 2002. 

Building America System Performance Test 

Practices: Part 2, Air-Exchange Measurements. 

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Renewable Energy Laboratory. 

Hendron, R. 2005. Building America Research 

Benchmark Definition, Updated December 29, 

2004. NREL/TP-550-37529. Golden, CO: 

National Renewable Energy Laboratory. 

Hendron, R. 2006. Building America Performance 

Analysis Procedures for Existing Homes. 

NREL/TP-550-38238. Golden, CO: National 

Renewable Energy Laboratory. 

Hendron, R., Anderson, R., Judkoff, R., Christensen, 

C., Eastment, M., Norton, P., Reeves, P., 

Hancock, E. 2004. Building America 

Performance Analysis Procedures, Rev. 1. 

9
NREL/TP-550-35567. Golden, CO: National 

Renewable Energy Laboratory. 

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Buildings to Represent the U.S. Housing Stock. 

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Judkoff, R.; Balcomb, J. D.; Hancock, C. E.; Barker, 

G.; and Subbarao, K. 2000. Side-By-Side 

Thermal Tests of Modular Offices: A Validation 

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Matson, N., Wray, C., Walker, I., and Sherman, M. 

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Whole-House Energy Analysis Procedures for Existing Homes: 

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14. ABSTRACT (Maximum 200 Words)

This paper describes a proposed set of guidelines for analyzing the energy savings achieved by a package of 

retrofits or an extensive rehabilitation of an existing home. It also describes certain field test and audit methods that 

can help establish accurate building system performance characteristics that are needed for a meaningful simulation 

of whole-house energy use. Several sets of default efficiency values have been developed for older appliances that 

cannot be easily tested and for which published specifications are not readily available. These proposed analysis 

procedures are documented more comprehensively in NREL Technical Report TP-550-38238. 

15. SUBJECT TERMS

Building America; energy savings; residential buildings; retrofitting; building simulation models; field test; energy 

audit; homes appliances 

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