7-E-i

APPENDIX 7-E. DETERMINATION OF FURNACE ENERGY USE IN THE LCC 

ANALYSIS 

TABLE OF CONTENTS

7-E.1 INTRODUCTION ................................................................................................. 7-E-1

7-E.2 DETERMINATION OF AVERAGE ANNUAL FUEL ENERGY 

CONSUMPTION (EF)........................................................................................... 7-E-1

7-E.3 DETERMINATION OF AVERAGE ANNUAL ELECTRICAL ENERGY 

CONSUMPTION (EAE)......................................................................................... 7-E-2

7-E.4 DETERMINATION OF NATIONAL AVERAGE NUMBER OF BURNER 

OPERATING HOURS (BOHSS) ........................................................................... 7-E-3

7-E.5 DETERMINATION OF IMPACT ON FURNACE ENERGY USE WITH 

MORE EFFICIENT FURNACE FANS ................................................................ 7-E-6

7-E.6 ASSIGNING FURNACE EQUIPMENT CHARACTERISTICS TO SAMPLE 

HOUSEHOLDS..................................................................................................... 7-E-8

7-E.6.1 Input Capacity of Existing and New Equipment ................................................... 7-E-8

7-E.6.2 Airflow Size of Existing Equipment.................................................................... 7-E-10

7-E.6.3 AFUE of Existing Equipment.............................................................................. 7-E-11

7-E.6.4 AFUE of New Equipment.................................................................................... 7-E-13

LIST OF TABLES

Table 7-E.5.1 Average Values for Delay and Ignition Times.................................... 7-E-8

Table 7-E.6.1 Distribution of Input Capacities for Non-Weatherized Gas 

Furnaces............................................................................................. 7-E-10

Table 7-E.6.2 Distribution of Airflow for Furnaces................................................. 7-E-11

Table 7-E.6.3 Number of Observations for Each Age Group .................................. 7-E-12

Table 7-E.6.4 Historical Fraction of Regional Non-Weatherized Gas Furnace 

Shipments by AFUE Bins.................................................................. 7-E-13

Table 7-E.6.5 Distribution of AFUE for Non-Weatherized Gas Furnaces............... 7-E-14
7-E-1

APPENDIX 7-E. DETERMINATION OF FURNACE ENERGY USE IN THE LCC 

ANALYSIS

7-E.1 INTRODUCTION

DOE accounted for the fact that more efficient furnace fans will tend to contribute less 

heat and thereby require additional furnace operation. Since the heating load of each sample 

housing unit is known, it is possible to estimate what the furnace energy consumption would be 

if more efficient fan equipment, rather than the baseline equipment, was used in each housing 

unit.

The furnace energy consumption of non-furnace components in the LCC analysis is 

determined using the 2007 ASHRAE SPC 103R “Method of Testing for Annual Fuel Efficiency 

of Residential Central Furnaces and Boilers”.1

 This approach requires the calculation of the 

average annual fuel energy consumption (EF), the average annual electrical energy consumption 

(EAE), and the national average number of burner operating hours (BOH) of furnaces.

The following calculations describe the determination of EF, EAE, and BOH for gas- and 

oil-fired furnaces.

7-E.2 DETERMINATION OF AVERAGE ANNUAL FUEL ENERGY 

CONSUMPTION (EF) 

The average annual fuel consumption is calculated in Appendix C section 2 of the 

ASHRAE 103/2007 test procedure:1

EF = BOHSS * (QIN - QP) + 8,760 * QP , for single-stage furnaces,

EF = (BOHH * QIN) + (BOHR * QIN,R) + [8,760 - (BOHH + BOHR )]* QP, for two-stage furnaces 

and

EF = (BOHM * QIN,M) + (BOHR * QIN,R)+ [8,760 - (BOHM + BOHR )]* QP, for continuous 

modulatinga1 furnaces

where,

BOHSS = national average number of burner operating hours (see derivation in section 7-

E.4),

BOHH = national average number of burner operating hours at the maximum operating 

mode for two-stage furnaces (see derivation in section 7-E.4),

BOHR = national average number of burner operating hours at the reduced operating mode 

for two-stage or continuous modulating furnaces (see derivation in section7-E.4),

 a

 In this Technical Support Documentation, “continuous modulating” term is used instead of “step-modulating”. 

Both terms are interchangeable used in the literature.
7-E-2

BOHM = national average number of burner operating hours at the modulating operating 

mode for continuous modulating furnaces (see derivation in section7-E.4),

QIN = steady-state nameplate input rate in Btu/h for single-stage furnaces or steady-state 

nameplate maximum input rate in Btu/h for two-stage and continuous modulating 

furnaces,

QIN,R = steady-state reduced fuel input rate,

QIN,M = steady-state modulating fuel input rate, and

QP = pilot flame fuel input rate in Btu/h.

QIN is based on the baseline value for each product class. We set QIN,R to be 69% of QIN

for non-condensing two-stage equipment, 67% for condensing two-stage equipment, and 40% 

for continuous modulation equipment, where this value represents the average ratio QIN/QIN,R as 

derived using manufacturer product literature and AHRI March 2012 Directory data for all listed 

two-stage furnace models.2

From the test procedure,

1 QIN,M is calculated using QOUT,M and EffySS,M (as defined in 

section 11.4.8.10 or 11.5.8.8 in the ASHRAE SPC 103/2007 test procedure).1 QP is zero for all

product classes, except for the baseline manufactured-home gas furnace and gas boiler. 

7-E.3 DETERMINATION OF AVERAGE ANNUAL ELECTRICAL ENERGY 

CONSUMPTION (EAE) 

Using the ASHRAE SPC 103/2007 test procedure,1 the average annual auxiliary 

electrical energy consumption is calculated in Appendix C section 3:

EAE = BOHSS (yP * PE + yIG *PEIG + y * BE), for single-stage furnaces,

and

EAE = BOHR (yP,R*PER + yIG,R *PEIG,R + yR*BER) + BOHH or M (yP*PEH + yIG *PEIG,H + 

y*BEH)

b2

, for two-stage and continuous modulating furnaces,

where

BOHss = as defined in section 7-E.4,

BOHH = as defined in section 7-E.4,

BOHM = as defined in section 7-E.4

BOHR = as defined in section 7-E.4

yP = ratio of induced or forced draft blower on-time to average burner on-time,

yP,R = ratio of induced or forced draft blower on-time to average burner on-time, 

measured at the reduced fuel input rate,

 b

 The ASHRAE test procedure does not deal with ignitor energy consumption. The ratio of ignitor on-time to 

burner on-time and the ignitor power consumption variables come from the DOE test procedure.3
7-E-3

PE = burner (or draft inducer) electrical power input at full-load steady-state operation 

in kW,

PER = burner (or draft inducer) electrical power input at full-load steady-state operation 

in kW, measured at the reduced fuel input rate,

PEH = burner (or draft inducer) electrical power input at full-load steady-state operation 

in kW, measured at the maximum fuel input rate,

yIG = ratio of burner interrupted-ignition device on-time to average burner on-time,

yIG,R = ratio of burner interrupted-ignition device on-time to average burner on-time, 

measured at the reduced fuel input rate,

PEIG = electrical input rate to the interrupted ignition device on the burner,

PEIG,R = electrical input rate to the interrupted ignition device on the burner, measured at 

the reduced fuel input rate,

PEIG,H = electrical input rate to the interrupted ignition device on the burner, measured at 

the maximum fuel input rate,

y = ratio of blower or pump on-time to burner on-time,

yR = ratio of blower or pump on-time to burner on-time, measured at the reduced fuel 

input rate,

BE = circulating-air fan or water pump electrical energy input rate in kW,

BER = circulating-air fan or water pump electrical energy input rate in kW, measured at 

the reduced fuel input rate, and

BEH = circulating-air fan or water pump electrical energy input rate in kW, measured at 

the maximum fuel input rate.

The values yP and yP,R are calculated using tP (post-purge time). For this calculation, 

DOE took tP to be 5 seconds for furnaces, which is less than or 30 seconds and is therefore set 

equal to 0 seconds, according to Appendix C section 1 of the ASHRAE SPC 103/2007. DOE 

calculated the values y and yP,R using t+ (blower or pump on-delay) and t- (blower or pump offdelay). For furnaces, t+ = 2 min and t- = 0.5 min, which are values obtained for the generic 

furnace models. For gas furnaces, PE is equal to 75 W for non-condensing furnaces and 90 W 

for condensing furnaces. For oil furnaces, PE is set to 220 W. 6 For design options which 

include modulating controls, we set PER and PEH to have the same values as PE, since it is 

assumed that there is no inducer modulation. For gas furnaces, PEIG, PEIG,R, and PEIG,H are set 

equal to 400 W.7 For oil furnaces, PEIG is equal to 45 watts for oil equipment without 

interrupted ignition, and 25 watts with oil equipment with interrupted ignition.8 For design 

options which include modulating controls, we set PEIG,R and PEIG,H to have the same values as 

PEIG, since it is assumed that there is no ignition modulation. 

7-E.4 DETERMINATION OF NATIONAL AVERAGE NUMBER OF BURNER 

OPERATING HOURS (BOHSS) 

From the ASHRAE SPC103/2007 test procedure,

1 the national average number of burner 

operating hours for furnaces and boilers is calculated in Appendix C section 1:

BOHSS = 2080 * 0.77 * A * (QOUT / (1 + α)) - 2080 * B, for single-stage furnaces,
7-E-4

BOHH = XH * (2080) * (0.77) * AH * (QOUT / (1 + α)) - 2080 * BH, for two-stage furnaces 

at the maximum operating mode,

BOHR = XR * (2080) * (0.77) * AR * (QOUT / (1 + α)) - 2080 * BR, for two-stage and 

continuous modulating furnaces operating at the reduced operating mode,

and

BOHM = XH * (2080) * (0.77) * AM * (QOUT / (1 + α)) - 2080 * BM, for continuous 

modulating furnaces operating at the modulating operating mode, 

where

2080 = national average heating load hours,

0.77 = adjustment factor to adjust the calculated design heating requirements and heating 

load hours to the actual heating load experienced by the heating system,

A = 100,000/ [341300(yP * PE + yIG,R *PEIG,R + y * BE) + (QIN - QP) * EffyHS]

c

AH = 100,000/ [341300(yP * PEH + yIG,R *PEIG,R + y * BEH) + (QIN - QP) * EffyU,H]

a

, 

3

, 

AR = 100,000/ [341300(yP,R * PER + yIG,R *PEIG,R + yR * BER) + (QIN,R - QP) * EffyU,R]

a

, 

AM = 100,000/ [341300(yP * PEH + yIG,R *PEIG,R + y * BEH) + (QIN,M - QP) * EffyU,M]

a

, 

B = 2 * (QP) * (EffyHS) * (A) / 100,000,

BH = 2 * (QP) * (EffyU,H) * (AH) / 100,000,

BR = 2 * (QP) * (EffyU,R) * (AR) / 100,000,

BM = 2 * (QP) * (EffyU,M) * (AM) / 100,000,

QOUT = maximum fuel input rate heating capacity,

α = oversize factor set to 0.7,

XH = fraction of heating load at maximum fuel input rate operating mode,

XR = fraction of heating load at reduced fuel input rate operating mode (1-XH),

QIN = as defined in above,

QIN,R = as defined in above,

QIN,M = as defined in above, 

QP = as defined in above, 

yP = as defined in above,

yP,R = as defined in above,

PE = as defined in above,

PER = as defined in above,

PEH = as defined in above,

yIG = as defined in above,

yIG,R = as defined in above,

PEIG = as defined in above,

PEIG,R = as defined in above,

PEIG,H = as defined in above,

 c

 The ASHRAE test procedure does not deal with ignitor energy consumption. The ratio of ignitor on-time to 

burner on-time and the ignitor power consumption variables come from the DOE test procedure.3
7-E-5

y = as defined in section above,

yR = as defined in section above,

BE = as defined in section above,

BER = as defined in section above,

BEH = as defined in section above,

EffyHS = ratio of the average length of the heating season in hours to the average heating load 

hours,

EffyU,H = average part load efficiency at the maximum fuel input rate,

EffyU,R = average part load efficiency at the reduced fuel input rate, and

EffyU,M = average part load efficiency at the modulating fuel input rate.

The modified equations used in the LCC spreadsheet are as follows (Note that the 

maximum value for BOH is set to 8760):

BOHSS = A * HHL - 2080 * B, for single-stage furnaces,

BOHH = XH * AH * HHL - 2080 * BH, for two-stage furnaces at the maximum operating 

mode,

BOHR = XR * AR * HHL - 2080 * BR, for two-stage and continuous modulating furnaces 

operating at the reduced operating mode, 

and

BOHM = XH * AM * HHL - 2080 * BM, for continuous modulating furnaces operating at 

the modulating operating mode, 

To calculate factors A, AH, AR, AM, B, BH, BR, and BM, DOE calculated yP, yP,R, PE, PER, 

PEH, yIG, yIG,R, PEIG, PEIG,R, PEIG,H, y, yR, BE, BER, BEH, PE, yIG, PEIG, y, BE, QIN, and QP yP , as 

described in section 7-E.3 of this appendix. For factor B, if QP = 0, then B = 0, which is true for 

all cases except for the baseline manufactured-home gas furnace and the baseline gas boiler. We 

calculated EffyHS, heating seasonal efficiency, as defined in sections 11.2.11, 11.3.11.3, 

11.4.11.3, and 11.5.11.3 in ASHRAE SPC 103/2007 test procedure.

1

 For QP = 0, EffyHS is equal 

to the annual fuel utilization efficiency (AFUE). For QP > 0, EffyHS is calculated using EffySS (as 

defined in section 11.2.8.11). EffySS is calculated using QOUT (as defined below), K (factor that 

adjusts the jacket losses, where K = 1.7 for non-weatherized furnaces and Lj (jacket loss, where 

Lj = 1 is the default value as described in section 11.2.8.11)

QOUT for all product classes is calculated using the following equations based on AHRI 

Directory data for Non-Weatherized Gas Furnaces:2

QOUT = QIN (0.7247 * AFUE + 0.22346), for non-condensing equipment, and

QOUT = QIN (0.8127 * AFUE + 0.17557), for condensing equipment.
7-E-6

DOE calculated XH by using TC (balance-point temperature as defined in section 11.4.8.4

of ASHRAE SPC 103/2007 test procedure1

), α (the oversize factor, as calculated in Equation 

11), QOUT, and QOUT,R (reduced fuel input rate heating capacity). QOUT,R is set equal to 69% QOUT

for non-condensing equipment and 67% QOUT for condensing equipment, as derived using 

manufacturer product literature and AHRI Directory data for all listed two-stage furnace 

models.2 XR is set equal to 1-XH. EffyU,H = EffyU,R and therefore using the equation in section 

11.5.11.3 of ASHRAE SPC 103/2007 test procedure is equal to EffySS. EffyU,M is calculated 

using the equation in section 11.4.9.2.3 of ASHRAE SPC 103/2007 test procedure.

1

7-E.5 DETERMINATION OF IMPACT ON FURNACE ENERGY USE WITH

MORE EFFICIENT FURNACE FANS

DOE accounted for the fact that more efficient furnace fans will tend to contribute less 

heat and thereby require additional furnace operation. Since the heating load of each sample 

housing unit is known, it is possible to estimate what the furnace energy consumption would be 

if more efficient fan equipment, rather than the baseline equipment, was used in each housing 

unit.

DOE calculated the furnace fuel consumption (FuelUse) for each furnace fan efficiency 

level using the following formula based on the current American Society of Heating, 

Refrigerating and Air-Conditioning Engineers (ASHRAE) test procedure SPC 103-2007 section 

C d:

, for single-stage furnace, and 

FuelUse= (BOHH * QIN) + (BOHR * QIN,R), for two-stage furnaces

Where:

BOH =steady-state burner operating hours (hr),

QIN = input capacity of existing furnace (kBtu/h,).

BOHH = burner operating hours at the maximum operating mode for two-stage furnaces 

(see derivation in section 7-E.4),

BOHR = burner operating hours at the reduced operating mode for two-stage or 

continuous modulating furnaces (see derivation in section 7-E.4), and

QIN,R = reduced fuel input rate.

 d For natural draft equipment this formula is modified to include the pilot light consumption.

FuelUse = BOH × QIN
7-E-7

Recall from above that BOH is calculated using BE (furnace fan electrical energy input 

rate), which is equal to the furnace fan power during the heating operation calculated for each 

furnace fan efficiency level. 

DOE also calculated the non-furnace fan furnace electricity consumption (i.e., the 

electricity used by the induce draft blower and the electricity used by the ignitor) for each 

furnace fan efficiency level using the following formula:

,

e

ElecUsenon-furnac_fan = BOHR (yP,R*PER + yIG,R *PEIG,R) + BOHH (yP*PEH + yIG *PEIG,H)

for single-stage furnace, and

f2

, for 

two-stage

Where:

BOH = steady-state burner operating hours (hr),

yP = ratio of induced-draft blower on-time to burner on-time,

PE = power consumption of the draft-inducer blower-motor (kW),

yIG = ratio of ignitor on-time to burner on-time, and 

PEIG = power consumption of the ignitor (kW).

BOHH = burner operating hours at the maximum operating mode for two-stage 

furnaces (see derivation in section 7-E.4),

BOHR = burner operating hours at the reduced operating mode for two-stage or 

continuous modulating furnaces (see derivation in section 7-E.4), and

yP,H = ratio of induced-draft blower on-time to burner on-time, measured at the 

maximum fuel input rate,

PEH = power consumption of the draft-inducer blower-motor (kW), measured at 

the maximum fuel input rate,

yIG,H = ratio of ignitor on-time to burner on-time, measured at the maximum fuel 

input rate, and 

PEIG,H = power consumption of the ignitor (kW) measured at the maximum fuel 

input rate.

yP,R = ratio of induced-draft blower on-time to burner on-time, measured at the 

reduced fuel input rate,

PER = power consumption of the draft-inducer blower-motor (kW), measured at 

the reduced fuel input rate,

 e For two-stage equipment this formula includes parameters for the operation at full, modulating, and reduced load. f The ASHRAE test procedure does not deal with ignitor energy consumption. The ratio of ignitor on-time to burner 

on-time and the ignitor power consumption variables come from the DOE test procedure.3

( ) non furnace fan SS p ig PEig ElecUse − _ = BOH × y × BE + y × PE + y ×
7-E-8

yIG,R = ratio of ignitor on-time to burner on-time, measured at the reduced fuel 

input rate, and 

PEIG,R = power consumption of the ignitor (kW) measured at the reduced fuel 

input rate.

Once the heating load of each sample housing unit is known, it is possible to estimate 

what the energy consumption would be if more efficient furnace fan equipment, rather than the 

baseline equipment, were used in each housing unit.

The ratio of blower on-time to burner on-time and the ratio of induced draft blower ontime to burner on-time are from the current ASHRAE test procedure SPC 103-20071

 using delay 

times (pre-purge, post-purge, on-delay, and off-delay) derived from DOE’s 2007 Furnace and 

Boiler Final Rule.4 The ratio of ignitor on-time to burner on-time comes from the DOE test 

procedure and the ignition time derived from the 2007 final rule. The delay times are defined as 

follows: pre-purge and post-purge times are the lengths of time the draft inducer operates before 

and after a firing cycle. On-delay is the amount of time the blower waits to begin operating after 

the burner starts firing. Off-delay is the time the blower keeps operating after the burner turns 

off. Ignition time is the length of time the hot surface ignitor is on before gas is sent to the 

burner. The average values for the delay and ignition times are shown in the next table. 

Table 7-E.5.1 Average Values for Delay and Ignition Times

Pre-Purge Post-Purge On-Delay Off-Delay Ignition

15 seconds 5 seconds 30 seconds 120 seconds 37 seconds

A common value for the power consumption of the draft inducer, PE, for basic noncondensing model furnaces is 75 W, and the average value is about 75 W, so DOE selected 75 W 

for all the non-condensing models. DOE found no correlation between the PE and input capacity 

or between PE and airflow capacity. For condensing furnaces, DOE used a PE of 90 W, which 

closely matches the mean for that group. 

7-E.6 ASSIGNING FURNACE EQUIPMENT CHARACTERISTICS TO 

SAMPLE HOUSEHOLDS

To estimate the heating load of each sample housing unit, DOE represented the existing 

furnace by assigning an input capacity, airflow capacity, and AFUE to the furnace in the RECS 

sample housing units. 

7-E.6.1 Input Capacity of Existing and New Equipment

DOE assigned an input capacity for the existing furnace of each housing unit based on an 

algorithm that correlates the housing unit size and outdoor design temperature with the 

distribution of input capacity of furnaces. DOE assumed that, for the new furnace installation, 
7-E-9

the input capacity would remain the same. The following steps describe the assignment process 

for furnaces:

1) DOE ranked all the RECS housing units in ascending order by size (heating square foot) 

multiplied by a scaling factor to account for the outdoor design temperature (see equation 

below) and calculated the percentile rank of each housing unit using the statistical weight 

of each of the sample records.

2) DOE constructed percentile tables by input capacity of furnaces based on the historical 

shipment information and number of models in AHRI Directory.

3) After selecting a housing unit from the RECS database during each Monte Carlo 

iteration, DOE noted the size of the selected housing unit and determined the percentile 

rank from Step 1.

4) To avoid a one-to-one deterministic relation between the housing unit size and input 

capacity, DOE added a random term to the percentile identified in Step 3 so that the 

correlation was not perfect. DOE used a normal distribution to characterize the random 

term. The random term has a mean of zero and a standard deviation of 8 percent.

5) Using the percentile from Step 4, DOE looked up the input capacity from the input 

capacity percentile table in Step 2. 

DOE used ASHRAE design data to develop estimates of the average 1 percent design dry 

bulb temperature for each household. Using this data, DOE then developed a scaling factor to be 

applied to the home heating square footage and equal to: 

SFdesign,h = (65- Tdesign, h) / (65 - 42)

Where: 

SFdesign,h = heating design scaling factor, and

Tdesign, h = average 1 percent ASHRAE design dry bulb temperature (°F) for heating.

The design scaling factor is used as a proxy to represent lower heating loads for the same 

household area in cooler climates and supports the allocation of the sizes across observations, but 

that the total relative allocation of sizes is unaffected. The end result was a distribution of sizes 

assigned to the weighted RECS samples that matches the distribution of sizes for shipments of 

residential furnaces by input capacity. Table 7-E.6.1shows the distribution of input capacities for 

the most commonly available input capacity bins for non-weatherized gas furnaces based on the 

2012 AHRI Residential Furnace Directory.

2 See the LCC spreadsheet, worksheet “Furnace & 

AC Spec” for the distributions of input capacities for other product classes.
7-E-10

Table 7-E.6.1 Distribution of Input Capacities for Non-Weatherized Gas Furnaces

Non-Condensing Condensing

Input Capacity 

kBtu/h

2012 AHRI 

Directory 

Fraction of 

Models

%

Cumulative 

Fraction of 

Models

%

2012 AHRI 

Directory 

Fraction of 

Models

%

Cumulative 

Fraction of 

Models

%

40 10.9 10.9 10.9 10.9

50 3.3 14.2 1.8 12.7

60 17.6 31.8 17.1 29.8

70 5.4 37.2 6.7 36.5

80 18.5 55.7 20.4 56.9

90 1.8 57.5 7.5 64.4

100 17.4 75.0 16.0 80.4

110 6.5 81.5 6.7 87.1

120 9.1 90.6 10.5 97.6

130 3.4 94.0 2.2 99.8

140 3.4 97.5 0.2 100.0

150 2.0 99.5 0.0 100.0

160 0.5 10.9 0.0 100.0

7-E.6.2 Airflow Size of Existing Equipment

DOE classified furnaces by nominal maximum airflow in cfm at 0.5 in. w.g. of external 

static pressure. DOE assigned the airflow capacity of existing furnaces for housing units that had 

air conditioners in a manner similar to how it assigned furnace input capacity. Larger air 

conditioners go to larger housing units, according to the distribution of sizes of air conditioners 

sold the year the air conditioner was installed in that housing unit. DOE used the air conditioner 

nominal size of two, three, four, or five tons to set the airflow capacity with a ratio of 400 cfm 

per ton of cooling. The steps were:

1) DOE ranked all the RECS housing units in ascending order by size (cooling square foot) 

multiplied by a scaling factor to account for the outdoor design temperature (see equation 

below) and calculated the percentile rank of each housing unit using the statistical weight 

of each of the sample records.

2) Based on historical shipment information of residential central air conditioners by 

capacity, DOE constructed the airflow capacity percentiles table for air conditioners. (See 

Table 7-E.6.2). Since there are no available shipment data on the airflow capacity of 

furnaces, DOE used the airflow capacity of residential central air conditioners as a proxy.

3) After selecting a housing unit from the RECS database during each Monte Carlo 

iteration, DOE noted the size of the selected housing unit and determined the percentile 

rank from Step 1.

4) To avoid a one-to-one deterministic relation between the housing unit size and input 

capacity, DOE added a random term to the percentile identified in Step 3 so that the 
7-E-11

correlation was not perfect. DOE used a normal distribution to characterize the random 

term. The random term has a mean of zero and a standard deviation of 8 percent.

5) Using the percentile from Step 4, DOE looked up the airflow from the airflow percentile 

table in Step 2. DOE selected an input capacity and airflow combination with the 

identified airflow capacity, based on commonly available models. If no input capacity 

and airflow combination with the identified airflow capacity was available, DOE selected 

the input capacity and airflow combination with the same input capacity and the closest 

airflow capacity as a substitute.

DOE used ASHRAE design data to develop estimates of the average 1 percent design dry 

bulb temperature for each household. Using these data, DOE then developed a scaling factor to 

be applied to the home cooling square footage and equal to: 

SFdesign,c = (Tdesign, c – 65) / (95 - 65)

Where: 

SFdesign,c = cooling design scaling factor, and

Tdesign, c = average 1 percent ASHRAE design dry bulb temperature (°F) for cooling.

It is noted that the design scaling factor is used as a proxy to represent lower cooling

loads for the same household area in warmer climates and supports the allocation of the sizes 

across observations, but that the total relative allocation of sizes is unaffected. This end result 

was a distribution of sizes assigned to the weighted RECS samples that matches the distribution 

of sizes for shipments of residential furnaces. Table 7-E.6.2shows the distribution of airflow 

ratings for the representative product classes listed above, based on AHRI shipment data. 5

Table 7-E.6.2 Distribution of Airflow for Furnaces

Airflow Rating 

cfm

2007-2011 AHRI 

Shipments

%

Cumulative Fraction

%

600 9.5 9.5

800 19.6 29.1

1000 16.5 45.6

1200 22.5 68.0

1400 8.7 76.8

1600 12.5 89.2

2000 10.8 100.0

7-E.6.3 AFUE of Existing Equipment

DOE assigned the AFUE of existing furnaces based on the equipment age of the existing 

furnace as given by RECS and historical shipments by efficiency. The following steps describe 

this process:
7-E-12

1) After DOE selected a housing unit from the RECS database during each Monte Carlo 

iteration, DOE randomly assigned a percentile value and extracted the furnace age 

information from RECS. Using the extracted furnace age, DOE assigned an installation 

year from the installation year range for the applicable RECS equipment age bin (see

Table 7-E.6.3).

2) Based on the historical furnace shipment information sorted by AFUE, DOE constructed 

percentile tables by AFUE shipments of furnaces for 2005 and prior years. AHRI 

shipments data for non-weatherized gas furnaces indicate that housing units in the 

northern region receive more efficient furnaces. Therefore, DOE developed two historical 

AFUE shipment distributions—one for the northern region and one for the southern 

region—for non-weatherized gas furnaces.

3) DOE determined the AFUE by looking it up from the AFUE percentile table from Step 

(2) corresponding to the age of the existing equipment in the housing unit and whether 

the housing unit was located in the northern or southern regions (See Table 7-E.6.4). See 

the LCC spreadsheet, worksheet “Furnace & AC Spec” for the distributions of input 

capacities for other product classes.

Table 7-E.6.3 Number of Observations for Each Age Group

RECS Bin Less than 2 

Years Old

2 to 4 

Years Old

5 to 9 

Years Old

10 to 19 

Years Old

20 Years 

or Older

Total

Installation Years 2004-2005 2001-2005 1996-2000 1986-1995 1966-1985

Equipment Type

Non-Weatherized 

Gas Furnaces

206 229 367 477 302 1,726

13.2% 13.3% 21.3% 27.0% 17.8% 100.0%

Manufactured Home 

Gas Furnaces

11 14 25 25 27 109

8.5% 12.5% 24.4% 23.5% 23.3% 100.0%

Oil-Fired Furnaces 10 21 29 47 39 150

9.0% 14.1% 14.5% 31.7% 29.7% 100.0%
7-E-13

Table 7-E.6.4 Historical Fraction of Regional Non-Weatherized Gas Furnace 

Shipments by AFUE Bins

Year North Region South Region

>78 AFUE 78 to <90 >90 AFUE >78 AFUE 78 to <90 >90 AFUE

2005 0.0% 48.8% 51.2% 0.0% 81.6% 18.4%

2004 0.0% 52.2% 47.8% 0.0% 83.6% 16.4%

2003 0.0% 53.7% 46.3% 0.0% 83.6% 16.4%

2002 0.0% 59.0% 41.0% 0.0% 85.2% 14.8%

2001 0.0% 57.7% 42.3% 0.0% 86.0% 14.0%

2000 0.0% 64.6% 35.4% 0.0% 89.6% 10.4%

1999 0.0% 64.9% 35.1% 0.0% 89.5% 10.5%

1998 0.0% 64.6% 35.4% 0.0% 89.8% 10.2%

1997 0.0% 62.9% 37.1% 0.0% 87.8% 12.2%

1996 0.0% 64.8% 35.2% 0.0% 89.8% 10.2%

1995 0.0% 68.3% 31.7% 0.0% 88.9% 11.1%

1994 0.0% 66.6% 33.4% 0.0% 87.6% 12.4%

1993 0.0% 70.2% 27.4% 0.0% 86.8% 10.2%

1992 2.4% 59.3% 34.0% 3.0% 80.2% 10.7%

1991 6.7% 23.9% 29.7% 9.1% 30.9% 9.3%

1990 46.3% 22.3% 25.3% 59.8% 27.4% 7.9%

1989 52.4% 17.4% 24.3% 64.6% 21.2% 7.6%

1988 58.3% 19.6% 25.7% 71.2% 24.2% 8.1%

1987 54.8% 18.3% 23.7% 67.8% 22.2% 7.4%

1986 58.0% 18.7% 10.2% 70.4% 20.1% 3.2%

1985 71.1% 17.3% 16.2% 76.7% 19.6% 5.1%

1984 66.5% 18.2% 17.8% 75.3% 20.9% 5.6%

1983 64.0% 7.8% 22.9% 73.5% 9.4% 7.2%

1982 69.3% 8.2% 19.2% 83.4% 9.6% 6.0%

1981 72.6% 8.6% 15.6% 84.4% 9.7% 4.9%

1980 75.9% 9.0% 11.9% 85.4% 9.8% 3.7%

1979 79.1% 3.9% 5.9% 86.5% 4.1% 1.9%

1978 90.2% 1.4% 0.0% 94.1% 1.4% 0.0%

1977 98.6% 0.9% 0.0% 98.6% 0.9% 0.0%

1976 99.1% 0.5% 0.0% 99.1% 0.5% 0.0%

1975 99.5% 0.0% 0.0% 99.5% 0.0% 0.0%

1966 to 1974 100.0% 0.0% 0.0% 100.0% 0.0% 0.0%

7-E.6.4 AFUE of New Equipment

DOE assigned the AFUE of new furnaces based on distribution of AFUE of furnaces 

equipment and the RECS household location standards in 2018 for furnaces (e.g. minimum 

efficiency of 90% AFUE for northern region households with a non-weatherized gas furnace). 

Table 7-E.6.5 shows the distribution of AFUE for the most commonly available AFUE bins for 

non-weatherized gas furnaces based on the 2012 AHRI Residential Furnace Directory.

2 See the 

LCC spreadsheet, worksheet “Furnace & AC Spec” for the distributions of AFUE for other 

product classes.
7-E-14

Table 7-E.6.5 Distribution of AFUE for Non-Weatherized Gas Furnaces

Non-Condensing Condensing

AFUE

%

2012 AHRI 

Directory 

Fraction of 

Models

%

Cumulative 

Fraction of 

Models

%

2012 AHRI 

Directory 

Fraction of 

Models

%

Cumulative 

Fraction of 

Models

%

80 99.8 99.8 0.0 0.0

81 0.0 99.8 0.0 0.0

82 0.0 99.8 0.0 0.0

83 0.2 100.0 0.0 0.0

90 0.0 100.0 1.8 1.8

91 0.0 100.0 2.4 4.2

92 0.0 100.0 18.2 22.4

93 0.0 100.0 6.4 28.7

94 0.0 100.0 2.7 31.5

95 0.0 100.0 33.5 64.9

96 0.0 100.0 21.1 86.0

97 0.0 100.0 10.7 96.7

98 0.0 100.0 3.3 100.0
7-E-15

REFERENCES

1. American Society of Heating Refrigerating and Air-Conditioning Engineers Inc., 

ASHRAE Standard: Method of Testing for Annual Fuel Utilization Efficiency of 

Residential Central Furnaces and Boilers, 2007. Report No. ANSI/ASHRAE 103-2007. 

2. Air Conditioning Heating and Refrigeration Institute, Consumer's Directory of Certified 

Efficiency Ratings for Heating and Water Heating Equipment (AHRI Directory March 

2012), 2012. (Last accessed March, 2012.) 

<http://www.ahridirectory.org/ahridirectory/pages/home.aspx>

3. U.S. Department of Energy-Office of Energy Efficiency and Renewable Energy, Title 10, 

Code of Federal Regulations, Chapter II Part 430 Appendix N, Subpart B-Uniform Test 

Method for Measuring the Energy Consumption of Furnaces, January 1, 2012. 

4. Department Of Energy, 10 CFR Part 430 Energy Conservation Program for Consumer 

Products: Energy Conservation Standards for Residential Furnaces and Boilers; Final 

Rule. Federal Register, 2007. 72 No.222: pp. 65132-65170 

5. Air-Conditioning Heating and Refrigeration Institute, AHRI Shipments Data for Air 

Conditioners by Capacity 2007-2011. <http://www.ahrinet.org/monthly+shipments.aspx>