7-i

CHAPTER 7. ENERGY USE ANALYSIS

TABLE OF CONTENTS

7.1 INTRODUCTION ........................................................................................................... 7-1

7.2 GENERAL APPROACH TO THE ENERGY USE ANALYSIS................................... 7-1

7.3 HOUSEHOLD SAMPLE ................................................................................................ 7-2

7.4 FURNACE FAN POWER CONSUMPTION................................................................. 7-4

7.4.1 System Curves ................................................................................................................. 7-4

7.4.2 Furnace Fan Curves ......................................................................................................... 7-6

7.4.3 Fan Power ........................................................................................................................ 7-7

7.4.4 Determination of Fan Performance by Product Class and Efficiency Level................... 7-9

7.5 OPERATING HOURS .................................................................................................. 7-17

7.5.1 Heating Mode................................................................................................................. 7-17

7.5.2 Cooling Mode ................................................................................................................ 7-23

7.5.3 Constant Circulation Mode ............................................................................................ 7-28

7.6 FURNACE FAN STANDBY ENERGY USE .............................................................. 7-30

7.7 CHANGES IN HEATING AND AIR-CONDITIONING ENERGY USE WITH 

MORE-EFFICIENT FURNACE FANS........................................................................ 7-31

7.7.1 Impact on Furnace Fuel Use with More Efficient Furnace Fans................................... 7-31

7.7.2 Impact on Central Air Conditioner Energy Use with More Efficient Furnace Fans..... 7-32

7.8 SUMMARY OF ENERGY USE RESULTS................................................................. 7-33

LIST OF TABLES

Table 7.1.1 Furnace Fan Product Classes Analyzed............................................................... 7-1

Table 7.3.1 Household Samples for Furnace Fan Products.................................................... 7-3

Table 7.4.1 Values Used for External Static Pressure ............................................................ 7-5

Table 7.4.2 Coefficients for CFM equation for Non-Weatherized (Non-Condensing) 

Gas Furnace Fan, 3-Ton..................................................................................... 7-10

Table 7.4.3 Coefficients for Watts/CFM Equation for Non-Weatherized (NonCondensing) Gas Furnaces, 3-Ton..................................................................... 7-12

Table 7.5.1 Heating Degree-Day Adjustment Factors.......................................................... 7-21

Table 7.5.2 Range of Adjusted Heating Load for Each Furnace Fan Product Class, 

million Btu/h ...................................................................................................... 7-22

Table 7.5.3 Range of Baseline Furnace Fan Heating Operating Hours for Each 

Furnace Fan Product Class, hours...................................................................... 7-23

Table 7.5.4 Cooling Degree Day Adjustment Factors.......................................................... 7-26

Table 7.5.5 Range of Annual Cooling Load for Each Furnace Fan Product Class, 

million Btu/h ...................................................................................................... 7-27

Table 7.5.6 Range of Baseline Furnace Fan Cooling Operating Hours for Each 

Furnace Fan Product Class, hours...................................................................... 7-28

Table 7.5.7 Results from Constant-Circulation Use Studies and Estimated National 

Constant-Circulation Hours............................................................................... 7-29
7-ii

Table 7.5.8 Average Baseline Constant Circulation Furnace Fan Operating Hours for 

Each Furnace Fan Product Class, hours............................................................. 7-30

Table 7.8.1 Average Annual Energy Consumption and Savings for Furnace Fans Used 

in Non-Weatherized Gas Furnaces .................................................................... 7-33

Table 7.8.2 Average Annual Energy Consumption and Savings for Furnace Fans Used 

in Weatherized Gas Furnace Fans and Oil-Fired Furnaces ............................... 7-34

Table 7.8.3 Average Annual Energy Consumption and Savings for Furnace Fans Used 

in Manufactured Home Gas Furnaces................................................................ 7-34

Table 7.8.4 Average Annual Energy Consumption and Savings for Furnace Fans Used 

in Electric Furnaces and Manufactured Home Electric Furnaces...................... 7-35

Table 7.8.5 Average Annual Energy Consumption and Savings for Furnace Fans Used 

in Hydronic Air Handlers................................................................................... 7-35

LIST OF FIGURES

Figure 7.4.1 Sample of System Curves with a Typical Fan Curve .......................................... 7-6

Figure 7.4.2 Example Fit of CFM for 3-Ton PSC Furnace in Heating Mode.......................... 7-7

Figure 7.4.3 Example Fit of Watts/CFM for 3-Ton Single-Stage Furnace.............................. 7-9

Figure 7.4.4 CFM Curves for Non-Weatherized (Non-Condensing) Gas Furnace Fan, 

3-Ton (Heating Mode)....................................................................................... 7-11

Figure 7.4.5 CFM Curves for Non-Weatherized (Non-Condensing) Gas Furnace Fan, 

3-Ton (Cooling Mode)....................................................................................... 7-11

Figure 7.4.6 CFM Curves for Non-Weatherized (Non-Condensing) Gas Furnace Fan, 

3-Ton (Constant Circulation Mode)................................................................... 7-12

Figure 7.4.7 Watt/CFM Curves for Non-Weatherized (Non-Condensing) Gas Furnace 

Fan, 3-Ton (Heating Mode)............................................................................... 7-13

Figure 7.4.8 Watt/CFM Curves for Non-Weatherized (Non-Condensing) Gas Furnace 

Fan, 3-Ton (Cooling Mode)............................................................................... 7-13

Figure 7.4.9 Watt/CFM Curves for Non-Weatherized (Non-Condensing) Gas Furnace 

Fan, 3-Ton (Constant Circulation Mode)........................................................... 7-14

Figure 7.4.10 Resulting Watt vs. Pressure Curves for Non-Weatherized (NonCondensing) Gas Furnace Fan, 3-Ton (Heating Mode)..................................... 7-15

Figure 7.4.11 Resulting Watt vs. Pressure Curves for Non-Weatherized (NonCondensing) Gas Furnace Fan, 3-Ton (Cooling Mode) .................................... 7-16

Figure 7.4.12 Resulting Watt vs. Pressure Curves for Non-Weatherized (NonCondensing) Gas Furnace Fan, 3-Ton (Constant Circulation Mode)................ 7-17
7-1

CHAPTER 7. ENERGY USE ANALYSIS

7.1 INTRODUCTION

The purpose of the energy use analysis is to determine the annual energy consumption of 

furnace fans in representative U.S. homes and to assess the energy savings potential of increased 

fan efficiency. In contrast to the DOE test procedure, which uses typical operating conditions in 

a laboratory setting, the energy use analysis seeks to estimate the range of energy consumption of 

the products in the field. DOE estimated the annual energy consumption of furnace fans at 

specified energy efficiency levels across a range of climate zones and household characteristics. 

The energy use analysis provides estimates of the distribution of annual energy consumption for 

furnace fans at the efficiency standard levels considered.

DOE developed energy consumption estimates for the key product classes analyzed in the 

engineering analysis (chapter 5 of the technical support document (TSD)). These are listed in 

Table 7.1.1.

Table 7.1.1 Furnace Fan Product Classes Analyzed

Non-Weatherized, Non-Condensing Gas Furnace Fan

Non-Weatherized, Condensing Gas Furnace Fan

Weatherized Gas Furnace Fan

Oil Furnace Fan

Electric Furnace / Modular Blower Fan

Manufactured Home Non-Weatherized, Non-Condensing Gas Furnace Fan

Manufactured Home Non-Weatherized, Condensing Gas Furnace Fan

Manufactured Home Electric Furnace / Modular Blower Fan

Hydronic Air Handler Fan (Heat/Cool)

7.2 GENERAL APPROACH TO THE ENERGY USE ANALYSIS

Estimating annual energy consumption of furnace fans requires calculating the energy 

use at different operating modes: heating, cooling, constant circulation, and standby. DOE 

estimated the total annual energy consumption of furnace fans for each household sampled using 

the following equation:

FFEUtotal = FFOHheating × FFPheating + FFOHcooling × FFPcooling + FFOHcont fan

× FFPcont fan + FFOHstandby × FFPstandby

 Where:

FFEUtotal = Total annual energy consumption by furnace fan, kW/yr,

FFOHheating = furnace fan operating hours during the heating season, h,

FFPheating = furnace fan power during the heating operation, kW,
7-2

FFOHcooling = furnace fan operating hours during the cooling season, h,

FFPcooling = furnace fan power during the cooling operation, kW,

FFOHcont fan = furnace fan operating hours during constant circulation fan 

operation, h,

FFPcont fan = furnace fan power during the constant circulation fan operation, kW,

FFOHstandby = furnace fan operating hours during standby, h, and

FFPstandby = furnace fan power during the standby operation, kW.

7.3 HOUSEHOLD SAMPLE

DOE’s calculation of the annual energy use of residential furnace fans relied on data from 

Energy Information Administration’s 2005 Residential Energy Consumption Survey (RECS 

2005).

1 RECS collects energy-related data for occupied primary housing units in the United 

States. The RECS 2005 included data from 4,381 housing units that represent almost 111.1 

million households. The subset of RECS 2005 records used to study furnace fans met all of the 

following criteria:

• used a furnace as the main or secondary source of heat;

• used a heating fuel that is natural gas, liquefied petroleum gas (LPG), electricity, or fuel 

oil;

• heated only one housing unit; and

• had a heating energy consumption greater than zero.

DOE divided the furnace subset into further subsets designed to include households that 

use one of the furnace fan product classes (Table 7.3.1). Appendix 7-A presents the variables 

included and their definitions.

The RECS 2005 weighting indicates how commonly each household configuration 

occurs in the general population in 2005. DOE made some adjustments to EIA’s weightings for 

each RECS 2005 household in order to create a furnace fan population weight for 2018. The first 

adjustment was to compensate for the fact that the RECS 2005 sample does not distinguish 

between weatherized and non-weatherized gas furnaces. DOE also took into account the growth 

in population by region from 2005 to 2018 based on U.S. census population projections. Finally, 

DOE adjusted the weightings to account for households with multiple furnaces. Appendix 7-A

provides further details on these adjustments.
7-3

Table 7.3.1 Household Samples for Furnace Fan Products

Product Class Criteria No. of 

Records

RECS 

2005

2018

Estimate

Number 

of 

Houses 

million

Number 

of 

Furnaces 

million

Non-Weatherized, 

Non-Condensing Gas 

Furnace Fan

Primary or Secondary Heating Equipment = Gas Furnacea

Region = South

Housing Type = non-mobile home

736 19.6 14.5

Non-Weatherized, 

Condensing Gas 

Furnace Fan

Primary or Secondary Heating Equipment = Gas Furnace

Housing Type = non-mobile home

1726 45.5 35.6

Weatherized Gas 

Furnace Fan

Primary or Secondary Heating Equipment = Gas Furnace

Region = South

Housing Type = non-mobile home

Primary or Secondary Cooling Equipment = Central Air 

Conditioner

576 15.4 17.9

Oil Furnace Fan Primary or Secondary Heating Equipment = Oil Furnace

Housing Type = non-mobile home

150 2.9 3.3

Electric Furnace / 

Modular Blower Fan

Primary or Secondary Heating Equipment = Electric Furnace

Housing Type = non-mobile home

40 1.3 0.8

Manufactured Home 

Non-Weatherized, 

Non-Condensing Gas 

Furnace Fan

Primary or Secondary Heating Equipment = Gas Furnace

Region = South

Housing Type = mobile home

565 15.6 3.6

Manufactured Home 

Non-Weatherized, 

Condensing Gas 

Furnace Fan

Primary or Secondary Heating Equipment = Gas Furnace

Housing Type = mobile home

51 1.2 1.2

Manufactured Home 

Electric Furnace / 

Modular Blower Fan

Primary or Secondary Heating Equipment = Electric Furnace

Housing Type = mobile home

109 2.5 1.6

Hydronic Air 

Handler Fan 

(Heat/Cool)

Primary or Secondary Heating Equipment = Gas Furnace

Region = South

Housing Type = non-mobile home

Primary or Secondary Cooling Equipment = Central Air 

Conditioner

Water Heater Equipment = Gas Water Heater

Household Square Footage <2000 sq ft

68 1.9 2.1

 a Natural Gas or LPG Furnace.
7-4

7.4 FURNACE FAN POWER CONSUMPTION

The electricity consumption (and overall efficiency) of a furnace fan depends on the 

speed at which the motor operates, the external static pressure difference across the blower, and 

the airflow through the blower. The power consumption of the furnace fan is determined using 

the individual sample housing unit operating conditions (the pressure and airflow) at which a 

particular furnace fan will operate when performing heating, cooling, and constant circulation

functions.

These operating conditions can be graphically displayed as the intersection of a system 

curve of the air-distribution system in the housing unit (which plots the airflow across the supply 

and return air ducts as a function of static pressure) with the fan curve of the furnace (which plots

the airflow through the furnace as a function of static pressure).2 The intersection of these two 

curves is the airflow and the static pressure at which the furnace will operate in that housing unit.

Furnace fan curves, reported as tables of airflow rise versus static pressure through the 

furnace, are available from manufacturers in the product literature for most furnace models. 

Some of the manufacturers also supply blower-motor input power as a function of static pressure 

across the furnace.

Air power is calculated from the air speed through the furnace and the pressure rise 

across the furnace. The overall air-moving efficiency is air power divided by the electric power 

to the blower motor. 

All of the electric power of the blower motor eventually is converted into heat that 

contributes heat to the building’s interior. DOE takes this into account by increasing the heating 

load and/or decreasing the cooling load for more efficient furnace fans. 

7.4.1 System Curves

DOE modeled system curves as quadratic curves, which is standard in heating, 

ventilation, and air conditioning (HVAC) design and fan selection handbooks.3 The curves are 

based on Bernoulli’s equations for fluid flow and are expressed as the following equation:

Q = � P

α

Where:

Q = airflow (CFM),

P = external static pressure (in.w.g.), and

α = a constant coefficient.
7-5

DOE selected the external static pressure (ESP) in the system curve equation for each 

sample housing unit. DOE identified four installation types with unique ESP considerations: 

units paired with an evaporator coil; heating-only units or units with an internal evaporator coil; 

manufactured home units paired with an evaporator coil; and manufactured home heating-only 

units. To develop distributions of ESP values for each of these types, DOE gathered field data 

from available studies and research reports to determine an appropriate distribution of ESP 

values. DOE compiled over 1,300 field ESP measurements from several studies that included 

furnace fans in single-family and manufactured homes in different regions of the country. The 

data and sources are described in appendix 7-B. Table 7.4.1 gives the weighted average ESP 

values for each type. DOE designed each distribution as a normal distribution based on the field 

studies. DOE randomly sampled a static pressure value at the nominal maximum airflow from 

one of the four distributions, depending on the type of equipment installed in the housing unit. 

Table 7.4.1 Values Used for External Static Pressure

Installation Type

Associated Product Class Weighted 

Average 

ESP

(in. w.c.)

Standard 

Deviation 

(in. w.c.)

Units paired with an evaporator coil Furnaces paired with a CAC 

unit

0.73 0.12

Heating-only units or Units with an 

internal evaporator coil 

Furnaces not paired with a 

CAC unit or Weatherized gas 

furnaces

0.52 0.12

Manufactured home paired with an 

evaporator coil

Manufactured home furnaces 

paired with a CAC unit

0.37 0.6

Manufactured home heating-only 

units

Manufactured home furnaces 

not paired with a CAC unit

0.17 0.6

Figure 7.4.1 shows an example of a plot of system curves intersecting a furnace fan 

curve.
7-6

Figure 7.4.1 Sample of System Curves with a Typical Fan Curve

7.4.2 Furnace Fan Curves

Depending on the resistance (measured as static pressure) of the supply and return air 

ducts, a furnace will move more or less air. When these airflow values are plotted graphically 

against pressure, they are referred to as fan curves. 

DOE developed fan curves for PSC, PSC with controls, X13, and ECM furnace models 

by fitting airflow and pressure data points from manufacturer product literature and 

measurements conducted during the engineering analysis to a second-order polynomial. DOE

did this separately for each of the four main nominal air handler sizes (2-ton, 3-ton, 4-ton, and 5-

ton). The cubic feet per minute (CFM) is given by the following equation:

CFM = m0 + m1 × (P) + m2 × (P2)

Where:

CFM =airflow in CFM reported by manufacturer,

m0,1,2,and 3 = coefficients derived from 2nd degree polynomial approximation, and

P = external static pressure (in. w.g.).

0

400

800

1200

1600

0.00 0.25 0.50 0.75 1.00

External Static Pressure (in. w.g.)

Airflow (CFM)

Highest 1%

median

Lowest 10%

1200 CFM Generic Single-Stage

Furnace Model (Heating Tap)
7-7

Figure 7.4.2 shows an example of a CFM curve for a 3-ton non-condensing PSC gas 

furnace fitted with the manufacturer’s raw data.

Figure 7.4.2 Example Fit of CFM for 3-Ton PSC Furnace in 

Heating Mode

7.4.3 Fan Power

Once the operating point of air flow and static pressure is determined, by finding the 

intersection of the fan performance curve and the system curve, the watts per cubic feet per 

minute (CFM) of airflow are determined from the equations developed by DOE using 

manufacturer product literature and measurements conducted during the engineering analysis. 

The power consumption of the fan at this operating point, BE, is calculated by multiplying the

watts/CFM by the CFM at the operating point:

BE = �

Watts

CFM � × Q

Where:

BE = circulating air fan electrical energy consumption (watts),

Watts/CFM = blower electricity consumption in watts reported by manufacturer 

divided by the airflow in CFM at the same static pressure (watts/CFM), and

0

500

1000

1500

2000

2500

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

Pressure (in.w.g.)

Air Flow (CFM)

L1RA072*12B

L1RA090*12B

M1BB-086-***

M1GB-090-***

M1GH-077-***

M1GH-090-***

M1MB-056-***

M1MB-090-***

RGPN-10(E,N)AMER

GUIC070**30

TUD060C936K*

TUE060A936L*

RGPN-07(E,N)AMER

G40DF-36A-070-*

G50DF-36A-070-*

TDD060C936F*

TDE060A936M*

DPGB075A3*

MPGA075B3*

RGPJ-07EAUER

M1BB-086-***

M1GB-090-***

M1GH-077-***

M1GH-090-***

M1MB-056-***

M1MB-090-***

P4HUA12N03201

P4HUA12N04801

P4HUA12N06401

ABA080NH3R

N8MPL050B12

N8MPN050B12

P4DNA12N03201

P4DNA12N04801

P4DNA12N06401

T8MPL050B12

T8MPN050B12

58DLA045-12

58DLX045-12*

58STA045-12

58STX045-12*

G40DF-36C-110-**

G50DF-36C-110-**

58DLA070-12

58DLX070-12*

58STA070-12

58STX070-12*

RGLJ-07EAUER

G40DF-36B-090-*
7-8

Q = airflow (CFM).

Some manufacturers of furnace fans report watts across a range of external static 

pressures. Furthermore, DOE conducted measurements on several furnace fan models during the 

engineering analysis. For these models, DOE divided watts at these pressures by air flow in CFM

at these same pressures. These values of watts per CFM across a range of pressures were fit to a 

second-order polynomial for the basic furnace models made by the manufacturer. DOE did this 

separately for each of the four nominal air handler sizes. The watts per CFM is given by the 

following equation:

Watts

CFM = m0 + m1 × (P) + m2 × (P2) 

Where:

Watts/CFM = blower electricity consumption in watts reported by manufacturer 

divided by the airflow in CFM at the same static pressure,

m0,1,and 2 = coefficients derived from second-degree polynomial approximation, 

and

P = external static pressure (in. w.g.).

Figure 7.4.3 shows the watts per CFM curve for 3-ton condensing single-stage furnace 

fitted to the manufacturers’ data. A similar process of fitting curves to data was done for each 

nominal blower size.
7-9

Figure 7.4.3 Example Fit of Watts/CFM for 3-Ton Single-Stage 

Furnace

7.4.4 Determination of Fan Performance by Product Class and Efficiency Level 

In order to generate the fan performance data used in the analysis DOE applied the 

following procedure (the 3-ton baseline PSC motor for non-weatherized, non-condensing gas 

furnaces is used as an example):

STEP 1: Using the airflow and power curves at each airflow speed (heating, cooling, and 

constant circulation), DOE found the airflow and power at DOE’s proposed furnace 

fan test procedure conditions. For example, DOE’s reference system curve external 

static pressure is 0.65 in. wc at the maximum cooling airflow speed for nonweatherized gas furnaces. For the 3-ton baseline PSC motor for non-weatherized 

(non-condensing) gas furnaces the maximum airflow CFM was calculated to be 1158 

cubic feet per minute.

STEP 2: DOE used the equation above to calculate the BE at each airflow speed (heating, 

cooling, and constant circulation) with DOE’s proposed furnace fan test procedure 

conditions. For example, for the 3-ton baseline PSC motor for non-weatherized (noncondensing) gas furnaces BE was calculated to be 382 watts at heating, 495 watts at 

cooling, and 382 watts at constant circulation.

STEP 3: Using the calculated maximum airflow CFM and BE values at the external static 

pressure prescribed by DOE’s reference system curve, Furnace Efficiency Rating 

0

0.1

0.2

0.3

0.4

0.5

0.6

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Pressure (in.w.g.)

Watt/CFM

G51MP-36B-045-**

G43UF-36B-070-**

G51MP-36B-070-**

G43UF-36C-090-**

G43UF-36C-090H-**

G51MP-36C-090-**

data fit
7-10

(FER) values were evaluated. For example, for the 3-ton baseline PSC motor for nonweatherized (non-condensing) gas furnaces FER was calculated to be 363.

STEP 4: The constant curve fit parameter m0, that is derived from plotting the watts/CFM vs. 

the ESP, is then used to adjust the airflow and power curve in order to match the FER 

values derived from the engineering analysis (for all product classes and efficiency 

levels). For example, for the 3-ton baseline PSC motor for non-weatherized (noncondensing) gas furnaces the FER value derived in the engineering analysis was 380, 

so the adjustment multiplier to convert the FER value calculated in step 3 was 

calculated to be 1.04.

Table 7.4.2 shows the airflow (CFM) vs. pressure coefficients determined for nonweatherized (non-condensing) gas furnaces (3-ton) at each efficiency level (EL). Figure 7.4.4 to 

Figure 7.4.6 shows the resulting curves at various pressures and operating modes. See appendix 

7-C for further details.

Table 7.4.2 Coefficients for CFM equation for Non-Weatherized (Non-Condensing) 

Gas Furnace Fan, 3-Ton

EL Heating Cooling Constant Circulation

m0 m1 m2 m0 m1 m2 m0 m1 m2

0 1158 -12 -507 1523 -280 -432 1158 -12 -507

1 1158 -12 -507 1523 -280 -432 931 99 -527

2 1059 269 -405 1277 198 -516 667 -117 -44

3 1139 -403 -62 1427 -323 -15 1001 -880 214

4 1043 24 -101 1203 8 -26 679 3 -64

5 1043 24 -101 1203 8 -26 679 3 -64
7-11

Figure 7.4.4 CFM Curves for Non-Weatherized (Non-Condensing) 

Gas Furnace Fan, 3-Ton (Heating Mode)

Figure 7.4.5 CFM Curves for Non-Weatherized (Non-Condensing) 

Gas Furnace Fan, 3-Ton (Cooling Mode)

600

700

800

900

1000

1100

1200

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Airflow (CFM)

External Static Pressure (in w.c.)

Baseline (PSC)

Improved PSC

PSC w/ Controls

X13

ECM (Variable Speed)

ECM + BC Impeller

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Airflow (CFM)

External Static Pressure (in w.c.)

Baseline (PSC)

Improved PSC

PSC w/ Controls

X13

ECM (Variable Speed)

ECM + BC Impeller
7-12

Figure 7.4.6 CFM Curves for Non-Weatherized (Non-Condensing) 

Gas Furnace Fan, 3-Ton (Constant Circulation Mode)

Table 7.4.3 shows the watts/CFM vs. pressure curves coefficients determined for nonweatherized (non-condensing) gas furnaces (3-ton) at each efficiency level. Figure 7.4.7 to 

Figure 7.4.9 shows the resulting curves at various pressures. Figure 7.4.10 to Figure 7.4.12 show 

the resulting Watts vs. pressure curves. See appendix 7-C for further details.

Table 7.4.3 Coefficients for Watts/CFM Equation for Non-Weatherized (NonCondensing) Gas Furnaces, 3-Ton

EL Heating Cooling Constant Circulation

m0 m1 m2 m0 m1 m2 m0 m1 m2

0 0.45 -0.21 0.19 0.46 -0.12 0.15 0.45 -0.21 0.19

1 0.45 -0.21 0.19 0.46 -0.12 0.15 0.44 -0.20 0.21

2 0.30 0.16 0.02 0.35 0.16 -0.03 0.22 0.15 0.14

3 0.15 0.10 0.10 0.24 0.12 0.04 0.13 0.01 0.42

4 0.12 0.24 -0.03 0.13 0.29 -0.04 0.07 0.24 0.00

5 0.09 0.24 -0.03 0.10 0.29 -0.04 0.06 0.24 0.00

0

200

400

600

800

1000

1200

1400

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Airflow (CFM)

External Static Pressure (in w.c.)

Baseline (PSC)

Improved PSC

PSC w/ Controls

X13

ECM (Variable Speed)

ECM + BC Impeller
7-13

Figure 7.4.7 Watt/CFM Curves for Non-Weatherized (NonCondensing) Gas Furnace Fan, 3-Ton (Heating Mode)

Figure 7.4.8 Watt/CFM Curves for Non-Weatherized (NonCondensing) Gas Furnace Fan, 3-Ton (Cooling Mode)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Watts/CFM

External Static Pressure (in w.c.)

Baseline (PSC)

Improved PSC

PSC w/ Controls

X13

ECM (Variable Speed)

ECM + BC Impeller

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Watss/CFM

External Static Pressure (in w.c.)

Baseline (PSC)

Improved PSC

PSC w/ Controls

X13

ECM (Variable Speed)

ECM + BC Impeller
7-14

Figure 7.4.9 Watt/CFM Curves for Non-Weatherized (NonCondensing) Gas Furnace Fan, 3-Ton (Constant 

Circulation Mode)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Watts/CFM

External Static Pressure (in w.c.)

Baseline (PSC) Improved PSC

PSC w/ Controls X13

ECM (Variable Speed) ECM + BC Impeller
7-15

Figure 7.4.10 Resulting Watt vs. Pressure Curves for NonWeatherized (Non-Condensing) Gas Furnace Fan, 3-

Ton (Heating Mode)

0

100

200

300

400

500

600

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Watts

External Static Pressure (in w.c.)

Baseline (PSC)

Improved PSC

PSC w/ Controls

X13

ECM (Variable Speed)

ECM + BC Impeller
7-16

Figure 7.4.11 Resulting Watt vs. Pressure Curves for NonWeatherized (Non-Condensing) Gas Furnace Fan, 3-

Ton (Cooling Mode)

0

100

200

300

400

500

600

700

800

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Watss

External Static Pressure (in w.c.)

Baseline (PSC)

Improved PSC

PSC w/ Controls

X13

ECM (Variable Speed)

ECM + BC Impeller
7-17

Figure 7.4.12 Resulting Watt vs. Pressure Curves for NonWeatherized (Non-Condensing) Gas Furnace Fan, 3-

Ton (Constant Circulation Mode)

7.5 OPERATING HOURS

The DOE test procedures for furnaces and air conditioners were used to estimate heating 

and cooling mode operating hours for the furnace fan.

7.5.1 Heating Mode 

DOE used the furnace test procedure4 to determine furnace fan operating hoursb during 

the heating season using the following formula:

FFOHheating = y × BOH, for single stage furnaces.

 Where:

FFOHheating = furnace fan operating hours during the heating season, h,

y = ratio of blower on-time to average burner on-time, and

BOH = burner operating hours, h.

 b Approach described for single stage operation only; see Appendix 7-E for multistage details

0

100

200

300

400

500

600

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Watts

External Static Pressure (in w.c.)

Baseline (PSC)

Improved PSC

PSC w/ Controls

X13

ECM (Variable Speed)

ECM + BC Impeller
7-18

Using DOE’s furnace test procedure, the ratio of blower on-time to average burner ontime (y) is calculated using the following formula:

y = 1 +

t+ − t−

tON

Where:

t

+ = off-period (blower off delay) between burner shutdown and blower shutdown

in minutes,

t

-

= on-period (blower on delay) between burner shutdown and blower shutdown

in minutes, and

tON = average burner on-time in minutes.

The blower off-delay (t

+

) and blower on-delay (t

-

) values are derived from manufacturer 

default blower delay settings for non-weatherized gas furnace models in the 2007 Furnace 

Database from DOE’s 2007 Furnace and Boiler Final Rule.5 The median values using these data 

are 120 seconds (or 2 minutes) for blower off-delay (t

+

) and 30 seconds (or 0.5 minutes) for 

blower on-delay (t

-

). The average burner on-time (tON) is equal to 3.87 minutes for single-stage 

furnaces with a fan delay based on DOE’s furnace test procedure. Therefore, the ratio of blower 

on-time to average burner on-time (y) is estimated to be 1.39 using the median values. 

The burner operating hours are calculated using the following formulac

:

BOH = A * HHL, for single-stage furnaces.

Where:

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

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

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

operation in kW,

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

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

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

BE = furnace fan electrical energy input rate in kW,

QIN = steady-state nameplate input rate in Btu/h,

 c Approach described for single stage operation and a furnace without pilot ignition only; see Appendix 7-E for 

multistage operation details and derivation of the formula.
7-19

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

heating load hours,

HHL = house heating load in MMBtu/h.

Details about the calculation of the parameters used to calculate the value A (such as yP, 

PE, yIG, PEIG, y, BE, QIN, and EffyHS) are provided in appendix 7-E.

The annual house-heating load (HHL) is the total amount of heat output from the furnace 

that the house needs during the heating season. This includes heat from the burner and heat from 

the blower and the blower motor. DOE determined HHL for each sampled housing unit, based 

on the burner operating hours (BOH) and the characteristics of the assigned existing furnace, 

using the following calculations:

Where:

QYR,RECS = annual fuel consumption for heating based on RECS 2005 (kBtu/yr),

AFUEex = AFUE of the existing furnace (see appendix 7-E),

3.412 = constant to convert kW to kBtu/hr,

BEex = power consumption of the blower motor of the existing furnace (kW),

BOHex = burner operating hours of existing household (hr/yr),

N = number of cycles per hour (set equal to 5 for furnaces),

t

+ = off delay (seconds),

t

- = on delay (seconds), and

Adj_Factor = adjustment factors (discussed below).

DOE calculated BOHex for the existing furnace as:

Where:

BOHex = burner operating hours of existing household (hr/yr),

Adj Factor t t HHL QYR RECS AFUEex BE BOHex N _ 3600

3.412 , ×





















 



















 − = × + × × + ×

+ −

IN ex

YR RECS

ex Q

Q BOH

,

, =
7-20

QYR,RECS = as defined above (kBtu/yr), and

QIN,ex = input capacity of the existing furnace (see appendix 7-E) (kBtu/hr).

DOE made adjustments to the house heating load to reflect the expectation that newly 

built housing units in 2018 will have a somewhat different house heating load than the housing 

units in the RECS 2005 sub-sample. The adjustment involves multiplying the calculated HHL for 

each RECS 2005 housing unit by a building shell efficiency index derived from the National 

Energy Modeling System (NEMS) simulation performed for EIA’s AEO 2012.

6 The building 

shell efficiency index sets the heating load value at 1.00 for an average home in 2005 (by type) 

in each census division. The values listed represent the change in heating load based on the 

difference in physical size and shell attributes for homes in the future (which takes into account 

physical size difference and efficiency gains from better insulation and windows). This factor 

differs for new construction and replacement households. The value for households in 2018 is 

0.86 for replacements and 0.87 for new construction, which means that the average new home in 

2018 will require less heat energy to maintain indoor comfort. To add variability, the factor is 

varied by plus or minus 15 percent. 

DOE also made adjustments to the HHL calculated using RECS 2005 data to reflect 

historical average climate conditions. Table 7.5.1 shows the 2002-2011 average heating degree 

days (HDD) as well as the 2005 average HDD for the 29 geographical areas. The adjustment 

factors are calculated using the equation below.

Where:

HDDres_stock_2005 = HDD in 2005 for the specific region where the housing unit is 

located, and

HDD10_yr_avg = 10-year average HDD (2002–2011) based on NOAA data7 for the 

specific region where the housing unit is located.d

 d The last 10-year average is used to normalize the HDD values, which is similar to what is done in AEO 2012.

_ _ 2005

10 _ _ _ _ lim

res stock

yr avg

average c ate HDD

HDD

Adj Factor =
7-21

Table 7.5.1 Heating Degree-Day Adjustment Factors

Geographical Area Average HDD Adjustment Factor

2002-2011 2005

1 CT, ME, NH, RI, VT 6576 6746 0.97

2 MA 6184 6467 0.96

3 NY 5770 5912 0.98

4 NJ 5105 5311 0.96

5 PA 5656 5806 0.97

6 IL 6047 5800 1.04

7 IN, OH 5687 5759 0.99

8 MI 6655 6608 1.01

9 WI 7365 6975 1.06

10 IA, MN, ND, SD 7857 7326 1.07

11 KS, NE 5455 4988 1.09

12 MO 4943 4622 1.07

13 VA 4224 4328 0.98

14 DE, DC, MD, WV 4500 4621 0.97

15 GA 2807 2709 1.04

16 NC, SC 3171 3180 1.00

17 FL 692 647 1.07

18 AL, KY, MS 3251 3153 1.03

19 TN 3757 3625 1.04

20 AR, LA, OK 2727 2434 1.12

21 TX 1855 1686 1.10

22 CO 7109 6949 1.02

23 ID, MT, UT, WY 6964 6744 1.03

24 AZ 1946 1788 1.09

25 NV, NM 3908 3581 1.09

26 CA 2575 2450 1.05

27 OR, WA 5267 5132 1.03

28 AK NA NA 1.03

29 HI NA NA 1.05

Note: Data for Alaska and Hawaii was not available. The region 27 adjustment factor was used for Alaska, while 

region 26 adjustment factor was used for Hawaii.

For households in which it is clear that the fuel use for heating is associated solely with 

the use of furnace equipment as the primary or secondary heating equipment, DOE used the 

annual fuel consumption for heating the housing unit from RECS 2005. DOE adjusted the house 

heating load for households that used both a furnace (either as the primary or secondary heating 

equipment) and other heating equipment using the same fuel. RECS 2005 reports the percentage 

of heating energy consumption attributable to secondary products. DOE derived the house 

heating load applicable to the furnace by subtracting the estimated amount of heat provided by 

the other heating system. In the case when it was determined that a household had multiple 

furnaces, the house heating load was divided by the number of furnaces. Details are presented in 

appendix 7-D.

Table 7.5.2 shows the results for the range in adjusted heating load among sample 

households.
7-22

Table 7.5.2 Range of Adjusted Heating Load for Each Furnace Fan Product Class, 

million Btu/h

Product Class Min Max Average

Percentiles

5% 25% 50% 75% 95%

Non-Weatherized, 

Non-Condensing Gas 

Furnace Fan

0.31 143.44 20.25 3.99 9.40 16.29 26.78 49.08

Non-Weatherized, 

Condensing Gas 

Furnace Fan

0.36 215.43 37.94 9.57 23.21 34.74 48.37 77.91

Weatherized Gas 

Furnace Fan

0.36 156.88 20.34 3.85 9.50 16.42 26.55 49.57

Oil Furnace Fan 2.37 140.24 55.49 24.19 35.86 56.14 71.50 94.55

Electric Furnace / 

Modular Blower Fan

0.29 31.08 6.61 1.73 3.54 5.86 8.46 14.27

Manufactured Home 

Non-Weatherized, 

Non-Condensing Gas 

Furnace Fan

3.89 78.73 22.82 6.38 12.68 21.37 28.03 47.98

Manufactured Home 

Non-Weatherized, 

Condensing Gas 

Furnace Fan

3.65 101.59 33.15 9.86 21.51 31.58 42.58 66.16

Manufactured Home 

Electric Furnace / 

Modular Blower Fan

0.30 29.41 7.90 1.80 4.10 6.77 10.51 19.17

Hydronic Air 

Handler Fan 

(Heat/Cool)

0.62 69.61 12.60 2.50 3.74 9.11 16.10 35.70

Table 7.5.3 shows the results for the baseline heating furnace fan operating hours among 

sample households.
7-23

Table 7.5.3 Range of Baseline Furnace Fan Heating Operating Hours for Each 

Furnace Fan Product Class, hours

Product Class Min Max Average

Percentiles

5% 25% 50% 75% 95%

Non-Weatherized, 

Non-Condensing Gas 

Furnace Fan

8 4826 434 93 207 355 560 1040

Non-Weatherized, 

Condensing Gas 

Furnace Fan

9 3749 591 159 336 508 746 1313

Weatherized Gas 

Furnace Fan

9 4835 393 87 188 321 505 916

Oil Furnace Fan 24 2448 716 230 438 680 945 1336

Electric Furnace / 

Modular Blower Fan

8 3322 274 68 138 211 336 696

Manufactured Home 

Non-Weatherized, 

Non-Condensing Gas 

Furnace Fan

100 2478 661 183 371 613 816 1396

Manufactured Home 

Non-Weatherized, 

Condensing Gas 

Furnace Fan

77 2644 797 263 486 734 1018 1593

Manufactured Home 

Electric Furnace / 

Modular Blower Fan

9 1545 370 69 205 316 478 892

Hydronic Air 

Handler Fan 

(Heat/Cool)

15 2252 339 70 112 254 405 913

7.5.2 Cooling Mode 

Furnace fan operating hours during the cooling season are calculated using the following 

formula:

FFOHcooling = yC × COH

Where:

FFOHcooling = furnace fan operating hours during the cooling season;

yC = ratio of blower on-time to average compressor on-time; and

COH = cooling operating hours.

Some furnace fans come with a cooling blower off delay feature. To account for this 

DOE estimated the ratio of blower on-time to average compressor on-time (yC ) using the 

following formula:
7-24

yC = 1 +

tC

+ − tC

−

tON,C

Where:

tC

+ = off-period (blower off delay in cooling mode) between compressor shutdown 

and blower shutdown in minutes,

tC

− = on-period (blower on delay in cooling mode) between compressor start-up 

and blower start-up in minutes, and

tON,C = average compressor on-time in minutes.

The blower off-delay (tC

+) and blower on-delay (tC

−) values are derived from 

manufacturer default blower delay settings. The median values using these data are 45 seconds 

for blower off-delay (tC

+) and 2 seconds for blower on-delay (tC

−). The average burner on-time 

(tON,C) is equal to 6 minutes for single-stage central air conditioners based on DOE’s central air 

conditioner test procedure. Using these assumptions, the ratio of blower on-time to average 

burner on-time (yC) is estimated to be 1.12. 

The cooling operating hours are calculated using the following formula:

COH = HCL

CoolingCapacity × Adj_Factormotor

Where:

COH = cooling operating hours, hour/year, 

HCL = house cooling load, MMBtu/year,

CoolingCapacity = cooling capacity of air conditioner, Btu/h (see appendix 7-F), 

and

Adj_Factormotor = adjustment factor to account for impact of motor heat on 

cooling operating hours.

The house cooling load (HCL) assumes that the household has a default furnace fan 

motor power output of 365 watts per 1000 CFM (used in the CAC test procedure). To properly 

account for increased or decreased cooling operating hours due to the higher or lower motor 

power output for different furnace fan efficiencies, DOE used the following equation to 

determine the adjustment factor:

Adj_Factormotor = 1

(1 + 3.412 ×

365

1000 ∗ CFM − FFPcooling

CoolingCapacity )
7-25

Where:

365

1000 ∗ CFM = default central air conditioner blower output used for calculating

SEER, watts,

CFM = nominal cooling load CFM measured at 400 CFM per AC ton, cu. ft. per 

min,

FFPcooling = furnace fan power during the cooling operation, kW, and

CoolingCapacity = cooling capacity of air conditioner, Btu/h.

The house cooling load is derived using the EIA’s RECS 20058 cooling energy use data 

for the sample households as follows:

HCL = CoolingEnergyUseRECS × SEERex

CoolingCapacityex

× Adj_Factor

Where:

HCL = house cooling load, MMbtu/year, 

CoolingEnergyUseRECS = annual electricity consumption for cooling based on 

RECS 2005 (kBtu/yr),

SEERex = SEER of the existing central air conditioner (see appendix 7-F),

CoolingCapacity = cooling capacity of existing central air conditioner, Btu/h (see 

appendix 7-F), and

Adj_Factor = adjustment factors (discussed below).

DOE made adjustments to the house cooling load to reflect the expectation that newly 

built housing units in 2018 will have a somewhat different house cooling load than the housing 

units in the RECS 2005 sub-sample. Similar to furnace fan energy use calculation above, the 

building shell efficiency index sets the cooling load value at 1.00 for an average home in 2005 

(by type) in each census division. DOE developed adjustment factors to represent the change in 

cooling load based on the difference in physical size and shell attributes for homes in the future 

(which takes into account physical size difference and efficiency gains from better insulation and 

windows). This factor differs for new construction and replacement households. The value for 

households in 2018 is 0.94 for replacements and 1.01 for new construction. To add variability, 

the factor is varied by plus or minus 15 percent. 

DOE also made adjustments to the HCL calculated using RECS 2005 data to reflect 

historical average climate conditions. Table 7.5.4 shows the 2002-2011 average heating degree 

days (HDD) as well as the 2005 average CDD for the 29 geographical areas. The adjustment 

factors are calculated using the equation below.
7-26

Where:

CDDres_stock_2005 = CDD in 2005 for the specific region where the housing unit is 

located, and

CDD10_yr_avg = 10-year average CDD (2002–2011) based on NOAA data7 for the 

specific region where the housing unit is located.

Table 7.5.4 Cooling Degree Day Adjustment Factors

Geographical Areas Average CDD Adjustment Factor

2002-2011 2005

1 CT, ME, NH, RI, VT 485 562 0.86

2 MA 522 576 0.91

3 NY 737 943 0.78

4 NJ 932 1121 0.83

5 PA 765 901 0.85

6 IL 924 1151 0.80

7 IN, OH 879 1027 0.86

8 MI 622 828 0.75

9 WI 552 747 0.74

10 IA, MN, ND, SD 637 792 0.81

11 KS, NE 1327 1491 0.89

12 MO 1325 1534 0.86

13 VA 1206 1250 0.97

14 DE, DC, MD, WV 1004 1034 0.97

15 GA 1832 1804 1.02

16 NC, SC 1654 1644 1.01

17 FL 3558 3436 1.04

18 AL, KY, MS 1813 1832 0.99

19 TN 1517 1576 0.96

20 AR, LA, OK 2266 2392 0.95

21 TX 2841 2908 0.98

22 CO 352 345 1.02

23 ID, MT, UT, WY 575 533 1.08

24 AZ 3171 3130 1.01

25 NV, NM 1753 1740 1.01

26 CA 923 837 1.10

27 OR, WA 235 227 1.04

28 AK NA NA 1.04

29 HI NA NA 1.10

Note: Data for Alaska and Hawaii was not available. The region 27 adjustment factor was used for Alaska, while 

region 26 adjustment factor was used for Hawaii.

DOE is calculating multi-stage cooling the same way as single-stage equipment (i.e., at 

the highest cooling mode only) and therefore used the same number of operating hours, since:

_ _ 2005

10 _ _ _ _ lim

res stock

yr avg

average c ate CDD

CDD

Adj Factor =
7-27

1) Multi-stage heating is not necessarily associated with multi-stage cooling equipment (e.g. 

multi-stage cooling is much less common than multi-stage furnace equipment); and

2) SEER already captures cases when multi-stage heating and cooling equipment are 

matched.

For households in which it is clear that the electricity use for cooling is associated solely 

with the use of central air conditioning equipment, DOE used the annual electricity consumption 

for cooling the household from RECS 2005. DOE adjusted the house cooling load for 

households that used both a central air conditioner and a room air conditioner. RECS 2005 

reports the percentage of cooling energy consumption attributable to room air conditioners. DOE 

derived the house cooling load applicable to the central air conditioner by subtracting the 

estimated amount of cooling provided by the other cooling system.

Table 7.5.5 shows the range in cooling load among sample households for each furnace 

fan product class. The table also provides the fraction of households that have central air 

conditioning.

Table 7.5.5 Range of Annual Cooling Load for Each Furnace Fan Product Class, 

million Btu/h

Product Class

Fraction 

with 

Central AC

Min Max Avg.

Percentiles

5% 25% 50% 75% 95%

Non-Weatherized, 

Non-Condensing Gas 

Furnace Fan

76.0% 0.11 107.34 14.55 1.97 6.31 11.84 18.94 37.02

Non-Weatherized, 

Condensing Gas 

Furnace Fan

72.1% 0.25 107.34 8.49 1.51 3.81 6.37 10.61 21.91

Weatherized Gas 

Furnace Fan

100.0% 0.11 107.34 14.16 1.97 5.95 11.61 18.77 34.63

Oil Furnace Fan 34.0% 1.30 15.57 7.60 2.23 3.76 6.32 11.43 15.57

Electric Furnace / 

Modular Blower Fan

85.1% 0.76 101.14 14.41 2.72 7.03 12.42 19.42 31.97

Manufactured Home 

Non-Weatherized, 

Non-Condensing Gas 

Furnace Fan

54.5% 1.27 22.87 9.72 1.90 4.62 8.40 15.63 21.88

Manufactured Home 

Non-Weatherized, 

Condensing Gas 

Furnace Fan

41.1% 0.24 22.87 5.74 2.16 3.28 4.29 5.73 15.80

Manufactured Home 

Electric Furnace / 

Modular Blower Fan

78.3% 1.22 29.17 13.33 2.86 9.23 12.87 18.30 26.27

Hydronic Air 

Handler Fan 

(Heat/Cool)

100.0% 0.78 31.14 9.87 0.78 3.31 6.31 17.15 24.66
7-28

Table 7.5.6 shows the results for the baseline furnace fan cooling operating hours among 

sample households.

Table 7.5.6 Range of Baseline Furnace Fan Cooling Operating Hours for Each 

Furnace Fan Product Class, hours

Product Class Min Max Average

Percentiles

5% 25% 50% 75% 95%

Non-Weatherized, 

Non-Condensing Gas 

Furnace Fan

0 7879 902 0 136 729 1332 2563

Non-Weatherized, 

Condensing Gas 

Furnace Fan

0 7127 420 0 0 290 591 1379

Weatherized Gas 

Furnace Fan

0 8240 1162 174 552 970 1532 2877

Oil Furnace Fan 0 1035 139 0 0 0 214 663

Electric Furnace / 

Modular Blower Fan

0 8760 1240 0 455 1100 1760 3178

Manufactured Home 

Non-Weatherized, 

Non-Condensing Gas 

Furnace Fan

0 3633 625 0 0 302 1052 2331

Manufactured Home 

Non-Weatherized, 

Condensing Gas 

Furnace Fan

0 3506 240 0 0 0 359 1078

Manufactured Home 

Electric Furnace / 

Modular Blower Fan

0 4330 1323 0 322 1367 2017 3028

Hydronic Air 

Handler Fan 

(Heat/Cool)

0 5885 1157 0 423 962 1527 3113

7.5.3 Constant Circulation Mode 

The amount of constant-circulation hours are based on data from surveys. One survey 

was conducted by researchers in Wisconsin in 2003.9 The second survey was conducted by the 

Center for Energy and the Environment (CEE) in Minnesota, the results of which were provided 

by CEE in a written comment that is included in the docket for the furnace fan test procedure.e

Table 7.5.5

DOE combined both studies and derived average annual furnace fan constant-circulation

operating hours for each survey, as shown in .

DOE assumed a value for average number of fan constant-circulation hours for each 

survey response. For “no constant circulation” responses, DOE assumed zero constantcirculation hours. For “year-round” responses, DOE assumed 100 percent of non-heating or 

cooling furnace fan operating hours, which DOE calculated by subtracting furnace fan heating 

and cooling operating hours from the total annual hours (8,760). For “during heating season” 

 e Docket Number EERE-2010-BT-STD-0011. (CEE, No. 22 at pp. 1-3) 
7-29

responses, DOE assumed 15 percent of non-heating or cooling furnace fan operating hours. For 

“during cooling season” responses, DOE assumed 15 percent of non-heating or cooling furnace 

fan operating hours. For other or “some constant circulation” responses, DOE assumed 5 percent 

of non-heating or cooling furnace fan operating hours. 

DOE did not use these data directly, because it believes they are not representative of 

consumer practices for the U.S. as a whole. In Wisconsin and Minnesota, many homes have low 

air infiltration, and there is a high awareness of indoor air quality issues, which leads to 

significant use of constant circulation. To account for this, DOE developed separate regional 

fractions that took into account information from manufacturer product literature and regional 

climate conditions. Furnace fan manufacturer literature states that constant circulation fan 

operation is not recommended for humid climates. Therefore, DOE assumed that the fraction 

using constant circulation would only be 10 percent in the South Hot Humid regionf

Table 7.5.7 Results from Constant-Circulation Use Studies and Estimated National 

Constant-Circulation Hours

of what was 

reported in the Wisconsin and Minnesota studies (i.e. 3.1 percent compared to 31 percent in the 

studies). For the rest of the country (North and South Hot Dry regions), DOE assumed that the 

fraction using constant circulation would be 50 percent of what was reported in the Wisconsin 

and Minnesota studies (i.e. 15.5 percent compared to 31 percent in the studies).

Table 7.5.8 shows the results for the average baseline constant circulation furnace fan 

operating hours among sample households.

 f Regions as defined in the Furnace and Central Air Conditioner Final Rule.10

How Often is 

Constant 

Circulation Fan 

Used?

Combined Data from 

Studies

Estimated North 

and South-Hot Dry 

Region Fractions 

for LCC Analysis

Estimated SouthHot Humid Region 

Fractions for LCC 

Analysis

Number of 

Households

Percentage 

(%)

No constant fan 69 68% 84% 97%

Year-round 14 14% 7% 1%

During heating 

season

4 4% 2% 0.4%

During cooling 

season

4 4% 2% 0.4%

Other (some 

constant fan)

10 10% 5% 1%

Total 101 100% 100% 100%
7-30

Table 7.5.8 Average Baseline Constant Circulation Furnace Fan Operating Hours for 

Each Furnace Fan Product Class, hours

Product Class Average

Non-Weatherized, Non-Condensing Gas Furnace Fan 316

Non-Weatherized, Condensing Gas Furnace Fan 558

Weatherized Gas Furnace Fan 249

Oil Furnace Fan 552

Electric Furnace / Modular Blower Fan 257

Manufactured Home Non-Weatherized, NonCondensing Gas Furnace Fan 342

Manufactured Home Non-Weatherized, Condensing 

Gas Furnace Fan 567

Manufactured Home Electric Furnace / Modular 

Blower Fan 213

Hydronic Air Handler Fan (Heat/Cool) 412

7.6 FURNACE FAN STANDBY ENERGY USE

Furnaces with higher efficiency furnace fans tend to have higher standby energy use. To 

account for this effect, for all products other than hydronic air handlers, DOE first estimated the 

difference in power consumption between the baseline efficiency level (EL 0) and the higher 

furnace fan efficiencies.g This difference in power consumption was estimated to be 0 watts for 

EL1 and EL2 and 3 watts for EL3 and above, based on test data from the 2011 Furnace 

rulemaking.10 The power consumption is then multiplied by the standby hours calculated for 

each sampled household.

Hydronic air handlers are the only product in this rulemaking that have no standby and 

off-mode power included in existing test procedures. The proposed furnace fan test procedure 

incorporates test methods to measure the standby mode and off mode energy of hydronic air 

handlers. In this rulemaking, an integrated metric was developed that combines the steady-state 

standby mode and off mode electrical energy consumption measurements for hydronic air 

handlers with the active mode energy use for this product (see chapter 5 for additional details).

The LCC analysis uses the integrated metric for hydronic air handlers and thus accounts for the 

standby use associated with this product.

 g EISA 2007 requires that standby energy consumption be considered in energy consumption unless the test 

procedure already accounts for standby mode and off mode energy use. Furnace fans are integrated in the electrical 

systems of the HVAC products in which they are used and controlled by the main control board. Therefore, there is 

no standby mode and off mode energy use associated with furnace fans used in these products that would not 

already be measured by the established test procedures.
7-31

7.7 CHANGES IN HEATING AND AIR-CONDITIONING ENERGY USE WITH 

MORE-EFFICIENT FURNACE FANS

DOE accounted for the effect of improved furnace fan efficiency on the heating and 

cooling load of the sample homes. With improved furnace fan efficiency there is less heat from 

the motor, which means that the heating system needs to operate more and the cooling system 

needs to operate less.

7.7.1 Impact on Furnace Fuel 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 formulah

:

, for single-stage furnace

Where:

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

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

Recall from section 7.5.1 that BOH is calculated using BE (furnace fan electrical energy 

input rate), which is equal to the FFPheating (furnace fan power during the heating operation) 

variable calculated for each furnace fan efficiency level. The differential in fuel use between the 

baseline equipment (EL 0) and more efficient design options (EL 1 and above) for each 

efficiency level is shown in the results tables in section 7.8.

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:

,

i

for single-stage furnace,

Where:

BOH = as defined above,

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

For two-stage equipment this formula includes parameters for the operation at full, modulating, and reduced load. 

FuelUse = BOH × QIN

( ) non furnace fan SS p ig PEig ElecUse − _ = BOH × y × BE + y × PE + y ×
7-32

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).

The differential in non-furnace fan furnace electricity consumption between the baseline 

equipment (EL 0) and more efficient design options (EL 1 and above) for each efficiency level is 

included in the total electricity use shown in the results tables in section 7.8.

The details for calculating furnace energy consumption at each considered fan efficiency 

level appear in appendix 7-E.

7.7.2 Impact on Central Air Conditioner 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 less cooling operation by the central air conditioner. Since the cooling

load of each sample housing unit is known, it is possible to estimate what the air conditioner

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

equipment, were used in each housing unit.

DOE calculated the non-furnace fan cooling energy using the following formula:

CoolingEnergyUsenon−furnace_fan = COH × Powernon−furnace_fan

Where:

COH = as defined above in section 7.5.2,

Powernon-furnace_fan = power consumption of all non-furnace fan components of the 

central air conditioner (kW).

DOE calculated the non-furnace fan cooling power consumption as follows:

Powernon−furnace_fan = (

CoolingCapacity

SEER − 3651000 ∗ CFM)

Where:

365

1000 ∗ CFM = default central air conditioner blower output, watts,

CFM = nominal cooling load CFM measured at 400 CFM per AC ton, CFM,

SEER = SEER of central air conditioner, Btu/(W.h), and
7-33

CoolingCapacity = cooling capacity of air conditioner, Btu/h.

The differential in non-furnace fan furnace electricity consumption between the baseline 

equipment (EL 0) and more efficient design options (EL 1 and above) for each efficiency level is 

included in the total electricity use shown in the results tables in section 7.8.

The details for calculating the central air conditioner energy consumption at each 

considered fan efficiency level appear in appendix 7-F.

7.8 SUMMARY OF ENERGY USE RESULTS

This section presents the average annual energy use and the average energy savings for 

each considered energy efficiency level compared to the baseline energy efficiency for each

furnace fan product class. For the efficiency levels above the baseline the electricity use includes 

the difference from the baseline in the non-furnace fan cooling energy use, non-furnace fan 

furnace electricity consumption, and furnace standby energy use. Thus, the electricity savings 

account for these indirect impacts on the higher furnace fan efficiency levels.

For the LCC and PBP analyses, DOE used the full distribution of energy use values 

calculated for the sample households.

Table 7.8.1 Average Annual Energy Consumption and Savings for Furnace Fans 

Used in Non-Weatherized Gas Furnaces

Efficiency 

Level

Non- Condensing Furnace Condensing Furnace

Annual 

Electricity 

Use 

(kWh)

Electricity 

Use Savings

(kWh)

Additional 

Fuel Use 

(MMBtu)

Annual 

Electricity 

Use (kWh)

Electricity 

Use 

Savings 

(kWh)

Additional 

Fuel Use 

(MMBtu)

Baseline 

(PSC)

798 NA NA 768 NA NA

Improved 

PSC

784 13 0.00 736 32 0.00

PSC w/ 

Controls

779 19 -0.04 643 125 -0.03

X13 508 290 0.28 421 347 0.39

ECM + 

Multi-Stage

532 265 0.33 410 357 0.44

ECM + 

Backwardcurved 

Impeller

478 319 0.36 372 396 0.48
7-34

Table 7.8.2 Average Annual Energy Consumption and Savings for Furnace Fans 

Used in Weatherized Gas Furnace Fans and Oil-Fired Furnaces

Efficiency 

Level

Weatherized Gas Furnace Oil-Fired Furnace

Annual 

Electricity 

Use 

(kWh)

Electricity 

Use Savings 

(kWh)

Additional 

Fuel Use 

(MMBtu)

Annual 

Electricity 

Use (kWh)

Electricity 

Use 

Savings 

(kWh)

Additional 

Fuel Use 

(MMBtu)

Baseline 

(PSC)

886 NA NA 639 NA NA

Improved 

PSC

879 7 0.00 606 32 -0.01

PSC w/ 

Controls

833 54 0.03 471 168 0.07

X13 516 370 0.29 310 329 0.56

ECM + 

Multi-Stage

476 411 0.34 282 357 0.65

ECM + 

Backwardcurved 

Impeller

420 466 0.37 255 384 0.71

Table 7.8.3 Average Annual Energy Consumption and Savings for Furnace Fans 

Used in Manufactured Home Gas Furnaces

Efficiency 

Level

Non- Condensing Furnace Condensing Furnace

Annual 

Electricity 

Use 

(kWh)

Electricity 

Use Savings 

(kWh)

Additional 

Fuel Use 

(MMBtu)

Annual 

Electricity 

Use (kWh)

Electricity 

Use 

Savings 

(kWh)

Additional 

Fuel Use 

(MMBtu)

Baseline 

(PSC)

545 NA NA 572 NA NA

Improved 

PSC

533 12 0.00 545 27 -0.01

PSC w/ 

Controls

431 114 0.15 399 172 0.22

X13 297 247 0.46 267 304 0.61

ECM + 

Multi-Stage

236 309 0.50 211 360 0.68

ECM + 

Backwardcurved 

Impeller

211 333 0.53 192 380 0.71
7-35

Table 7.8.4 Average Annual Energy Consumption and Savings for Furnace Fans 

Used in Electric Furnaces and Manufactured Home Electric Furnaces

Efficiency Level Electric Furnace Manufactured Home Electric 

Furnace

Annual 

Electricity Use 

(kWh)

Net Electricity 

Use Savings*

(kWh)

Annual 

Electricity Use 

(kWh)

Net Electricity 

Use Savings*

(kWh)

Baseline (PSC) 594 NA 529 NA

Improved PSC 585 9 526 4

PSC w/ Controls 591 2 446 83

X13 440 154 365 164

ECM + MultiStage455 139 295 234

ECM + 

Backwardcurved Impeller

416 178 268 261

* Accounts for additional energy used for heating.

Table 7.8.5 Average Annual Energy Consumption and Savings for Furnace Fans 

Used in Hydronic Air Handlers

Efficiency 

Level

Annual 

Electricity 

Use (kWh)

Net 

Electricity 

Use Savings 

(kWh)

Additional 

Fuel Use 

(MMBtu)

Baseline (PSC) 838 NA NA

Improved PSC 827 11 0.00

PSC w/ 

Controls

844 -6 -0.04

X13 533 305 0.25

ECM + MultiStage367 471 0.31

ECM + 

Backwardcurved 

Impeller

329 509 0.32

Switching 

Mode Power 

Supply

309 529 0.32

Toroidal 

Transformer

296 543 0.32
7-36

REFERENCES

1. U.S. Department of Energy - Energy Information Administration, Residential Energy 

Consumption Survey: 2005 Public Use Data Files, 2005.

<http://www.eia.doe.gov/emeu/recs/recspubuse05/pubuse05.html>

2. Michael R. Lindeburg, P., Fans and Ductwork. In Mechanical Engineering Reference 

Manual for the PE Exam, P. Michael R. Lindeburg, Editor. Tenth ed. 1997. Professional 

Publications, Inc.: Belmont, CA. p. 20-1, 20-26

3. American Society of Heating Refrigeration and Air-Conditioning Engineers, ASHRAE 

1997 Handbook - Fundamentals. 1997. Atlanta, GA.p. 3.12.

4. 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. 

5. U.S. Department of Energy - Energy Efficiency & Renewable Energy, Technical Support 

Document: Energy Efficiency Standards for Consumer Products: Residential Furnaces 

and Boilers, 2007. Washington, DC. 

6. Energy Information Administration, Annual Energy Outlook 2010 with Projections to 

2035, 2010. Washington, DC. Report No. DOE/EIA-0383(2010). 

<http://www.eia.doe.gov/oiaf/aeo/>

7. National Oceanic and Atmospheric Administration, NNDC Climate Data Online, (Last 

accessed February 2009.) <www7.ncdc.noaa.gov/CDO/CDODivisionalSelect.jsp>

8. U.S. Department of Energy: Energy Information Administration, Residential Energy 

Consumption Survey (RECS), 2005. (Last accessed September, 2011.) Public use data 

files. <http://www.eia.doe.gov/emeu/recs/recspubuse05/pubuse05.html>

9. Pigg, S., Electricity Use by New Furnaces: A Wisconsin Field Study, October, 2003. 

Energy Center of Wisconsin. Madison. Report No. 230-1. prepared for Focus on Energy. 

<http://www.ecw.org/ecw/productdetail.jsp?productId=499&numPerPage=1000&sortAtt

ribute=initiative.title&sortOrder=ASC>

10. U.S. Department of Energy - Energy Efficiency & Renewable Energy, Technical Support 

Document: Energy Efficiency Standards for Consumer Products: Residential Furnaces, 

Central Air Conditioners, and Heat Pumps, 2011. Washington, DC.