7-C-i

APPENDIX 7-C. CALCULATION OF FURNACE BLOWER FAN ENERGY

CONSUMPTION

TABLE OF CONTENTS

7-C.1 INTRODUCTION ................................................................................................. 7-C-1

7-C.2 SYSTEM CURVES............................................................................................... 7-C-1

7-C.3 FURNACE FAN CURVES................................................................................... 7-C-2

7-C.4 FAN POWER......................................................................................................... 7-C-8

7-C.5 DETERMINATION OF FAN CURVES FOR EACH EFFICIENCY LEVEL 

AND PRODUCT CLASS.................................................................................... 7-C-12

LIST OF TABLES

Table 7-C.3.1 Coefficients for CFM equation for PSC motors.................................. 7-C-3

Table 7-C.3.2 Coefficients for CFM equation for Two-Stage and Continuous 

Modulating furnaces with ECM motors .............................................. 7-C-6

Table 7-C.4.1 Coefficients for W/CFM equation for PSC motors............................. 7-C-9

Table 7-C.4.2 Coefficients for W/CFM equation for Two-Stage and Continuous 

Modulating furnaces with ECM motors ............................................ 7-C-11

Table 7-C.5.1 Coefficients for CFM equation for Non-Weatherized (NonCondensing) Gas Furnace Fan, 3-Ton ............................................... 7-C-13

Table 7-C.5.2 Coefficients for Watts/CFM Equation for Non-Weatherized (NonCondensing) Gas Furnaces, 3-Ton..................................................... 7-C-16

LIST OF FIGURES

Figure 7-C.2.1 Sample of System Curves with a Typical Fan Curve .......................... 7-C-2

Figure 7-C.3.2 Example Fit of CFM for 3-ton Single-Stage (High Fire) Furnace....... 7-C-4

Figure 7-C.3.3 Fan Curves for Single-Stage Virtual Model Furnaces......................... 7-C-5

Figure 7-C.3.4 Fan Curves for Two-Stage Virtual Model Furnaces – High Fire ........ 7-C-7

Figure 7-C.3.5 Fan Curves for Two-Stage Virtual Model Furnaces – Low Fire ......... 7-C-7

Figure 7-C.4.1 Example Fit of Watts/CFM for 3-ton Single-Stage Furnace ............... 7-C-9

Figure 7-C.4.2 Watts/CFM vs. Pressure Curves for Single-Stage Virtual Model 

Furnaces............................................................................................. 7-C-10

Figure 7-C.4.3 Watts/CFM vs. Pressure Curves for Two-Stage Virtual Model 

Furnaces – High Fire.......................................................................... 7-C-11

Figure 7-C.4.4 Watts/CFM vs. Pressure Curves for Two-Stage Virtual Model 

Furnaces – Low Fire .......................................................................... 7-C-12

Figure 7-C.5.2 CFM Curves for Non-Weatherized (Non-Condensing) Gas Furnace 

Fan, 3-Ton (Heating Mode)............................................................... 7-C-14

Figure 7-C.5.3 CFM Curves for Non-Weatherized (Non-Condensing) Gas Furnace 

Fan, 3-Ton (Cooling Mode)............................................................... 7-C-15
7-C-ii

Figure 7-C.5.4 CFM Curves for Non-Weatherized (Non-Condensing) Gas Furnace 

Fan, 3-Ton (Continuous Fan Mode) .................................................. 7-C-16

Figure 7-C.5.5 Watt/CFM Curves for Non-Weatherized (Non-Condensing) Gas 

Furnace Fan, 3-Ton (Heating Mode) ................................................. 7-C-17

Figure 7-C.5.6 Watt/CFM Curves for Non-Weatherized (Non-Condensing) Gas 

Furnace Fan, 3-Ton (Cooling Mode)................................................. 7-C-18

Figure 7-C.5.7 Watt/CFM Curves for Non-Weatherized (Non-Condensing) Gas 

Furnace Fan, 3-Ton (Continuous Fan Mode) .................................... 7-C-19

Figure 7-C.5.8 Resulting Watt vs. Pressure Curves for Non-Weatherized (NonCondensing) Gas Furnace Fan, 3-Ton (Heating Mode)..................... 7-C-20

Figure 7-C.5.9 Resulting Watt vs. Pressure Curves for Non-Weatherized (NonCondensing) Gas Furnace Fan, 3-Ton (Cooling Mode) .................... 7-C-21

Figure 7-C.5.10 Resulting Watt vs. Pressure Curves for Non-Weatherized (NonCondensing) Gas Furnace Fan, 3-Ton (Continuous Fan Mode)........ 7-C-22
7-C-1

APPENDIX 7-C. CALCULATION OF FURNACE BLOWER FAN ENERGY

CONSUMPTION

7-C.1 INTRODUCTION

The electricity consumption (and overall efficiency) of a blower motor depends on the 

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

the airflow through the blower. To calculate blower-motor electricity consumption, DOE 

determined the operating conditions (the pressure and airflow) at which a particular furnace in a 

particular housing unit will operate. These operating conditions can be graphically displayed as 

the intersection of a system curve of the ducts 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). 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 each furnace. 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 the electric power of the blower motor eventually is converted to heat 

that contributes to meeting the building heating load. 

7-C.2 SYSTEM CURVES

The system curve of the air-distribution system is a graphical representation of the 

airflow through the supply and return ducts in a house for different static pressure. The airflow 

and pressure drop at which the furnace will operate can be determined by the intersection of the 

system curve of the house and the fan curve of the furnace circulating air blower.1

The Department modeled system curves as quadratic curves, which is standard in heating, 

ventilation, and air conditioning (HVAC) design and fan selection handbooks.2

 The curves are 

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

Q = � P

α

where:
7-C-2

Q = airflow (cfm),

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

α = a constant coefficient.

The Department selected the coefficient in the system curve equation for each housing 

unit. It randomly sampled a coefficient from one of four distributions, depending on the nominal 

maximum airflow of the virtual model furnace selected for that housing unit. The Department 

designed each distribution so that 10 percent of samples would have static pressures below 0.5 

in.w.g., and 1 percent of the samples would have static pressures greater than 1 in.w.g at the 

nominal maximum airflow. This is in line with several field studies.3

 To keep the system curves 

from clumping at the higher pressures, the Department used a log-normal distribution of values 

of the coefficient. See Figure 7-C.2.1 for an example of a plot of system curves intersecting a 

furnace fan curve.

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)

Figure 7-C.2.1 Sample of System Curves with a Typical Fan Curve

7-C.3 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. 
7-C-3

The Department developed fan curves for the single-stage (High Fire modes) virtual 

furnace models and for two-stage (High Fire and Low Fire modes) by fitting the manufacturer 

airflow and pressure data points from the basic model furnaces4, 5, 6, 7, 8, 9, 10 to a second-order 

polynomial. The Department did this separately for each of the four nominal air handler sizes. 

The CFM for PSC blower motors is given by the following equation:

CFM = m0 + m1 × (P) + m2 × (P2) Eq. 1

where,

CFM = airflow in CFM reported by manufacturer,

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

Table 7-C.3.1 for actual coefficient values), and

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

Table 7-C.3.1 Coefficients for CFM equation for PSC motors

High Fire (Single-Stage) Low Fire

m0 m1 m2 m0 m1 m2

2-ton 840.8 -42.5 -494.9 712.8 -87.7 -400.4

3-ton 1158.0 -12.1 -507.2 930.6 99.1 -527.3

4-ton 1522.7 -40.3 -527.0 1158.6 36.1 -463.6

5-ton 1877.5 -102.8 -485.0 1469.0 37.8 -453.2

Figure 7-C.3.2 shows an example of a CFM curve for a 3-ton Non-Condensing SingleStage Furnace fitted with the manufacturers’ raw data.
7-C-4

Figure 7-C.3.2 Example Fit of CFM for 3-ton Single-Stage (High 

Fire) Furnace

Figure 7-C.3.3 shows the fan curves for PSC furnaces. Appendix 7-G contains the data 

on the basic models that were used to develop these fan curves.

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-C-5

Figure 7-C.3.3 Fan Curves for Single-Stage Virtual Model 

Furnaces

The two-stage and continuous modulating design options in this analysis use brushless 

permanent magnet motors (or sometimes referred as Electronically Commutated Motors (ECM)). 

Unlike PSC motors, these motors are electronically commutated and the speed they operate at 

can be varied across a wide range. These motors are controlled to operate the blower fans at a 

wide variety of air flows and static pressures. In furnaces with these motors currently on the 

market, the controls are designed to provide a near constant air flow across the entire range of 

pressures at which they operate.

Because of the versatility of the motors, manufacturers only offer furnaces with blowers 

nominally designed for operation with five-ton and three-ton air conditioners. The 

manufacturers provide control options to decrease the airflow for installations that use smaller air 

conditioners.

To develop fan curves for furnaces with ECM motors, the Department fit quadratic 

curves through the air flow and pressure data points reported by manufacturers.11, 12, 13, 14, 15, 16, 17 

DOE did this separately for high-fire and low-fire operation. See Figure 7-C.3.4 through Figure 

7-C.3.5 for charts showing the fit lines. Table 7-C.3.2 shows the coefficients for two-stage and 

continuous modulating furnaces with ECM motors below. Data from the basic models that were 

used to develop these fan curves is shown in Appendix 7-H, Determination of Basic Furnace 

Models. 

0

500

1000

1500

2000

2500

0.00 0.25 0.50 0.75 1.00

External Static Pressure (in. w.g.)

Airflow (CFM)

2000 CFM

1600 CFM

1200 CFM

800 CFM
7-C-6

CFM = m0 + m1 × (P) + m2 × (P2)

where,

CFM = airflow in CFM reported by manufacturer,

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

Table 7-C.3.2 for actual coefficient values), and

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

Table 7-C.3.2 Coefficients for CFM equation for Two-Stage and Continuous 

Modulating furnaces with ECM motors

High Fire Low Fire

m0 m1 m2 m0 m1 m2

2-ton 785.1 46.9 -135.1 580.7 17.5 -81.5

3-ton 1043.2 23.5 -101.1 779.3 2.6 -64.0

4-ton 1326.2 57.6 -61.9 946.7 6.5 13.8

5-ton 1571.9 5.6 -30.5 1160.9 -17.7 1.1

To be consistent with the analysis it did for the single-stage furnaces with PSC blower 

motors, the Department created virtual models for furnaces intended to act as air handlers for 

four and two ton air conditioners, even though these are not currently offered by manufacturers. 

To generate the fan curves for the virtual furnaces intended to be used with 4 ton air 

conditioners, DOE calculated the average of the slopes and intercepts of the virtual furnaces with 

air handler for 5 ton and 3 ton air conditioners. This was done separately for high and low fire 

operations for non-condensing and condensing furnaces.

For the virtual furnace models intended to operate with two-ton air conditioners, the fan 

curves were created by extrapolating the values for the slopes and intercepts of the virtual 

furnace models with air handlers intended to operate with three-ton and five- ton air 

conditioners. This was also done separately for high fire and low fire operation for both noncondensing and condensing furnaces. See Figure 7-C.3.4 through Figure 7-C.3.5 for charts 

showing the fan curves for these air handlers.
7-C-7

Figure 7-C.3.4 Fan Curves for Two-Stage Virtual Model Furnaces 

– High Fire

Figure 7-C.3.5 Fan Curves for Two-Stage Virtual Model Furnaces 

– Low Fire

0

500

1000

1500

2000

2500

0.00 0.25 0.50 0.75 1.00

External Static Pressure (in. w.g.)

Airflow (CFM)

2000 CFM

1600 CFM

1200 CFM

800 CFM

0

500

1000

1500

2000

2500

0.00 0.25 0.50 0.75 1.00

External Static Pressure (in. w.g.)

Airflow (CFM)

2000 CFM

1600 CFM

1200 CFM

800 CFM
7-C-8

7-C.4 FAN POWER

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

intersection of the fan curve and the system curve, the watts per cubic feet per minute (CFM) of 

airflow are determined using the equations developed in this appendix. The power consumption 

of the fan at this operating condition, 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 = determined below, and

Q = airflow (cfm).

For furnaces with air handlers with permanent split capacitor (PSC) blower motors, one 

manufacturer reports watts across a range of pressures. For these models, the Department 

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. The Department did this separately for each of the 

four nominal air handler sizes. The watts per CFM for PSC blower motors 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 2nd degree polynomial approximation (see 

Table 7-C.4.1 for actual coefficient values), and

P = external static pressure (in.w.g.).
7-C-9

Table 7-C.4.1 Coefficients for W/CFM equation for PSC motors

High Fire (Single-Stage) Low Fire

m0 m1 m2 m0 m1 m2

2-ton 0.395 -0.161 0.258 0.384 -0.140 0.332

3-ton 0.432 -0.209 0.185 0.425 -0.204 0.209

4-ton 0.416 -0.191 0.156 0.428 -0.195 0.152

5-ton 0.449 -0.124 0.096 0.449 -0.130 0.086

Figure 7-C.4.1 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 air handler size.

Figure 7-C.4.1 Example Fit of Watts/CFM for 3-ton Single-Stage 

Furnace

Figure 7-C.4.2 shows the fit curves of Watts/CFM for pressures from 0 in.w.g. to 1.0 

in.w.g. Data from the models that were used to develop these fan curves is shown in Appendix 

H, Determination of Basic Furnace and Boiler Models.

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-C-10

Figure 7-C.4.2 Watts/CFM vs. Pressure Curves for Single-Stage 

Virtual Model Furnaces

For the two-stage and continuous modulating furnaces with ECM motors, the Department 

calculated watts per CFM equations using data from basic models of several manufacturers. 

These data are in the reduced set of furnace models database. 

This was done for basic model furnaces nominally designed for use with 3 ton and 5 ton 

air conditioners. The watts per CFM data points of these basic models were fit to straight lines 

using Equation 4. To be consistent with other analyses, the Department calculated the slope and 

intercept for the watts per CFM curves for furnaces intended to operate with 2 ton and 4 ton air 

conditioners by interpolating from the values for 3 ton and 5 ton air handlers. Figure 7-C.4.3

through Figure 7-C.4.4 show the lines for the basic models. Table 7-C.4.2 shows the coefficients 

for two-stage and continuous modulating furnaces with ECM motors using Eq. 3. Data from the 

models used to develop these fan curves is shown in Appendix H, Determination of Basic 

Furnace and Boiler Models. 

Watts

CFM = m0 + m1 × (P) + m2 × (P2) Eq. 4

where,

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

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

0.0

0.2

0.4

0.6

0.00 0.25 0.50 0.75 1.00

External Static Pressure (in. w.g.)

Watts/CFM

2000 CFM

1600 CFM

1200 CFM

800 CFM
7-C-11

m0,1, and 2 = coefficients derived from second degree polynomial (see Table FC.4.2 for actual coefficient values), and

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

Table 7-C.4.2 Coefficients for W/CFM equation for Two-Stage and Continuous 

Modulating furnaces with ECM motors 

High Fire Low Fire

m0 m1 m2 m0 m1 m2

2-ton 0.143 0.247 -0.048 0.090 0.239 0.005

3-ton 0.160 0.239 -0.029 0.100 0.240 0.003

4-ton 0.170 0.311 -0.084 0.104 0.251 0.012

5-ton 0.190 0.264 -0.029 0.117 0.246 0.004

Figure 7-C.4.3 Watts/CFM vs. Pressure Curves for Two-Stage 

Virtual Model Furnaces – High Fire

0.0

0.2

0.4

0.6

0.00 0.25 0.50 0.75 1.00

External Static Pressure (in. w.g.)

Watts/CFM

2000 CFM

1600 CFM

1200 CFM

800 CFM
7-C-12

Figure 7-C.4.4 Watts/CFM vs. Pressure Curves for Two-Stage 

Virtual Model Furnaces – Low Fire

7-C.5 DETERMINATION OF FAN CURVES FOR EACH EFFICIENCY LEVEL 

AND PRODUCT CLASS

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 coefficients to generate for airflow (cfm) vs. pressure and watts/cfm vs. 

pressure curves at each airflow speed (heating, cooling, and continuous fan), DOE 

found the airflow cfm and watts per CFM at DOE’s reference system curve external 

static pressure. For example, DOE’s reference system curve external static pressure 

is 0.65 in.w.g at the maximum cooling airflow speed for non-weatherized gas 

furnaces. For the 3-ton baseline PSC motor for non-weatherized (non-condensing) 

gas furnaces the maximum airflow CFM was calculate to be 1158 cubic feet per 

minute.

STEP 2: Using the BE equation above, DOE multiplied the airflow times the watt/cfm at each 

pressure from Step 1 to calculate BE at each airflow speed (heating, cooling, and 

continuous fan) in terms of DOE’s reference system curve external static pressure. 

For example, for the 3-ton baseline PSC motor for non-weatherized (non-condensing) 

0.0

0.2

0.4

0.6

0.00 0.25 0.50 0.75 1.00

External Static Pressure (in. w.g.)

Watts/CFM

2000 CFM

1600 CFM

1200 CFM

800 CFM
7-C-13

gas furnaces BE was calculate to be 382 watts at heating, 495 watts at cooling, and 

382 watts at continuous fan.

STEP 3: Using the calculated maximum airflow CFM and BE values at DOE’s reference 

system curve external static pressure, DOE was able to calculate Furnace Efficiency 

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

STEP 4: The constant curve fit parameter (m0) in the pressure and watts/cfm vs. pressure 

curves was then adjusted using an adjustment multiplier in order to match the FER 

values derived in the engineering analysis. For example, for the 3-ton baseline PSC 

motor for non-weatherized (non-condensing) 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 as 1.04.

Table 7-C.5.1 shows the airflow (cfm) vs. pressure coefficients determined for nonweatherized (non-condensing) gas furnaces (3-ton) at each efficiency level (EL). Figure 7-C.5.2

to Figure 7-C.5.4 show the resulting curves at various pressures and operating modes.

Table 7-C.5.1 Coefficients for CFM equation for Non-Weatherized (Non-Condensing) 

Gas Furnace Fan, 3-Ton

EL Heating Cooling Continuous Fan

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-C-14

Figure 7-C.5.2 CFM Curves for Non-Weatherized (Non-Condensing) 

Gas Furnace Fan, 3-Ton (Heating 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
7-C-15

Figure 7-C.5.3 CFM Curves for Non-Weatherized (Non-Condensing) 

Gas Furnace Fan, 3-Ton (Cooling Mode)

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-C-16

Figure 7-C.5.4 CFM Curves for Non-Weatherized (Non-Condensing) 

Gas Furnace Fan, 3-Ton (Continuous Fan Mode)

Table 7-C.5.2 shows the watts/cfm vs. pressure curves coefficients determined for nonweatherized (non-condensing) gas furnaces (3-ton) at each efficiency level. Figure 7-C.5.5 to 

Figure 7-C.5.7 show the resulting curves at various pressures. Figure 7-C.5.8 to Figure 7-C.5.10

show the resulting Watts vs. pressure curves.

Table 7-C.5.2 Coefficients for Watts/CFM Equation for Non-Weatherized (NonCondensing) Gas Furnaces, 3-Ton

EL Heating Cooling Continuous Fan

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-C-17

Figure 7-C.5.5 Watt/CFM Curves for Non-Weatherized (NonCondensing) Gas Furnace Fan, 3-Ton (Heating 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-C-18

Figure 7-C.5.6 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

Watss/CFM

External Static Pressure (in w.c.)

Baseline (PSC)

Improved PSC

PSC w/ Controls

X13

ECM (Variable Speed)

ECM + BC Impeller
7-C-19

Figure 7-C.5.7 Watt/CFM Curves for Non-Weatherized (NonCondensing) Gas Furnace Fan, 3-Ton (Continuous Fan 

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-C-20

Figure 7-C.5.8 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-C-21

Figure 7-C.5.9 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-C-22

Figure 7-C.5.10 Resulting Watt vs. Pressure Curves for NonWeatherized (Non-Condensing) Gas Furnace Fan, 3-

Ton (Continuous Fan 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-C-23

REFERENCES

1. 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

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

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

3. Proctor, J. and D. Parker, Hidden Power Drains: Residential Heating and Cooling Fan 

Power Demand. In ACEEE 2000 Summer Study on Energy Efficiency in Buildings. 2000. 

Asilomar, CA, August 20-25. American Council for an Energy-Efficient Economy.1: pp. 

225-234. 

4. Lennox Industries Inc., Lennox Engineering Data: G50DF (Elite Series Downflow Gas 

Furnace), 2003. Lennox Industries, Inc. 

<http://pirl.lennox.com/C03e7o14l/76E0ZC21u/ehb_g50df_0307.pdf>

5. Lennox Industries Inc., Lennox Engineering Data: G50UH (Elite Series 

Upflow/Horizontal Gas Furnace), 2003. Lennox Industries, Inc. 

<http://pirl.lennox.com/C03e7o14l/76E0ZC21u/ehb_g50uh_0307.pdf>

6. Lennox Industries Inc., Lennox Engineering Data: G40DF (Merit Series 

Upflow/Horizontal Gas Furnace), 2003. Lennox Industries, Inc. 2003.) 

<http://pirl.lennox.com/C03e7o14l/76E0ZC21u/ehb_g40df_0307.pdf>

7. Lennox Industries Inc., Lennox Engineering Data: G43UF (Merit Series Upflow Gas 

Furnace), 2004. Lennox Industries, Inc. 

<http://pirl.lennox.com/C03e7o14l/76E0ZC21u/ehb_g43uf_0412.pdf>

8. Lennox Industries Inc., Lennox Engineering Data: G41UF (Merit Series Downflow Gas 

Furnace), 2004. Lennox Industries, Inc. 

<http://pirl.lennox.com/C03e7o14l/76E0ZC21u/ehb_g41uf_0402.pdf>

9. Lennox Industries Inc., Lennox Engineering Data: G51MP (Elite Series Multi-Position 

Gas Furnace), 2004. Lennox Industries, Inc. 

<http://pirl.lennox.com/C03e7o14l/76E0ZC21u/ehb_g51mp_0412.pdf>

10. Lennox Industries Inc., Lennox Engineering Data: G40UH (Merit Series 

Upflow/Horizontal Gas Furnace), 2004. Lennox Industries, Inc. 

<http://pirl.lennox.com/C03e7o14l/76E0ZC21u/ehb_g40uh_0407.pdf>
7-C-24

11. Carrier Co., 58MVP, Deluxe 4-Way Multipoise Variable-Capacity Direct-Vent 

Condensing Gas Furnace, 2004. Carrier Co. Catalog No. 535-80141, Form 58MVP–

12SM. 

12. Carrier Co., 58CVA/CVX, InfinityTM 80, Variable Speed, 4-Way Multipoise Furnace, 

2004. Carrier Co. Form 58CV-3PD. Catalog No. 525-80043. 

13. Lennox Industries Inc., Lennox Engineering Data: G60DFV (Down-flow - Variable 

Speed Blower - Two-Stage Heat). 2004, Lennox Industries, Inc. 

14. Lennox Industries Inc., Lennox Engineering Data: G60UHV (Up-Flow/Horizontal - Two 

Stage Heat - Variable Speed Blower). 2003, Lennox Industries, Inc. 

15. Lennox Industries Inc., Lennox Engineering Data: G61MPV (Multi-Position - Variable 

Speed Blower - Two-Stage Heat - Direct Vent/Non-Direct Vent). 2004, Lennox 

Industries, Inc. 

16. Trane Co., Trane Product Data: XV 80, 2004. Trane Co. 

17. Trane Co., Trane Product Data: XV 90, 2004. Trane Co.