7-i

CHAPTER 7. ENERGY CONSUMPTION OF FURNACES AND BOILERS

TABLE OF CONTENTS

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

7.2 METHOD FOR NON-WEATHERIZED GAS FURNACES ................... 7-1

7.3 VIRTUAL FURNACE MODELS ....................................... 7-2

7.3.1 Basic Actual Furnace Models ..................................... 7-3

7.3.2 Input Capacity and Maximum Airflow .............................. 7-4

7.3.2.1 Non-weatherized gas furnaces. ....................... 7-4

7.3.2.2 Other Product Classes. .............................. 7-5

7.3.3 Blower Size .................................................. 7-6

7.3.4 Motor Size ................................................... 7-6

7.3.5 Supply-Air Outlet Area .......................................... 7-7

7.3.6 Power Consumption of Draft Inducer .............................. 7-11

7.3.7 Delay Times and Ignitor Power .................................. 7-11

7.4 ASSIGNING EXISTING EQUIPMENT TO SAMPLE HOUSES .............. 7-11

7.4.1 Furnace Input Capacity ......................................... 7-11

7.4.2 Airflow Capacity ............................................. 7-13

7.4.3 Efficiency Characteristics of Existing Equipment ..................... 7-13

7.4.4 Electricity Consumption of the Existing Furnace Blower ................ 7-14

7.5 CALCULATING FURNACE BLOWER ELECTRICITY CONSUMPTION ..... 7-14

7.5.1 System Curves ............................................... 7-15

7.5.2 Furnace Fan Curves ........................................... 7-16

7.5.3 Overall Air-Moving Efficiency ................................... 7-17

7.5.4 Blower-Motor Electricity Consumption ............................ 7-21

7.6 ANNUAL HEATING AND COOLING LOADS IN SAMPLE HOUSES ........ 7-21

7.6.1 Annual House-Heating Load .................................... 7-21

7.6.2 Annual House-Cooling Load .................................... 7-22

7.7 FURNACE ENERGY CONSUMPTION ................................. 7-23

7.7.1 Fuel Consumption ............................................ 7-23

7.7.2 Electricity Consumption ........................................ 7-23

7.8 BOILER ENERGY CONSUMPTION ................................... 7-25

7.9 RESULTS ........................................................ 7-25

7.9.1 Non-Weatherized Gas Furnace Energy Use ......................... 7-25

7.9.2 Weatherized Gas Furnace Energy Use ........................ 7-28

7.9.3 Mobile Home Furnace Energy Use ................................ 7-30

7.9.4 Oil Furnace Energy Use ........................................ 7-32

7.9.5 Gas Boiler Energy Use ........................................ 7-34

7.9.6 Hot-Water Oil Boiler Energy Use ................................. 7-36
7-ii

LIST OF TABLES

Table 7.3.1 Characteristics of Basic Furnace Models ............................. 7-3

Table 7.3.2 Virtual Model Furnaces: Capacity and Airflow ........................ 7-4

Table 7.3.3 Relevant Sizes of Virtual Models for Non-Weatherized and 

Weatherized Gas Furnaces ....................................... 7-5

Table 7.3.4 Relevant Sizes of Virtual Models for Mobile Home Furnaces ............. 7-5

Table 7.3.5 Relevant Sizes of Virtual Models for Oil-Fired Furnaces ................. 7-5

Table 7.3.6 Assigned Blower Size by Airflow Capacity ........................... 7-6

Table 7.3.7 Assigned Motor Size by Airflow Capacity ........................... 7-6

Table 7.3.8 Supply-Air Outlet Area (in Square Feet) for Virtual Non-Condensing 

Gas Furnace Models ........................................... 7-10

Table 7.3.9 Supply-Air Outlet Area (in Square Feet) for Virtual Condensing 

Gas Furnace Models ........................................... 7-10

Table 7.3.10 Values for Delay and Ignition Times .............................. 7-11

Table 7.9.1 Non-Weatherized Gas Furnace Energy Use ......................... 7-26

Table 7.9.2 Weatherized Gas Furnace Energy Use ............................. 7-28

Table 7.9.3 Mobile Home Furnace Energy Use ................................ 7-30

Table 7.9.4 Oil Furnace Energy Use ........................................ 7-32

Table 7.9.5 Hot-Water Gas Boiler Energy Use ................................ 7-34

Table 7.9.6 Oil Boiler Energy Use .......................................... 7-36

LIST OF FIGURES

Figure 7.3.1 Number of GAMA Listed Furnace Models by Input Capacity ............. 7-3

Figure 7.3.2 Supply-Air Outlet Area for Non-Condensing Natural Gas Furnaces ........ 7-8

Figure 7.3.3 Supply-Air Outlet Area for Condensing Natural Gas Furnaces ............ 7-9

Figure 7.4.1 Percent of Existing Furnaces by Input Capacity ...................... 7-12

Figure 7.5.1 Sample of System Curves with a Typical Fan Curve ................... 7-16

Figure 7.5.2 Fan Curves for 800 cfm Virtual Furnace Model ...................... 7-17

Figure 7.5.3 Fan Curves for 1200 cfm Virtual Furnace Model ..................... 7-17

Figure 7.5.4 Fan Curves for 1600 cfm Virtual Furnace Model ..................... 7-17

Figure 7.5.5 Fan Curves for 2000 cfm Virtual Furnace Model ..................... 7-17

Figure 7.5.6 Overall Air-Moving Efficiency of Existing Furnaces ................... 7-19

Figure 7.5.7 Overall Air-Moving Efficiency of Non-Condensing Virtual Furnace Models . 7-20

Figure 7.5.8 Overall Air-Moving Efficiency of Condensing Virtual Furnace Models ..... 7-20

Figure 7.9.1 Range of Annual Gas Use, Non-Weatherized Gas Furnaces ............. 7-26

Figure 7.9.2 Range of Annual Gas Usage by Region, 90 percent AFUE, 

Non-Weatherized Gas Furnace ................................... 7-27
7-iii

Figure 7.9.3 Range of Winter Electricity Use, Non-Weatherized Gas Furnaces ......... 7-27

Figure 7.9.4 Annual Gas Use, Weatherized Gas Furnaces ......................... 7-29

Figure 7.9.5 Winter Electricity Use, Weatherized Gas Furnaces .................... 7-29

Figure 7.9.6 Annual Gas Use, Mobile Home Furnaces ........................... 7-30

Figure 7.9.7 Winter Electricity Use, Mobile Home Furnaces ....................... 7-31

Figure 7.9.8 Range of Annual Oil Use, Oil Furnaces ............................. 7-33

Figure 7.9.9 Range of Winter Electricity Use, Oil Furnaces ....................... 7-33

Figure 7.9.10 Range of Annual Gas Use, Hot-Water Gas Boilers .................... 7-35

Figure 7.9.11 Range of Winter Electricity Use, Hot-Water Gas Boilers ................ 7-35

Figure 7.9.12 Range of Annual Oil Use, Hot-Water Oil Boilers ...................... 7-37

Figure 7.9.13 Range of Winter Electricity Use, Hot-Water Oil Boilers ................ 7-37
7-1

CHAPTER 7. ENERGY CONSUMPTION OF FURNACES AND BOILERS

7.1 INTRODUCTION

The furnace and boiler energy-efficiency standards rulemaking considers the change in lifecycle cost (LCC) due to increased energy efficiency of household heating equipment. Energy

consumption is the key part of the operating-cost input of the LCC calculation. The energy

consumption of a furnace or boiler includes either gas or oil and electricity. In many cases, a

furnace blower operates outside the heating season when the air handler is in use for cooling

purposes, so DOE included this consumption in its calculations.

In the engineering analysis, the Department calculated energy consumption of baseline

model-sized furnaces and boilers using the DOE test procedure for these types of equipment. For

the LCC Analysis, DOE estimated energy consumption of furnaces and boilers in actual houses.

To represent actual houses with furnaces and boilers in the United States, DOE used a set of

houses from DOE's Energy Information Administration (EIA)’s Residential Energy Consumption

Survey of 1997 (RECS97).1 For each house, RECS97 reports space-heating energy consumption

and space-cooling electricity consumption, which are based on the existing household equipment. 

The Department’s method estimated the energy consumption of alternative (more-efficient)

equipment, if they were used in each house in place of the existing equipment.

The Department developed the method of calculation described in this chapter for nonweatherized gas furnaces, the most common among the six product classes in the rulemaking

analysis. The Department generalized the energy consumption calculation for this product class

to the other furnace product classes. Fuel consumption calculations for boilers are similar to

those for the furnace product classes. The electricity calculations for boilers are simpler than for

furnaces, because boilers do not provide thermal distribution for space cooling as furnaces often

do.

7.2 METHOD FOR NON-WEATHERIZED GAS FURNACES

To begin the analysis, the Department developed representative conceptual furnace

models. These “virtual” models incorporated typical features of currently-marketed furnaces. 

The Department based the virtual furnaces on models selected from directories and product

literature. The virtual models capture the range of actual furnace sizes. The analysis assigned an

appropriate virtual furnace to each sample house as a way of modeling energy consumption of

alternative furnace designs.

Estimating the annual energy consumption of alternative furnaces in each house required

DOE to estimate the heating and cooling loads of each house. These loads represent the amount

of heating and cooling required to keep a house comfortable during an entire year. The

Department estimated the heating and cooling loads from the heating and cooling energy

consumption and the assumed characteristics of the existing furnace and air conditioner in each
a

 Furnaces are capable of providing several levels of airflow. For heating operation, a low level of airflow is used. If

the furnace provides airflow for an air conditioner during cooling operation, it is typically set to provide a higher level

of airflow when the air conditioner is operating.

7-2

sample house. The Department assigned the characteristics of the existing equipment to each

sample house, depending on the size and climate zone of each house and the age of the heating

equipment. The estimation of heating loads also required calculation of the electricity

consumption of the furnace blower, since heat from the furnace blower contributes to heating the

house. 

To complete the analysis, the Department calculated how much energy would be required

by furnaces with various design options to meet the same heating and cooling load of each sample

house.

7.3 VIRTUAL FURNACE MODELS

To conduct the analysis, the Department developed conceptual furnace models. The

Department intended these generic furnace models to represent typical furnaces with basic

features, but not to describe specific, existing furnaces. The Department derived the

characteristics of the virtual furnace models from existing “basic” furnace models, after examining

directories and product literature of existing furnaces. See Appendix 7.1, Reduced Set of Furnace

Models, Database for more details.

As a starting point for choosing values of input capacity for the virtual furnace models, the

Department looked at the number of models listed by input capacity in the Gas Appliance

Manufacturers Association (GAMA) Directory of April 20022 (see Figure 7.3.1). The

Department selected models that were non-weatherized gas furnaces, that were not designed for

mobile homes, and that were not discontinued. Using these selection criteria, DOE reduced the

36,032 gas furnace models in the GAMA Directory to 15,881 models. For virtual furnaces, DOE

selected twelve input capacities that were the most common and that spanned the range on the

market. The Department made these selections based on the assumption that the sizes that have

the most models are the most popular. 

The Department defined airflow capacity as the nominal maximum airflow at 0.5 inches

water gauge (in.w.g.) external static pressure, as listed in the product literature for each model.a

Manufacturers usually code this airflow capacity in the model number (see Appendix 7.2 on

Decoding of Manufacturer Model Numbers, for more details.) Most of the furnaces fit into four

airflow capacity sizes: 800 cubic feet per minute (cfm), 1200 cfm, 1600 cfm, and 2000 cfm. 

These airflow capacities correspond to nominal air-conditioner sizes of two tons, three tons, four

tons, and five tons, respectively. The Department used the same set of airflow and capacity sizes

for both non-condensing and condensing furnaces.
7-3

Figure 7.3.1 Number of GAMA Listed Furnace Models by Input

Capacity

7.3.1 Basic Actual Furnace Models

The Department selected actual furnace models that represent the fundamental

characteristics of non-condensing and condensing furnaces with no special features. The

Department used the characteristics listed in Table 7.3.1 to select basic furnace models. These

characteristics are the most common among models on the market (see Appendix 7.1, Reduced

Set of Furnace Models Database). The Department selected several dozen furnace models that

have these features. It looked in detail at these basic models to determine specific characteristics

to use for creating virtual furnaces. 

Table 7.3.1 Characteristics of Basic Furnace Models

Non-Condensing Gas Furnace Condensing Gas Furnace

single stage burner single stage

80% AFUE 90-92% AFUE

permanent split capacitor (PSC) blower motor PSC blower motor

forward-curved impeller blades forward-curved impeller blades

up-flow or horizontal air-flow down-flow, up-flow, or horizontal air-flow
7-4

The basic furnace models are listed by brand and series in Appendix 7.3A, which contains

basic non-condensing model data, and Appendix 7.3B, basic non-condensing model data. 

7.3.2 Input Capacity and Maximum Airflow

7.3.2.1 Non-weatherized gas furnaces. 

For virtual furnace models, DOE selected 25 combinations (“bins”) of input capacity and

maximum airflow. The marked cells in Table 7.3.2 reflect the input capacity and nominal

maximum airflow for the virtual furnace models. The selection reflects the most common input

and nominal maximum airflow capacities of models in the GAMA Directory April 2002,3 in

product literature, and listed on furnace manufacturer web sites. Most basic models on the

market fit into the 25 bins of input capacity and airflow capacity. Some models do not exactly

match the bins, but their values are close enough that DOE included them in one of the 25 bins. 

For example, 40 kBTU/h and 45 kBTU/h models are grouped together into a single 45 kBTU/h

bin. Most bins have at least two actual models. 

Table 7.3.2 Virtual Model Furnaces: Capacity and Airflow

Input Capacity (kBTU/h)

M

a

xim

u

m

Airflo

w

(at 0.5" Static

Pressure)

45 50 60 70 75 80 90 100 115 120 125 140

800 cfm

(2 tons)

x x x

1200 cfm

(3 tons)

x x x x x x x x

1600 cfm

(4 tons)

x x x x x x x x

2000 cfm

(5 tons)

x x x x x x

The Department created one virtual model to represent all the models assigned to each

bin. The Department used specifications from the actual models in each bin to determine the

specifications for the corresponding virtual model. These specifications include blower size,

motor size, supply-air outlet area, power consumption of the draft inducer and the igniter, and

several delay times. The specifications are described in the sections below.
7-5

7.3.2.2 Other Product Classes. 

Because of the limited number of sizes available for mobile home gas furnaces and oilfired furnaces, DOE selected a subset of the 25 input and airflow capacity combinations to

represent each product class. In its analysis of weatherized gas furnaces, DOE used the same

virtual models as it used in the analysis of non-weatherized gas furnaces. For mobile home

furnaces and oil-fired furnaces, the Department used a subset of the 25 virtual furnace models,

because the market in those product classes is limited to a smaller number of sizes of furnaces. 

Tables 7.3.3-7.3.5 list the relevant sizes for non-weatherized and weatherized gas, mobile home,

and oil-fired furnaces.

Table 7.3.3 Relevant Sizes of Virtual Models for Non-Weatherized and Weatherized Gas

Furnaces

Input Capacity (kBtu/h)

Max.

Airflow

(tons)

45 50 60 70 75 80 90 100 115 120 125 140

2 X X X

3 X X X X X X X X

4 X X X X X X X X

5 X X X X X X

Table 7.3.4 Relevant Sizes of Virtual Models for Mobile Home Furnaces

Input Capacity (kBtu/h))

Max.

Airflow

(tons)

60 70 75 80 90 100 115 120 125 140

2 X X X

3 X X X

4 X X X

5 X X X

Table 7.3.5 Relevant Sizes of Virtual Models for Oil-Fired Furnaces

Input Capacity (kBtu/h)

Max.

Airflow

(tons)

45 50 60 70 75 80 90 100 115 120 125 140

2

3 X X X

4 X X

5 X X X
7-6

7.3.3 Blower Size

The Department selected a blower size (listed as nominal diameter in inches by nominal

width in inches) for each virtual furnace model (Table 7.3.6). The blower size is typical for the

basic furnace models in each bin. Blower size increases with airflow capacity, but not with input

capacity. The Department used four blower sizes—the same ones for condensing and noncondensing virtual furnace models. For the blower sizes of basic furnace models, see

Appendix 7.3, Determination of Basic Model Furnaces.

Table 7.3.6 Assigned Blower Size by Airflow Capacity

Airflow Capacity (cfm) Blower Size (inches)

2-ton models (800 cfm) 9 X 8

3-ton models (1200 cfm) 10 X 8

4-ton models (1600 cfm) 10 X 10

5-ton models (2000 cfm) 11 X 10

7.3.4 Motor Size

The motors for the basic furnace models are six-pole permanent split capacitor (PSC)

induction motors. The motors in the basic furnaces come with three to five taps that are used to

set the motor speed. The Department assumed that, at high speed, the motors operate with a

speed of 1075 revolutions per minute (rpm) to provide the nominal maximum airflow at 0.5

in.w.g.

The Department assigned motor size to virtual furnace models, as shown in Table 7.3.7, to

reflect typical-size motors of the basic furnace models. Motor sizes are the same for noncondensing and condensing furnaces. The larger the nominal maximum airflow, the larger the

motor size. For the blower motor size and number of taps on basic model furnaces, see Appendix

7.3, Determination of Basic Model Furnaces, which lists the blower-motor sizes and number of

blower motor taps of basic furnace models.

Table 7.3.7 Assigned Motor Size by Airflow Capacity

Airflow Capacity (cfm) Motor Size (HP)

2-ton models (800 cfm) 1/5

3-ton models (1200 cfm) 1/3

4-ton models (1600 cfm) 1/2

5-ton models (2000 cfm) 3/4
7-7

7.3.5 Supply-Air Outlet Area

The supply-air outlet area is the opening from the furnace to the supply duct. The supplyair outlet area for basic furnace models increases with airflow capacity and input capacity. To

capture this trend, DOE constructed a linear fit of the supply-air outlet area to input capacity and

airflow capacity for condensing and non-condensing furnaces (see Appendix 7.3, Determination

of Basic Model Furnaces, for supply-air outlet areas of basic furnace models). The Department

used the following equations to determine the supply-air outlet area of the non-condensing and

condensing virtual model furnace models:

where:

S = supply-air outlet area (sq. ft.),;

Q = nominal maximum airflow (cfm) at 0.5 in.w.g. static pressure,; and

Qin = input capacity (kBtu/h).

Figures 7.3.2 and 7.3.3 show the data points for supply-air outlet area for basic furnace

models and the linear plane fit used to fit these points.
7-8

Figure 7.3.2 Supply-Air Outlet Area for Non-Condensing Natural Gas Furnaces 
7-9

Figure 7.3.3 Supply-Air Outlet Area for Condensing Natural Gas Furnaces
7-10

Tables 7.3.8 and 7.3.9 show the values DOE used for supply-air outlet areas for noncondensing and condensing virtual gas furnaces.

The supply-air outlet area is larger for condensing models. The larger opening

compensates for the increased pressure drop due to the secondary, condensing heat exchanger.

This larger supply-air outlet area reduces the pressure drop across the furnace, so that the

pressure rise for condensing furnaces is the same as non-condensing model furnaces at the same

airflow.

Table 7.3.8 Supply-Air Outlet Area (in Square Feet) for Virtual Non-Condensing Gas

Furnace Models

Input Capa city (kBTU/h)

45 50 60 70 75 80 90 100 115 120 125 140

Maximum

Airflow ( at 0.5" Static Pressure )

800 cfm(2 tons)

1.58 1.62 1.71

1200 cfm(3 tons)

1.78 1.82 1.91 2.00 2.04 2.08 2.17 2.26

1600 cfm(4 tons)

2.20 2.24 2.29 2.37 2.46 2.59 2.63 2.68

2000 cfm(5 tons)

2.57 2.66 2.79 2.83 2.88 3.01

Table 7.3.9 Supply-Air Outlet Area (in Square Feet) for Virtual Condensing Gas

Furnace Models

Input Capa city (kBTU/h)

45 50 60 70 75 80 90 100 115 120 125 140

Maximum

Airflow ( at 0.5" Static Pressure )

800 cfm(2 tons)

1.72 1.76 1.83

1200 cfm(3 tons)

1.94 1.98 2.05 2.13 2.16 2.20 2.27 2.35

1600 cfm(4 tons)

2.35 2.39 2.42 2.50 2.57 2.68 2.72 2.75

2000 cfm(5 tons)

2.06 2.79 2.90 2.94 2.97 3.08
7-11

7.3.6 Power Consumption of Draft Inducer

A common value for the power consumption of the draft inducer, PE, for basic

non-condensing model furnaces is 75 watts, and the average value is about 75 W, so DOE

selected 75 W for all the non-condensing models. The Department found no correlation between

the PE and input capacity or between PE and airflow capacity. For condensing furnaces, the

Department used a PE of 90 W, which closely matches the mean for that group. See Appendix

7.3, Determination of Basic Model Furnaces, for the power consumption of the draft inducer in

the basic models.

7.3.7 Delay Times and Ignitor Power

Pre-purge and post-purge times are the lengths of time the draft inducer operates before

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

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

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

Pre-purge, post-purge, on-delay, and off-delay times are not related to airflow or input

capacity. The Department selected common values for the delay and ignition times of condensing

and non-condensing virtual furnace models (Table 7.3.10). For these data on basic furnace

models, see Appendix 7.3, Determination of Basic Model Furnaces.

Table 7.3.10 Values for Delay and Ignition Times

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

15 seconds 5 seconds 30 seconds 120 seconds 37 seconds

7.4 ASSIGNING EXISTING EQUIPMENT TO SAMPLE HOUSES

To estimate the heating and cooling load of each sample house, DOE assigned the input

capacity, airflow capacity, annual fuel utilization efficiency (AFUE), and for the air conditioner (if

the house has one), the seasonal energy-eficiency ratio (SEER). As part of the heating- and

cooling-load calculations, DOE estimated the electricity consumption and efficiency of the furnace

blower motor. The Department used the input capacity and nominal maximum airflow capacity

assigned to the existing furnace to choose the virtual furnace model for the house, for use in the

rest of the LCC analysis.

7.4.1 Furnace Input Capacity

The Department assigned an input capacity for the existing furnace of each house based on

an algorithm that correlates input capacity with the house size, the year the furnace was installed,

and the distribution of input capacity of new furnaces sold the year the furnace was installed. The

following steps describe the assignment process.
7-12

Figure 7.4.1 Percent of Existing Furnaces by Input Capacity

(1) The Department ranked all the RECS97 houses in ascending order by size (square foot)

and calculated the percentile rank of each house using the statistical weight of each of the

sample records.

(2) The Department constructed percentile tables by input capacity of furnaces sold each year

for 1997 and prior years, based on the historical shipment information for each year.4

(3) After selecting a house from the RECS97 database during each Monte Carlo iteration,

DOE noted the size of the selected house and determined the percentile rank from Step 1.

(4) To avoid a one-to-one deterministic relation between the house size and input capacity,

DOE added a random term to the percentile identified in Step 3 so that the correlation was

not perfect. The Department used a normal distribution to characterize the random term. 

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

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

capacity percentile table in Step 2 for the age of the equipment. 

(6) Figure 7.4.1 shows the percent of existing furnaces by input capacity assigned to the

sample houses.

7.4.2 Airflow Capacity

The Department classified furnaces by nominal maximum airflow in cfm at 0.5 in.w.g. of

external static pressure. The Department assigned the airflow capacity of existing furnaces for

houses that had air conditioners in a similar manner that it assigned furnace input capacity. Larger

air conditioners go to larger houses, according to the distribution of sizes of air conditioners sold
7-13

the year the air conditioner was installed in that house. The Department used the air conditioner

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

ton of cooling. The steps were:

(1) Based on the historical shipment information of residential central air conditioners by

capacity, DOE constructed the airflow capacity percentiles tables for air conditioners sold

in 1997 and prior years. The Department restricted the airflow sizes to two, three, four,

or five tons—the equivalent of 800, 1200, 1600, or 2000 cfm at 0.5 in.w.g. static

pressure. The variation of the distribution of the four airflow sizes over the years is small. 

Most of the annual sales of residential central air conditioners from 1976 to 1994 are in

these airflow sizes.

(2) Since there are no available shipment data on the airflow capacity of furnaces, the

Department used the airflow capacity of residential central air conditioners as a proxy.

Using the adjusted percentile of house size from Step (4) in the Input Capacity section,

DOE determined the airflow capacity by looking up the percentile in the corresponding

distribution of nominal air conditioner size for the age of the cooling equipment. The

Department selected a virtual model with the identified airflow capacity. If no virtual

model with the identified airflow capacity was available, the Department selected the

virtual model with the same input capacity and the closest airflow capacity as a substitute.

(3) If the RECS record indicated that the house did not have an air conditioner, DOE still

used the procedure from step (2) to determine the airflow capacity. In this case, DOE

used the age of the house (or 30 years if the house was older than 30 years) as a substitute

for the age of the cooling equipment. 

7.4.3 Efficiency Characteristics of Existing Equipment

GAMA shipments data indicate that houses in colder regions receive more-efficient

furnaces.4 Therefore, DOE correlated the AFUE of existing furnaces with the heating degree

days (HDD) to base 65°F associated with each sample house. The following steps describe this

process:

(1) The Department sorted the RECS houses in ascending order of HDDs, and calculated the

percentile rank of each house by HDD using the statistical weight of each sample house.

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

percentile tables by AFUE shipments of furnaces for 1997 and prior years.

(3) After DOE selected a house from the RECS database during each Monte Carlo iteration,

it noted the HDD of the selected house. The Department looked up the percentile rank of

that house from the HDD percentile table developed in Step (1). 

(4) The Department added a random uncertainty term to the HDD percentile found in Step

(3) to account for variability within the sample. The Department used a normal

distribution to characterize the uncertainty term. The distribution of values of the

uncertainty term has a mean of zero and a standard deviation of 8 percent.
b

 A very small share of existing furnaces use belt-drive blowers with shaded-pole motors. That arrangement was less

efficient than direct-driven PSC motors, but the airflow from these old model furnaces was less, so electricity

consumption was not significantly reduced when this technology became obsolete.5

7-14

(5) Using the adjusted HDD percentile from Step (4), DOE determined the AFUE by looking

it up from the AFUE percentile table from Step (2) corresponding to the age of the

existing equipment in the house.

Houses with central air conditioners use the circulating-air blower in the furnace to

circulate the conditioned air during the cooling season. If a house had an air conditioner, DOE

assigned it a SEER level. Unlike AFUE, SEER was not correlated with any other housing

factors. The Department constructed SEER distributions for all years from historical shipment

data; it randomly selected a SEER from the distribution for the year of the age of equipment in

each house. 

7.4.4 Electricity Consumption of the Existing Furnace Blower

All furnaces manufactured since about 1980 use forward-curved impellers driven directly

by a PSC motor. Thus, most existing furnaces have a blower and blower motor similar to those in

the virtual furnace models.b Therefore, in assigning the electricity consumption of the existing

furnace blower for each house, DOE assumed that the electricity use of the existing furnace was

equivalent to the electricity use of the virtual furnace model described in section 7.2. 

The Department calculated electricity use by the existing furnace from the fan curves,

overall efficiency, airpower, and time delays of the virtual furnace model of the same input

capacity and airflow capacity. 

7.5 CALCULATING FURNACE BLOWER ELECTRICITY CONSUMPTION

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 house will operate. These operating conditions can be graphically displayed as the

intersection of a system curve of the ducts in the house (which plots the static pressure across the

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

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

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

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

furnace, are available from manufacturers in the product literature for each furnace. One of the
7-15

manufacturers also supplies blower-motor input power as a function of airflow through 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.

7.5.1 System Curves

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

pressure drop generated across the supply and return ducts in a house for different airflows. 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.4

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

ventilation, and air conditioning (HVAC) design and fan selection handbooks.6 The curves are

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

where:

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

" = a constant coefficient, and 

Q = airflow (cfm).

The Department selected the coefficient in the system curve equation for each house. It

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

maximum airflow of the virtual model furnace selected for that house. 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.7 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 7.5.1 for an example of a plot of system curves intersecting a furnace fan

curve.

7.5.2 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 pressure values are plotted graphically

against airflow, they are referred to as fan curves. 
7-16

The Department assigned three fan curves to each virtual furnace model: one for cooling

operation, one for heating, and a third for the low-fire heating operation of modulating design

options. In cooling operation, the fan curve passes through the nominal maximum airflow at 0.5

in.w.g. external static pressure. During normal heating operation, airflow is 80 percent of the

nominal maximum airflow at 0.5 in.w.g. external static pressure. The airflow for low-fire heating

operation at 0.5 in.w.g. static pressure is 2/3 of the nominal maximum airflow at the same external

static pressure.

Figure 7.5.1 Sample of System Curves with a Typical Fan Curve

The Department developed fan curves for the virtual furnace models as detailed in

Appendix 7.4, Furnace Fan Curves. Figures 7.5.2–7.5.5 show the fan curves for that virtual

furnace models. From the left, the line closest to vertical axis shows a fan curve for that virtual

furnace model operating in low-fire mode, the middle line is for the virtual furnace model

operating in heating mode, and the line furthest to the right, which passes through 0.5 in. w.g.

static pressure at the nominal maximum of airflow, is the fan curve for the virtual furnace models

operating in cooling mode.
7-17

Figure 7.5.2 Fan Curves for 800 cfm

Virtual Furnace Model

Figure 7.5.3 Fan Curves for 1200 cfm

Virtual Furnace Model

Figure 7.5.5 Fan Curves for 2000 cfm

Virtual Furnace Model

Figure 7.5.4 Fan Curves for 1600 cfm

Virtual Furnace Model

7.5.3 Overall Air-Moving Efficiency

The overall air-moving efficiency is the air power divided by the electric power used by

the blower motor. 

Air power (air horsepower, or AHP), the power added to the air because of its motion and

pressure increase as it is forced through the furnace, is calculated as:8

where:
c

 The velocity pressure is the increase in pressure caused by the motion of air.

7-18

= air power (watts),

= airflow (cfm),

= a conversion factor to express air horsepower in watts,

= a conversion factor to express the velocity pressure of standard air

in w.g.,c

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

= cross-sectional airflow area defined as the supply-air outlet area

(sq.ft.).

In addition to airflow at a range of external static pressures, one manufacturer reports fan

motor electricity consumption.9, 10, 11, 12, 13, 14 This allowed DOE to calculate the overall efficiency

from data in that manufacturers’ product literature. 

where:

= overall air moving efficiency,

= fan motor electricity consumption (W), and

= air power (W).

The Department calculated air power and overall efficiency for each point in the fan

operating tables for each of the models. To generalize this relation of overall air-moving

efficiency to airflow, the Department transformed airflows to percentages of airflow at free flow

for all the furnaces. The Department did this calculation separately for condensing and noncondensing furnaces. The transformation of airflow to fraction-of-airflow-at-free-flow allowed

DOE to plot all of the curves of overall air-moving efficiency together (as an example of the

transformed data, see Figures 7.5.6–7.5.8).

The Department fit these curves to a single equation of overall efficiency as a function of

the ratio of airflow to free airflow as follows:

where:
7-19

= overall air moving efficiency,

= ratio of airflow to free flow, and

= empirically determined coefficients.

Figures 7.5.7 and 5.7.8 show the curve fit for high-fire heating and low-fire heating, and

cooling for non-condensing and condensing furnaces.

For details of the overall air-moving efficiency and tables of coefficients for each of the

virtual furnaces and operating modes, see Appendix 7.6, Overall Air-Moving Efficiency.

Figure 7.5.6 Overall Air-Moving Efficiency of Existing Furnaces
7-20

Figure 7.5.7 Overall Air-Moving Efficiency of Non-Condensing

Virtual Furnace Models

Figure 7.5.8 Overall Air-Moving Efficiency of Condensing Virtual

Furnace Models
7-21

7.5.4 Blower-Motor Electricity Consumption 

The circulating-air blower-motor electricity consumption in steady-state at full load is a

function of airflow (Q), external static pressure (P), and the overall air-moving efficiency of the

furnace (0overall). 

For a baseline model furnace, the Department calculated the circulating-air fan-motor

electricity consumption for the forward-curved impeller with a direct-drive PSC motor as the air

power divided by the overall air-moving efficiency of the blower and blower motor: 

where:

= blower motor electricity consumption (W),

= air power (W), and

= overall air moving efficiency.

7.6 ANNUAL HEATING AND COOLING LOADS IN SAMPLE HOUSES

7.6.1 Annual House-Heating Load

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.

Burner operating hours (BOH), the number of hours the furnace burner is on during a

year, is a key variable in the calculation of HHL. The Department calculated BOH for the

existing furnace as:

where:

= burner operating hours (hrs/yr),

= annual fuel consumption for heating the house, from

RECS97 (kBtu/yr), and

= input capacity of the existing furnace (kBtu/hr).
7-22

The Department determined HHL for each sampled household, based on the BOH and the

characteristics of the assigned existing furnace, using the following calculations:

where:

= input capacity of existing furnace (kBTU/hr),

= AFUE of existing furnace,

3.412 = constant to convert kW to kBTU/hr,

= ratio of blower on-time to burner on-time in the heating mode

(from DOE test procedure), and

= power consumption of the blower motor (kW).

The power consumption of the blower motor depends on the steady-state operating

conditions (the pressure and airflow) for the furnace. This calculation is explained in section 7.5,

Calculating Furnace Blower Electricity Consumption. 

7.6.2 Annual House-Cooling Load

The annual house-cooling load (HCL) is the total amount of cooling provided to the house

for the entire cooling season. It includes the cooling provided by the existing air conditioner, and

accounts for the heat from the blower and blower motor. The Department calculated HCL from

the cooling energy consumption reported in RECS97 and the SEER of the assigned existing air

conditioners:

where:

= annual house-cooling load (kBtu/h/yr),

= annual house-cooling electricity consumption, from RECS97

kWh/yr), and

= SEER of the existing air conditioner (kBtu/h/kW).
7-23

7.7 FURNACE ENERGY CONSUMPTION

Once the heating and cooling loads of each sample house are known, it is possible to

estimate what the energy consumption of alternative (more-efficient) furnaces would be if moreefficient furnaces, rather than the existing equipment, were used in each house.

7.7.1 Fuel Consumption

For each design option, BOH is different, since the AFUE and blower-motor electricity

consumption are different. Therefore, each design option requires a different operating time to

heat the same house. The Department calculated BOH as:

where:

= input capacity of existing furnace (kBTU/h);

= AFUE of design option or efficiency level being considered;

3.412 = a constant to convert kW to kBTU/h;

= the ratio of blower on-time to burner on-time (heating mode); and

= the power consumption of the blower motor (kW).

The BE varies with airflow and static pressure, which are determined by the intersection of

the furnace fan curve and the duct system curve.

The Department calculated the furnace fuel consumption for each design option and

efficiency level using the following formula:

where:

= burner operating hours (h), and

= input capacity of existing furnace (kBTU/h).

7.7.2 Electricity Consumption
d

 The DOE and ASHRAE test procedures do not count the electricity used by controls when the furnace is not firing.

e

 The ASHRAE test procedure does not deal with ignitor energy consumption.

7-24

The Department calculated furnace electricity consumption for the blower, the draft

inducer, and the igniter.d The blower moves heated air through the house whenever the furnace

burner is on (and the heat exchanger has reached a certain set-point temperature). It also operates

in the cooling season (summer) if the house is air-conditioned. The electricity use calculation was

carried out separately for winter and summer. The Department calculated the winter electricity

consumption as:

where:

= burner operating hours (h),

= ratio of blower on-time to burner on-time,

= power consumption of the blower motor (kW),

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

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

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

= power consumption of the ignitor (kW).

The ratio of blower on-time to burner on-time and the ratio of induced draft blower ontime to burner on-time are from the American Society of Heating, Refrigerating and

Air-Conditioning Engineers (ASHRAE) test procedure15 using delay times for the virtual model

furnaces. The ratio of ignitor on-time to burner on-time comes from the DOE test procedure

16

and the ignition time of the virtual model furnaces.e

Summer electricity use is due to the furnace circulating-air blower that moves the air

cooled by the air conditioner. During cooling mode, the blower motor will operate at a high

speed, so the airflow and static pressure conditions will be different from the heating mode

conditions. The Department calculated summer electricity use as:

where:

= air-conditioner operating hours (h/yr), and

= power consumption of the blower-motor in cooling mode (kW).
7-25

The details for calculating energy consumption of modulating furnaces appear in Appendix

7.7, Gas and Electricity Use for Modulating Furnaces.

7.8 BOILER ENERGY CONSUMPTION

To assign the input capacity for the energy consumption calculation for hot-water gas and

oil boilers, the Department used the input capacities of the virtual model furnaces for boilers,

weighted according to the shipment data from GAMA.3 The Department calculated the heating

load for the house and the energy consumption of different model designs in a similar manner for

furnaces. The power consumption of the circulating pump motor is 62 watts for the baseline

model design.17

7.9 RESULTS

This section presents annual gas or oil consumption and winter electricity consumption for

selected design options in each product class.

7.9.1 Non-Weatherized Gas Furnace Energy Use

The average annual household energy use for each design option for non-weatherized gas

furnaces is shown in Table 7.9.1. The range of annual gas use for each design option is shown in

Figure 7.9.1. Figure 7.9.2 shows the range of gas use for the 90 percent AFUE condensing

furnace across the different regions of the country. Figure 7.9.3 shows the range of winter

electricity consumption.
7-26

Figure 7.9.1 Range of Annual Gas Use, Non-Weatherized

Gas Furnaces

Table 7.9.1 Non-Weatherized Gas Furnace Energy Use

Design Option Average Annual

Gas Use (MMBtu)

Average Winter Electricity Use*

(kWh)

78% 66.5 487 

80% 64.9 476 

80% 2-stage Mod. 63.5 492 

81%, 8% Cat. III 64.1 470 

81% 2-stage Mod, no Cat. III 62.8 487 

82% 63.3 464 

82% 2-stage Mod 62.0 481

83% 62.6 459 

90% 57.9 421 

92% Incr. HX Area 56.6 412 

96% Step Mod ECM 54.0 226 

* The average summer electricity use (for the blower) is 156 kWh for all of the design options shown.
7-27

Figure 7.9.2 Range of Annual Gas Usage by Region, 90

percent AFUE, Non-Weatherized Gas Furnace

Figure 7.9.3 Range of Winter Electricity Use, NonWeatherized Gas Furnaces
7-28

7.9.2 Weatherized Gas Furnace Energy Use

The average annual energy use for each design option for weatherized gas furnaces is

shown in Table 7.9.2. The range of annual gas use for weatherized gas furnaces for each design

option is shown in Figure 7.9.4. Figure 7.9.5 shows the range of winter electricity consumption. 

Table 7.9.2 Weatherized Gas Furnace Energy Use

Design Option Average Annual

Gas Use (MMBtu)

Average Winter Electricity Use*

(kWh)

78% AFUE - Baseline Model 40.3 298 

80% AFUE - Incr. HX Area 39.3 291 

80% AFUE - Improved Insulation 39.1 290 

80% AFUE - Improved Heat Xfer 39.3 291 

81% AFUE - Incr. HX Area 38.8 288 

81% AFUE - Improved Insulation 38.7 286 

81% AFUE - Improved Heat Xfer 38.8 288 

82% AFUE - Incr. HX Area 38.3 284 

82% AFUE - Improved Insulation 38.2 283 

82% AFUE - Improved Heat Xfer 38.3 284 

83% AFUE - Incr. HX Area 37.9 281 

83% AFUE - Improved Insulation 37.8 280 

83% AFUE - Improved Heat Xfer 37.9 281 

* The average summer electricity use (for the blower) is 372 kWh for all of the design options shown.
7-29

Figure 7.9.4 Annual Gas Use, Weatherized Gas Furnaces

Figure 7.9.5 Winter Electricity Use, Weatherized Gas

Furnaces 
7-30

7.9.3 Mobile Home Furnace Energy Use

The average annual energy use for each design option for mobile home furnaces is shown

in Table 7.9.3. Figure 7.9.6 shows the range of annual gas use. Figure 7.9.7 shows the range of

winter electricity consumption.

Table 7.9.3 Mobile Home Furnace Energy Use

Design Option Average Annual Gas

Use (MMBtu)

Average Winter Electricity

Use (kWh)*

75% AFUE - Baseline Model 51.0 374 

80% AFUE - Incr. HX Area 45.2 405 

80% AFUE - 2-stage Mod 44.0 415.4

81% AFUE - Incr. HX Area 44.7 400 

81% AFUE - 2-stage Mod 43.5 410.6 

82% AFUE - Incr. HX Area 44.1 395 

90% AFUE - Condensing 40.4 360 

* The average summer electricity use (for the blower) is 229 kWh for all of the design options shown.

Figure 7.9.6 Annual Gas Use, Mobile Home Furnaces
7-31

Figure 7.9.7 Winter Electricity Use, Mobile Home Furnaces
7-32

7.9.4 Oil Furnace Energy Use 

The average annual energy use for each design option for oil furnaces is shown in Table

7.9.4. The range of annual gas use for each design option is shown in Figure 7.9.8. Figure 7.9.9

show the range of winter electricity consumption. 

Table 7.9.4 Oil Furnace Energy Use

Design Option Average Annual Gas

Use

Average Winter

Electricity Use*

78% AFUE - Baseline Model 87.8 787 

80% AFUE- Incr. HX Area 85.7 768 

81% AFUE- Incr. HX Area 84.7 759 

81% AFUE Atom Burner 2-stage Mod. 82.6 870 

82% AFUE- Incr. HX Area 83.7 750

82% AFUE Atom Burner 2-stage Mod. 81.6 860 

83% AFUE- Incr. HX Area 82.7 741 

83% AFUE Atom Burner 2-stage Mod. 80.7 850 

84% AFUE- Incr. HX Area 81.7 733 

84% AFUE Atom Burner 2-stage Mod. 79.8 840 

85% AFUE- Incr. HX Area 80.8 724 

85% AFUE Atom Burner 2-stage Mod. 78.9 831 

* The average summer electricity use (for the blower) is 71 kWh.
7-33

Figure 7.9.8 Range of Annual Oil Use, Oil Furnaces

Figure 7.9.9 Range of Winter Electricity Use, Oil Furnaces
7-34

7.9.5 Gas Boiler Energy Use 

The average annual energy use for each design option for hot-water gas boilers is shown

in Table 7.9.5. The range of annual gas use for each design option is shown in Figure 7.9.10. 

Figure 7.9.11 shows the range of winter electricity consumption. 

Table 7.9.5 Hot-Water Gas Boiler Energy Use

Design Option Average Annual Gas Use

(MMBtu)

Average Winter

Electricity Use

(kWh)

80%AFUE Baseline Model 93.5 382 

81% AFUE Imp Ht Xfer / Elec. Ign 88.8 384 

81% AFUE 2-stage mod. + Indc Draft 87.4 572 

82% AFUE Imp Ht Xfer / Elec. Ign 87.7 379 

82% AFUE 2-stage mod. + Indc Draft 86.4 565

83% AFUE Imp Ht Xfer / Elec. Ign 86.7 375 

83% AFUE 2-stage mod. + Indc Draft 85.4 559

84% AFUE Imp Ht Xfer / Elec. Ign 85.7 371 

84% AFUE 2-stage mod. + Indc Draft 84.4 552 

88% AFUE 81.8 354 

91% AFUE 79.3 304 

99% AFUE 73.0 280 
7-35

Figure 7.9.10 Range of Annual Gas Use, Hot-Water Gas

Boilers

Figure 7.9.11 Range of Winter Electricity Use, Hot-Water

Gas Boilers
7-36

7.9.6 Hot-Water Oil Boiler Energy Use

The average annual household energy use for each design option for hot-water oil boilers

is shown in Table 7.9.6. The range of annual gas use for each design option is shown in Figure

7.9.12. Figure 7.9.13 shows the range of winter electricity consumption. 

Table 7.9.6 Oil Boiler Energy Use

Design Option Average Annual Gas

Use

(MMBtu)

Average Winter

Electricity Use (kWh)

80%AFUE Baseline Model 108.6 418 

81%AFUE 107.3 413 

81%AFUE Atom Burner 2-stage Mod. 105.7 625 

82%AFUE 106.0 408 

82%AFUE Atom Burner 2-stage Mod. 104.4 618 

83%AFUE 104.7 402 

83%AFUE Atom Burner 2-stage Mod. 103.2 611 

84%AFUE 103.5 398 

84%AFUE Atom Burner 2-stage Mod. 102.0 604

86%AFUE 101.1 389 

86%AFUE Atom Burner 2-stage Mod. 99.7 590 

90%AFUE 97.0 303 

95%AFUE 91.9 287 
7-37

Figure 7.9.12 Range of Annual Oil Use, Hot-Water Oil

Boilers

Figure 7.9.13 Range of Winter Electricity Use, Hot-Water Oil

Boilers
7-38

REFERENCES

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

Consumption Survey: Household Energy Consumption and Expenditures 1997, 1999.

Washington, DC. Report No. DOE/EIA-0321(97).

<http://www.eia.doe.gov/emeu/recs/recs97/publicusefiles.html>

2. Gas Appliance Manufacturers Association, Consumers' Directory of Certified Efficiency

Ratings for Residential Heating and Water Heating Equipment, including First

Supplement, April, 2002. Cortland, NY. Prepared by Intertek Testing Services.

3. Gas Appliance Manufacturers Association, Consumers' Directory of Certified Efficiency

Ratings for Residential Heating and Water Heating Equipment, including First

Supplement, April, 2001. Cortland, NY. Prepared by Intertek Testing Services.

4. Kendall, M., Appendix A - Furnace Shipments; Appendix B - Boiler. Comment # 24

submitted to Docket Number: EE-RM/STD-01-350 Shipments, April 10, 2002, GAMA.

Arlington, VA. 

5. Phillips, E., Blower Efficiency in Domestic Heating Systems, June, 1995, UNIES Ltd.

Winnipeg, Manitoba. Report No. CEA 9202 U 921. 

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

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

7. Proctor, J. and Parker, D., 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. 

8. Lindeburg, M. R., Fans and Ductwork, Chapter 20. In Mechanical Engineering

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

Professional Publications, Inc.: Belmont, CA. p. 20-23.

9. Lennox Industries Inc., Lennox Industries Engineering Data: 90UGF (Elite 90-S Upflow

Gas Furnace) Bulletin #210171., 1997. Lennox Industries Inc. 

10. Lennox Industries Inc., Lennox Engineering Data: G26 (Elite 90 Series Upflow Gas

Furnace), Bulletin #210027, 1998. Lennox Industries Inc. 

11. Lennox Industries Inc., Lennox Engineering Data: GHR26 (Elite 90 Series

Horizontal/Downflow Gas Furnace) Bulletin # 210093, 1998. Lennox Industries, Inc. 
7-39

12. Lennox Industries Inc., Lennox Engineering Data: G23 (Elite 80 Upflow Gas Furnace)

Bulletin #210026, 1998. Lennox Industries Inc. 

13. Lennox Industries Inc., Lennox Engineering Data: G40DF (Merit Series Downflow Gas

Furnace) Bulletin No. 210320., 2002. Lennox Industries, Inc. (Last accessed July, 2003).

<http://www.lennoxcommercial.com/tech_pdf/ehb_g40df_0206.pdf>

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

Upflow/Horizontal Gas Furnace) Bulletin No. 210320., 2002. Lennox Industries, Inc.

(Last accessed July, 2003).

<http://www.lennoxcommercial.com/tech_pdf/ehb_g40uh_0206.pdf>

15. American Society for Heating Refrigeration and Air-Conditioning Engineers, Method of

Testing for Annual Fuel Ultilization Efficiency of Residential Central Furnaces and

Boilers, 1993, ANSI/ASHRAE. Atlanta, GA. Report No. Standard 103-1993. 

16. Title 10, Code of Federal Regulations, Part 430- Energy Conservation Program for

Consumer Products, Appendix N to Subpart B of Part 430-Uniform Test Method for

Measuring the Energy Consumption of Furnaces and Boilers, January 1, 1999. Chapter

II.

17. Taco Inc., 110-120 Red Baron Circulators, 2003.