7-i

CHAPTER 7. ENERGY USE ANALYSIS

TABLE OF CONTENTS

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

7.2 BUILDING SAMPLE ..................................................................................................... 7-2

7.3 RESIDENTIAL BOILER ENERGY CONSUMPTION................................................. 7-5

7.3.1 Space Heating Fuel Consumption.................................................................................... 7-6

7.3.1.1 Determination of Space Heating Burner Operating Hours (BOHSH) ............ 7-6

7.3.1.2 Determination of Equipment Sizing ............................................................ 7-10

7.3.2 Water Heating Energy Consumption............................................................................. 7-10

7.3.3 Electricity Consumption ................................................................................................ 7-11

7.4 SUMMARY OF ENERGY USE RESULTS................................................................. 7-13

7.4.2 Standby Energy Consumption Results for Boilers ........................................................ 7-15

LIST OF TABLES

Table 7.1.1 Residential Boiler Product Classes Analyzed...................................................... 7-1

Table 7.2.1 Selection of RECS 2009 Records for Boilers (Replacements)............................ 7-3

Table 7.2.2 Selection of RECS 2009 Records for Boilers (New Construction)..................... 7-4

Table 7.2.3 Selection of CBECS 2003 Records for Boilers (Replacements) ......................... 7-4

Table 7.2.4 Selection of CBECS 2003 Records for Boilers (New Construction) .................. 7-5

Table 7.3.1 Range of Original Heating Energy Use based on RECS 2009 and CBECS 

2003 data for Each Boiler Product Class, MMBtu/year ...................................... 7-7

Table 7.3.2 Adjustment to AFUE Based on RWT Application.............................................. 7-8

Table 7.3.3 Range of Adjusted Heating Load for Each Boiler Product Class, 

MMBtu/year......................................................................................................... 7-9

Table 7.3.4 Range of Baseline Boiler Heating Annual Operating Hours for Each 

Boiler Product Class, hours................................................................................ 7-10

Table 7.3.5 Range of Standby Hours for Each Boiler Product Class, Hours........................ 7-12

Table 7.4.1 Average Annual Energy Consumption and Savings for Residential Boilers .... 7-14

Table 7.4.2 Average Annual Standby Consumption and Savings for Residential 

Boilers................................................................................................................ 7-15
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 

residential boilers in use in the United States and to assess the energy savings potential of 

increases in annual fuel utilization efficiency (AFUE). In contrast to the U.S. Department of 

Energy (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 boilers at specified energy efficiency 

levels across a range of climate zones, building characteristics, and heating applications.

For the calculation of the energy consumed by residential boilers, DOE considered the 

energy use associated with providing space heating and domestic water heating in either 

residential or commercial buildings.

a DOE did not include within the energy use estimates 

energy used for snow melt systems, pool or spa heating, or steam or hot water production for 

industrial or commercial processes.b The energy use analysis provides estimates of the 

distribution of annual energy consumption for boilers at the efficiency standard levels 

considered.

DOE developed energy consumption estimates for the key product classes listed in Table 

7.1.1. The boilers analyzed utilize gas or oil fuel for heating water or steam and the associated 

electric energy to power a water pump, a draft inducer, an ignitor, and other auxiliary equipment. 

Standby energy use is calculated for all product classes mentioned in Table 7.1.1 and also for 

electric hot water and electric steam boilers. 

Table 7.1.1 Residential Boiler Product Classes Analyzed

Gas-Fired Hot Water Boilers

Gas-Fired Steam Boilers

Oil-Fired Hot Water Boilers

Oil-Fired Steam Boilers

DOE estimated the energy consumption of boilers in housing units and commercial 

buildings by developing a building sample for each of the four product classes based on the 

Energy Information Administration’s (EIA) 2009 Residential Energy Consumption Survey 

(RECS 2009) and on EIA’s 2003 Commercial Building Energy Consumption Survey (CBECS 

 a Space heating applications for residential boilers include radiant heating (In-floor, radiant panels, radiators, 

baseboard) and forced air using fan coils or central air handlers. Domestic water heating applications for residential 

boilers include indirect water heating, combination equipment, and tankless coil. 

b Examples of industrial and/or commercial processes include car washes, steam for dry cleaning, restaurant water 

heating, manufacturing, etc.
7-2

2003).1, 2 These are the latest available surveys for residential and commercial buildings.c This 

sample is further described in section 7.2.

DOE used the RECS 2009 or CBECS 2003 reported heating energy consumption (based 

on the existing heating system) to calculate the space heating load of each household or building. 

The heating load represents the amount of heating required to keep a housing unit comfortable 

throughout an average year. In households or buildings in which DOE identified that the boiler 

also serves domestic hot water heating needs, DOE used the RECS 2009 or CBECS 2003 

reported water heating energy (based on the existing heating system) to calculate the water 

heating load of each household or building.

DOE assigned the energy efficiency of existing systems based on the design of the 

distribution systems (heating application), a historical distribution of energy efficiencies for 

boilers, and data with respect to the age of the existing boiler. In addition, DOE made 

adjustments based on historical weather data, average return water temperature, projections of 

shell efficiency and building square footage, and for homes that had secondary heating 

equipment that used the same fuel as the boiler. To complete the analysis, DOE calculated the 

energy consumption of alternative (more energy-efficient) products, if they replaced existing 

systems in each housing unit or commercial building.

7.2 BUILDING SAMPLE

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

Energy Information Administration’s (EIA) RECS 2009 and CBECS 2003.

1, 2 The RECS 2009

included energy-related data from 12,083 housing units that represent almost 113.6 million 

households. The CBECS 2003 included energy-related data from 5,215 buildings representing 

4.9 million buildings. 

The subset RECS 2009 or CBECS 2003 records used in the analysis met all of the 

following criteria:

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

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

oil; and

• had a heating energy consumption greater than zero.

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

use one of the boiler product classes (Table 7.2.1 and Table 7.2.2 for residential applications and 

Table 7.2.3 and Table 7.2.4 for commercial applications). The new construction sample includes 

only buildings built after 1990, which DOE believes would have more similar building 

 c EIA is currently working on the 2013 version of RECS, which is not expected to be available until 2015. 

Additionally, EIA determined that the 2007 Commercial Buildings Energy Consumption Survey did not yield valid 

statistical estimates of building counts, energy characteristics, consumption and expenditures and therefore did not 

release the majority of the data tables and public use files.
7-3

characteristics to the new construction buildings in 2020 (e.g. building insulation, regional 

distribution of the buildings, and so on).

The RECS 2009 and CBECS 2003 weighting indicates how commonly each household or 

commercial building configuration occurs in the general population in 2009 and 2003, 

respectively. DOE adjusted EIA’s weightings for each RECS 2009 and CBECS 2003 household

to create boiler population weights in 2020 by accounting for the fraction of boilers that produce 

steam compared to hot water, buildings with multiple boilers, and projected growth of the 

number of boilers by 2020. Appendix 7-A presents the variables included and their definitions, 

as well as further information about the derivation of the household and building samples, the 

adjustments to the boiler population weights, and sampling fractions for each of the four samples 

(residential (new construction and replacement) and commercial (new construction and 

replacement)). 

To sample between the residential and commercial samples, DOE used the shipments 

model described in chapter 9 to estimate that 7 percent of residential boiler shipments will be 

installed in commercial buildings. To sample between the new construction and replacement

markets, DOE estimated that the new construction market accounts for 20 percent of gas-fired 

hot water boilers, 0 percent of gas-fired steam boilers, 5 percent of oil-fired hot water boilers, 

and 0 percent of oil-fired steam boilers.

Table 7.2.1 Selection of RECS 2009 Records for Boilers (Replacements)

Product Class Algorithm No. of 

Records

RECS 

2009

DOE 

2020

Number 

of 

Houses 

million

Number 

of Boilers 

million

Gas-Fired Hot Water Boiler Heating Equipment = Gas Boilerd

Heated Square footage <10,000 sq ft

646 6.05 4.12

Gas-Fired Steam Boiler

Heating Equipment = Gas Boiler

House Built = before 1970

Heated Square footage <10,000 sq ft

471 4.55 0.49

Oil-Fired Hot Water Boiler Heating Equipment = Oil Boiler

Heated Square footage <10,000 sq ft

482 3.99 2.63

Oil-Fired Steam Boiler

Heating Equipment = Oil Boiler

House Built = before 1970

Heated Square footage <10,000 sq ft

359 3.08 0.31

Electric Hot Water or Steam 

Boilere

Heating Equipment = Electric Boiler

Heated Square footage <10,000 sq ft

49 0.49 0.26

 d Natural Gas or LPG Boiler.

e The sample is assumed to be the same for both hot water and steam electric boilers
7-4

Table 7.2.2 Selection of RECS 2009 Records for Boilers (New Construction)

Product Class Algorithm No. of 

Records

RECS 

2009

DOE 

2020

Number 

of 

Houses 

million

Number 

of Boilers 

million

Gas-Fired Hot Water Boiler

Heating Equipment = Gas Boiler

Heated Square footage <10,000 sq ft

House Age >= 1990

51 0.50 0.44

Gas-Fired Steam Boiler NAf 0 0.00 0.00

Oil-Fired Hot Water Boiler

Heating Equipment = Oil Boiler

Heated Square footage <10,000 sq ft

House Age >= 1990

49 0.33 0.26

Oil-Fired Steam Boiler NA 0 0.00 0.00

Electric Hot Water or Steam 

Boiler

Heating Equipment = Electric Boiler

Heated Square footage <10,000 sq ft

House Age >= 1990

4* 0.05 0.05

*Note: Used electric boiler replacement sample instead due to the low number of households (4 households does not 

constitute a representative sample)

Table 7.2.3 Selection of CBECS 2003 Records for Boilers (Replacements)

Product Class Algorithm No. of 

Records

CBECS 

2003

DOE 2020

Number of 

Buildings 

million

Number 

of Boilers 

million

Gas-Fired Hot Water Boiler Heating Equipment = Gas Boilerg

Heated Square footage <10,000 sq ft

286 0.26 0.29

Gas-Fired Steam Boiler

Heating Equipment = Gas Boiler

Building Built = before 1970

Heated Square footage <10,000 sq ft

193 0.19 0.03

Oil-Fired Hot Water Boiler Heating Equipment = Oil Boiler

Heated Square footage <10,000 sq ft

75 0.11 0.11

Oil-Fired Steam Boiler

Heating Equipment = Oil Boiler

Building Built = before 1970

Heated Square footage <10,000 sq ft

60 0.09 0.01

Electric Hot Water or Steam 

Boiler

Heating Equipment = Electric Boiler

Heated Square footage <10,000 sq ft

138 0.10 0.13

 f DOE assumed that there are no steam boilers in the new construction market.

g Natural Gas or LPG Boiler.
7-5

Table 7.2.4 Selection of CBECS 2003 Records for Boilers (New Construction)

Product Class Algorithm No. of 

Records

CBECS 

2009

DOE 2020

Number of 

Buildings 

million

Number of 

Boilers 

million

Gas-Fired Hot Water Boiler

Heating Equipment = Gas Boiler

Heated Square footage <10,000 sq ft

Building Age >= 1990

31 0.02 0.05

Gas-Fired Steam Boiler NAh 0 0.00 0.00

Oil-Fired Hot Water Boiler

Heating Equipment = Oil Boiler

Heated Square footage <10,000 sq ft

Building Age >= 1990

10 0.02 0.02

Oil-Fired Steam Boiler NA 0 0.00 0.00

Electric Hot Water or Steam 

Boiler

Heating Equipment = Electric Boiler

Heated Square footage <10,000 sq ft

Building Age >= 1990

24 0.02 0.02

7.3 RESIDENTIAL BOILER ENERGY CONSUMPTION

To calculate the energy use of residential boilers in each of the product classes, DOE 

determined the energy consumption associate with space heating, water heating and any 

auxiliary electrical use during the periods of heating (space and water). For the space heating 

energy consumption determination, DOE estimated the input capacity and burner operational 

hours of the existing boiler using building heating loads and boiler characteristics. For the 

domestic water heating energy consumption determination, DOE identified the building water 

heating load and the AFUE of the existing boiler. 

The electrical consumption was determined using the burner operating hours associated 

with space and water heating and individual electrical measurements of all electrical 

components. Standby electrical consumption was also considered in the electrical energy use. 

The sum of the space heating, water heating and electrical energy consumptions represents the 

estimated annual energy use of a sampled boiler. Additional details used for determining the total 

energy use can be found in the following sections.

The calculation used for the determination of the total energy use is as follows:

Total Energy Use = FuelUseSH + FuelUseWH + ElecUse

Eq. 7.3.1

Where:

FuelUseSH= total fuel consumption as a result of space heating loads,

FuelUseWH= total fuel consumption as a result of water heating loads, and

 h DOE assumed that there are no steam boilers in the new construction market.
7-6

ElecUse = electrical consumption of all electrical components.

7.3.1 Space Heating Fuel Consumption

The Department calculated the annual fuel consumption (FuelUse) for each single-stage

boiler using the following formula from the current American Society of Heating, Refrigerating 

and Air-Conditioning Engineers (ASHRAE) test procedure SPC 103-2007 section C:i,j

FuelUseSH = BOHSH × QIN

Eq. 7.3.2

Where:

BOHSH = space heating burner operating hours (hr/yr), and

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

DOE derived BOH from the building heating load served by a single boiler. Building heating 

load was determined from annual fuel consumption for heating reported in RECS and CBECS 

based on the AFUE of the existing boiler.

7.3.1.1 Determination of Space Heating Burner Operating Hours (BOHSH)

DOE calculated space heating burner operating hours for a single-stage boiler are:

BOHSH = BHLBOILER

QUseful

Eq. 7.3.3

Where:

QUseful = total useful energy output of the boiler equipment, including useful heat from auxiliary 

electrical components (kBtu/hr), and

BHLBOILER = building heating load served by a single boiler (kBtu/yr).

The total useful energy output (QUseful) includes the output heating capacity of the boiler 

as well as useful heat from auxiliary electrical components (such as the electronic ignition, water 

pump, and power to the burner) during the periods of space heating. See appendix 7-B for more 

details.

The annual building-heating load (BHLBoiler) is the total amount of heat output from the 

boiler that the house or building needs during the heating season.k This includes heat from the 

 i

This formula assumes that the equipment does not have a pilot light, which is true for all residential boilers sold 

after September 2012.

j

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

reduced load.
7-7

burner and heat from the other electrical components. DOE determined BHLTotal for each 

sampled housing unit or building, based on the efficiency of the assigned existing boiler, using 

the following calculations:

BHLBoiler = �QYR×AFUEex,adj�×Adj_Factor(s)

BoilerCount

Eq. 7.3.4

Where:

QYR = annual fuel consumption for heating based on RECS 2009 or CBECS 2003 (kBtu/yr),

AFUEex,adj = AFUE of the existing boiler (AFUEex) adjusted for return water temperaturel

(see 

appendix 7-B),

Adj_Factor = adjustment factors (discussed below), and

BoilerCount = number of boilers used to fulfill the building heating load.

Both RECS 2009 and CBECS 2003 report space heating energy use (QYR) for each of the 

sampled buildings. Table 7.3.1 shows the original RECS 2009 and CBECS 2003 heating energy 

use. 

Table 7.3.1 Range of Original Heating Energy Use based on RECS 2009 and CBECS 

2003 data for Each Boiler Product Class, MMBtu/year

Product Class Min Max Average

Percentiles

5% 25% 50% 75% 95%

Gas-Fired Hot Water Boilers 0.1 4725.4 92.7 21.3 52.7 73.8 104.7 197.7

Gas-Fired Steam Boilers 0.5 3833.7 98.6 28.3 59.4 79.1 113.7 193.8

Oil-Fired Hot Water Boilers 0.0 2219.0 93.7 30.2 51.4 71.2 109.7 189.7

Oil-Fired Steam Boilers 0.0 2219.0 98.1 28.3 50.3 69.4 114.0 216.8

Electric Hot Water Boilers 0.0 364.3 15.5 3.1 7.7 11.7 19.9 39.5

Electric Steam Boilers 0.0 364.3 15.5 3.1 7.7 11.7 19.9 39.5

The AFUE of the existing boiler (AFUEex) is determined by matching historical AFUE to 

the data to the reported age of the boiler in RECS 2009 or distribution of boiler age for CBECS 

2003 buildings.m DOE adjusted the AFUE of existing boilers to reflect the variability of 

efficiency in various hydronic space heating applications. This adjustment is the result of DOE 

associating a specific space heating application with each sampled household or building. The 

 k BHL is the load served by a single boiler. DOE made the assumption that some of the building structures would be 

served by multiple residentially sized boilers based on RECS data, heating load of the building exceeds 300 Btu/h, 

and/or the application (such as multi-family and commercial applications). l

Return water temperature represents the average annual return water temperature for the different space heating 

applications.

m CBECS 2003 does not report the age of the equipment, so DOE created a uniform distribution to estimate the age 

of the equipment.
7-8

AFUE of the existing boilers was adjusted up or down depending on the selected return water

temperature (RWT) application. Appendix 7-B provides additional detail regarding the 

derivation of the adjustment values.

Table 7.3.2 provides the adjustment values based on RWT application type. High RWT is 

applied to 100 percent of non-condensing boiler installations. For condensing boiler installations 

Low RWT is applied to 100 percent of new construction, 50 percent of replacement buildings 

built after 1990, and to 10 percent of replacement buildings built before 1990. DOE assumes that 

all other condensing boiler installations would be in High RWT applications.

Table 7.3.2 Adjustment to AFUE Based on RWT Application

Low RWT (100°F) Medium RWT (120°F)n High RWT (150°F)

Non-Condensing Not Applicable As reported -0.6%

Condensing +3% As reported -3%

DOE made adjustments to the BHL to reflect the expectation that the buildings in 2020

will have a somewhat different BHL than the buildings in the RECS 2009 and CBECS 2003 

boiler sample. The adjustment involves multiplying the calculated BHL for each RECS 2009 or 

CBECS 2003 building by the building shell efficiency indexo based on information from the 

National Energy Modeling System (NEMS) simulation performed for EIA’s Annual Energy 

Outlook (AEO 2013).

3 This factor differs for residential and commercial buildings as well as new 

construction and replacement buildings. The factor applied in the analysis for residential 

buildings is 0.93 for replacements and 1.03 for new construction, while for commercial buildings 

it ranged from 0.74 to 0.98 for replacements (depending on building type) and 0.89 for new 

construction. This means that buildings on average will have lower space heating load compared 

to residential buildings in 2009 or commercial buildings in 2003, except for new construction 

residential buildings.

DOE also made adjustments to the BHLTOTAL calculated using heating degree days 

reported in RECS 2009 and CBECS 2003 for each building, National Oceanic and Atmospheric 

Administration (NOAA) data by region to reflect historical average climate conditions. The 

adjustment factors are calculated using the following equation:

AdjFactoraverageclimate = HDD10_yr_avg

HDDbldg_2009

Eq. 7.3.5

Where:

 n Medium water temperature of 120°F is assumed to be equivalent to the test conditions specified in the DOE AFUE 

test.

o The building shell efficiency index sets the heating load value at 1.00 for an average home in 2009 (by type) in 

each census division. The values listed below 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).
7-9

HDDbldg_2009 = HDD in 2009 for the specific region where the housing unit is located, and

HDD10_yr_avg = 10-year average HDD (2003–2012) based on National Oceanic and Atmospheric 

Administration (NOAA) data4 for the specific region where the housing unit is located.p

The adjustment factors for residential buildings range from 0.91 to 1.02 and on average 

0.95 for the boiler building sample (i.e., 2009 was in general colder than an the 10-year average).

DOE also account for future climate trends based on AEO 2013 HDD projections.

3

DOE determined that some of the sampled buildings used multiple heating equipment 

with the same fuel as the boiler(s), such as a central furnace, wall furnace, room heater, stove, or 

fireplace. Therefore, DOE adjusted the calculated BHL when necessary to reflect the use of 

secondary heating equipment using the same fuel as the boiler(s). The adjustment factors are 

calculated using reported survey information from both RECS 2009 and CBECS 2003 regarding 

the fraction of heating that was met by different heating equipment.

Table 7.3.3 shows the results for the range in adjusted heating load among sample 

households and buildings.

Table 7.3.3 Range of Adjusted Heating Load for Each Boiler Product Class, 

MMBtu/year

Product Class Min Max Average

Percentiles

5% 25% 50% 75% 95%

Gas-Fired Hot Water Boilers 0.0 2896.3 61.2 14.2 34.4 49.3 70.8 127.0

Gas-Fired Steam Boilers 0.3 2160.5 59.9 15.1 35.6 49.6 68.6 118.2

Oil-Fired Hot Water Boilers 0.0 1604.1 63.5 19.1 34.9 48.3 74.0 128.7

Oil-Fired Steam Boilers 0.0 1604.1 63.8 17.0 31.9 44.6 74.4 133.8

Electric Hot Water Boilers 0.0 289.9 8.5 1.2 2.9 7.5 10.3 20.8

Electric Steam Boilers 0.0 289.9 8.5 1.2 2.9 7.5 10.3 20.8

Table 7.3.4 shows the results for the baseline heating boiler operating hours among 

sample households and buildings.

 p The last 10-year average is used to normalize the HDD values, which is similar to what is done in AEO 2013.
7-10

Table 7.3.4 Range of Baseline Boiler Heating Annual Operating Hours for Each 

Boiler Product Class, hours

Product Class Min Max Average

Percentiles

5% 25% 50% 75% 95%

Gas-Fired Hot Water 

Boilers 0.2 8760.0 515.7 152.4 286.1 412.5 634.6 1082.3

Gas-Fired Steam Boilers 1.4 8760.0 466.1 127.0 266.7 372.0 562.7 1105.2

Oil-Fired Hot Water 

Boilers 0.1 6383.5 455.8 115.9 268.1 385.4 525.8 1049.6

Oil-Fired Steam Boilers 0.1 6497.0 447.3 83.7 250.1 365.8 507.4 1118.2

7.3.1.2 Determination of Equipment Sizing

To support calculation of space heating energy use, DOE had to establish a methodology 

for deriving the boiler capacities of each of the sampled buildings. The Department calculated 

the input capacity for the existing boiler of each housing/building unit based on information 

derived from the RECS and CBECs data. The sizing approach determines the input capacity of 

the sampled household/building by accounting for building characteristics that include the 

building square footage, building vintage, foundation type, shell characteristics, number of 

floors, outdoor design temperature and two factors that correct the building heating loss. 

These characteristics are needed to estimate the building total heat loss. DOE utilized 

information from several boiler manufacturers and distributors to develop a methodology to 

derive the heat loss per square foot. Using the total heat loss value, DOE identified boiler models 

with an output capacity capable of meeting the calculated heat loss of the home. Appendix 7-B 

presents the variables used as well as further information about the building characteristics and 

heat loss values used for the sizing of boiler equipment.

Qin = AdjustedHeatLoss

AFUEbaseline

Eq. 7.3.6

Where:

AdjustedHeatLoss = estimated building heat loss adjusted for building characteristics (kBtu/h),

AFUEbaseline = AFUE of the baseline boiler for each product class, for example, 82 percent AFUE 

for gas-fired hot water boilers (see appendix 7-B).

7.3.2 Water Heating Energy Consumption

Boilers are often used to provide hot water in addition to space heating. The most 

common means of doing so are through an indirect water heater, tankless coil, or as an integrated 

part of the boiler. 
7-11

RECS 2009 and CBECS 2003 do not provide any information about when a boiler is 

used to provide hot water. DOE assumed that 50 percent of the installations in buildings 

reported in RECS or CBECS to use the same fuel for both space and water heating also use 

boilers for water heating, except when RECS reports the use of tankless water heating in which 

case DOE assumed that 100 percent would be serviced by a boiler.q

To calculate the water heating energy use, DOE calculated the boiler fuel use for water 

heating for each efficiency level based on the following equation:

FuelUseWH = WHL × (AFUE − Adj_FactorWH)

Eq. 7.3.7

Where:

WHL = water heating energy use based on RECS 2009 or CBECS 2003,

AFUE = AFUE of the selected efficiency level, and

Adj_FactorWH = adjustment factor to take into account difference between AFUE and recovery 

efficiency for water heating (assumed to be -2%).

DOE used the following equation to calculate the water heating load (WHL):

WHL = �QYR,HW × (AFUEex − Adj_FactorWH)�

Eq. 7.3.8

Where:

QYR,HW = annual fuel consumption for water heating based on RECS 2009 or CBECS 2003 

(kBtu/yr),

AFUEex = AFUE of the existing boiler (see appendix 7-B), and

Adj_FactorWH = as defined previously.

7.3.3 Electricity Consumption

The Department calculated boiler electricity consumption for the circulating pump, the 

draft inducer, and the ignitor.r The circulating pump moves water through the house whenever 

the boiler burner is on (adjusted for delay times between burner and pump operation). It also 

operates in the cooling season (summer) if there is a call for water heating (only in instances 

where the boiler also serves the home’s or building’s water heating loads). In the case of 

modulating condensing boilers, in order to accommodate for lower firing rates, the inducer will 

provide lower combustion airflow to regulate the excess air in the combustion process. DOE has 

assumed that modulating condensing boilers are equipped with inducer fans with PSC motors

and two-stage controls. Low-firing operation corresponds to a firing input rate of 90% or less of 

 q DOE believes that almost all the RECS households that reported a tankless water heater together with a boiler 

actually are using the boiler to provide water heating either as a tankless coil or other combination unit type. r The DOE and ASHRAE test procedures do not count the electricity used by controls when the boiler is not firing.
7-12

the full input capacity. The inducers are assumed to run at 70% airflow rate when the modulating 

unit operates at low-fire. DOE also took into account the electricity consumption of such 

auxiliary equipment as condensate pumps and heat tape, which are sometimes installed with 

higher efficiency equipment. For single-stage boilers, the Department calculated the electricity 

consumption as: s

ElecUseTOTAL = (BOHSH + BOHWH) × CompE + ElecUseStby

Eq. 7.3.9

Where:

BOHSH = as defined previously,

BOHWH = as defined previously,

CompE = power of multiple electrical components required during boiler operation, (kW) (refer 

to the test procedure variables detailed in Appendix 7-B), and

ElecUseStby = energy consumption during standby (kWh).

For the standby and off mode evaluation, the Department calculated the standby 

electricity consumption as:

ElecUseStby = StbyE × (8760 − BOHSS + BOHWH)

Eq. 7.3.10

Where:

BOHSH = as defined previously,

BOHWH = as defined previously, and 

StbyE = power consumption during standby (kW).

Table 7.3.5 summarizes the standby hour results.

Table 7.3.5 Range of Standby Hours for Each Boiler Product Class, Hours

Product Class Min Max Average

Percentiles

5% 25% 50% 75% 95%

Gas-Fired Hot Water 

Boilers 3584.3 8759.8 8267.0 7720.5 8145.1 8362.8 8480.9 8613.3

Gas-Fired Steam Boilers 2992.7 8758.7 8313.4 7693.4 8219.5 8405.5 8504.1 8639.7

Oil-Fired Hot Water 

Boilers 4068.5 8759.9 8323.4 7766.6 8250.9 8389.8 8501.2 8648.4

Oil-Fired Steam Boilers 4036.7 8759.9 8332.7 7691.4 8269.3 8408.4 8520.9 8679.7

Electric Hot Water 

Boiler 916.1 8760.0 6518.8 4045.3 5719.5 6507.3 7906.0 8407.0

Electric Stem Boilers 916.1 8760.0 6518.8 4045.3 5719.5 6507.3 7906.0 8407.0

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

and reduced load. See appendix 7-B.
7-13

Some higher efficiency installations require the use of auxiliary equipment such as 

condensate pumps and heat tape. The electricity consumption of this equipment is calculated by 

DOE and added to the total electricity consumption. If a household required a condensate pump, 

DOE assumed that it consumed 60 watts and operated at the same time as the burner. If a 

household required heat tape to prevent the condensate pipe from freezing, Details of how DOE 

determined whether a household required a condensate pump can be found in appendix 8-D.

Further details for calculating electricity consumption appear in appendix 7-B.

7.4 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 

boiler product class. The results reflect energy use in both the residential and commercial 

samples.t

The LCC and PBP analysis uses the results calculated for each sample building.

 t

Residential boilers used commercial applications account for 7 percent of the building sample. See Appendix 9-B.
7-14

Table 7.4.1 Average Annual Energy Consumption and Savings for Residential 

Boilers

Design Option

Annual Fuel Use

Annual Electricity 

Consumption of

Auxiliary 

Components 

Total Savings Total Savings

MMBtu/yr MMBtu/yr kWh/yr kWh/yr

Gas-fired Hot Water Boiler

0 82% AFUE - Baseline 88.7 - 202.8 -

1 83% AFUE – Increased HX Area 87.6 1.1 209.3 -6.6

2 84% AFUE – Increased HX Area 86.6 2.1 206.4 -3.6

3 85% AFUE – Increased HX Area 85.5 3.1 221.5 -18.7

4 90% AFUE – Condensing Baseline 80.4 8.2 302.3 -99.5

5 92% AFUE – Increased HX Area 79.4 9.3 298.5 -95.7

6 96% AFUE – Max Tech 76.1 12.6 294.3 -91.5

Gas-fired Steam Boiler

0 80% AFUE - Baseline 86.4 - 153.5 -

1 82% AFUE – Increased HX Area 84.3 2.1 154.0 -0.6

2 83% AFUE – Max Tech 83.3 3.1 154.6 -1.1

Oil-fired Hot Water Boiler

0 84% AFUE - Baseline 84.2 - 273.4 -

1 85% AFUE – Increased HX Area 83.2 1.0 265.7 7.8

2 86% AFUE – Increased HX Area 82.3 1.9 259.0 14.4

3 91% AFUE – Max Tech 78.7 5.5 287.4 -14.0

Oil-fired Steam Boiler

0 82% AFUE - Baseline 86.1 - 245.3 -

1 84% AFUE – Increased HX Area 84.0 2.0 242.6 2.7

2 85% AFUE – Increased HX Area 83.0 3.0 238.3 7.0

3 86% AFUE – Max Tech 82.1 4.0 239.1 6.2
7-15

7.4.2 Standby Energy Consumption Results for Boilers

Table 7.4.2 shows the average annual standby energy use for boilers and the average 

energy savings for each energy efficiency level, compared to the baseline.

Table 7.4.2 Average Annual Standby Consumption and Savings for Residential 

Boilers

EL Design Option

Annual Electricity Consumption for 

Standby

Total Savings

kWh/yr kWh/yr

Gas-fired Hot Water Boiler

0 Baseline 119.0

1 Linear PS, Toroidal Xfmr 107.1 11.9

2 Switch Mode PS 104.7 14.3

3 SMPS, Toroidal Xfmr 99.1 7.9

Gas-fired Steam Boiler

0 Baseline 124.5

1 Linear PS, Toroidal Xfmr 112.1 12.5

2 Switch Mode PS 109.6 14.9

3 SMPS, Toroidal Xfmr 103.8 8.3

Oil-fired Hot Water Boiler

0 Baseline 124.2

1 Linear PS, Toroidal Xfmr 111.8 12.4

2 Switch Mode PS 109.3 14.9

3 SMPS, Toroidal Xfmr 103.5 8.3

Oil-fired Steam Boiler

0 Baseline 124.3

1 Linear PS, Toroidal Xfmr 111.8 12.4

2 Switch Mode PS 109.3 14.9

3 SMPS, Toroidal Xfmr 103.5 8.3

Electric Hot Water Boiler

0 Baseline 104.1

1 Linear PS, Toroidal Xfmr 91.1 13.0

2 Switch Mode PS 88.5 15.6

3 SMPS, Toroidal Xfmr 82.4 6.1

Electric Steam Boiler

0 Baseline 104.1

1 Linear PS, Toroidal Xfmr 91.1 13.0

2 Switch Mode PS 88.5 15.6

3 SMPS, Toroidal Xfmr 82.4 6.1
7-16

REFERENCES

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

Consumption Survey: 2009 RECS Survey Data, 2013. (Last accessed March, 2013.) 

<http://www.eia.gov/consumption/residential/data/2009/>

2. U.S. Department of Energy: Energy Information Administration, Commercial Buildings 

Energy Consumption Survey, 2003. (Last accessed September, 2013.) 

<http://www.eia.doe.gov/emeu/cbecs/>

3. Energy Information Administration, Annual Energy Outlook 2013 with Projections to 

2040, 2013. Washington, DC. <http://www.eia.gov/forecasts/aeo/pdf/0383(2013).pdf>

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

accessed March 15, 2013.) <www7.ncdc.noaa.gov/CDO/CDODivisionalSelect.jsp>