8-H-1

APPENDIX 8-H. BASE CASE DISTRIBUTION OF EFFICIENCY LEVELS

TABLE OF CONTENTS

8-H.1 INTRODUCTION ................................................................................................ 8-H-2

8-H.2 HISTORICAL EFFICIENCY DISTRIBUTIONS ............................................... 8-H-2

8-H.2.1 Energy Star Data ................................................................................................... 8-H-2

8-H.3 ESTIMATE OF 2013 EFFICIENCY DISTRIBUTIONS BY PRODUCT 

CLASS AND EFFICIENCY LEVEL................................................................... 8-H-3

8-H.4 PROJECTED MARKET SHARES FROM 2013 TO 2020 AND BEYOND...... 8-H-7

8-H.4.1 Condensing Unit Market Share............................................................................. 8-H-7

8-H.5 ESTIMATE OF 2020 EFFICIENCY DISTRIBUTIONS BY PRODUCT 

CLASS .................................................................................................................. 8-H-9

8-H.5.2 Gas-fired Hot Water Boiler Condensing Fraction by Region............................. 8-H-10

LIST OF TABLES

Table 8-H.2.1 Market Penetrations of Energy Star Qualified Residential Boilers...........8-H-3

Table 8-H.3.2 Fraction of Residential Boiler Models in 2013 by AFUE .........................8-H-4

Table 8-H.3.3 Fraction of Residential Boiler Models in 2013 by Efficiency Level.........8-H-5

Table 8-H.3.4 Distribution of Residential Boiler Efficiency in 2013 ...............................8-H-6

Table 8-H.5.5 Base Case Distribution of Residential Boiler Efficiency in 2020..............8-H-9

Table 8-H.5.6 Fraction of Condensing Gas-fired Hot Water Boiler Shipments in 2020 

by Census Division ..................................................................................8-H-10

LIST OF FIGURES

Figure 8-H.4.1 Historical Data and Projection of Base Case Market Share for 

Condensing Gas-fired Hot Water Residential Boilers...............................8-H-8

Figure 8-H.4.2 Projection of Base Case Market Share for Condensing Oil-fired Hot 

Water Residential Boilers..........................................................................8-H-8
8-H-2

APPENDIX 8-H. BASE CASE DISTRIBUTION OF EFFICIENCY LEVELS

8-H.1 INTRODUCTION

The Department of Energy (DOE) derived base case efficiency distributions of efficiency 

levels by product class, which recognizes that consumers already purchasing products at 

efficiencies greater than or equal to a prospective standard level are not impacted by the 

standard. This appendix describes the distributions used.

DOE did not have access to sales data describing the actual distribution of efficiencies in 

current sales, nor was such information provided by industry for this rulemaking. As a 

consequence, DOE developed estimates of the distribution of AFUE levels for each of the four 

residential boiler product classes: gas-fired hot water boiler, gas-fired steam boiler, oil-fired hot 

water boiler, and oil-fired steam boiler. The development of these distributions was based on the 

following key data inputs:

• From Energy Star data, the average fraction of Energy Star shipments for gas and oilfired boilers from 2003 - 2012.

1

• Number of shipments that are hot water vs. steam.

2

• AHRI Directory of Certified Product Performance, which allowed review of specific 

efficiencies sold into the market for each product class.

3

8-H.2 HISTORICAL EFFICIENCY DISTRIBUTIONS

8-H.2.1 Energy Star Data

The Energy Star program for residential boilers started on April 1, 2002,

4 and 

performance criteria for Energy Star boilers was set at 85% AFUE. Table 8-H.2.1 shows the 

market penetrations of Energy Star qualified residential boilers from 2003-2012. Some of the 

growth in higher efficiency boilers has been due to incentive programs (e.g. Federal tax 

incentives, State, and utility incentives). Federal tax credits started in 2005 and remain in effect

until 12/31/2013.

5

Since there are no gas-fired steam boilers with greater than 85% AFUE, DOE estimated 

that steam boilers account for 0 percent of the Energy Star qualified gas-fired boilers in the 

period from 2003 to 2012. DOE also estimated that 94.6% of oil-fired boilers that qualified the 

Energy Star performance criteria are hot water boilers, based on the AHRI model directory of 

oil-fired boilers’ model fractions by AFUE in 2013 shown in Table 8-H.3.2. The gas-fired and 

oil-fired boilers’ shipments that qualify the current Energy Star performance criteria were 

adjusted by the response rate. The adjusted Energy Star shipments, estimated historical 

shipments, and the disaggregated market shares of boilers are summarized in Table 8-H.2.1.
8-H-3

Table 8-H.2.1 Market Penetrations of Energy Star Qualified Residential Boilers

Adjusted Energy Star Shipment Estimated Shipments Adjusted Market penetration

Year Gas Boiler Oil Boiler HWGB SGB HWOB SOB HWGB SGB HWOB SOB

2003 113,216 61,733 239,843 38,105 169,680 17,706 47.2% 0.0% 34.4% 19.0%

2004 106,667 127,778 264,588 36,846 167,444 19,460 40.3% 0.0% 72.2% 35.7%

2005 68,014 103,005 252,465 37,127 152,742 17,256 26.9% 0.0% 63.8% 32.5%

2006 84,077 104,528 229,231 30,243 127,531 16,016 36.7% 0.0% 77.5% 35.5%

2007 76,309 99,226 232,969 33,932 130,301 15,494 32.8% 0.0% 72.0% 34.8%

2008 115,374 79,106 259,742 32,374 132,785 11,061 44.4% 0.0% 56.3% 38.9%

2009 88,000 76,000 204,370 23,540 98,626 9,616 43.1% 0.0% 72.9% 43.0%

2010 102,041 76,531 208,711 21,957 106,340 9,951 48.9% 0.0% 68.1% 41.8%

2011 88,172 68,817 218,112 25,615 99,611 9,084 40.4% 0.0% 65.3% 41.2%

2012 111,224 58,163 246,590 28,516 84,952 7,483 45.1% 0.0% 64.7% 42.3%

5-year average 100,962 71,723 227,505 26,400 104,463 9,439 44.4% 0.0% 65.5% 41.4%

8-H.3 ESTIMATE OF 2013 EFFICIENCY DISTRIBUTIONS BY PRODUCT 

CLASS AND EFFICIENCY LEVEL

DOE developed data on the share of models in each product class that are of the different 

designs based on the latest AHRI certification directory and additional models for non-AHRI 

member manufacturers from CEC, Energy Star, and NRCAN boiler certification directories 3, 6,7

shown in Table 8-H.3.2. See Appendix 7D for a full description on the development of the 

reduced set of models DOE used.
8-H-4

Table 8-H.3.2 Fraction of Residential Boiler Models in 2013 by AFUE 

AFUE

Gas-Fired 

Hot Water

Gas-Fired 

Steam

Gas-Fired 

Hot Water

Oil-Fired 

Steam

80 0.0%

81 27.7%

82 19.7% 61.4% 22.6%

83 10.2% 10.8% 23.7%

84 11.6% 20.2% 29.0%

85 15.1% 32.9% 18.3%

86 0.9% 31.9% 6.5%

87 0.2% 9.4%

88 0.9% 1.2%

89 0.0% 0.4%

90 10.7% 2.2%

91 4.0% 1.4%

92 2.6% 0.0%

93 8.3% 0.4%

94 3.1%

95 12.4%

96 0.3%

Energy Star

Qualified (>85) 58.4% 0.0% 79.8% 24.7%

To create the fractions of boilers by efficiency levels, DOE used the following criteria to 

process the AHRI model directory data:

1. The 90% AFUE bin of gas-fired hot water boilers includes 90%-91% models

2. The 92% AFUE bin of gas-fired hot water boilers includes 92%-94% AFUE and 50% of 

95% AFUE models

3. The 96% AFUE bin of gas-fired hot water boilers includes 96% AFUE and above and 

50% of 95% AFUE models

4. The 81% AFUE models of gas-fired steam boilers are split 50/50 between the 80% and 

82% AFUE bin

5. The 90% AFUE bin of oil-fired hot water boilers include both 90% and 91% AFUE

models

6. The 83% AFUE models of oil-fired steam boilers are split 50/50 between the 82% and 

84% AFUE bin.

Table 8-H.3.4 shows the adjusted fractions of residential boiler models by efficiency 

level in 2013.
8-H-5

Table 8-H.3.3 Fraction of Residential Boiler Models in 2013 by Efficiency Level 

EL Design Option Fraction of Models

Gas-fired Hot Water Boiler

0 82% AFUE – Baseline 19.7%

1 83% AFUE – Increased HX Area 10.2%

2 84% AFUE – Increased HX Area 11.6%

3 85% AFUE – Increased HX Area 17.1%

4 90% AFUE – Condensing Baseline 14.7%

5 92% AFUE – Increased HX Area 20.1%

6 96% AFUE – Max Tech 6.5%

Gas-fired Steam Boiler

0 80% AFUE – Baseline 13.9%

1 82% AFUE – Increased HX Area 75.3%

2 83% AFUE – Max Tech 10.8%

Oil-fired Hot Water Boiler

0 84% AFUE – Baseline 20.2%

1 85% AFUE – Increased HX Area 32.9%

2 86% AFUE – Increased HX Area 42.9%

3 91% AFUE – Max Tech 4.0%

Oil-fired Steam Boiler

0 82% AFUE – Baseline 34.4%

1 84% AFUE – Increased HX Area 40.9%

2 85% AFUE – Increased HX Area 18.3%

3 86% AFUE – Max Tech 6.5%

DOE used the 5-year averaged (2008-2012) market shares of gas-fired hot water boilers 

and oil-fired boilers that qualify the Energy Star performance criteria, shown in Table 8-H.2.1, 

and the AHRI model directory data in 2013, shown in Table 8-H.3.2, to derive the distribution of 

efficiency levels of residential boilers in 2013. The fraction of gas-fired hot water boiler models 

that qualify the current Energy Star performance criteria in Table 8-H.3.2 (58.4%), is larger than 

the 5-year averaged market shares of shipment between 2008 and 2012 in Table 8-H.2.1

(44.4%). The 2013 distributions of gas-fired hot water boilers with 85% or above AFUEs are 

calculated by multiplying the fractions of models with the factor 44.4%/58.4%. The base case 

distributions of gas-fired hot water boilers with less than 85% AFUEs are calculated by 

multiplying the fractions of models with the factor (1-44.4.3%)/(1-58.4%):

Base case distribution of gas-�ired hot water boilers

= �

Fractions of models ×

44.4%

58.4% if AFUE≥85

Fractions of models ×

1 − 44.4%

1 − 58.4% if AFUE<85
8-H-6

The fraction of oil-fired hot water boiler models that qualify for the current Energy Star 

performance criteria (79.8%) is larger than the 5-year averaged market share of shipment 

between 2008 and 2012 in Table 8-H.2.1 (65.6%). The distributions of oil-fired boilers with 85%

or above AFUEs are calculated by multiplying the fractions of models with the factor 

65.5%/79.8%. Gas-fired hot water boilers with less than 85% AFUE will cover the rest of the 

market, with their shares kept in the same proportional relationship as the model fractions. 

Distribution of HWOB with AFUE≥85 = Fractions of models ×

65.6%

79.8%

The calculated distribution of residential boiler efficiency in 2013 is summarized in Table 

8-H.3.4. 

Table 8-H.3.4 Distribution of Residential Boiler Efficiency in 2013

EL Design Option 2013 Efficiency Distribution

Gas-fired Hot Water Boiler

0 82% AFUE – Baseline 25.7%

1 83% AFUE – Increased HX Area 13.4%

2 84% AFUE – Increased HX Area 15.2%

3 85% AFUE – Increased HX Area 13.4%

4 90% AFUE – Condensing Baseline 11.5%

5 92% AFUE – Increased HX Area 15.8%

6 96% AFUE – Max Tech 5.1%

Gas-fired Steam Boiler

0 80% AFUE – Baseline 13.9%

1 82% AFUE – Increased HX Area 75.3%

2 83% AFUE – Max Tech 10.8%

Oil-fired Hot Water Boiler

0 84% AFUE – Baseline 19.4%

1 85% AFUE – Increased HX Area 33.3%

2 86% AFUE – Increased HX Area 43.3%

3 91% AFUE – Max Tech 4.0%

Oil-fired Steam Boiler

0 82% AFUE – Baseline 28.8%

1 84% AFUE – Increased HX Area 34.2%

2 85% AFUE – Increased HX Area 27.4%

3 86% AFUE – Max Tech 9.7%
8-H-7

8-H.4 PROJECTED MARKET SHARES FROM 2013 TO 2020 AND BEYOND

8-H.4.1 Condensing Unit Market Share 

Currently, Energy Star is working on new performance criteria: 90% AFUE for gas-fired 

boilers (i.e., condensing technology) and 87% AFUE for oil-fired boilers.8 Energy Star plans to 

implement these new criteria by the end of 2014.

DOE expects that adoption of Energy Star’s new performance criteria will gradually 

increase the market share of condensing boilers, but at a slower rate than in the past. There are 

several reasons why future growth is likely to be slower. First, incentives have been a main 

driver for growth of higher efficiency boilers, and the Federal tax credits for such boilers are due 

to expire at the end of 2013. Second, the remaining homes with non-condensing boilers are more 

likely to have difficult installations or lower energy savings from efficiency upgrades.

DOE estimated that the condensing market share of gas-fired hot water boiler at 2020 

equals the market penetration of gas-fired hot water boiler that qualify the Energy Star 

performance criteria at 2013. DOE also estimated that the condensing market share of gas-fired 

hot water boiler would double from 2020 to 2050.

For oil-fired hot water boilers, DOE estimated that the trend from 2013 to 2020 would 

roughly follow the trend in recent years (see Figure 8-H.4.2), and then would slow somewhat 

after 2020.

For both gas- and oil-fired hot water boilers, the market shares of condensing units in the 

years between 2013 and 2020 and between 2020 and 2049 are interpolated using the estimated 

market shares in 2013, 2020, and 2049. Figure 8-H.4.1 and Figure 8-H.4.2 plot the historical data 

and projections of market share of condensing gas-fired hot water boilers and condensing oilfired hot water boilers, respectively. See Appendix 7-B for derivation of historical fraction of 

condensing gas-fired hot water boilers and condensing oil-fired hot water boilers.
8-H-8

Figure 8-H.4.1 Historical Data and Projection of Base Case Market Share for 

Condensing Gas-fired Hot Water Residential Boilers

Figure 8-H.4.2 Projection of Base Case Market Share for Condensing Oil-fired Hot 

Water Residential Boilers

DOE estimated that the market shares of condensing gas-fired and oil-fired steam boilers 

will be negligible during the period of analysis (2020-2049). 

0%

10%

20%

30%

40%

50%

60%

70%

2000 2010 2020 2030 2040 2050

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

2000 2010 2020 2030 2040 2050
8-H-9

8-H.5 ESTIMATE OF 2020 EFFICIENCY DISTRIBUTIONS BY PRODUCT 

CLASS 

DOE used the efficiency distribution in 2013 and the projections of base case market 

share of condensing boilers from 2013 to 2020 to project the efficiency distributions in 2020. 

The base case distributions of condensing gas-fired and oil-fired hot water boilers in 2020 are 

calculated by multiplying the market shares in 2013 with a factor that considers the increase of 

market shares of condensing boilers from 2013 to 2020. The non-condensing gas-fired and oilfired hot water boilers will cover the rest of the market, with their shares kept in the same 

proportional relationship as the market shares in 2013. DOE also estimated that the base case 

distributions of gas-fired and oil-fired steam boilers in 2020 keep the same values as in 2013. 

The calculated base case distribution of residential boiler’s efficiency in 2020 is summarized in 

Table 8-H.5.5. In addition, for gas-fired hot water boilers, DOE accounted for the regional 

differences in the market shares by efficiency levels (see section 8-H.5.1).

Table 8-H.5.5 Base Case Distribution of Residential Boiler Efficiency in 2020

EL Design Option 2020 Efficiency Distribution

Gas-fired Hot Water Boiler

0 82% AFUE – Baseline 21.1%

1 83% AFUE – Increased HX Area 11.0%

2 84% AFUE – Increased HX Area 12.5%

3 85% AFUE – Increased HX Area 11.0%

4 90% AFUE – Condensing Baseline 15.8%

5 92% AFUE – Increased HX Area 21.6%

6 96% AFUE – Max Tech 7.0%

Gas-fired Steam Boiler

0 80% AFUE – Baseline 13.9%

1 82% AFUE – Increased HX Area 75.3%

2 83% AFUE – Max Tech 10.8%

Oil-fired Hot Water Boiler

0 84% AFUE – Baseline 18.6%

1 85% AFUE – Increased HX Area 31.9%

2 86% AFUE – Increased HX Area 41.5%

3 91% AFUE – Max Tech 8.1%

Oil-fired Steam Boiler

0 82% AFUE – Baseline 28.8%

1 84% AFUE – Increased HX Area 34.2%

2 85% AFUE – Increased HX Area 27.4%

3 86% AFUE – Max Tech 9.7%
8-H-10

8-H.5.2 Gas-fired Hot Water Boiler Condensing Fraction by Region

Based on data provided by AHRI for shipments by state of cast-iron and condensing gasfired hot water boilers from 2008-2012, the fraction of condensing gas-fired hot water boiler 

shipments by state varies significantly. DOE used this data to estimate the fraction of 

condensing shipments by census division in 2020. The estimated fraction of condensing 

shipments by census division in 2020 is summarized in Table 8-H.5.6. 

Table 8-H.5.6 Fraction of Condensing Gas-fired Hot Water Boiler Shipments in 2020 by 

Census Division

ID Census Division 

Fraction of Condensing 

Gas-fired Hot Water Boiler 

Shipments (2008-2012)

Projected 2020 Fraction of 

Condensing Gas-fired Hot 

Water Boiler Shipments

1 New England 41.3% 65.9%

2 Middle Atlantic 15.0% 23.9%

3 East North Central 36.1% 57.7%

4 West North Central 44.4% 71.0%

5 South Atlantic 27.7% 44.2%

6 East South Central 38.2% 61.1%

7 West South Central 56.2% 89.8%

8 Mountain 61.5% 98.3%

9 Pacific 64.0% 100.0%

United States 28.6% 45.8%
8-H-11

REFERENCES

1. U.S. Environmental Protection Agency: ENERGY STAR, Unit Shipment Data Archives, 

(Last accessed September, 2013.) 

<http://www.energystar.gov/index.cfm?c=partners.unit_shipment_data_archives>

2. Science Applications International Corporation, Development of Issues Papers for GHG 

Reduction Project Types: Boiler Efficiency Projects, Table 2, January 7, 2009. 

<http://www.climateactionreserve.org/wp-content/uploads/2009/03/future-protocoldevelopment_boiler-efficiency.pdf>

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

Efficiency Ratings for Heating and Water Heating Equipment (AHRI Directory 

September 2013), 2013. (Posted September 2013) (Last accessed September, 2013.) 

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

4. Energy Star, Energy Star Program Requirements for Boilers, 2012. 

<http://www.energystar.gov/ia/partners/product_specs/program_reqs/Boilers_Program_R

equirements.pdf>

5. Database of State Incentives for Renewables and Efficiency (DSIRE), Residential Energy 

Efficiency Tax Credit, 2013. (Last accessed September, 2013.) 

<http://www.dsireusa.org/incentives/incentive.cfm?Incentive_Code=US43F>

6. California Energy Commission, California Energy Commission Appliance Efficiency 

Database, 2013. (Last accessed September, 2013.) 

<http://www.appliances.energy.ca.gov/Default.aspx>

7. Natural Resources Canada, Compare Product Models' Energy Efficiency, 2013. (Last 

accessed September, 2013.) <http://oee.nrcan.gc.ca/pmllmp/index.cfm?action=app.welcome-bienvenue>

8. Energy Star, Boiler Specification Version 3.0, (Last accessed September, 2013.) 

<https://www.energystar.gov/products/specs/boilers_specification_version_3_0_pd>