CHAPTER 3. MARKET AND TECHNOLOGY ASSESSMENT

TABLE OF CONTENTS

3.1 Introduction............................................................................................................. 3-1

3.1.1 Equipment Definitions, Scope of Coverage and Background .................... 3-1

3.1.2 Equipment Classes...................................................................................... 3-3

3.1.2.1 Existing Equipment Classes.........................................................3-3

3.1.2.2 New Equipment Classes ..............................................................3-4

3.2 Market Assessment ................................................................................................. 3-6

3.2.1 Trade Association ....................................................................................... 3-6

3.2.1.1 Air-Conditioning, Heating, and Refrigeration Institute...............3-6

3.2.1.2 American Boiler Manufacturers Association...............................3-7

3.2.1.3 Additional Manufacturers............................................................3-7

3.2.2 Regulatory Programs .................................................................................. 3-8

3.2.2.1 Current Federal Energy Conservation Standards.........................3-8

3.2.2.2 State Energy Conservation Standards..........................................3-9

3.2.2.3 Canadian Energy Conservation Standards...................................3-9

3.2.3 Non-Regulatory Programs........................................................................ 3-10

3.2.3.1 Energy Star Program..................................................................3-10

3.2.3.2 Federal Energy Management Program ......................................3-10

3.2.3.3 Rebate Programs........................................................................3-11

Minnesota Energy Resources.....................................................3-11

Pacific Gas and Electric Company. ...........................................3-11

San Diego Gas and Electric Company.......................................3-12

Southern California Gas Company. ...........................................3-12

3.2.4 Shipments.................................................................................................. 3-13

3.2.5 Equipment Lifetime .................................................................................. 3-13

3.2.6 Market Performance Data ......................................................................... 3-13

3.2.6.1 Small (300kBtu/h - 2,500kBtu/h) Gas-Fired Natural Draft Hot 

Water Commercial Packaged Boilers........................................3-17

3.2.6.2 Large (>2,500kBtu/h) Gas-Fired Natural Draft Hot Water 

Commercial Packaged Boilers...................................................3-20

3.2.6.3 Small (300kBtu/h - 2,500kBtu/h) Oil-Fired Natural Draft Hot 

Water Commercial Packaged Boilers........................................3-22

3.2.6.4 Large (>2,500kBtu/h) Oil-Fired Natural Draft Hot Water 

Commercial Packaged Boilers...................................................3-24

3.2.6.5 Small (300kBtu/h‒2,500kBtu/h) Gas-Fired Natural Draft Steam 

Commercial Packaged Boilers...................................................3-24

3.2.6.6 Large (>2,500kBtu/h) Gas-Fired Natural Draft Steam Commercial 

Packaged Boilers........................................................................3-27

3.2.6.7 Small (300kBtu/h-2,500kBtu/h) Oil-Fired Natural Draft Steam 

Commercial Packaged Boilers...................................................3-29

3.2.6.8 Large (>2,500kBtu/h) Oil-Fired Natural Draft Steam Commercial 

Packaged Boilers........................................................................3-32

3.2.6.9 Small (300kBtu/h-2,500kBtu/h) Gas-Fired Mechanical Draft Hot 

Water Commercial Packaged Boilers........................................3-33

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3.2.6.10 Large (>2,500kBtu/h) Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers...................................................3-38

3.2.6.11 Small (300kBtu/h ‒ 2,500kBtu/h) Oil-Fired Mechanical Draft Hot 

Water Commercial Packaged Boilers........................................3-42

3.2.6.12 Large (>2,500kBtu/h) Oil-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers...................................................3-44

3.2.6.13 Small (300kBtu/h‒2,500kBtu/h) Gas-Fired Mechanical-Draft 

Steam Commercial Packaged Boilers........................................3-46

3.2.6.14 Large (>2,500kBtu/h) Gas-Fired Mechanical Draft Steam 

Commercial Packaged Boilers...................................................3-49

3.2.6.15 Small (300kBtu/h‒2,500kBtu/h) Oil-Fired Mechanical Draft Steam 

Commercial Packaged Boilers...................................................3-51

3.2.6.16 Large (>2,500kBtu/h) Oil-Fired Mechanical Draft Steam 

Commercial Packaged Boilers...................................................3-53

3.3 Technology Assessment........................................................................................ 3-55

3.3.1 Boiler Equipment...................................................................................... 3-55

Construction Materials...............................................................3-56

Tank/Pressure Vessel.................................................................3-56

Burner ........................................................................................3-56

Heat Exchangers ........................................................................3-56

Controls......................................................................................3-58

Draft ...........................................................................................3-58

3.3.2 Technology Options that Improve Combustion Efficiency and/or Thermal 

Efficiency.................................................................................................. 3-59

Jacket Insulation Optimization (Thermal Efficiency Only).......3-59

Heat Exchanger Improvements (Including Condensing Heat 

Exchanger).................................................................................3-60

Burner Derating .........................................................................3-62

Improved Burner Technology....................................................3-62

Combustion Air Preheaters........................................................3-63

Economizers...............................................................................3-63

Blowdown Waste Heat Recovery ..............................................3-63

Integrated, High-Efficiency Steam Boilers................................3-64

3.3.3 Technology Options to Reduce Seasonal Boiler Energy Consumption ... 3-64

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LIST OF FIGURES

Figure 3.1.1. Proposed Commercial Packaged Boiler Equipment Classes...................... 3-5

Figure 3.2.1. Qualifying Checks on Air-Conditioning, Heating, and Refrigeration 

Institute Database for Commercial Packaged Boilers................................... 3-16

Figure 3.2.2. Distribution of Small Gas-fired Natural Draft Hot Water 

Commercial Packaged Boilers Based on Input Rating ................................. 3-17

Figure 3.2.3. Distribution of Small Gas-Fired Natural Draft Hot Water 

Commercial Packaged Boilers Based on Thermal Efficiency ...................... 3-19

Figure 3.2.4. Comparison of Average Thermal Efficiency with Small Gas-Fired 

Natural Draft Hot Water Commercial Packaged Boilers Sub Category 

Based on Input Rating................................................................................... 3-19

Figure 3.2.5. Distribution of Large Gas-Fired Natural Draft Hot Water 

Commercial Packaged Boilers Based on Input Rating ................................. 3-20

Figure 3.2.6. Distribution of Large Gas-Fired Natural Draft Hot Water 

Commercial Packaged Boilers Based on Combustion Efficiency ................ 3-21

Figure 3.2.7. Comparison of Average Combustion Efficiency with Large GasFired Natural Draft Hot Water Commercial Packaged Boilers Sub 

Category Based on Input Rating ................................................................... 3-22

Figure 3.2.8. Distribution of Small Oil Fired Natural Draft Hot Water Boilers 

Based on Input Ratings ................................................................................. 3-22

Figure 3.2.9. Distribution of Small Oil-Fired Natural Draft Hot Water 

Commercial Packaged Boilers Based on Thermal Efficiency ...................... 3-23

Figure 3.2.10. Comparison of Average Thermal Efficiency of Small Oil-Fired 

Natural Draft Hot Water Commercial Packaged Boilers Sub Category 

Based on Input Rating................................................................................... 3-24

Figure 3.2.11. Distribution of Small Gas-Fired Natural Draft Steam Commercial 

Packaged Boilers Based on Input Rating...................................................... 3-25

Figure 3.2.12. Distribution of Small Gas-Fired Natural Draft Steam Commercial 

Packaged Boilers Based on Thermal Efficiency........................................... 3-26

Figure 3.2.13. Comparison of Average Thermal Efficiency of Small Gas-Fired 

Natural Draft Steam Commercial Packaged Boilers Sub Category 

Based on Input Rating................................................................................... 3-27

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Figure 3.2.14. Distribution of Large Gas-Fired Natural Draft Steam Commercial 

Packaged Boilers Based on Input Rating...................................................... 3-27

Figure 3.2.15. Distribution of Large Gas-Fired Natural Draft Steam Commercial 

Packaged Boilers Based on Thermal Efficiency........................................... 3-29

Figure 3.2.16. Comparison of Average Thermal Efficiency of Large Gas-Fired 

Natural Draft Steam Commercial Packaged Boilers Sub Category 

Based on Input Rating................................................................................... 3-29

Figure 3.2.17. Distribution of Small Oil-Fired Natural Draft Steam Boilers Based 

on Input Ratings............................................................................................ 3-30

Figure 3.2.18. Distribution of Small Oil-Fired Natural Draft Steam Commercial 

Packaged Boilers Based on Thermal Efficiency........................................... 3-31

Figure 3.2.19. Comparison of Average Thermal Efficiency of Small Oil-Fired 

Natural Draft Steam Commercial Packaged Boilers Sub Category 

Based on Input Rating................................................................................... 3-31

Figure 3.2.20. Distribution of Large Oil-Fired Natural Draft Steam Commercial 

Packaged Boilers Based on Input Rating...................................................... 3-32

Figure 3.2.21. Distribution of Large Oil-Fired Natural Draft Steam Commercial 

Packaged Boilers Based on Thermal Efficiency........................................... 3-33

Figure 3.2.22. Comparison of Average Thermal Efficiency of Large Oil-Fired 

Natural Draft Steam Commercial Packaged Boilers Sub-Category 

Based on Input Rating................................................................................... 3-33

Figure 3.2.23. Classification of Small Gas Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based on Material Used in the Primary 

Heat Exchanger............................................................................................. 3-34

Figure 3.2.24. Classification of Small Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Condensing Boilers Based on Material Used in 

the Primary Heat Exchanger ......................................................................... 3-35

Figure 3.2.25. Distribution of Small Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based on Input Rating ................................. 3-35

Figure 3.2.26. Distribution of Small Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based On Thermal Efficiency ..................... 3-37

Figure 3.2.27. Comparison of Average Thermal Efficiency of Small Gas-Fired 

Mechanical Draft Hot Water Commercial Packaged Boilers Sub 

Category Based on Input Rating ................................................................... 3-38

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Figure 3.2.28. Classification of Large Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based on Material Used in the Primary 

Heat Exchanger............................................................................................. 3-39

Figure 3.2.29. Classification of Large Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Condensing Boilers Based on Material Used in 

the Primary Heat Exchanger ......................................................................... 3-39

Figure 3.2.30. Distribution of Large Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based on Input Rating ................................. 3-40

Figure 3.2.31. Distribution of Large Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based On Combustion Efficiency ............... 3-41

Figure 3.2.32. Comparison of Average Combustion Efficiency of Large Gas-Fired 

Mechanical Draft Hot Water Commercial Packaged Boilers Sub 

Category Based on Input Rating ................................................................... 3-42

Figure 3.2.33. Distribution of Small Oil-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based on Input Rating ................................. 3-42

Figure 3.2.34. Distribution of Small Oil-Fired Mechanical Draft Hot Water 

Commercial Packaged boilers Based on Thermal Efficiency....................... 3-43

Figure 3.2.35. Comparison of Average Thermal Efficiency of Small Oil-Fired 

Mechanical Draft Hot Water Commercial Packaged Boilers Sub 

Category Based on Input Rating ................................................................... 3-44

Figure 3.2.36. Distribution of Large Oil-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based On Input Rating ................................ 3-45

Figure 3.2.37. Distribution of Large Oil-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based On Combustion Efficiency ............... 3-46

Figure 3.2.38. Comparison of Average Combustion Efficiency of Small Oil-Fired 

Mechanical Draft Hot Water Commercial Packaged Boilers Sub 

Category Based on Input Rating ................................................................... 3-46

Figure 3.2.39. Distribution of Small Gas-Fired Mechanical Draft Steam 

Commercial Packaged Boilers Based on Input Rating ................................. 3-47

Figure 3.2.40. Distribution of Small Gas-Fired Mechanical Draft Steam 

Commercial Packaged Boilers Based on Thermal Efficiency ...................... 3-48

Figure 3.2.41. Comparison of Average Thermal Efficiency of Small Gas-Fired 

Mechanical Draft Steam Commercial Packaged Boilers Sub Category 

Based on Input Rating................................................................................... 3-48

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Figure 3.2.42. Distribution of Large Gas-Fired Mechanical Draft Steam 

Commercial Packaged Boilers Based on Input Rating ................................. 3-49

Figure 3.2.43. Distribution of Large Gas-Fired Mechanical Draft Steam 

Commercial Packaged Boilers Based on Thermal Efficiency ...................... 3-50

Figure 3.2.44. Comparison of Average Thermal Efficiency of Large Gas-Fired 

Mechanical Draft Steam Commercial Packaged Boilers Sub Category 

Based on Input Rating................................................................................... 3-51

Figure 3.2.45. Distribution of Small Oil-Fired Mechanical Draft Steam 

Commercial Packaged Boilers Based On Input Rating ................................ 3-51

Figure 3.2.46. Distribution of small oil-fired mechanical draft steam commercial 

packaged boilers based on thermal efficiency .............................................. 3-52

Figure 3.2.47. Comparison of Average Thermal Efficiency of Small Oil-Fired 

Mechanical Draft Steam Commercial Packaged Boiler Sub Category 

Based on Input Rating................................................................................... 3-53

Figure 3.2.48. Distribution of Large Oil-Fired Mechanical Draft Steam 

Commercial Packaged Boilers Based On Input Rating ................................ 3-53

Figure 3.2.49. Distribution of Large Oil-Fired Mechanical Draft Steam 

Commercial Packaged Boilers Based On Thermal Efficiency ..................... 3-54

Figure 3.2.50. Comparison of Average Thermal Efficiency of Large Oil-Fired 

Mechanical Draft Steam Commercial Packaged Boilers Sub Category 

Based on Input Rating................................................................................... 3-55

Figure 3.3.1. Fin-tube heat exchanger with louvered fins12 ......................................... 3-61

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LIST OF TABLES

Table 3.1.1. Existing Equipment Classes for Commercial Packaged Boilers................. 3-4

Table 3.2.1. Commercial Packaged Boiler Manufacturers Represented in the AirConditioning, Heating, and Refrigeration Institute Ratings Directory1

.......... 3-7

Table 3.2.2. Current Federal Energy Conservation Standards for Commercial 

Packaged Boilers under 10 CFR 431.87 ......................................................... 3-8

Table 3.2.3. Canadian Energy Conservation Standards Proposed by NRCan –

updated on November 2011 ............................................................................ 3-9

Table 3.2.4. FEMP Recommended Thermal Efficiency Levels for Commercial 

Packaged Boilers........................................................................................... 3-10

Table 3.2.5. Rebate Offered by PG&E for Commercial Space Heating Boilers........... 3-11

Table 3.2.6. Rebates offered by SoCalGas for Space Heating Boilers.......................... 3-12

Table 3.2.7. Rebates offered by SoCalGas for Process Heating Boiler......................... 3-13

Table 3.2.8 Number of Boiler Models in each Equipment Class .................................. 3-14

Table 3.2.9. New Equipment Standards with Existing Minimum Efficiency Levels.... 3-15

Table 3.2.10. List of Companies in the Air-Conditioning, Heating, and 

Refrigeration Institute Directory that Manufacture Small Gas-Fired 

Natural Draft Hot Water Commercial Packaged Boilers.............................. 3-18

Table 3.2.11. List of Companies in the Air-Conditioning, Heating, and 

Refrigeration Institute Directory that Manufacture Large Gas-Fired 

Natural Draft Hot Water Commercial Packaged Boilers.............................. 3-20

Table 3.2.12. List of Companies in the Air-Conditioning, Heating, and 

Refrigeration Institute Directory that Manufacture Small Oil-Fired 

Natural Draft Hot Water Commercial Packaged Boilers.............................. 3-22

Table 3.2.13. List of Companies in the Air-Conditioning, Heating, and 

Refrigeration Institute Directory that Manufacture Small Gas-Fired 

Natural Draft Steam Commercial Packaged Boilers..................................... 3-25

Table 3.2.14. List of Companies in the Air-Conditioning, Heating, and 

Refrigeration Institute Directory that Manufacture Large Gas-Fired 

Natural Draft Steam Commercial Packaged Boilers..................................... 3-28

Table 3.2.15. List of Companies in the Air-Conditioning, Heating, and 

Refrigeration Institute Directory that Manufacture Small Oil-Fired 

Natural Draft Steam Commercial Packaged Boilers..................................... 3-30

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Table 3.2.16. List of Companies in the Air-Conditioning, Heating, and 

Refrigeration Institute Directory that Manufacture Small Gas-Fired 

Mechanical Draft Hot Water Commercial Packaged Boilers....................... 3-36

Table 3.2.17. List of Companies in the Air-Conditioning, Heating, and 

Refrigeration Institute Directory that Manufacture Large Gas-Fired 

Mechanical Draft Hot Water Commercial Packaged Boilers....................... 3-40

Table 3.2.18. List of Companies in the Air-Conditioning, Heating, and 

Refrigeration Institute Directory that Manufacture Small Oil-Fired 

Mechanical Draft Hot Water Commercial Packaged Boilers....................... 3-43

Table 3.2.19. List of Companies in the A Air-Conditioning, Heating, and 

Refrigeration Institute Directory that Manufacture Large Oil-Fired 

Mechanical Draft Hot Water Commercial Packaged Boilers....................... 3-45

Table 3.2.20. List of Companies in the Air-Conditioning, Heating, and 

Refrigeration Institute Directory that Manufacture Small Gas-Fired 

Mechanical Draft Steam Commercial Packaged Boilers.............................. 3-47

Table 3.2.21. List of Companies in the Air-Conditioning, Heating, and 

Refrigeration Institute Directory that Manufacture Large Gas-Fired 

Mechanical Draft Steam Commercial Packaged Boilers.............................. 3-49

Table 3.2.22. List of Companies in the Air-Conditioning, Heating, and 

Refrigeration Institute Directory that Manufacture Small Oil-Fired 

Mechanical Draft Steam Commercial Packaged Boilers.............................. 3-52

Table 3.2.23. List of Companies in the Air-Conditioning, Heating, and 

Refrigeration Institute Directory that Manufacture Large Oil-Fired 

Mechanical Draft Steam Commercial Packaged Boilers.............................. 3-54

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CHAPTER 3. MARKET AND TECHNOLOGY ASSESSMENT

3.1 INTRODUCTION

This chapter details the market and technology assessment that the U.S. 

Department of Energy (DOE) has conducted in support of the preliminary analysis for the 

energy conservation standards rulemaking for commercial packaged boilers.

The goal of the market assessment is to develop a qualitative and quantitative 

characterization of the commercial packaged boiler industry and market structure, based 

on information that is publicly available and on data submitted by manufacturers and 

other interested parties. Issues addressed include commercial packaged boiler 

characteristics, market share and equipment classes; existing regulatory and nonregulatory efficiency improvement initiatives; overview of historical equipment 

shipments and lifetimes and trends in the equipment markets. The technology assessment 

is an investigation into technologies that will improve the energy efficiency of 

commercial packaged boilers, and results in a preliminary list of technologies that can 

improve the thermal and/or combustion efficiency of commercial packaged boilers. In 

addition, technology options which can improve seasonal efficiency are also discussed as 

part of this assessment.

A commercial packaged boiler (CPB), which is defined later in this chapter (see 

section 3.1.1), is a boiler designed to provide space heating or hot water to commercial

institutions. These boilers are differentiated from residential boilers by their rated input

capacity. Residential boilers have an input capacity up to (but not equal to) 300 thousand 

British thermal units per hour (kBtu/h), whereas commercial packaged boilers have 

capacities of 300 kBtu/h or more. This chapter further describes the scope of the 

assessment and divides commercial packaged boilers into various equipment classes. 

These equipment classes are directly analyzed by DOE to understand various aspects of 

the CPB market such as number of models under each equipment class, types of boilers 

(e.g., modulating or condensing), heat exchanger materials, and potential technology 

options for enhancing efficiency etc. The equipment classes created by DOE to analyze 

boilers are based on general characteristics of boilers and are discussed in detail in later 

sections.

3.1.1 Equipment Definitions, Scope of Coverage and Background

The Energy Policy and Conservation Act, as amended, (EPCA) defines a 

“packaged boiler” as “a boiler that is shipped complete with heating equipment, 

mechanical draft equipment, and automatic controls; usually shipped in one or more 

sections.” (42 U.S.C. 6311(11)(B)) DOE’s regulations further refined the “packaged 

boiler” definition to exclude a boiler that is custom designed and field constructed. 

Additionally, if the boiler is shipped in more than one section, the sections may be 

produced by more than one manufacturer, and may be originated or shipped at different 

times and from more than one location. 10 CFR 431.82

3-1
In its regulations as set forth in 10 CFR 431.82, DOE defines a “commercial 

packaged boiler” as a type of packaged low pressure boiler that is industrial equipment 

with a capacity, (rated maximum input) of 300,000Btu/h or more which, to any 

significant extent, is distributed in commerce: (1) For heating or space conditioning 

applications in buildings; or (2) For service water heating in buildings but does not meet 

the definition of a ‘hot water supply boiler’ in [part 431]. 

A “packaged low pressure boiler” is defined as “a packaged boiler that is: (1) A 

steam boiler designed to operate at or below a steam pressure of 15 psig [pounds per 

square inch gauge]; or (2) A hot water boiler designed to operate at or below a water 

pressure of 160 psig and a temperature of 250 °F; or (3) A boiler that is designed to be 

capable of supplying either steam or hot water, and designed to operate under the 

conditions in paragraphs (1) and (2) of this definition.” 10 CFR 431.82.

On August 28, 2013, DOE released the Rulemaking Framework Document for 

Commercial Packaged Boilers (Framework document). On that same day DOE also 

issued the Notice of Public Meeting and Availability of the Framework Document for 

commercial packaged boilers, which was published in the Federal Register on September 

3, 2013. 78 FR 54197. As part of the Framework document and the notice of public 

meeting (NOPM), DOE sought comments from interested parties and stakeholders on 

various aspects of the rulemaking, such as scope of coverage, approach used, analyses 

methodologies etc. In response DOE received several responses which are summarized in 

chapter 2 of this Technical Support Document (TSD). 

DOE’s regulations for commercial packaged boilers that are currently in effect 

cover small and large, gas-fired and oil-fired, hot water and steam commercial packaged 

boilers that meet the definitions outlined above, as applicable.a

 DOE notes that although 

Federal energy conservation standards for electric commercial packaged boilers have not 

been established, the definitions set forth above do not preclude DOE from adopting 

standards for such equipment if justified. In other words, electric commercial packaged 

boilers are within the scope of DOE’s authority under EPCA.

DOE plans to maintain the scope of coverage as defined by its current regulations 

for this analysis of amended thermal and combustion efficiency standards for commercial 

packaged boilers. However for the scope of the current rulemaking, DOE is not 

considering standards for electric commercial packaged boilers. This is primarily because 

a review of the electric commercial packaged boilers market revealed that these boilers 

account for a relatively small number of annual shipments (approximately 1,500-2,100 

units), and the efficiency of such equipment already approaches 100-percent under the 

current metric (i.e., thermal efficiency). Thus, DOE believes that there is little to no 

room for improvement in efficiency, unless DOE were to consider adopting levels 

requiring installation of heat pump technology (a technological leap when setting initial 

a DOE’s regulations for commercial packaged boilers are divided into equipment classes based on input 

capacity (i.e., size category). Throughout this preliminary TSD, DOE refers to units with an input capacity 

of ≥ 300,000 Btu/h and ≤ 2,500,000 Btu/h as “small” and units with an input capacity ≥ 2,500,000 Btu/h as 

“large.” For more information please refer to 10 CFR 431.87.

3-2

 
standards). However, DOE did not consider heat pump technology in this rulemaking 

analysis, as it has not been demonstrated feasible for use in electric commercial packaged 

boilers.

On August 13, 2013, DOE published in the Federal Register a notice of proposed 

determination (NOPD) of coverage to explicitly clarify its statutory authority to regulate 

natural draft commercial packaged boilers. 78 FR 49202. As explained in the proposed 

determination, under DOE’s interpretation of the relevant statutory provisions, natural 

draft commercial packaged boilers are currently included as covered equipment with 

standards at 10 CFR part 431, subpart E. However, DOE is undertaking a coverage 

determination to explicitly clarify its statutory authority under EPCA to cover natural 

draft commercial packaged boilers. If the outcome of the NOPD is positive DOE will 

classify boiler models further into natural draft and mechanical draft CPBs. Although 

outcome of NOPD is pending, DOE plans to cover natural draft boilers as part of this 

rulemaking. As a result, DOE has analyzed a total of 16 equipment classes for this TSD.

As noted previously in the discussion of definitions, commercial packaged boilers 

are defined as having an input capacity greater than or equal to 300,000 Btu/h. Currently, 

there is no upper limit to the input capacity of a CPB. As discussed in chapter 2 of this 

TSD, DOE received several comments on this topic, but has tentatively concluded that it 

will not alter the scope of coverage for the rulemaking to exclude very large CPBs. 

Therefore, all CPBs having input capacity greater than or equal to 300,000Btu/h are 

covered under this rulemaking.

3.1.2 Equipment Classes

3.1.2.1 Existing Equipment Classes 

EPCA, as amended, established mandatory Federal energy conservation standards 

for certain commercial equipment, including CPBs, based on the American Society of 

Heating, Refrigerating and Air Conditioning Engineers/ Illuminating Engineering Society 

(ASHRAE/IES) Standard 90.1, “Energy Standard for Buildings Except Low-Rise 

Residential Buildings.” Section 42 U.S.C 6313(a)(6) of EPCA provides that, if 

ASHRAE/IES Standard 90.1 is amended with respect to packaged boilers, DOE shall 

publish in the Federal Register for public comment an analysis of the energy savings 

potential of amended energy efficiency standards. Further, EPCA requires DOE to 

establish an amended uniform national standard for commercial packaged boiler at the 

minimum level specified in the amended ASHRAE/IES Standard 90.1, unless DOE 

determines by rule and supported by clear and convincing evidence that adoption of a 

more stringent standard is technologically feasible and economically justified. In 2007, 

ASHRAE amended the efficiency levels of commercial packaged boilers. Subsequently, 

in July 2009, DOE published in the Federal Register a final rule (July 2009 final rule)

amending the energy conservation standards for commercial packaged boilers to 

correspond to levels in ASHRAE 90.1-2007. 74 FR 36312. 

ASHRAE/IES Standard 90.1‒2007 divides commercial packaged boilers into 10 

equipment classes on the basis of fuel type (i.e., oil or gas (natural or propane)), size (i.e.,

3-3
small (300-2,500 kBtu/h) or large (>2,500 kBtu/h)) and heating media (steam or hot 

water). The gas-fired steam boilers are further divided based on the draft type (i.e. natural 

draft or mechanical draft). In the July 2009 final rule, DOE adopted efficiency levels and 

equipment classes based on Standard 90.1‒2007 that required compliance beginning on 

March 2, 2012. Table 3.1.1 below shows the division of equipment classes based on 

ASHRAE/IES Standard 90.1‒2007. 

As mentioned earlier, there are very few annual shipments and limited potential 

for improving efficiency for electric commercial packaged boilers, and therefore, this 

equipment class was not covered as part of the ASHRAE/IES Standard 90.1‒2007 

standards, or the July 2009 final rule. As discussed above, a preliminary investigation has 

shown that the market and technologies for this equipment has not significantly changed

and, thus, electric boilers were not considered for this preliminary analysis. 

Table 3.1.1. Existing Equipment Classes for Commercial Packaged Boilers

Commercial Packaged Boiler 

Equipment Class

Description of Characteristics

Small Gas-Fired Hot Water Fuel input of 300−2,500 kBtu/h; fueled by 

propane or natural gas; hot water output 

Small Gas-Fired Steam All Except 

Natural Draft

Fuel input of 300−2,500 kBtu/h; fueled by 

propane or natural gas; steam output; draft 

mechanism other than natural draft (e.g.,

forced or induced draft mechanism)

Small Gas-Fired Steam Natural Draft Fuel input of 300−2,500 kBtu/h; fueled by 

propane or natural gas; steam output; natural 

draft mechanism

Small Oil-Fired Hot Water Fuel input of 300−2,500 kBtu/h; fueled by oil; 

hot water output

Small Oil-Fired Steam Fuel input of 300−2,500 kBtu/h; fueled by oil; 

steam output

Large Gas-Fired Hot Water Fuel input of >2,500 kBtu/h; fueled by propane 

or natural gas; hot water output 

Large Gas-Fired Steam All Except 

Natural Draft

Fuel input of >2,500 kBtu/h; fueled by propane 

or natural gas; steam output; draft mechanism 

other than natural draft (e.g., forced or induced 

draft mechanism)

Large Gas-Fired Steam Natural Draft Fuel input of >2,500 kBtu/h; fueled by propane 

or natural gas; steam output; natural draft 

mechanism

Large Oil-Fired Hot Water Fuel input of >2,500 kBtu/h; fueled by oil; hot 

water output

Large Oil-Fired Steam Fuel input of >2,500 kBtu/h; fueled by oil; 

steam output

3.1.2.2 New Equipment Classes

 

3-4
As a result of the August 2013 proposed determination of coverage, DOE 

considered separate equipment classes for natural draft commercial packaged boilers.

Although, the outcome of the NOPD is pending, for the purpose of the rulemaking, DOE 

has tentatively decided to analyze separate equipment classes for natural draft boilers.

With the introduction of these equipment classes, all CPBs are divided into 16 categories 

(excluding electric boilers). The equipment classes are shown in the chart below (Figure 

3.1.1)

Figure 3.1.1. Proposed Commercial Packaged Boiler Equipment Classes

3-5
3.2 MARKET ASSESSMENT

The following market assessment identifies the manufacturer trade associations 

and domestic and international manufacturers of commercial packaged boilers. The 

market assessment also identifies existing regulatory and non-regulatory programs for 

commercial boilers, and summarizes relevant characteristics and market performance 

data for each equipment class.

3.2.1 Trade Association

To gain insight into the commercial packaged boiler industries, DOE researched 

various associations available to manufacturers, suppliers, and users of such equipment. 

DOE identified the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) and 

the American Boiler Manufacturers Association (ABMA) as the only trade groups that 

support, or have an interest in, the commercial packaged boiler industry. 

3.2.1.1 Air-Conditioning, Heating, and Refrigeration Institute 

AHRI is a national trade association for manufacturers of heating, ventilation, airconditioning, and refrigeration (HVACR) which includes commercial packaged boiler 

manufacturers. AHRI was established in January of 2008 when the Air-Conditioning and 

Refrigeration Institute (ARI) merged with the Gas Appliance Manufacturers Association 

(GAMA). AHRI develops and publishes technical standards for residential and 

commercial air conditioning, heating, and refrigeration equipment using rating criteria 

and procedures for measuring and certifying product performance. AHRI maintains the 

Directory of Certified Product Performance, which is a database of ratings for all 

manufacturers who elect to participate in the program (AHRI’s certified directory). AHRI 

maintains a certified performance directory for commercial boilers. Table 3.2.1 shows the 

manufacturers of AHRI certified commercial boilers in the 2014 directory. The directory 

consists of 2354 boiler models.

1

DOE used the data in this directory in its market assessment. DOE also examined

other data sources such as manufacturer literature, technical reports, and any other 

relevant information to provide a broad insight into the commercial packaged boilers 

market.

3-6
Table 3.2.1. Commercial Packaged Boiler Manufacturers Represented in the AirConditioning, Heating, and Refrigeration Institute Ratings Directory1

A.O. Smith Water Products Co. Heat Transfer Products Inc.

Advanced Thermal Hydronics LAARS Heating Systems Company

AERCO International, Inc. Lochinvar Corporation

BIASI, S.p.A. c/o QHT, Inc. New Yorker Boiler Co., Inc. (Burnham 

Holdings, Inc.)

Bosch Thermotechnology Corp. NY Thermal Inc.

Bradford White Corporation Parker Boiler Company

Bryan Steam LLC P B Heat, LLC

Burnham Commercial (Burnham 

Holdings, Inc.) Pennco (ECR International, Inc.)

Camus Hydronics Ltd. Raypak, Inc.

Cleaver-Brooks RBI Water Heaters (Mestek, Inc.)

Columbia Boiler Company of Pottstown Slant/Fin Corporation

Crown Boiler Co. (Burnham Holdings, 

Inc.) Smith Cast Iron Boilers

De Dietrich Thermal Solutions Products, LLC 

(Burnham Holdings, Inc.)

Dunkirk Boilers (ECR International, Inc.) Triangle Tube Phase III Inc.

Fulton Heating Solutions Utica Boilers (ECR International, Inc.)

Hamilton Engineering Inc. Viessmann Manufacturing Company, Inc.

Harsco Industrial Patterson-Kelley Weil-McLain

3.2.1.2 American Boiler Manufacturers Association 

ABMA is a national, nonprofit trade association of commercial, institutional, 

industrial, and electricity-generating boiler system manufacturing companies (> 400,000

Btu/h heat input), dedicated to the advancement and growth of the boiler and combustion 

equipment industry.b

DOE identified the following ABMA manufacturers as manufacturers of 

commercial packaged boiler equipment: Aesys Technologies, LLC; AJAX Boiler, 

Burnham Commercial; Cleaver-Brooks; Johnston Boiler Company; Miura Boiler; 

Superior Boiler Works, Inc., Vapor Power International, LLC.c

3.2.1.3 Additional Manufacturers

DOE also reviewed the CSA-Internationald and SCAQMDe boiler databases to 

identify commercial boiler manufacturers that may not be members of a trade association

or actively participate in an efficiency certification program. DOE identified 10 

b See http://www.abma.com/. c For more information, visit http://www.abma.com/membership-directory.html

d For more information, visit www.csa-international.org/Default.asp?language=english e For more information, visit www.aqmd.gov/

3-7

 
additional boiler manufacturers from the two databases: Fulton Boiler; Parker Boiler; 

Patterson-Kelley Company (division of Harsco); Triad Boiler Systems; CAMUS 

Hydronics, Ltd.; Gasmaster Industries; General Boiler Co., Inc.; Hurst Boiler; Lattner 

Boiler; and Unilux Boiler.

3.2.2 Regulatory Programs

The following section details current regulatory programs requiring energy 

conservation standards for commercial packaged boilers. Section 3.2.2.1 addresses

Federal energy conservation standards and section 3.2.2.2 provides an overview of 

existing State standards. Section 3.2.2.3 reviews Canadian standards programs that may 

affect the companies servicing the North American market.

3.2.2.1 Current Federal Energy Conservation Standards

The existing Federal energy conservation standards as set forth in 10 CFR 431.87 

cover 10 equipment classes. Apart from gas-fired steam boilers, no other equipment class 

is currently divided based on draft type. As a result, both natural draft and mechanical 

draft boilers have the same energy conservation standard (except for gas steam boiler 

equipment classes). Further, the energy efficiency descriptor for large hot water CPB

equipment classes is combustion efficiency, while for all other equipment classes the 

descriptor is thermal efficiency. Table 3.2.2 shows the current energy efficiency 

standards for commercial packaged boilers. 

Table 3.2.2. Current Federal Energy Conservation Standards for Commercial 

Packaged Boilers under 10 CFR 431.87

Equipment type Subcategory Size category (input)

Efficiency 

level—

Effective date: 

March 2, 2012*

Hot Water Commercial 

Packaged Boilers Gas-fired ≥300,000 Btu/hr and ≤2,500,000 Btu/hr 80% ET

Hot Water Commercial 

Packaged Boilers Gas-fired >2,500,000 Btu/hr 82% EC

Hot Water Commercial 

Packaged Boilers Oil-fired ≥300,000 Btu/hr and ≤2,500,000 Btu/hr 82% ET

Hot Water Commercial 

Packaged Boilers Oil-fired >2,500,000 Btu/hr 84% EC

Steam Commercial 

Packaged Boilers

Gas-fired—all, 

except natural draft

≥300,000 Btu/hr and 

≤2,500,000 Btu/hr 79% ET

Steam Commercial 

Packaged Boilers

Gas-fired—all, 

except natural draft >2,500,000 Btu/hr 79% ET

Steam Commercial 

Packaged Boilers

Gas-fired—natural 

draft

≥300,000 Btu/hr and 

≤2,500,000 Btu/hr 77% ET**

Steam Commercial 

Packaged Boilers

Gas-fired—natural 

draft >2,500,000 Btu/hr 77% ET**

Steam Commercial Oil-fired ≥300,000 Btu/hr and 81% ET

3-8
Packaged Boilers ≤2,500,000 Btu/hr

Steam Commercial 

Packaged Boilers Oil-fired >2,500,000 Btu/hr 81% ET

* ET means “thermal efficiency.” EC means “combustion efficiency.”10 CFR part 431.82.

**On March 2, 2022 the minimum efficiency standard for small and large gas-fired natural draft steam 

commercial packaged boilers will be 79% ET.

3.2.2.2 State Energy Conservation Standards

Under EPCA, states may petition to have more-stringent energy conservation 

standards than those codified under subpart E of 10 CFR Part 431. (42 U.S.C. 6316(b)(2); 

6297(d)). At this time, no states have been granted a petition from DOE to establish 

more-stringent energy conservation standards than the levels EPCA established for 

commercial packaged boilers.

3.2.2.3 Canadian Energy Conservation Standards

In May 2010, the Natural Resources Canada (NRCan) Office of Energy 

Efficiency, proposed energy conservation standards for gas- and oil-fired commercial 

packaged boilers according to the standards set forth in ASHRAE 90.1‒2007. After 

release of the proposed standards, additional updates were published in August 2010 and 

November 2011. As part of the August 2010 update, NRCan made three changes to its 

original proposal. NRCan changed its proposed near-condensing efficiency level for

small gas-fired boilers from 85-percent to 84-percent (thermal efficiency) and for large 

gas-fired boilers from 87-percent to 86-percent (combustion efficiency). NRCan also

decided to allow boilers with near-condensing efficiency levels only for replacement 

markets and to require boilers to achieve efficiencies requiring condensation only for new 

construction beginning in 2015.

In the November 2011 update, NRCan amended efficiency levels and changed 

effective dates for certain equipment classes of boilers. The latest version of the proposed 

energy conservation standards for Canada is shown in the Table 3.2.3 below:

Table 3.2.3. Canadian Energy Conservation Standards Proposed by NRCan –

updated on November 20112

Boiler Type Prescriptive RequirementsMinimum Efficiency*Date of Manufacture

Small Gas Hot Water No standing pilot 80% ET March 2, 2012

Small Gas Hot Water No standing pilot 84% ET March 2, 2015

Small Gas Steam No standing pilot 77% ET March 2, 2012

Small Gas Steam No standing pilot 79% ET March 2, 2015

Small Oil Hot Water Nil 82% ET March 2, 2012

Small Oil Steam Nil 81% ET March 2, 2012

Large Gas Hot Water No standing pilot 82% Ec March 2, 2012

Large Gas Hot Water No standing pilot 85% Ec March 2, 2015

Large Oil Hot Water Nil 84% Ec March 2, 2012

Large Gas Steam No standing pilot 77% ET March 2, 2012

Large Gas Steam No standing pilot 79% ET March 2, 2015

3-9
Large Oil Steam Nil 81% ET March 2, 2012

Changes from the May 2010 bulletin are in bold and italic.

*ET refers to Thermal Efficiency; EC refers to Combustion Efficiency

3.2.3 Non-Regulatory Programs

3.2.3.1 Energy Star Program

ENERGY STAR, a voluntary labeling program backed by the U.S. 

Environmental Protection Agency (EPA) and DOE, identifies energy efficient products 

through a qualification process. f To qualify, a product must exceed Federal minimum 

standards by a specified amount, or if no Federal standard exists, then exhibit selected 

energy-saving features. The ENERGY STAR program works to recognize the top 

quartile of products on the market, meaning that approximately 25-percent of products on 

the market meet or exceed the ENERGY STAR levels. Currently, there is an ENERGY 

STAR program for residential packaged boilers, but there is no ENERGY STAR program 

for commercial packaged boilers.

3.2.3.2 Federal Energy Management Program

DOE’s Federal Energy Management Program (FEMP) works to reduce the cost 

and environmental impact of the Federal government by advancing energy efficiency and 

water conservation, promoting the use of distributed and renewable energy, and 

improving utility management decisions at Federal sites.g FEMP helps Federal buyers 

identify and purchase energy efficient equipment.

FEMP designates standards for commercial packaged boilers purchased by the 

Federal government. FEMP specifies different efficiency levels for commercial packaged 

boilers based on fuel type, size, and output. FEMP levels are specified using the thermal 

efficiency metric. Table 3.2.4 presents the designated FEMP commercial packaged boiler 

standards levels.

Table 3.2.4. FEMP Recommended Thermal Efficiency Levels for Commercial 

Packaged Boilers3

f For more information, visit www.energystar.gov g For more information, visit www.energy.gov/eere/femp

3-10

 
Equipment Class Recommended Thermal 

Efficiency (ET) (%)

Small Gas-Fired Hot Water 80

Large Gas-Fired Hot Water 80

Small Gas-Fired Steam 79

Large Gas-Fired Steam 80

Small Oil-Fired Hot Water 83

Large Oil-Fired Hot Water 83

Small Oil-Fired Steam 83

Large Oil-Fired Steam 83

3.2.3.3 Rebate Programs

DOE has identified and reviewed various local utility rebate programs. Some of 

the local utilities reviewed by DOE include Minnesota Energy Resources, Pacific Gas 

and Electric Company (PG&E), San Diego Gas and Electric (SDG&E), and the Southern 

California Gas Company (SoCalGas).

Minnesota Energy Resources.

The Minnesota Energy Resources Commercial Custom Rebate program offers businesses 

cash rebates as an incentive to install energy efficient commercial equipment, including 

boilers and boiler retrofits. Minnesota Energy Resources does not have a standard rebate 

amount; rather it individually reviews each application it receives. Rebate amounts are 

awarded based on the type and efficiency of boiler. Rebate amounts for hot water boilers 

having efficiency greater than 90 -are higher than those for efficiency greater than 85-

percent and less than 90-percent. For steam boilers rebate is available for boilers having 

thermal efficiency greater than 83-percent.

4

Pacific Gas and Electric Company.

PG&E offers energy efficiency rebates to commercial customers who use energy 

efficient space-heating boilers in their businesses or commercial facilities. PG&E offers 

different rebates amounts depending on the characteristics of the space-heating boiler. 

Table 3.2.5 below describes the rebates offered by PG&E for space-heating boilers.

5

Table 3.2.5. Rebate Offered by PG&E for Commercial Space Heating Boilers

Description of Boiler Rebate Amount

Space heating atmospheric water boiler thermal efficiency of ≥ 85% and input 

rating 300 kBtu/h and ≤ 2500 kBtu/h $1/kBtu/h

Space heating forced draft water boiler thermal efficiency of ≥ 85% and input 

rating 300 kBtu/h and ≤ 2500 kBtu/h $1/kBtu/h

Space heating condensing water boiler thermal efficiency of ≥ 94% and input 

rating 300 kBtu/h and ≤ 2500 kBtu/h

$2/kBtu/h

Space heating atmospheric water boiler combustion efficiency of ≥ 85% and 

input rating > 2500 kBtu/h $1/kBtu/h

Space heating forced draft water boiler combustion efficiency of ≥ 85% or 

thermal efficiency of ≥83% and input rating > 2500 kBtu/h $1/kBtu/h

Space heating condensing water boiler thermal efficiency of ≥ 94% and input $2/kBtu/h

3-11
rating > 2500 kBtu/h

Space heating atmospheric steam boiler thermal efficiency of ≥ 85% and input 

rating 300 kBtu/h and ≤ 2500 kBtu/h $1/kBtu/h

Space heating forced draft steam boiler thermal efficiency of ≥ 85% and input 

rating 300 kBtu/h and ≤ 2500 kBtu/h $1/kBtu/h

Space heating atmospheric steam boiler combustion efficiency of ≥ 80% or 

81% thermal efficiency and input rating > 2500 kBtu/h $1/kBtu/h

Space heating forced draft steam boiler combustion efficiency of ≥ 80% or 

81% thermal efficiency and input rating > 2500 kBtu/h

$1/kBtu/h

San Diego Gas and Electric Company.

SDG&E offers rebates and incentives to commercial customers through two

programs. The first program is its Energy Efficiency Business Incentive program. This 

program provides cash incentives to businesses that improve boiler performance through

replacement of boiler parts resulting in natural gas savings. The incentive amounts to $1 

per therm (~100 cu.ft of natural gas) of natural gas saved with the gas being supplied by 

SDG&E, PG&E or SoCalGas. This program is not offered to space-heating commercial 

boilers with input ratings ≤ 5,000 kBtu/h and process (non-space-heating) boilers with

input ratings < 10,000 kBtu/h for industrial end-use customers.

6

The second program offered is the Energy Efficiency Business Rebates program. 

This is available for a wide range of products and equipment from the agricultural, 

commercial and industrial sectors. For commercial boilers, SDG&E provides a rebate of 

$0.5 per kBtu/h for any commercial space heating boiler having an input rating of 300

kBtu/h to 2,500 kBtu/h with a combustion efficiency greater than or equal 85-percent. 

For process boilers (non-space-heating) having an input rating more than 75,000 Btu/h 

and a thermal efficiency greater than or equal to 84-percent, SDG&E offers a rebate of 

$0.5 per kBtu/h.

7 

Southern California Gas Company.

SoCalGas offers Energy-Efficiency Rebates for Business (EERB) for replacing 

inefficient gas-fired equipment with more-efficient models. Rebates are offered for 

commercial, industrial or agricultural customer with an active, valid, and non-delinquent 

account. Eligible customers can receive rebates for space-heating hot water and processheating boilers. For a space-heating boiler, which is installed by a licensed contractor and 

has an input rating greater than or equal to 300 kBtu/h, SoCal Gas offers the following 

rebates:

Table 3.2.6. Rebates offered by SoCalGas for Space Heating Boilers8

Type of Boiler Required Efficiency Rebate Amount

Medium/Large – steam ≥83% Combustion Efficiency $0.50/(kBtu/h)

Medium/Large hot water (Tier 

I) ≥85% Combustion Efficiency $0.50/(kBtu/h)

Medium/Large hot water (Tier 

II) ≥90% Combustion Efficiency $4.00/(kBtu/h)

3-12
For process heating boilers having a capacity of less than or equal to 10,000 

kBtu/h, SoCalGas offers the following rebates:

Table 3.2.7. Rebates offered by SoCalGas for Process Heating Boiler8

Type of Boiler Required Efficiency Rebate Amount

Steam ≥83% Combustion Efficiency $0.75/(kBtu/h)

Hot water (Tier I) ≥85% Combustion Efficiency $0.75/(kBtu/h)

Hot water (Tier II) ≥90% Combustion Efficiency $1.50/(kBtu/h)

3.2.4 Shipments

Information about annual equipment shipment trends allows DOE to estimate the 

impacts of energy conservation standards on the commercial packaged boiler industry. 

For commercial packaged boilers, very little information about historical shipments is 

publicly available. DOE used information from the 2009 commercial packaged boiler 

final rule analysis, along with information from the several other sources (e.g., the AHRI 

directory, Appliance Magazine, Energy) to develop its shipments model for commercial 

packaged boilers.9 Additional details about commercial boiler shipments are discussed in 

Chapter 9 of this TSD (Shipments Analysis).

3.2.5 Equipment Lifetime

During manufacturer interviews, estimates of commercial packaged boiler

lifetime typically ranged from 25 to 30 years, with an average lifetime expected to be 

roughly 25 years. For its analysis of lifetime, DOE used national survey data, published 

studies, and projections based on manufacturer shipment data to calculate the distribution 

of commercial packaged boiler lifetimes. More information about commercial packaged 

boiler equipment lifetime can be found in the life-cycle cost and payback period analyses 

section in Chapter 8 (Life-Cycle Cost and Payback Period Analysis) and Appendix 8-F of 

this TSD.

3.2.6 Market Performance Data

DOE reviewed performance data for commercial packaged boilers currently on 

the market. DOE reviewed commercial packaged boiler equipment literature available 

from manufacturers, including those listed as ABMA and AHRI members. However for 

the analysis, DOE decided to use a database of boiler models which are certified by 

AHRI. Many of the non-AHRI manufacturers reviewed by DOE had an efficiency metric 

listed but did not specify the type listed efficiency (i.e., whether combustion efficiency or 

thermal efficiency). Under 10 CFR 431.86, Federal energy conservation standards require 

efficiency ratings to be determined using the Hydronics Institute BTS-2000 Testing 

Standard, “Method to Determine Efficiency of Commercial Space Heating Boilers.”10

However, the efficiency ratings listed by non-AHRI boiler manufacturers were often 

derived using the American Society of Mechanical Engineering – Power Test Code (PTC 

4) test method that may not be directly comparable with BTS-2000. Considering these 

issues DOE obtained a directory comprising 2,354 models manufactured by 33

companies from AHRI’s website1. The directory provides a list of AHRI certified 

3-13
commercial boilers with important performance related information, such as type of fuel, 

input capacity, draft type and heating medium listed for each boiler model. To initiate the 

analysis, DOE categorized the entire list into the 16 equipment classes which are 

mentioned in Table 3.2.8. DOE identified the number of CPBs in each equipment class. 

Table 3.2.8 below shows the distribution of boiler models under each equipment class. 

Table 3.2.8 Number of Boiler Models in each Equipment Class

Full Name Abbreviation Number of Models

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) 

Gas-fired Natural Draft Hot Water CPB SGNDHW 236

Large (>2,500,000 Btu/h) Gas-fired Natural 

Draft Hot Water CPB LGNDHW 35

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) 

Oil-fired Natural Draft Hot Water CPB SONDHW 55

Large (>2,500,000 Btu/h) Oil-fired Natural 

Draft Hot Water CPB LONDHW 6

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) 

Gas-fired Natural Draft Steam CPB SGNDST 347

Large (>2,500,000 Btu/h) Gas-fired Natural 

Draft Steam CPB LGNDST 163

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) 

Oil-fired Natural Draft Steam CPB SONDST 52

Large (>2,500,000 Btu/h) Oil-fired Natural 

Draft Steam CPB LONDST 95

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) 

Gas-fired Mechanical Draft Hot Water CPB SGMDHW 757

Large (>2,500,000 Btu/h) Gas-fired Mechanical 

Draft Hot Water CPB LGMDHW 127

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) 

Oil-fired Mechanical Draft Hot Water CPB SOMDHW 48

Large (>2,500,000 Btu/h) Oil-fired Mechanical 

Draft Hot Water CPB LOMDHW 24

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) 

Gas-fired Mechanical Draft Steam CPB SGMDST 98

Large (>2,500,000 Btu/h) Gas-fired Mechanical 

Draft Steam CPB LGMDST 106

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) 

Oil-fired Mechanical Draft Steam CPB SOMDST 95

Large (>2,500,000 Btu/h) Oil-fired Mechanical 

Draft Steam CPB LOMDST 107

Residential Boilers (Input Rating <300kBtu/h) N/A 3

Total 2,354

Many boiler models have the capability to deliver both hot water and steam and 

often have only one efficiency rating listed in the AHRI database. In such instances, DOE 

classified these boilers into steam equipment classes because boilers capable of 

delivering both steam and hot water can be tested and rated for performance in only the 

steam mode, if the manufacturer chooses. (See 10 CFR 431.86) In view of existing 

3-14
energy conservation standards, steam equipment classes have lower efficiency standards 

compared to corresponding hot water equipment classes and thus it is likely that the 

rating in steam mode is more conservative.

After sorting the boiler models, DOE verified listed efficiency levels of the 

models with equipment literature. In the previous rulemaking, DOE combined natural 

draft and mechanical draft boilers into a single equipment class (except for gas-fired 

steam boilers). With the introduction of new equipment classes, formed by dividing these 

equipment classes further based on draft type, the existing energy conservations standards 

will apply to the six new equipment classes. These standards served as a baseline for

conducting various analyses for this rulemaking. Table 3.2.9. shows all 16 equipment 

classes along with their corresponding energy conservation standards or baseline 

efficiencies. 

Table 3.2.9. New Equipment Standards with Existing Minimum Efficiency Levels

Size Category Abbreviation Efficiency Standard

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) SGNDHW 80% ET

Large (>2,500,000 Btu/h) LGNDHW 82% EC

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) SONDHW 82% ET

Large (>2,500,000 Btu/h) LONDHW 84% EC

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) SGNDST 77% ET

Large (>2,500,000 Btu/h) LGNDST 77% ET

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) SONDST 81% ET

Large (>2,500,000 Btu/h) LONDST 81% ET

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) SGMDHW 80% ET

Large (>2,500,000 Btu/h) LGMDHW 82% EC

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) SOMDHW 82% ET

Large (>2,500,000 Btu/h) LOMDHW 84% EC

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) SGMDST 79% ET

Large (>2,500,000 Btu/h) LGMDST 79% ET

Small (≥300,000 Btu/h and ≤2,500,000 Btu/h) SOMDST 81% ET

Large (>2,500,000 Btu/h) LOMDST 81% ET

* ET refers to Thermal Efficiency and EC refers to Combustion Efficiency

During its review of the commercial packaged boiler performance data, DOE 

noticed that some boiler models did not have their relevant efficiency listed in the 

database. These models were rejected from the analysis. DOE also found several models 

with efficiency ratings below the Federal requirements and did not include those units in 

its analysis. Lastly, DOE found three boiler models listed among AHRI data, which were 

below input ratings for qualifying as a commercial packaged boiler, as defined by under 

10 CFR 431.82, and these models were also removed from the analysis. Figure 3.2.1

below shows the numbers of boiler models which were rejected and the remaining ones 

which were used for analysis. 

3-15
Figure 3.2.1. Qualifying Checks on Air-Conditioning, Heating, and Refrigeration 

Institute Database for Commercial Packaged Boilers 

To analyze each equipment class in terms of efficiency level, input rating, and 

manufacturer, listed models within each equipment class were further categorized by

input rating. Small-size boiler models had input rating categories of 100 kBtu/h step sizes 

(e.g., 300 kBtu/h – 400 kBtu/h, 400 kBtu/h – 500 kBtu/h, etc.). The lower limit of each 

input rating category was included within category range while the upper limit was 

excluded (e.g., 300 kBtu/h – 400 kBtu/h has a range of ≥ 300 kBtu/h to 400 kBtu/h). For 

the last input rating category for small boilers, however, DOE made an exception to 

include the upper limit within the range of the category (i.e., 2,400 kBtu/h – 2,500 kBtu/h 

had a range of ≥ 2,400 kBtu/h to ≤ 2,500 kBtu/h). This exception allowed boilers having 

a 2,500 kBtu/h input rating to be included as part of the last input rating category for 

small boilers rather than having a separate input rating category altogether.

Similarly, DOE classified large commercial packaged boiler equipment classes. 

Input rating categories set up for such boilers had a step size of 1,500 kBtu/h. Also, 

unlike the input rating categories of small boilers, these input rating categories exclude 

the lower limit of the category and include the upper limit (e.g., 2,500 kBtu/h – 4,000

kBtu/h has a range defined by >2,500 kBtu/h to ≤4,000 kBtu/h). As such, DOE created 

22 input rating categories for small CPB equipment classes and 11 input rating categories 

for large CPB equipment classes. The distribution of commercial packaged boilers within 

these input rating ranges is shown in the figures appearing later in this section.

Boilers were also grouped and examined based on efficiency. The efficiency 

groupings were created by rounding off the relevant efficiency metric for every boiler of 

each equipment class to the nearest integer. For example, all efficiency values between 

79.5 and 79.9-percent were rounded to 80-percent, while all efficiency values equal to or 

less than 79.4-percent were rounded to 79-percent. Examining boiler models by 

efficiency levels helped DOE analyze the influence of boiler characteristics (condensing, 

modulating, material used etc.) on efficiency.

Commercial Packaged 

Boilers Database 

[2354]

Accepted CPBs 

[1989]

Rejected CPBs 

[365]

Missing Relevant 

Efficiency Metric 

[227]

Below Minimum 

Efficiency Level 

[135]

Below 300kBtu/h 

Input Rating 

[3]

3-16
Using the aforementioned equipment classes, baselines, input rating categories,

and efficiency groupings, DOE conducted its market analysis for each equipment class 

based on input rating, distribution of boilers based on efficiency levels, equipment 

offering by each company, and variation of efficiency with respect to input rating. DOE 

also gave due consideration to important characteristics of boilers, such as condensing, 

modulating or material type, and assessed how these factors influence input rating and 

efficiency. The following sections describe equipment classes and the results of the 

market assessment for each class.

3.2.6.1 Small (300kBtu/h - 2,500kBtu/h) Gas-Fired Natural Draft Hot 

Water Commercial Packaged Boilers

Approximately 10-percent of the boiler models in the AHRI directory of 

commercial packaged boiler performance are included in the small gas-fired natural draft 

hot water equipment class. Under the existing standards, these boilers must have a 

minimum thermal efficiency of 80-percent. 

Nearly 50-percent of qualified boilers in this equipment class have a copper heat 

exchanger, while the rest have a heat exchanger made of cast iron. Because these boilers 

vent to the atmosphere through natural draft, none of the boilers were condensing type. 

The information from the AHRI database also revealed that none of the boilers had 

modulating burners. Figure 3.2.2 below shows the distribution of input ratings for boilers 

with cast iron and copper heat exchangers.

Figure 3.2.2. Distribution of Small Gas-fired Natural Draft Hot Water Commercial 

Packaged Boilers Based on Input Rating

Manufacturers.

There are 10 AHRI-member manufacturers which currently produce boilers of 

this equipment class. Raypak was the only company to produce boilers of all input rating 

0

5

10

15

20

25

30

300 - 400400 - 500500 - 600600 - 700700 - 800800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 2000

2000 - 2100

2100 - 2200

2200 - 23002300 - 2400

2400 - 2500

Number of Models

Input Ratings Category [kBtu/h]

Distribution of Boilers Based on Input Ratings

Cast Iron Copper

3-17
categories. Table 3.2.10. below, shows different manufacturers of small gas-fired hot 

water CPBs and the sizes which they manufacture.

Table 3.2.10. List of Companies in the Air-Conditioning, Heating, and Refrigeration 

Institute Directory that Manufacture Small Gas-Fired Natural Draft 

Hot Water Commercial Packaged Boilers

Name of Manufacturer

300 kBtu/h -

500kBtu/h

500kBtu/h -

700kBtu/h

700kBtu/h -

900kBtu/h

900kBtu/h -

1100kBtu/h

1100kBtu/h -

1300kBtu/h

1300 kBtu/h -

1500kBtu/h

1500kBtu/h -

1700kBtu/h

1700kBtu/h -

1900kBtu/h

1900kBtu/h -

2100kBtu/h

2100kBtu/h -

2300kBtu/h

2300kBtu/h -

2500kBtu/h

A.O. Smith Water Products Co. X X X X X X X X

Bosch Thermotechnology Corp X X X X X X X X X

Burnham Commercial X X

Lochinvar Corporation X X

Mestek, Inc. X

P B Heat, LLC X X

Raypak, Inc. X X X X X X X X X X X

RBI Water Heaters Division of 

Mestek, Inc. X X X X X X X X

Slant/Fin Corporation X X X

U.S. Boiler Co., Subsidiary of 

Burnham Holdings,Inc X

Characterization of Boilers Based on Efficiency. 

For the distribution of equipment based on energy efficiency levels, DOE

compared boilers having cast iron heat exchangers with those having copper heat 

exchangers. The analysis shows that most of the cast iron boilers were well spread out 

over different efficiency levels from 80 to 84-percent. Most boilers in this equipment 

class are rated 82-percent efficient, while 90-percent of these boilers had a copper heat 

exchanger. Some boilers also had efficiencies as high as 85-percent; all these boilers were 

made from copper. The chart below (Figure 3.2.3) shows distribution of boiler models 

with respect to thermal efficiency levels.

3-18
Figure 3.2.3. Distribution of Small Gas-Fired Natural Draft Hot Water Commercial 

Packaged Boilers Based on Thermal Efficiency 

Variation of Average Efficiency with Input Rating. 

DOE analyzed the distribution of thermal efficiencies with respect to input 

capacity. Performance of copper and cast iron were considered separately. Findings 

indicate higher thermal efficiencies for copper boilers as compared to cast iron. 

In general, the thermal efficiencies for boilers of all input sizes are fairly 

consistent. Comparisons indicate that cast iron boilers have lower efficiency when 

compared to copper boilers at the same input ratings. However, as boiler capacity 

increases, cast iron boiler efficiency shows an increase. Figure 3.2.4 below shows the 

variation of average thermal efficiency with input size.

Figure 3.2.4. Comparison of Average Thermal Efficiency with Small Gas-Fired 

Natural Draft Hot Water Commercial Packaged Boilers Sub Category 

Based on Input Rating

0

10

20

30

40

50

60

70

80 81 82 83 84 85

Number of Models

Thermal efficiency [%]

Distribution of Boilers Based on Thermal Efficiency

Cast Iron Copper

 78.00

 79.00

 80.00

 81.00

 82.00

 83.00

 84.00

 85.00

300 - 400400 - 500500 - 600600 - 700700 - 800800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 2000

2000 - 2100

2100 - 2200

2200 - 23002300 - 2400

2400 - 2500

Average Thermal Efficiency [%]

Input Rating Category [kBtu/h]

Average Thermal Efficiency Based on Input Rating

Cast Iron Copper

3-19
3.2.6.2 Large (>2,500kBtu/h) Gas-Fired Natural Draft Hot Water 

Commercial Packaged Boilers

Large gas-fired natural draft hot water CPBs are required under 10 CFR 431.87 to 

have a minimum efficiency standard of 82-percent combustion efficiency. All boiler 

models in this class are non-condensing and non-modulating. They are either made from 

cast iron or copper. Copper boiler models were found to have higher capacities than cast 

iron boilers. A review of AHRI’s database suggests that the models of this equipment 

class available on the market span input ratings from 2,500 kBtu/h to 5,500 kBtu/h. Only 

21 models were included in this equipment class. Figure 3.2.5 below shows distribution 

of boilers based on input rating.

Figure 3.2.5. Distribution of Large Gas-Fired Natural Draft Hot Water Commercial 

Packaged Boilers Based on Input Rating

Manufacturers.

There are four manufacturers in the AHRI directory that produce boilers of this 

equipment class. While all these manufacturers produce boilers having an input rating of 

2,500kBtu/h to 4,000kBtu/h, only one manufacturer produces boilers having inputs that 

range from 4,000kBtu/h to 5,500kBtu/h. Table 3.2.11. below shows a list of 

manufacturers which produce boilers of this equipment class.

Table 3.2.11. List of Companies in the Air-Conditioning, Heating, and Refrigeration 

Institute Directory that Manufacture Large Gas-Fired Natural Draft 

Hot Water Commercial Packaged Boilers

Name of Manufacturer 2500 -4000 [kBtu/h] 4000 -5500 [kBtu/h]

Laars Heating Systems Company X X

Raypak, Inc. X

RBI Water Heaters Division Of Mestek, 

Inc. X

Slant/Fin Corporation X

0

5

10

15

20

2500 - 4000 4000 - 5500

Number of Models

Input Rating Category [kBtu/h]

Distribution of Boilers Based on Input Ratings

Cast Iron Copper

3-20
Characterization of Boilers Based on Efficiency. 

The distribution of boilers based on combustion efficiency shows that most of the 

boilers in the large gas-fired natural draft hot water equipment class operate at 82-percent

combustion efficiency, with a smaller portion operating at 83-percent combustion 

efficiency. Analysis shows that a major portion of the boilers at 82-percent are copper 

boilers, while all boilers at 83-percent are cast iron. Figure 3.2.6 below shows the 

distribution of boiler models based on combustion efficiency levels.

Figure 3.2.6. Distribution of Large Gas-Fired Natural Draft Hot Water Commercial 

Packaged Boilers Based on Combustion Efficiency 

Variation of Combustion Efficiency with Input Rating. 

The combustion efficiency of boilers in this equipment class appears to vary 

moderately with input size, but this may be due to the limited amount of data available. 

Figure 3.2.7 below shows this trend in the form of a bar-graph. 

0

2

4

6

8

10

12

14

16

82 83

Number of Models

Combustion Efficiency [%]

Distribution of Boilers Based on Combustion Efficiency

Cast Iron Copper

81.6

81.8

82

82.2

82.4

82.6

82.8

2500 - 4000 4000 - 5500

Average Combustion Efficiency 

[%]

Input Rating Category [kBtu/h]

Average Combustion Efficiency Based on Input Rating

Cast Iron Copper

3-21
Figure 3.2.7. Comparison of Average Combustion Efficiency with Large Gas-Fired 

Natural Draft Hot Water Commercial Packaged Boilers Sub Category 

Based on Input Rating

3.2.6.3 Small (300kBtu/h - 2,500kBtu/h) Oil-Fired Natural Draft Hot Water

Commercial Packaged Boilers

Under 10 CFR 431.87, the small oil-fired natural draft hot water commercial 

packaged boilers are required to have a minimum efficiency of 82-percent. AHRI’s 

Directory of Certified Product Performance indicates that a small percentage of these 

boilers are made from steel, while the rest are made from cast iron. The steel boilers were 

found to have lower input ratings than the cast iron boilers. Figure 3.2.8 below shows 

distribution of boiler models for different input rating categories. 

Figure 3.2.8. Distribution of Small Oil Fired Natural Draft Hot Water Boilers Based 

on Input Ratings

Manufacturers 

Out of 33 manufacturers in the AHRI directory, only 5 produce these types of 

boilers. Table 3.2.12. below shows the different manufacturers and size of boilers 

produced by each manufacturer.

Table 3.2.12. List of Companies in the Air-Conditioning, Heating, and Refrigeration 

Institute Directory that Manufacture Small Oil-Fired Natural Draft 

Hot Water Commercial Packaged Boilers

Name of Manufacturer

300 kBtu/h -

500kBtu/h

500kBtu/h -

700kBtu/h

700kBtu/h -

900kBtu/h

900kBtu/h -

1100kBtu/h

1100kBtu/h -

1300kBtu/h

1300 kBtu/h -

1500kBtu/h

1500kBtu/h -

1700kBtu/h

1700kBtu/h -

1900kBtu/h

1900kBtu/h -

2100kBtu/h

2100kBtu/h -

2300kBtu/h

Bosch Thermotechnology Corp X X X X X X X X X

0

2

4

6

8

10

12

14

300 - 400400 - 500500 - 600600 - 700700 - 800800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 20002000 - 21002100 - 22002200 - 23002300 - 24002400 - 2500

Number of Models

Input Rating Category [kBtu/h]

Distribution of Boilers Based on Input Ratings

Cast Iron Steel

3-22
New Yorker Boiler Co., Subsidiary 

of Burnham Holdings Inc. X X

Slant/Fin Corporation X X X X X X X

U.S. Boiler Co., Subsidiary of 

Burnham Holdings,Inc X

Weil-Mclain X

Characterization of Boilers Based on Efficiency. 

Figure 3.2.9 below shows a bar chart indicating distribution of boilers with 

respect to efficiency levels. As with other natural draft equipment classes, all boilers are 

non-condensing or non-modulating. 

Figure 3.2.9. Distribution of Small Oil-Fired Natural Draft Hot Water Commercial 

Packaged Boilers Based on Thermal Efficiency

Variation of Average Efficiency with Input Rating. 

Based on AHRI’s directory, it may be noted that average thermal efficiencies of 

cast iron boilers increase with input capacity of the boiler. Figure 3.2.10 below shows 

average thermal efficiency of boilers for each input rating category. 

0

2

4

6

8

10

12

14

16

82 83 84 85 86 87

Number of Models

Thermal Efficiency [%]

Distribution of Boilers Based on Thermal Efficiency 

Cast Iron Steel

3-23
Figure 3.2.10. Comparison of Average Thermal Efficiency of Small Oil-Fired 

Natural Draft Hot Water Commercial Packaged Boilers Sub Category 

Based on Input Rating

3.2.6.4 Large (>2,500kBtu/h) Oil-Fired Natural Draft Hot Water 

Commercial Packaged Boilers

There are only six models of large oil-fired natural draft hot water commercial 

packaged boilers in the AHRI’s Directory of Certified Product Performance for

commercial packaged boilers. Boilers of this equipment class are required to have a 

combustion efficiency of at least 84-percent. All boilers of this class have an input rating 

between 2,500 kBtu/h and 4,000 kBtu/h. All of the boiler models are produced by 

Slant/Fin Corporation and have combustion efficiency in the range from 84-percent to 

86-percent.

3.2.6.5 Small (300kBtu/h‒2,500kBtu/h) Gas-Fired Natural Draft Steam 

Commercial Packaged Boilers

DOE analyzed 254 small gas-fired natural draft steam commercial packaged 

boilers listed in AHRI’s Directory of Certified Product Performance. All boilers in this 

equipment class are cast iron and non-condensing. Figure 3.2.11 below shows 

distribution of commercial packaged boilers with respect to boiler size. The distribution 

shows that the majority of commercial boilers in this equipment class are between 300-

400 kBtu/h.

 78.00

 80.00

 82.00

 84.00

 86.00

 88.00

300 - 400400 - 500500 - 600600 - 700700 - 800800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 20002000 - 21002100 - 22002200 - 23002300 - 24002400 - 2500

Average Thermal Efficiency [%]

Input Rating Category [kBtu/h]

Average Thermal Efficiency Based on Input Rating

Cast Iron Steel

3-24
Figure 3.2.11. Distribution of Small Gas-Fired Natural Draft Steam Commercial 

Packaged Boilers Based on Input Rating

Manufacturers.

There are 11 AHRI-member manufacturers that produce boilers in this equipment 

class. Table 3.2.13. below shows a list of manufacturers along with boiler size which 

these companies are able to produce.

Table 3.2.13. List of Companies in the Air-Conditioning, Heating, and Refrigeration 

Institute Directory that Manufacture Small Gas-Fired Natural Draft

Steam Commercial Packaged Boilers

Name of Manufacturer

300 kBtu/h -

500kBtu/h

500kBtu/h -

700kBtu/h

700kBtu/h -

900kBtu/h

900kBtu/h -

1100kBtu/h

1100kBtu/h -

1300kBtu/h

1300 kBtu/h -

1500kBtu/h

1500kBtu/h -

1700kBtu/h

1700kBtu/h -

1900kBtu/h

1900kBtu/h -

2100kBtu/h

2100kBtu/h -

2300kBtu/h

2300kBtu/h -

2500kBtu/h

Burnham Commercial X X X X X X X X X

Crown Boiler Co, Subsidiary

Of Burnham Holdings Inc. X X X X X X X X X X X

Dunkirk Boilers, ECR

International, Inc. X X X X X X X X X X X

P B Heat, LLC X X X X X X X X X X X

Pennco, ECR International, 

Inc. X X X X X X X X X X X

Slant/Fin Corporation X X X X X X X

Smith Cast Iron Boilers X X X X X X

U.S. Boiler Co., Subsidiary of 

Burnham Holdings,Inc X

Utica Boilers X X X X X X X X X X X

Utica Boilers, ECR

International, Inc. X X X X X X X X X X X

Weil-Mclain X X X X X X X X X X X

0

5

10

15

20

25

300 - 400400 - 500500 - 600600 - 700700 - 800800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 20002000 - 21002100 - 22002200 - 23002300 - 24002400 - 2500

Number of Models

Input Rating Category [kBtu/h]

Distribution of Boilers Based on Input Ratings

3-25
Characterization of Boilers Based on Efficiency. 

The baseline efficiency for this equipment class is a thermal efficiency value of 

77-percent. A major portion of the boilers – close to 67-percent had reported thermal 

efficiency levels of 78-percent. Figure 3.2.12 below shows distribution of equipment

based on thermal efficiencies.

Figure 3.2.12. Distribution of Small Gas-Fired Natural Draft Steam Commercial 

Packaged Boilers Based on Thermal Efficiency

Variation of Average Efficiency with Input Rating. 

The average thermal efficiency for each input rating was calculated to observe the 

dependence of efficiency on boiler size. Figure 3.2.13 below shows the variation of 

thermal efficiency with boiler input category. The average efficiency varies slightly with 

input size, but always remains between 77-percent and 78-percent.

0

20

40

60

80

100

120

140

160

180

77 78 79 80

Number of Models

Thermal Efficiency

Distribution of Boilers Based on Thermal Efficiency

3-26
Figure 3.2.13. Comparison of Average Thermal Efficiency of Small Gas-Fired 

Natural Draft Steam Commercial Packaged Boilers Sub Category 

Based on Input Rating

3.2.6.6 Large (>2,500kBtu/h) Gas-Fired Natural Draft Steam Commercial 

Packaged Boilers

Large gas-fired natural draft steam commercial packaged boilers are required to 

have minimum thermal efficiency standard of 77-percent. There are 163 boilers in this 

class, which is the largest representation of the large (>2,500kBtu/h) boiler equipment 

classes in the database. All boilers in this class are made of cast iron and are noncondensing and non- modulating. Figure 3.2.14 below shows distribution of boiler 

models over various input rating categories.

Figure 3.2.14. Distribution of Large Gas-Fired Natural Draft Steam Commercial 

Packaged Boilers Based on Input Rating

 76.5

 77.0

 77.5

 78.0

 78.5

 79.0

 79.5

300 - 400400 - 500500 - 600600 - 700700 - 800800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 20002000 - 21002100 - 22002200 - 23002300 - 24002400 - 2500

Average Thermal Efficiency [%]

Input Rating Category [kBtu/h]

Average Thermal Efficiency Based on Input Rating

0

20

40

60

80

2500 - 40004000 - 55005500 - 70007000 - 8500

8500 - 10000

10000 - 1150011500 - 1300013000 - 1450014500 - 1600016000 - 1750017500 - 19000

Number of Models

Input Rating Category [kBtu/h]

Distribution of Boilers Based on Input Ratings

3-27
Manufacturers. 

There are seven manufacturers listed in the AHRI Directory of Certified Product 

Performance which produce boilers in this equipment class. Table 3.2.14. below shows 

different manufacturers and the sizes of boiler they are capable of manufacturing.

Table 3.2.14. List of Companies in the Air-Conditioning, Heating, and Refrigeration 

Institute Directory that Manufacture Large Gas-Fired Natural Draft 

Steam Commercial Packaged Boilers

Name of 

Manufacturer

2500 -4000 

[kBtu/h]

4000 -5500 

[kBtu/h]

5500 -7000 

[kBtu/h]

7000 -8500 

[kBtu/h]

8500 -10000 

[kBtu/h]

10000 -11500 

[kBtu/h]

11500 -13000 

[kBtu/h]

13000 -14500 

[kBtu/h]

14500 -16000 

[kBtu/h]

16000 -17500 

[kBtu/h]

17500 -19000 

[kBtu/h]

Dunkirk Boilers, 

ECR International, 

Inc.

X

P B Heat, LLC X X X X X

Pennco, ECR 

International, Inc. X

Smith Cast Iron 

Boilers X X X X X X X X X X X

Utica Boilers X

Utica Boilers, ECR

International, Inc. X

Weil-Mclain X

Characterization of Boilers Based on Efficiency. 

All boiler models were characterized based on thermal efficiency. Approximately 

60-percent of the boilers operate at an efficiency level of 78-percent. Figure 3.2.15.

below shows distribution of boilers with respect to thermal efficiency levels.

0

20

40

60

80

100

78 79 80 81

Number of Models

Thermal Efficiency [%]

Distribution of Boilers Based on Thermal Efficiency

3-28
Figure 3.2.15. Distribution of Large Gas-Fired Natural Draft Steam Commercial 

Packaged Boilers Based on Thermal Efficiency

Variation of Average Efficiency with Input Rating. 

The average thermal efficiency for each input rating was calculated to assess 

impact of boiler size on performance. Figure 3.2.16. shows the variation of average 

thermal efficiency on input rating category. The trend shows that average thermal 

efficiency increased gradually until the input reached 10,000-11,500 kBtu/h, after which 

there is a gradual decline in performance.

Figure 3.2.16. Comparison of Average Thermal Efficiency of Large Gas-Fired 

Natural Draft Steam Commercial Packaged Boilers Sub Category 

Based on Input Rating

3.2.6.7 Small (300kBtu/h-2,500kBtu/h) Oil-Fired Natural Draft Steam 

Commercial Packaged Boilers

Small oil-fired natural draft steam commercial packaged boilers constitute 2.2-

percent of the database. These boilers are required to have a minimum thermal efficiency

of 81-percent. There are 37 qualified boilers within this equipment class listed in the 

AHRI Directory of Certified Product Performance. All boiler models of this equipment 

class are made from cast iron and are non-modulating and non-condensing. 

More than 50-percent of boilers manufactured in this equipment class have an 

input rating between 300 and 500 kBtu/h. Figure 3.2.17. below shows this distribution of 

boilers based on input rating categories.

77

78

79

80

81

2500 - 40004000 - 55005500 - 70007000 - 8500

8500 - 10000

10000 - 1150011500 - 1300013000 - 1450014500 - 1600016000 - 1750017500 - 19000

Average Thermal Efficiency [%]

Input rating category [kBtu/h]

Average Thermal Efficiency Based on Input Rating

3-29
Figure 3.2.17. Distribution of Small Oil-Fired Natural Draft Steam Boilers Based on 

Input Ratings

Manufacturers.

The 37 models listed in the AHRI directory for this equipment class are 

manufactured by six companies. Out of the 37 models, 25 models are manufactured by 

Slant/Fin Corporation alone. Other major manufacturing companies along with the boiler 

input ratings which they manufacture are listed in the Table 3.2.15. below.

Table 3.2.15. List of Companies in the Air-Conditioning, Heating, and Refrigeration 

Institute Directory that Manufacture Small Oil-Fired Natural Draft 

Steam Commercial Packaged Boilers

Name of Manufacturer

300 kBtu/h -

500kBtu/h

500kBtu/h -

700kBtu/h

700kBtu/h -

900kBtu/h

900kBtu/h -

1100kBtu/h

1100kBtu/h -

1300kBtu/h

1300 kBtu/h -

1500kBtu/h

1500kBtu/h -

1700kBtu/h

1700kBtu/h -

1900kBtu/h

1900kBtu/h -

2100kBtu/h

2100kBtu/h -

2300kBtu/h

2300kBtu/h -

2500kBtu/h

P B Heat, LLC X

Slant/Fin Corporation X X X X X X X X X

Smith Cast Iron Boilers X X X

U.S. Boiler Co., Subsidiary Of 

Burnham Holdings,Inc X

Weil-Mclain X

Characterization of Boilers Based on Efficiency. 

The distribution of boilers based on thermal efficiency shows that most CPBs in 

this equipment class operate at 82-percent efficiency with the least number of boilers at 

81-percent. Figure 3.2.18. shows this distribution.

0

2

4

6

8

10

12

14

16

18

300 - 400400 - 500500 - 600600 - 700700 - 800800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 20002000 - 21002100 - 22002200 - 23002300 - 24002400 - 2500

Number of Models

Input Rating Category [kBtu/h]

Distribution of Boilers Based on Input Ratings

3-30
Figure 3.2.18. Distribution of Small Oil-Fired Natural Draft Steam Commercial 

Packaged Boilers Based on Thermal Efficiency 

Variation of Average Efficiency with Input Rating. 

The average thermal efficiency for each input rating was calculated to assess 

impact of boiler size on efficiency. Figure 3.2.19 shows the variation of average thermal 

efficiency with input rating. The trend shows that average thermal efficiency peaks at an 

input rating of about 600-700kBtu/h.

Figure 3.2.19. Comparison of Average Thermal Efficiency of Small Oil-Fired 

Natural Draft Steam Commercial Packaged Boilers Sub Category 

Based on Input Rating

0

2

4

6

8

10

12

14

16

18

81 82 83

Number of Models

Thermal Efficiency [%]

Distribution of Boilers Based on Thermal Efficiency

 79.50

 80.00

 80.50

 81.00

 81.50

 82.00

 82.50

 83.00

300 - 400400 - 500500 - 600600 - 700700 - 800800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 20002000 - 21002100 - 22002200 - 23002300 - 24002400 - 2500

Average Thermal Efficiency [%]

Input Rating Category [kBtu/h]

Average Thermal Efficiency Based on Input Rating

3-31
3.2.6.8 Large (>2,500kBtu/h) Oil-Fired Natural Draft Steam Commercial 

Packaged Boilers

There are 95 large oil-fired natural draft steam CPB models included in AHRI’s 

Directory of Certified Product Performance of commercial packaged boilers. These 

boilers are required to have a minimum thermal efficiency of 81-percent. All boilers in

this equipment class listed in the AHRI directory are non-condensing and nonmodulating, and have a cast iron heat exchanger. Figure 3.2.20. below shows the 

distribution of boilers by input rating. 

Figure 3.2.20. Distribution of Large Oil-Fired Natural Draft Steam Commercial 

Packaged Boilers Based on Input Rating

The maximum number of boilers is in the 2500 kBtu/h to 4000 kBtu/h input rating 

range. The number of boilers gradually decreases with increasing boiler input rating. 

DOE also notes that the largest oil-fired boilers were found in this equipment class. 

Manufacturers.

Smith Cast Iron Boilers is the sole company listed in AHRI database which 

manufactures boilers in this equipment class. 

Characterization of Boilers Based on Efficiency. 

Boilers in this class have a thermal efficiency ranging from 81-percent to 86-

pecent. Figure 3.2.21. shows the distribution of boilers by thermal efficiency. More than 

50-percent of boilers are listed with thermal efficiency between 82-percent and 84-

percent while there are 33 boilers in the range between 81-percent and 82-percent.

0

5

10

15

20

25

2500 - 40004000 - 55005500 - 70007000 - 8500

8500 - 10000

10000 - 1150011500 - 1300013000 - 1450014500 - 1600016000 - 17500

Number of Models

Input Rating Category [kBtu/h]

Distribution of Boilers Based on Input Ratings

3-32
Figure 3.2.21. Distribution of Large Oil-Fired Natural Draft Steam Commercial 

Packaged Boilers Based on Thermal Efficiency 

Variation of Average Efficiency with Input Rating. 

Figure 3.2.22. below shows the average thermal efficiency as a function of input 

rating. The values vary moderately between input categories. There are no modulating or 

condensing boilers in this equipment class.

Figure 3.2.22. Comparison of Average Thermal Efficiency of Large Oil-Fired 

Natural Draft Steam Commercial Packaged Boilers Sub-Category 

Based on Input Rating

3.2.6.9 Small (300kBtu/h-2,500kBtu/h) Gas-Fired Mechanical Draft Hot 

Water Commercial Packaged Boilers

Small gas-fired mechanical draft hot water commercial packaged boilers

constitute about 32-percent of models in the AHRI Directory of

0

5

10

15

20

25

30

35

81 82 83 84 85

Number of Models

Thermal Efficiency [%]

Distribution of Boilers Based on Thermal Efficiency

81

81.5

82

82.5

83

83.5

2500 - 40004000 - 55005500 - 70007000 - 8500

8500 - 10000

10000 - 1150011500 - 1300013000 - 1450014500 - 1600016000 - 17500

Average Thermal Efficiency [%]

Input Rating Category [kBtu/h]

Average Thermal Efficiency Based on Input Rating

3-33
Certified Product Performance. This equipment class contains the highest number 

of boiler models as compared to all other equipment classes. Boilers in this equipment 

class are required to have a minimum thermal efficiency of 80 percent. Boilers in this 

equipment class are made from aluminum, cast iron, copper, stainless steel, or steel. 

Figure 3.2.23 below shows a pie chart which depicts the constitution of boilers in this 

equipment class based on materials used to make the primary heat exchanger. Figure 

3.2.24 depicts classification of condensing boilers based on the type of material used for 

making the primary heat exchanger.

In condensing boilers, the condensate that is removed from exhaust gases turns

acidic in nature, due to the presence of carbon dioxide in flue gases. As a result, materials 

chosen for the heat exchanger for this purpose are those which have capabilities to resist 

acidic corrosion. Considering this, DOE notes, that the classification of boiler shown in 

Figure 3.2.23 and Figure 3.2.24 is based on primary heat exchanger which does not come 

in contact with the acidic condensate. The secondary or condensing heat exchanger which 

does come in contact with the acidic condensate is made from a different material which 

is typically corrosion resistant. This observation was verified by DOE through literature 

review of condensing boiler models.

Figure 3.2.23. Classification of Small Gas Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based on Material Used in the Primary

Heat Exchanger

6%

6%

62%

23%

3%

Distribution of Boilers Based on Material of Primary 

Heat Exchanger

Aluminum

Cast Iron

Copper

Stainless Steel

Steel

Total: 728

3-34
Figure 3.2.24. Classification of Small Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Condensing Boilers Based on Material Used in 

the Primary Heat Exchanger

In this equipment class, out of 728 boiler models, 337 models were condensing 

boilers and 463 models were modulating. Figure 3.2.25. below shows the distribution of 

boilers based on boiler size. The figure also shows the number of condensing and 

modulating boilers in each input rating category. 

Figure 3.2.25. Distribution of Small Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based on Input Rating

This chart indicates that condensing boilers are well spread out over the entire 

boiler-size range. Most boilers within this equipment class have an input rating between

300 and 400 kBtu/h. Between input ratings of 2,100 to 2,500 kBtu/h, there are very few 

boilers.

13%

2%

29% 50%

6%

Distribution of Condensing Boilers Based on Material 

of Primary Heat Exchanger

Aluminum

Cast Iron

Copper

Stainless Steel

Steel

Total: 337

0

20

40

60

80

100

300 - 400400 - 500500 - 600600 - 700700 - 800800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 20002000 - 21002100 - 22002200 - 23002300 - 24002400 - 2500

Number of Models

Input Rating Category [kBtu/h]

Distribution of Boilers Based on Input Ratings

Other Boilers Condensing Boilers Condensing and Modulating Boilers Modulating Boilers

3-35
Manufacturers. 

Of the companies listed in the AHRI Directory of Certified Product Performance, 

27 out of 33 manufacture small gas-fired mechanical draft hot water commercial 

packaged boilers. Raypak, Lochinvar and Camus Hydronics appear to be the major 

manufacturers in this equipment class based on the number of models offered. Table 

3.2.16. below shows the list of manufacturers and the size of boiler which they produce.

Table 3.2.16. List of Companies in the Air-Conditioning, Heating, and Refrigeration 

Institute Directory that Manufacture Small Gas-Fired Mechanical 

Draft Hot Water Commercial Packaged Boilers

Name of Manufacturer

300 kBtu/h -

500kBtu/h

500kBtu/h -

700kBtu/h

700kBtu/h -

900kBtu/h

900kBtu/h -

1100kBtu/h

1100kBtu/h -

1300kBtu/h

1300 kBtu/h -

1500kBtu/h

1500kBtu/h -

1700kBtu/h

1700kBtu/h -

1900kBtu/h

1900kBtu/h -

2100kBtu/h

2100kBtu/h -

2300kBtu/h

2300kBtu/h -

2500kBtu/h

A.O. Smith Water Products Co. X X X X X X X X X X

Aerco International, Inc. X X X X X X

Aerco International, Inc. X

Bosch Thermotechnology Corp X X X X X X X X

Bryan Steam, LLC X X X

Burnham Commercial X X X X X X X X X X

Camus Hydronics Ltd. X X X X X X X X X X

Cleaver-Brooks X X X X X X

Crown Boiler Co, - Subsidiary Of 

Burnham Holdings Inc. X X X X X

DDR Americas, Inc. X X X X X X X X X X

Fulton Heating Solutions X X X X X

Harsco Industrial, Patterson-Kelley X X X X X X X

Heat Transfer Products Inc. X X X

Hydrotherm Division of Mestek, 

Inc. X X X X

Laars Heating Systems Company X X X X X X X X X

Lochinvar Corporation X X X X X X X X X X

P B Heat, LLC X X X

Parker Boiler Company X X X X X X

Raypak, Inc. X X X X X X X X X

RBI Water Heaters Division of 

Mestek, Inc. X X X X X X X X X X X

Slant/Fin Corporation X

Smith Cast Iron Boilers X X

Thermal Solutions Products LLC, 

Subsidiary Of Burnham Holdings 

Inc.

X X X X X X

Triangle Tube X

3-36
U.S. Boiler Co., Subsidiary of 

Burnham Holdings,Inc X X

Viessmann Manufacturing 

Company, Inc. X X X X X X X X X

Weil-Mclain X X X

 

Characterization of Boilers Based on Efficiency. 

Figure 3.2.26. shows the distribution of boiler in this equipment class by thermal 

efficiency. The distribution of these boilers is broadly divided based on condensing and 

non-condensing boilers and generally concentrated around two peaks: most of the noncondensing boilers have a thermal efficiency of 84 to 85-percent and most condensing 

boilers have a thermal efficiency of 94 to 95-percent.

Figure 3.2.26. Distribution of Small Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based On Thermal Efficiency 

Variation of Average Efficiency with Input Rating 

The presence of condensing boilers across the entire range of input ratings 

increases the average efficiency of boilers in this category substantially. All condensing 

boilers average over 93-percent. The average thermal efficiencies across all input ratings

were found to be between 84- percent and 93-percent. The average efficiency in this 

equipment class is significantly above the current minimum energy conservation standard 

of 80-percent. Figure 3.2.27 below shows the variation of average thermal efficiency with 

input rating category.

0

30

60

90

120

150

180

80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99

Number of Models

Thermal Efficiency [%]

Distribution of Boilers Based on Thermal Efficiency

Other Boilers Condensing Boilers Condensing and Modulating Boilers Modulating Boilers

3-37
Figure 3.2.27. Comparison of Average Thermal Efficiency of Small Gas-Fired 

Mechanical Draft Hot Water Commercial Packaged Boilers Sub 

Category Based on Input Rating

3.2.6.10 Large (>2,500kBtu/h) Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers

Approximately 5-percent of the boilers in AHRI’s Directory of Certified Product 

Performance are in the large gas-fired mechanical draft hot water equipment class. These 

boilers are required to have a minimum combustion efficiency of 79-percent. Similar to 

the small gas-fired mechanical draft hot water equipment class, boiler models in this 

equipment class are made from cast iron, steel, aluminum and copper. DOE analyzed the 

number of boilers of each heat exchanger material type. Figure 3.2.28 below is a pie chart 

that depicts the distribution of boiler models based on the material used in the primary 

heat exchanger. Figure 3.2.29 is a pie chart that shows classifications of condensing 

boilers based on material used to make the primary heat exchanger.

Similar to the observations in the small gas-fired mechanical draft hot water 

equipment class, DOE notes, that the classifications of boilers shown in Figure 3.2.28 and 

Figure 3.2.29 are based on primary heat exchangers that do not come in contact with the 

acidic condensate. The secondary or condensing heat exchanger that does come in 

contact with the acidic condensate is made from a different material that is typically 

corrosion resistant. This observation was subsequently validated by DOE through 

literature review of condensing boiler models.

 76.00

 80.00

 84.00

 88.00

 92.00

 96.00

 100.00

300 - 400400 - 500500 - 600600 - 700700 - 800800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 20002000 - 21002100 - 22002200 - 23002300 - 24002400 - 2500

Average Thermal Efficiency [%]

Input Rating Category [kBtu/h]

Average Thermal Efficiency Based on Input Rating

Overall thermal efficiency Condensing Boilers

3-38
Figure 3.2.28. Classification of Large Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based on Material Used in the Primary 

Heat Exchanger

Figure 3.2.29. Classification of Large Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Condensing Boilers Based on Material Used in 

the Primary Heat Exchanger

DOE also analyzed the distribution of boilers with respect to boiler input rating. 

Figure 3.2.30. below shows this analysis and highlights the type of boiler included in this 

equipment class (e.g., condensing and/or modulating, etc.) Out of the 83 models 

considered for the analysis, 61 boiler models had capacity ranging from 2,500-

4,000kBtu/h. No boiler had a capacity higher than 6,200kBtu/h. 

1%

46%

33%

18%

2%

Distribution of Boilers Based on Material of Primary 

Heat Exchanger

Aluminum

Cast Iron

Stainless Steel

Steel

Copper

Total: 83

2%

9%

57%

32%

Distribution of Condensing Boilers Based on Material 

of Primary Heat Exchanger

Aluminum

Cast Iron

Stainless Steel

Steel

Total: 47

3-39
Figure 3.2.30. Distribution of Large Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based on Input Rating

Manufacturers. 

A total of 17 manufacturers listed in the AHRI Directory of Certified Product 

Performance produced boilers in this equipment class. Bosch Thermotechnology Corp., 

Camus Hydronics Ltd. and DDR Americas Inc. produced majority of the models. Table 

3.2.17. below shows the list of manufacturers and the size of equipment they produced.

Table 3.2.17. List of Companies in the Air-Conditioning, Heating, and Refrigeration 

Institute Directory that Manufacture Large Gas-Fired Mechanical 

Draft Hot Water Commercial Packaged Boilers

Name of Manufacturer 2500 - 4000 

[kBtu/h]

4000 - 5500 

[kBtu/h]

5500 - 7000 

[kBtu/h]

A.O. Smith Water Products Co. X

Aerco International, Inc. X

Bosch Thermotechnology Corp X X

Bryan Steam, LLC X

Burnham Commercial X

Camus Hydronics Ltd. X X

DDR Americas, Inc. X X X

Fulton Heating Solutions X X

Harsco Industrial, Patterson-Kelley X

Hydrotherm Division Of Mestek, Inc. X

Lochinvar Corporation X

P B Heat, LLC X

Parker Boiler Company X X

RBI Water Heaters Division Of Mestek, Inc. X

Smith Cast Iron Boilers X

0

10

20

30

40

50

60

70

2500 - 4000 4000 - 5500 5500 - 7000

Number of Models

Input Rating Category [kBtu/h]

Distribution of Boilers Based on Input Ratings

Other Boilers Condensing Boilers Condensing and Modulating Boilers Modulating Boilers

3-40
Thermal Solutions Products LLC, 

Subsidiary Of Burnham Holdings Inc. X

Viessmann Manufacturing Company, Inc. X X

Characterization of Boilers Based on Efficiency. 

Similar to most equipment classes which have condensing boilers, the distribution 

of boiler combustion efficiency shows a concentration of equipment in two ranges – the 

non-condensing range (generally less than 86-percent) and the condensing range 

(generally over 92-percent). This is because condensing boilers typically achieve 

efficiencies which are substantially higher than non-condensing boilers. There are only 

three boilers in the range between condensing and non-condensing (roughly 88- to 91-

percent). A large number of non-condensing boilers were found to have a combustion 

efficiency of 85-percent, while the condensing boilers typically had combustion 

efficiencies around 94- to 95-percent. 

Figure 3.2.31. below shows the distribution of boilers over different combustion 

efficiency levels.

Figure 3.2.31. Distribution of Large Gas-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based On Combustion Efficiency 

Variation of Average Efficiency with Input Rating 

Average combustion efficiencies for this equipment class are between 89- and 90-

percent. These efficiency levels in each input category are raised significantly due to 

presence of high efficiency condensing boilers. The Figure 3.2.32. below shows average 

combustion efficiency levels of boilers in each input rating category. 

0

5

10

15

20

25

84 85 86 87 88 89 90 91 92 93 94 95 96 97

Number of Models

Combustion Efficiency [%]

Distribution of Boilers Based on Combustion Efficiency

Other Boilers Condensing Boilers Condensing and Modulating Boilers Modulating Boilers

3-41
Figure 3.2.32. Comparison of Average Combustion Efficiency of Large Gas-Fired 

Mechanical Draft Hot Water Commercial Packaged Boilers Sub 

Category Based on Input Rating

3.2.6.11 Small (300kBtu/h ‒ 2,500kBtu/h) Oil-Fired Mechanical Draft Hot 

Water Commercial Packaged Boilers

Small oil-fired mechanical draft hot water CPBs are required to have a minimum 

thermal efficiency of 82-percent. There are 48 commercial packaged boiler models in 

this equipment class, of which eight are condensing boilers. All condensing boilers of this 

equipment class listed in the database are made from steel. Figure 3.2.33. below shows 

the distribution of boiler models for each boiler input category.

Figure 3.2.33. Distribution of Small Oil-Fired Mechanical Draft Hot Water

Commercial Packaged Boilers Based on Input Rating

Manufacturers.

 84

 86

 88

 90

 92

 94

 96

2500 - 4000 4000 - 5500 5500 - 7000

Average Combustion Efficiency 

[%]

Input Rating Category [kBtu/h]

Average Combustion Efficiency Based on Input Rating

All Boilers Condensing Boilers

0

1

2

3

4

5

300 - 400400 - 500500 - 600600 - 700

700 -800

800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 20002000 - 21002100 - 22002200 - 23002300 - 24002400 - 2500

Number of Models

Input Rating Category [kBtu/h]

Distribution of Boilers Based on Input Ratings

Other Boilers Condensing Boilers

3-42
There are six companies listed in the AHRI Directory of Certified Product 

Performance that manufacture boilers in this equipment class. Table 3.2.18. below shows 

the names of the companies and the size of boilers they manufactured.

Table 3.2.18. List of Companies in the Air-Conditioning, Heating, and Refrigeration 

Institute Directory that Manufacture Small Oil-Fired Mechanical Draft 

Hot Water Commercial Packaged Boilers

Name of Manufacturer

300 kBtu/h -

500kBtu/h

500kBtu/h -

700kBtu/h

700kBtu/h -

900kBtu/h

900kBtu/h -

1100kBtu/h

1100kBtu/h -

1300kBtu/h

1300 kBtu/h -

1500kBtu/h

1500kBtu/h -

1700kBtu/h

1700kBtu/h -

1900kBtu/h

1900kBtu/h -

2100kBtu/h

2100kBtu/h -

2300kBtu/h

2300kBtu/h -

2500kBtu/h

Bosch Thermotechnology Corp X X X X X X

Burnham Commercial X X X X X X X X X

Crown Boiler Co. Subsidiary

Of Burnham Holdings Inc. X X X X X

Fulton Heating Solutions X

Slant/Fin Corporation X

Smith Cast Iron Boilers X X X X X X X X X X

Viessmann Manufacturing 

Company, Inc. X X X X X X X X X X

Characterization of Boilers Based on Efficiency

Non-condensing boilers, for this equipment class were spread over from 82-

percent to 88-percent with the most models at 87-percent and 88-percent efficiency 

levels. Condensing boilers were fairly evenly distributed between 92-percent and 98-

percent thermal efficiency. Figure 3.2.34. below shows distribution of boilers based on 

thermal efficiency class. 

Figure 3.2.34. Distribution of Small Oil-Fired Mechanical Draft Hot Water

Commercial Packaged boilers Based on Thermal Efficiency 

0

2

4

6

8

10

12

14

16

82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98

Number of Modelss

Thermal Efficiency [%]

Distribution of Boilers Based on Thermal Efficiency

Other Boilers Condensing Boilers

3-43
Variation of Average Efficiency with Input Rating 

The average thermal efficiency of models as a function of input rating was 

analyzed for this equipment class. The analysis shows an even distribution of thermal 

efficiency irrespective of input rating. Figure 3.2.35 below shows the variation of average 

thermal efficiency with input rating. Condensing boilers are also plotted in the same 

chart. This helped in understanding the sizes of condensing boilers in this equipment 

class. 

Figure 3.2.35. Comparison of Average Thermal Efficiency of Small Oil-Fired 

Mechanical Draft Hot Water Commercial Packaged Boilers Sub 

Category Based on Input Rating

3.2.6.12 Large (>2,500kBtu/h) Oil-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers

Large oil-fired mechanical draft boilers comprise only 1 percent of AHRI’s 

Directory of Certified Product Performance. These boilers are required, under subpart E 

of 10 CFR Part 431, to have a minimum combustion efficiency of 84-percent. Out of 24 

boiler models in this segment, six models are condensing and these condensing models 

each have a heat exchanger made from steel. All non-condensing boilers in this 

equipment class have a heat exchanger made from cast iron. Figure 3.2.36 below shows 

distribution of boilers of both types with respect to input size. 

 76

 80

 84

 88

 92

 96

 100

300 - 400400 - 500500 - 600600 - 700

700 -800

800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 20002000 - 21002100 - 22002200 - 23002300 - 24002400 - 2500

Average Thermal Efficiency [%]

Input Rating Category [kBtu/h]

Average Thermal Efficiency Based on Input Rating

Other Boilers Condensing Boilers

3-44
Figure 3.2.36. Distribution of Large Oil-Fired Mechanical Draft Hot Water

Commercial Packaged Boilers Based On Input Rating

Manufacturers.

There are four companies listed in the AHRI Directory of Certified Product 

Performance that manufacture boilers in this equipment class. Table 3.2.19. below 

describes the different boilers manufactured by different companies for each input rating.

Table 3.2.19. List of Companies in the A Air-Conditioning, Heating, and 

Refrigeration Institute Directory that Manufacture Large Oil-Fired 

Mechanical Draft Hot Water Commercial Packaged Boilers

Name of Manufacturer 2500 -4000 

[kBtu/h]

4000 -5500 

[kBtu/h]

5500 -7000 

[kBtu/h]

Bosch Thermotechnology Corp X X

Burnham Commercial X

Fulton Heating Solutions X X X

Viessmann Manufacturing 

Company, Inc. X X

Characterization of Boilers Based on Efficiency. 

As mentioned previously, there are six condensing boilers listed as part of this 

equipment class. As with other equipment classes with condensing boilers, the 

efficiencies are divided into two ranges: condensing and non-condensing. The minimum 

efficiency of a condensing boiler in this class is about 94-percent. Figure 3.2.37 below 

shows distribution of equipment for different combustion efficiencies. 

0

5

10

15

20

2500 - 4000 4000 - 5500 5500 - 7000

Number of Models

Input Rating Category [kBtu/h]

Distribution of Boilers Based on Input Ratings

Non Condensing Condensing Boilers Condensing and Modulating Boilers

3-45
Figure 3.2.37. Distribution of Large Oil-Fired Mechanical Draft Hot Water 

Commercial Packaged Boilers Based On Combustion Efficiency 

Variation of Average Efficiency with Input Rating 

The variation of combustion efficiency with input rating is shown in Figure 3.2.38

below. 

Figure 3.2.38. Comparison of Average Combustion Efficiency of Small Oil-Fired 

Mechanical Draft Hot Water Commercial Packaged Boilers Sub 

Category Based on Input Rating 

3.2.6.13 Small (300kBtu/h‒2,500kBtu/h) Gas-Fired Mechanical-Draft Steam 

Commercial Packaged Boilers

Small gas fired mechanical draft steam commercial packaged boilers are required 

to have a minimum thermal efficiency of 79-percent. There are 98 boilers in this 

0

2

4

6

8

10

87 88 89 90 91 92 93 94 95 96 97

Number of Models

Combustion Efficiency [%]

Distribution of Boilers Based on Combustion Efficiency

Other Boilers Condensing Boilers Condensing and Modulating Boilers

80

82

84

86

88

90

92

94

96

98

2500 -4000 4000 -5500 5500 -7000

Average Combustion Efficiency 

[%]

Input Rating Category [kBtu/h]

Average Combustion Efficiency Based on Input Rating

Other Boilers Condensing Boilers

3-46
equipment class listed in AHRI’s Directory of Certified Product Performance. All boilers 

of this class are non-condensing, non- modulating and are made from cast iron. Figure 

3.2.39. below shows distribution of equipment based on boiler input rating.

Figure 3.2.39. Distribution of Small Gas-Fired Mechanical Draft Steam Commercial 

Packaged Boilers Based on Input Rating

Manufacturers. 

The AHRI Directory of Certified Product Performance lists boiler models 

produced by five companies. Table 3.2.20. below shows the list of companies and the

input ratings manufactured by each company.

Table 3.2.20. List of Companies in the Air-Conditioning, Heating, and Refrigeration 

Institute Directory that Manufacture Small Gas-Fired Mechanical 

Draft Steam Commercial Packaged Boilers

Name of Manufacturer

300 kBtu/h -

500kBtu/h

500kBtu/h -

700kBtu/h

700kBtu/h -

900kBtu/h

900kBtu/h -

1100kBtu/h

1100kBtu/h -

1300kBtu/h

1300 kBtu/h -

1500kBtu/h

1500kBtu/h -

1700kBtu/h

1700kBtu/h -

1900kBtu/h

1900kBtu/h -

2100kBtu/h

2100kBtu/h -

2300kBtu/h

2300kBtu/h -

2500kBtu/h

Burnham Commercial X X X X X X X X X X X

Crown Boiler Co. Subsidiary

Of Burnham Holdings Inc. X X X X X X X X X X

P B Heat, LLC X X X X X X X X X X X

Smith Cast Iron Boilers X X X X X X X X X X X

Weil-Mclain X X X X X X X X X X

Characterization of Boilers Based on Efficiency. 

The distribution of boilers over different efficiency levels is shown in the Figure 

3.2.40. below. Most of the boilers in this equipment class have thermal efficiencies

between 80- and 81-percent. 

0

1

2

3

4

5

6

7

8

300 - 400400 - 500500 - 600600 - 700700 - 800800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 20002000 - 21002100 - 22002200 - 23002300 - 24002400 - 2500

Number of Models

Input Rating Category [kBtu/h]

Distribution of Boilers Based on Input Ratings

3-47
Figure 3.2.40. Distribution of Small Gas-Fired Mechanical Draft Steam Commercial 

Packaged Boilers Based on Thermal Efficiency 

Variation of Average Efficiency with Input Rating 

The average thermal efficiencies for each boiler input rating varies from 80- to

82-percent. Figure 3.2.41. below shows average thermal efficiency levels for each input 

rating category.

Figure 3.2.41. Comparison of Average Thermal Efficiency of Small Gas-Fired 

Mechanical Draft Steam Commercial Packaged Boilers Sub Category 

Based on Input Rating

0

5

10

15

20

25

30

35

40

79 80 81 82 83

Number of Models

Thermal Efficiency [%]

Distribution of Boilers Based on Thermal Efficiency

 78

 79

 80

 81

 82

300 - 400400 - 500500 - 600600 - 700700 - 800800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 20002000 - 21002100 - 22002200 - 23002300 - 24002400 - 2500

Average Thermal Efficiency [%]

Input Rating Category [kBtu/h]

Average Thermal Efficiency Based on Input Rating

3-48
3.2.6.14 Large (>2,500kBtu/h) Gas-Fired Mechanical Draft Steam 

Commercial Packaged Boilers

Large gas-fired mechanical draft steam CPBs are required, under subpart E of 10 

CFR Part 431, to achieve a minimum thermal efficiency of 79-percent. According to 

AHRI’s Directory of Certified Product Performance, 106 boiler models can be classified 

into this equipment class. All the listed models are made from cast iron and are noncondensing and non-modulating type. Figure 3.2.42. below shows distribution of boiler 

models based on capacity. Most commercial boilers in this equipment class have an input 

rating between 2,500 and 5,500 kBtu/h. 

Figure 3.2.42. Distribution of Large Gas-Fired Mechanical Draft Steam Commercial 

Packaged Boilers Based on Input Rating

Manufacturers. 

The AHRI Directory of Certified Product Performance lists four companies that

manufacture boilers if this equipment class. Table 3.2.21. below shows the size of boiler 

(input rating) manufactured by all four companies.

Table 3.2.21. List of Companies in the Air-Conditioning, Heating, and Refrigeration 

Institute Directory that Manufacture Large Gas-Fired Mechanical 

Draft Steam Commercial Packaged Boilers

Name of 

Manufacturer

2500 - 4000 

[kBtu/h]

4000 - 5500 

[kBtu/h]

5500 - 7000 

[kBtu/h]

7000 - 8500 

[kBtu/h]

8500 -

10000 

[kBtu/h]

Burnham Commercial X X X

P B Heat, LLC X X X

Smith Cast Iron 

Boilers X X X

Weil-Mclain X X X X X

0

5

10

15

20

25

30

35

40

45

50

2500 - 4000 4000 - 5500 5500 - 7000 7000 - 8500 8500 - 10000

Number of Models

Input Rating Category [kBtu/h]

Distribution of Boilers Based on Input Ratings

3-49
Characterization of Boilers Based on Efficiency. 

The thermal efficiency of boiler models in this equipment class varies from 79-

percent to 83-percent. Figure 3.2.43. below shows distribution of boiler models for 

different efficiency levels.

Figure 3.2.43. Distribution of Large Gas-Fired Mechanical Draft Steam Commercial 

Packaged Boilers Based on Thermal Efficiency 

Variation of Average Efficiency with Input Rating 

To assess the performance of boilers for different input ratings, DOE calculated 

average thermal efficiency at different input ratings. Results indicated that average 

thermal efficiency decreased with increased boiler size for this equipment class. Boilers 

in the 2,500‒5,500kBtu/h exhibited highest average thermal efficiency. Figure 3.2.44.

below shows the variation of average thermal efficiency with input rating.

0

5

10

15

20

25

30

35

79 80 81 82 83

Number of Models

Thermal Efficiency [%]

Distribution of Boilers Based on Thermal Efficiency

3-50
Figure 3.2.44. Comparison of Average Thermal Efficiency of Large Gas-Fired 

Mechanical Draft Steam Commercial Packaged Boilers Sub Category 

Based on Input Rating

3.2.6.15 Small (300kBtu/h‒2,500kBtu/h) Oil-Fired Mechanical Draft Steam 

Commercial Packaged Boilers

Small oil-fired mechanical draft steam boilers account for about 4-percent of 

commercial packaged boilers in the AHRI Directory of Certified Product Performance. 

Subpart E of 10 CFR Part 431 requires such commercial packaged boilers to have a 

minimum thermal efficiency of 81-percent. All boiler models listed in this equipment 

class are made from cast iron and are non-condensing and non-modulating. Figure 3.2.45.

below shows distribution all qualified boiler models based on their size. 

Figure 3.2.45. Distribution of Small Oil-Fired Mechanical Draft Steam Commercial 

Packaged Boilers Based On Input Rating

Manufacturers.

80.2

80.3

80.4

80.5

80.6

80.7

80.8

80.9

81

Average Thermal Efficiency [%]

2500 - 4000 4000 - 5500 5500 - 7000 7000 - 8500 8500 - 10000

Input Rating Category [kBtu/h]

Average Thermal Efficiency Based on Input Rating

0

1

2

3

4

5

6

7

8

9

300 - 400400 - 500500 - 600600 - 700

700 -800

800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 20002000 - 21002100 - 22002200 - 23002300 - 24002400 - 2500

Number of Models

Input Rating Category[kBtu/h]

Distribution of Boilers Based on Input Ratings

3-51
Table 3.2.22. below shows a list of companies in the AHRI Directory of Certified 

Product Performance which manufacture boilers of this equipment class. 

Table 3.2.22. List of Companies in the Air-Conditioning, Heating, and Refrigeration 

Institute Directory that Manufacture Small Oil-Fired Mechanical Draft 

Steam Commercial Packaged Boilers

Name of Manufacturer

300 kBtu/h -

500kBtu/h

500kBtu/h -

700kBtu/h

700kBtu/h -

900kBtu/h

900kBtu/h -

1100kBtu/h

1100kBtu/h 

-1300kBtu/h

1300kBtu/h 

-1500kBtu/h

1500kBtu/h 

-1700kBtu/h

1700kBtu/h 

-1900kBtu/h

1900kBtu/h 

-2100kBtu/h

2100kBtu/h 

-2300kBtu/h

2300kBtu/h 

-2500kBtu/h

Burnham Commercial X X X X X X X X X X

Crown Boiler Co. 

Subsidiary Of Burnham 

Holdings Inc.

X X X X X X X X X

P B Heat, LLC X X X X X X X X X X X

Smith Cast Iron Boilers X X X X X X X X X X X

Weil-Mclain X X X X X X X X X

Characterization of Boilers Based on Efficiency

Figure 3.2.46. below shows number of models by thermal efficiency. The 

majority (almost 80-percent) of models are within the 82- to 84-percent efficiency range. 

Figure 3.2.46. Distribution of small oil-fired mechanical draft steam commercial 

packaged boilers based on thermal efficiency 

Variation of Average Efficiency with Input Rating 

The average thermal efficiency for each input rating category was calculated and 

the result is shown below in Figure 3.2.47. The chart shows a reasonably even 

distribution of average thermal efficiencies with the minimum average thermal efficiency

across the entire input range at 82-percent and the maximum at 84-percent.

0

5

10

15

20

25

30

35

40

81 82 83 84 85 86

Number of Models

Thermal Efficiency [%]

Distribution of Boilers Based on Thermal Efficiency

3-52
Figure 3.2.47. Comparison of Average Thermal Efficiency of Small Oil-Fired 

Mechanical Draft Steam Commercial Packaged Boiler Sub Category 

Based on Input Rating

3.2.6.16 Large (>2,500kBtu/h) Oil-Fired Mechanical Draft Steam 

Commercial Packaged Boilers

Subpart E of 10 CFR Part 431 requires large oil-fired mechanical draft steam

CPBs to achieve a minimum thermal efficiency of 81-percent. All boilers listed in this 

equipment class use a cast iron heat exchanger. There are no condensing or modulating 

boilers in this equipment class. Figure 3.2.48. below shows that the majority of boilers 

under this equipment class have input ratings from 2,500kBtu/h to 5,500kBtu/h. 

Figure 3.2.48. Distribution of Large Oil-Fired Mechanical Draft Steam Commercial 

Packaged Boilers Based On Input Rating

 81.5

 82.0

 82.5

 83.0

 83.5

 84.0

300 - 400400 - 500500 - 600600 - 700

700 -800

800 - 900

900 - 1000

1000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 16001600 - 17001700 - 18001800 - 19001900 - 20002000 - 21002100 - 22002200 - 23002300 - 24002400 - 2500

Average Thermal Efficiency [%]

Input Rating Category [kBtu/h]

Average Thermal Efficiency Based on Input Rating

0

10

20

30

40

50

60

2500 - 4000 4000 - 5500 5500 - 7000 7000 - 8500

Number of Models

Input Rating Category [kBtu/h]

Distribution of Boilers Based on Input Ratings

3-53
Manufacturers.

There are four manufacturers listed in the AHRI Directory of Certified Product 

Performance which produce boilers in this equipment class. Weil-McLain also produces 

more than 50-percent of the total boiler models in this equipment class. Table 3.2.23.

below shows the manufacturers and the boiler size (input rating) that each company is 

currently producing.

Table 3.2.23. List of Companies in the Air-Conditioning, Heating, and Refrigeration 

Institute Directory that Manufacture Large Oil-Fired Mechanical Draft 

Steam Commercial Packaged Boilers

Manufacturer Name 2500 - 4000 

[kBtu/h]

4000 - 5500 

[kBtu/h]

5500 - 7000 

[kBtu/h]

7000 - 8500 

[kBtu/h]

Burnham Commercial X X X

P B Heat, LLC X X X

Smith Cast Iron Boilers X X X

Weil-Mclain X X X X

Characterization of Boilers Based on Efficiency. 

The efficiency of boilers in this equipment class varies from 81-percent to 86-

percent. Figure 3.2.49. shows the distribution of thermal efficiency ratings for this 

equipment class.

Figure 3.2.49. Distribution of Large Oil-Fired Mechanical Draft Steam Commercial 

Packaged Boilers Based On Thermal Efficiency 

Variation of Average Efficiency with Input Rating 

Average thermal efficiency does not vary substantially with input size. The 

average thermal efficiency was between 82-percent and 83-percent for all input ratings

0

5

10

15

20

25

30

35

81 82 83 84 85 86

Number of Models

Thermal Efficiency [%]

Distribution of Boilers Based on Thermal Efficiency

3-54
analyzed. Figure 3.2.50. below shows the variation of average thermal efficiency with 

input rating.

Figure 3.2.50. Comparison of Average Thermal Efficiency of Large Oil-Fired 

Mechanical Draft Steam Commercial Packaged Boilers Sub Category 

Based on Input Rating

3.3 TECHNOLOGY ASSESSMENT

The technology assessment focuses on understanding how commercial packaged 

boilers use energy and on identifying potential technology changes that would improve 

the efficiency of this equipment. Measures that improve the rated equipment efficiency 

are called technology options, and they are based on existing technologies, as well as 

working prototypes. In consultation with interested parties, DOE created a list of 

technology options for consideration in this rulemaking. After researching this list of 

technology options, DOE considered each option in light of the four screening criteria

discussed in chapter 4. Those technology options that pass the screening criteria will be 

considered suitable options for improving the efficiency of the equipment in the 

engineering analysis, and will assist DOE in determining the efficiency levels from the 

baseline through the max-tech design.

3.3.1 Boiler Equipment

Commercial packaged boilers are pressure vessels designed to transfer heat via 

combustion to water or steam, used for space heating, and in some applications domestic 

hot water as well. Commercial packaged boilers can be condensing or noncondensing in 

design. Condensing design boilers recover additional heat by condensing part of the 

water vapor produced by the burning fuel.

h A boiler consists of: (1) a tank/shell (or other 

form of pressure vessel to hold the water or steam); (2) a burner; (3) a combustion 

h This requires that the water returning to the boiler system be cold enough to sufficiently carry out the 

condensation process of the water vapor in the exhaust.

82

82.5

83

83.5

2500 - 4000 4000 - 5500 5500 - 7000 7000 - 8500

Average Thermal Efficiency [%]

Input Rating Category [kBtu/h]

Average Thermal Efficiency Based on Input Rating

3-55

 
chamber (also sometimes referred to as a firebox); (4) a heat exchanger; (5) automatic 

controls; and (6) mechanical draft equipment (e.g., forced or induced draft blower) if 

applicable (i.e. If the boiler is not of natural draft). The following provides further details 

regarding the components used in commercial packaged boilers.

Construction Materials

Non-condensing boilers are often made of cast iron, steel, copper, or copper-clad 

steel, and are usually designed to prevent corrosion and thermal shock. Condensing 

boilers are usually made of stainless steel or aluminum construction, because the acidic 

condensate would corrode copper, cast iron, or carbon steel. Condensing boilers may 

include secondary heat exchangers which, due to exposure to corrosive condensate

formation in the heat exchanger, must also be constructed of corrosion-resistant 

materials. 

Tank/Pressure Vessel

Boiler tanks (also called the pressure vessel or boiler shell) are frequently 

cylindrical in shape, but can also be of rectangular or other construction styles. The 

inside walls of the tank opposite combustion regions are sometimes lined with insulating 

materials to maintain sufficient flame temperature for clean combustion. The outside 

surfaces of the tank are usually covered with insulation to reduce heat losses through the 

boiler jacket.

Burner

Burners combine the fuel and air and then ignite the mixture to start the 

combustion process. The boiler fuel type dictates the type of burner that is used.

• Atmospheric burners typically use natural gas or propane in natural draft 

applications. An atmospheric burner uses the pressure-induced velocity of gas 

exiting an orifice to mix such gas with primary combustion air. An atmospheric 

burner then uses natural draft to mix secondary air into the flame during 

combustion.

• A gas-power burner is a type of burner that uses a blower to supply combustion 

air into the combustion zone. This may be an externally mounted gun-type burner 

similar to an oil-pressure atomizing burner, or an incorporated fan and gas 

delivery system within the boiler.

• An oil-power burner may be a pressure atomizing burner or an air atomizing 

burner. A pressure atomization oil burner uses oil pumped through a nozzle to 

create a fine mist that is then mixed with the combustion air and ignited at the 

front of the burner. An air atomizing burner uses compressed air to atomize the oil 

into a fine mist before being delivered and ignited in the combustion chamber.

Heat Exchangers

3-56
A heat exchanger is a device used to transfer heat from one medium to another.

All boilers come equipped with air-to-water heat exchangers. The primary boiler heat 

exchanger designs include: (1) water tube; (2) fire tube; (3) cast iron; and (4) tubeless.i

For water tube boilers, combustion gases circulate around water or steam-filled 

tubes. Heat transfer is achieved by radiation from the flames as well as by convection 

from the hot combustion gases. There may be up to several thousand water tubes in a 

boiler, depending on the size of the unit.j The water tubes are often welded together to 

form the walls of the combustion chamber, called a “waterwall.” Water-tube designs are 

often used in steam boilers. Finned copper water tube boilers are designed with rows of 

horizontal finned tubes located above the combustion chamber. Finned copper water 

tube boilers are generally hot water boilers. The water-tube design can enable more rapid 

start-up due to lower thermal mass and can enhance thermal shock resistance due to 

greater structural flexibility relating to thermal expansion and contraction.

For fire tube boilers, the boiler tank is filled with water and heat is transferred as 

hot combustion gases pass through one to several metal tubes or other passageways in the 

heat exchanger.k

 Fire tube boilers are often characterized by their number of passes (i.e., 

number of times combustion gases flow the length of the boiler). The combustion gas 

flows through the length of a bundle of tubes and then is turned around and passes back 

through an additional bundle of tubes.l

 Fire tube boiler combustion chambers may be 

dry-base, wet-base, or wet-leg. Dry-base chambers are refractory-lined chambers that 

direct the combustion gases from the firebox to the heat transfer tubes; the chamber is 

usually located beneath the fluid-backed sections. Wet-base chambers often utilize a 

water-cooled turn-around chamber to direct the flue gases from the combustion chamber

to the tube banks, although dry-backed turn-around chambers are also sometimes used. 

A wet-backed turn-around chamber is fully surrounded by fluid-backed sections except 

for the necessary openings – thereby eliminating the need for the refractory lining. Wetleg combustion chambers have fluid-backed sections on the top and sides of the chamber.

Cast iron boilers are made up of cast pressure sections bolted together or 

connected by push nipples to form a block assembly.m The water is contained inside cast 

i

ASHRAE 2008 HVAC Systems and Equipment Handbook (Available at: 

https://www.ashrae.org/resources--publications/handbook).

j

Characterization Industrial Commercial Boiler Population (2005) (Available at: 

https://www1.eere.energy.gov/manufacturing/distributedenergy/pdfs/characterization_industrial_commeric

al_boiler_population.pdf). k The heat is transferred in the first pass of fire tube boiler by radiation and convection then by convection 

on the remaining passes of the boiler.

l

DOE's Improving Steam System Performance: A Sourcebook for Industry (2012) (Available at: 

http://www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/steamsourcebook.pdf). m Heselton, Kenneth E. Marcel Dekker, Boiler operator's handbook (2005).

3-57

 
iron sections, and combustion gases flow through designated passages outside the

sections.

n

 Cast iron boilers may be of dry-base, wet-leg, or wet-base design.

Tubeless boilers use the outside of its shell as part of the heat exchanger surface. 

There is a central flue surrounded by water which serves the first pass of the combustion 

gases.o The combustion gases then exit the central flue through a nozzle that connects it

to the hollow shell wall which has internal steel fins that run the length of the boiler tank. 

Then the combustion gases make several passes through the shell wall before exiting the 

stack.p

Controls

A boiler must be capable of providing immediate response to load demand 

variations while maintaining its efficiency and safety features. Thus, boilers come 

equipped with a variety of controls. 

• The main operating control (pressure-actuated for steam boilers and 

temperature-actuated for hot water boilers) controls the firing rate of the 

fuel by monitoring hot water temperature or steam pressure.q Operating 

controls could provide on/off, high/low/off, and modulating functions.r

• The low-water cutoff switch stops fuel flow to the burner if minimum 

water levels are not detected.s

• The pressure gauge/regulator monitors boiler pressure and shuts off the 

fuel supply to the boiler if allowable boiler pressure is exceeded. 

Additionally, the temperature/pressure relief valve releases steam if the 

pressure gage/regulator fails and pressure builds dangerously high.t

• The flame safeguard control monitors the burner for proper operation and 

shuts off the fuel supply if a flame is not detected in the burner.

u

Draft

n BetterBricks “Boilers Introduction How Boilers Work” (Available at: 

http://www.betterbricks.com/sites/default/files/operations/om_of_boilers_final.pdf). o See http://www.spthermal.com/hurst.html. p Heselton, Kenneth E. Marcel Dekker, Boiler operator's handbook (2005). q BetterBricks “Boilers Introduction How Boilers Work” (Available at: 

http://www.betterbricks.com/sites/default/files/operations/om_of_boilers_final.pdf). r ASHRAE 2008 HVAC Systems and Equipment Handbook (Available at: 

https://www.ashrae.org/resources--publications/handbook). s ASHRAE 2008 HVAC Systems and Equipment Handbook (Available at: 

https://www.ashrae.org/resources--publications/handbook). t

See http://homerepair.about.com/od/heatingcoolingrepair/ss/Residential-Steam-Boiler-Controls.htm. u See https://www.osha.gov/dte/grant.../fy07/sh.../mod_7_boiler_safety2.pptx. 

3-58

 
Draft types include natural and mechanical draft, as well as a unique type periodic 

or intermittent forced draft achieved by pulse combustion. A natural draft boiler is 

designed to work with a negative pressure in the firebox and flue connection, where the 

pressure difference is developed by the buoyancy of hot gases in the chimney. A 

mechanical draft boiler has either a forced draft or induced draft blower. A forced draft 

boiler uses a blower upstream of the combustion chamber, and the fan is located at the 

inlet of the burner and pushes air through the burner, thereby ensuring that adequate air is 

delivered to the combustion process.v The blower pulls air from the boiler room or may 

be connected to a duct system which pulls in outside air, then delivers air to the 

combustion chamber at a positive pressure above atmospheric pressure. An induced draft 

boiler uses a blower located at the outlet side of the boiler heat exchanger to pull flue 

gases out of the boiler due to a negative pressure in the combustion chamber, thereby 

causing air flow into the inlet of the boiler.

3.3.2 Technology Options that Improve Combustion Efficiency and/or Thermal 

Efficiency

DOE identified technology options by reviewing commercial packaged boiler

manufacturer specification sheets and equipment literature, recent trade publications, 

technical journals, and patent filings. DOE also consulted with manufacturers during

interviews about these technology options. At this time, DOE is aware of a set of 

technology options (discussed in further detail below) that could be used to improve 

commercial packaged boiler thermal efficiency and/or combustion efficiency. 

Technology options that are applicable only to equipment subject to a thermal efficiency 

standard are noted. The following list includes technologies that would improve the rated 

efficiency:

1. Jacket insulation optimization (thermal efficiency only)

2. Heat exchanger improvements (including condensing heat exchanger, 

external and internal tube surface enhancement)

3. Burner derating

4. Improved burner technology

5. Combustion air preheaters

6. Economizers

7. Blowdown waste heat recovery

8. Integrated, high-efficiency steam boilers

Jacket Insulation Optimization (Thermal Efficiency Only)

Outside surfaces of boiler tank/pressure vessel are usually covered with insulation 

to reduce heat losses through the boiler jacket. At many times however, thermal 

insulation may either be under applied or over applied. Both cases lead to increased 

v DOE's Improving Steam System Performance: A Sourcebook for Industry (Available at: 

http://www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/steamsourcebook.pdf).

3-59

 
thermal losses in form of convection and radiation. To mitigate this problem, thermal 

insulation optimization techniques can be utilized to improve insulation performance.

Unnecessarily thick insulation leads to increase in surface area which would 

subsequently lead to increased losses. Too thin an insulation reduces overall thermal 

resistance which also leads to significant radiation and convection losses. The optimum 

insulation thickness for a simple cylinder depends on the outside heat transfer coefficient 

and the thermal conductivity of the insulation material. The outside heat transfer 

coefficient for natural convection can be calculated using empirical equations available in 

literature. Using such simple techniques, overall performance of boilers may be improved 

significantly. 

Heat Exchanger Improvements (Including Condensing Heat Exchanger)

At most operating temperatures, condensing commercial packaged boilers operate 

at higher efficiencies than non-condensing commercial packaged boilers by capturing 

latent heat resulting from the phase change of water vapor in combustion gases. The 

level of efficiency gain by condensing boilers, compared to non-condensing designs, is 

usually greater at low distribution system operating temperatures, when non-condensing 

boilers sometimes use supply/return water mixing valves to maintain boiler temperatures 

that are high enough to prevent condensation and possible related corrosion.

Improvements to the heat exchanger can be achieved by modifying baseline 

designs of standard boilers. A number of design modifications can be implemented which 

may increase thermal and/or combustion efficiencies. Some of these are listed below:

1. Increase heat exchanger surface area

2. Modify or add heat exchanger surface features

3. Modify or add heat exchanger baffles and turbulators; 

4. Increase the corrosion resistance of the primary heat exchanger or use a 

corrosion-resistant secondary heat exchanger to withstand flue gas 

condensation.

DOE notes that increasing the heat exchanger surface area may bring about

insignificant improvements in thermal efficiency. Through manufacturer interviews, 

DOE estimates that a 10-percent increase in surface area would result in a 1 to 2-percent

increase in thermal efficiency. 

An alternative way to increase heat transfer surface area is to add surface features,

such as fins. Many commercial boilers made from copper, use compact fin-tube heat 

exchangers. Cast Iron boilers also have pin fins on the water and/or air side of the heat 

exchanger. Though these features considerably improve performance, there may still be a 

possibility for improvement with regards to fin geometry and design. 

Many studies have been carried out for different fin designs for fin tube heat 

exchangers. One such study compared the air side performance of plate (straight), wavy 

and louvered fins on a fin tube heat exchanger. Results indicate that for a fixed fan power 

3-60
and capacity, 40-percent lower surface area would be required while using a louvered fin 

heat exchanger as compared to a plate fin-tube heat exchanger.

11 The study also 

compared heat transfer coefficient for heat exchangers having same fin density for all 

three types of fins and results show superior performance of louvered fin over wavy and 

plate fins.

11 Similar studies prove that there exists an opportunity to improve 

conventional heat exchanger design by using wavy fins and louvered fins over straight 

fins.12 Figure 3.3.1 shows a type of louvered fin used in cross-flow heat exchangers.

Figure 3.3.1. Fin-tube heat exchanger with louvered fins12

 

Another method to improve heat exchanger performance is the use of turbulators 

to increase convective heat transfer. Turbulators are used to impart turbulence in the flow 

of flue gases or water. Turbulent heat transfer generally delivers higher thermal transport 

as compared to laminar flow heat transfer. This is because turbulent flow causes shearing 

of thermal boundary layers which are formed when a fluid transfers heat with a surface. 

In these boundary layers, viscous forces dominate leading to conductive heat transfer and 

high thermal resistance. With introduction of turbulence, these layers get disturbed and 

heat transfer becomes dominated by convective forces. This allows greater amount of 

heat to be transferred.

This effect also occurs when hot flue gases flow through a fire tube boiler. By 

introducing turbulators flue gases can easily be converted into turbulent regime. 

Interviews with manufacturers suggest that almost 1 to 2-percent incremental efficiency 

can be obtained by adding turbulators inside fire tubes. Some typical turbulators which 

can be used include twisted tape, conical rings, wire coils, swirl flow generators etc.13

Internal ribs may also provide improvement in heat transfer by allowing the gases to 

remain in turbulent flow throughout the tube.

14

For water tube boilers alternative tube designs, such as corrugated tubes with or 

without internal rifling, show considerable promise. One extensive study suggests 

considerable heat transfer enhancement for different geometries of spirally corrugated 

tubes as compared to smooth circular tubes.15 In addition, considerable advancement in 

tube design has occurred over the past few years. A new addition which has come about 

with advancement of manufacturing techniques is the evolution of micro-fin surface 

tubes for boiling and condensation.16 Depending on wetting capabilities, microfin tubes 

allow formation of a thin film on the surface of the tubes and therefore provide a

substantial increase in heat transfer coefficient.

3-61
Internal rifling of water tubes corrugation is another approach which can be used 

to improve convective heat transfer.15,16 Similar to turbulators, rifling allows the fluid to 

approach turbulent regime by providing a circumferential velocity component to the flow. 

Viscous layers near the surface also get disturbed due to this centrifugal motion and this 

increases heat transfer near the surface. 

In addition to all of the above, switching from natural draft systems to mechanical 

draft systems can also be implemented. In natural draft systems, movement of air 

through the boiler is driven by buoyancy of flue gases. Mechanical draft systems allow 

forced convection dominated heat transfer where a pressure differential is maintained

across the boiler (by a blower or fan) in order to allow flow of flue gases. The velocity of 

flue gases passing through fire tubes or over the heat exchanging surface determines the 

heat transfer coefficient. 

Improving the heat exchanger for a boiler can improve the effectiveness of heat 

transfer from the hot combustion gases to the water that is distributed to the heated space. 

The improved effectiveness of the heat exchanger can increase combustion and thermal 

efficiency. High pressure-drop heat exchangers can also serve to reduce off-cycle draft 

losses by restricting the flow of air through the heat exchanger, and subsequent loss of 

heat, when the burner is not operating.

Burner Derating

Burner derating is the operation of a boiler at a reduced firing rate. Reducing 

burner firing rate for gas and oil boilers while keeping heat exchanger geometry, the 

surface area, and the fuel-to-air ratio the same, will increase the ratio of heat transfer 

surface area to energy input, thereby increasing the efficiency of the boiler. However, 

depending on the degree of reduction, a lower energy input means that less heat will be 

produced, and, thus, lower utility may be provided than with conventional burner firing 

rates.

Improved Burner Technology

Pulse Combustion

Pulse combustion burners operate on self-sustaining, resonating pressure waves 

that alternately depressurize the combustion chamber (drawing a fresh fuel-air mixture 

into the chamber) and pressurize it (through heating and expansion of the fuel/air mixture

during combustion). Pulse combustion systems feature high heat transfer rates, and can 

achieve higher efficiency levels than conventional boiler designs. 

Premix Burners

Premixing fuel gas and combustion air prior to arrival at the flame results in more 

complete combustion using lower levels of excess air. The lower levels of excess air not 

only reduce the amount of fuel required to heat the combustion air but also raise the 

temperature of the gases entering the heat exchanger, which enhances heat exchange and 

3-62
improves efficiency. Lower levels of excess air also raise the water vapor dew point,

which facilitates condensation and the recovery of latent heat and improves efficiency

when the unit is operating in condensing mode. 

Low-Pressure, Air-Atomized Oil Burner 

Fuel input rate is controlled by the size of the nozzle orifice. Pressure-atomizing 

nozzles that are designed for low firing rates suffer rapid fouling of the small internal 

passages, leading to inadequate spray patterns and poor combustion performance. To 

overcome the low input limitations of conventional oil burners, Brookhaven National 

Laboratory developed a low-pressure, air-atomized oil burner.w In addition, it can 

operate with low levels of excess combustion air for lean-burning, ultra-clean 

combustion. A lower level of excess air generally improves combustion efficiency.

Combustion Air Preheaters

Combustion air preheaters (also known as recuperators) are air-to-air heat 

exchangers that transfer energy from the flue gases back into the system. However, 

instead of transferring the energy into the feed water as is done with an economizer, the 

energy is transferred to increase the temperature of the incoming combustion air, thereby 

potentially resulting in improved efficiency.

The gas-gas heat transfer for such systems can be achieved using a fin tube –

cross flow heat exchanger. Modifications such as improved fin-tube designs and fin 

configuration would provide additional benefit.

Economizers

Economizers may allow for an increase in boiler thermal efficiencyx by 

transferring excess flue gas heat into incoming feed water.

y Economizers are usually airto-water heat exchangers. There are noncondensing and condensing economizers 

available on the market. Condensing economizers are designed to allow condensation of 

the exhaust gas.

Blowdown Waste Heat Recovery

In large steam commercial boilers, salt and sediment residue gets left out in the 

water stored in the boiler. These dissolved solids also known as TDS (total dissolved 

solids) are removed from the boiler in a process known as blowdown. Depending on size 

of boiler, blowdown can either be a continuous, periodic or maintenance time process. In 

either case, stored heat energy in blowdown water which would otherwise be wasted 

away in a drain, can be utilized to preheat incoming water. This blowdown process may

require a separator (available on the market) which separates water from steam. By 

w See: http://www.osti.gov/bridge/servlets/purl/248539-wWbYod/webviewable/248539.pdf. x Note that economizers would only show an increase in thermal efficiency if they are an integral 

component of the boiler.

y See https://www1.eere.energy.gov/manufacturing/tech_deployment/pdfs/steamsourcebook.pdf. 

3-63

 
integrating this technology, there is potential to reduce fuel requirement to achieve 

desired water temperature. This technique may also marginally increase efficiency levels 

as the stored heat derived from combustion gases is utilized to a greater extent.

Integrated, High-Efficiency Steam Boilers

Certain manufacturers have developed integrated, high-efficiency steam boilers 

that combine multiple design features to increase fuel-to-steam efficiency. Such features 

can include enhanced heat transfer surfaces (e.g., spiral fire tubes), as well as feed water 

economizers and high-turndown modulating burners capable of maintaining low levels of 

excess combustion air. Cleaver-Brooks, in partnership with DOE and the Gas 

Technology Institute (GTI), developed the first integrated, high-efficiency steam boilers 

called a "Super Boiler."z

DOE notes that the integrated high-efficiency steam boiler concept described 

above is essentially a combination of several different technology options integrated into 

a commercial boiler equipment. It does not refer to any particular technology option that 

can be applied to CPBs to improve efficiency. As a result, DOE has decided not to 

consider the concept as a potential technology option. DOE has presented the concept 

here purely for information purposes. 

3.3.3 Technology Options to Reduce Seasonal Boiler Energy Consumption

DOE is aware of a number of boiler technologies exist that reduce overall fuel 

consumption by improving the average seasonal efficiency, including the following 

technologies:

1. Modulating burners

2. Electronic ignition

3. Dampers

4. Temperature reset controls 

5. Thermal post-purge controls

6. Delayed-action oil pump solenoid valve

Modulating Burners

Two-stage and modulating burners can decrease losses caused by burner cycling 

at partial loads. However, modulating burners may not accomplish net energy efficiency

gains if excess combustion air levels must be increased at low firing rates (in order to 

maintain combustion performance) or if electrical power requirements for the burner do 

not decrease in linear proportion to the firing rate. In condensing boiler applications, an 

increase in excess combustion air ratio can result in reduced latent heat recovery due to 

decreased flue gas dew point temperatures. This can result in an energy loss that 

outweighs the benefit of reduced burner cycling.

z See http://www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/how_superboiler_works.pdf for 

further information.

3-64

 
Electronic Ignition

Boilers can be equipped with electronic ignition systems, which ignite burners on

demand using electrical components. 

There are different types of electronic ignition systems including:

(1) Intermittent Pilot Ignition: This is a device that lights a pilot light by 

generating a spark. The pilot light in turn lights the main burner.

(2) Direct Spark Ignition (DSI): DSI ignites the main burner directly by 

generating a spark.

(3) Interrupted Duty Ignition Systems: All modern oil burners have a type of 

electronic ignition called an interrupted duty ignition. A step-up 

transformer supplies power to two electrodes, which causes a spark to 

jump. The interrupted duty ignition system for an oil burner activates the 

spark until either a steady flame is established or the end of the trial-forignition (TFI) period.aa

(4) Hot Surface Ignition: The igniter in this system is an electrically heated 

resistance element that thermally ignites the main burner directly without 

the use of a pilot light. 

Unlike standing pilot ignition systems that consume fuel continuously, electronic 

devices and their control modules operate only during the active mode, which improves 

efficiency. Solid-state electronic ignition components can also achieve electricity savings 

compared to older, iron-core transformer technologies.

Dampers

Off-cycle (which refers to the burner off-cycle) dampers restrict the intake and 

exhaust air flow through the venting system during standby mode by closing when the 

burner is not operating, thereby trapping residual heat in the heat exchanger. During the 

burner off-cycle, the boiler loses heat by natural convection and conduction through the 

combustion air inlet and flue. Installing a damper at these points improves efficiency by 

preventing heat from escaping and minimizing off-cycle heat losses.

Temperature Reset Controls

Temperature reset controls monitor outside air temperature or burner operating 

hours (BOH) to estimate the required heating load, which can vary as a function of 

outdoor temperature, solar and wind conditions, internal heat gain, or thermostat 

aa “Trial for ignition” is the period during which the burner is attempting to ignite the fuel it is delivering to 

the nozzle.

3-65

 
setback/recovery. The hydronic water supply temperature is then modulated up or down

to enable the thermal distribution capacity to match the actual heating demand.bb

Thermal Post-Purge Controls

Thermal post-purge controls allow the hydronic circulating pump to continue 

operation after the termination of a thermostat demand for heat. The circulation pump 

continues to operate after the shutdown of the burner until the boiler temperature drops 

down to a programmed level that depends on type of boiler and fuel. The thermal postpurge concept functions most effectively when the control anticipates the end of the 

heating demand and shuts off the burner early enough so that the residual heat transferred 

during the post-purge cycle just satisfies the temperature requirement of the building. 

Substantial benefits are achieved by reduced boiler temperature during standby mode/off 

mode through reduced jacket and draft heat losses.

Delayed-Action Oil Pump Solenoid Valve

A delayed-action oil pump solenoid valve is installed between the oil pump and 

the burner nozzle to supplement the fuel pump regulator. It does so by delaying the fuel 

release by three to six seconds after the igniter and burner blower start until the oil 

pressure reaches the level required to fully discharge the oil into the combustion chamber 

without dripping. This ensures that the oil burns more completely, which improves 

efficiency since heat exchangers will suffer less fouling. 

bb 2008 ASHRAE Handbook – HVAC Systems and Equipment (Available at: 

https://www.ashrae.org/resources--publications/handbook).

3-66

 
REFERENCES

1. Air Conditioning, Heating and Refrigeration Institute’s certified directory of 

commercial boilers. URL: https://www.ahridirectory.org/ahridirectory/pages/home.aspx

2. Canadian Energy Conservation Standards proposed by National Resources Canada, 

updated as of November 2011. URL: http://www.nrcan.gc.ca/energy/regulations-codesstandards/bulletins/7145#Commercial_Packaged_Gas

3. U.S. Department of Energy-Office of Energy Efficiency and Renewable Energy. 

Federal Energy Management Program. How to Buy an Energy-Efficient Commercial 

Boiler. June 8, 2010. (Last Accessed March 11, 2014). 

http://www.nwfpa.org/nwfpa.info/component/content/article/301-how-to-buy-anenergy-efficient-commercial-boiler

4. Boiler Heating Systems and Components Rebates, Minnesota Energy Resources, URL: 

http://www.minnesotaenergyresources.com/business/boiler_rebates.aspx

5. Boilers and Water Heating Rebate Catalog, Energy-efficiency rebates for your 

business, Pacific Gas and Electric Company, URL: 

http://pge.com/includes/docs/pdfs/mybusiness/energysavingsrebates/incentivesbyindust

ry/boilers_waterheating_catalog_final.pdf

6. Energy Efficiency Business Incentives, San Diego Gas and Electric Company, URL: 

https://www.sdge.com/rebates-finder/save-energy-earn-incentives

7. Energy Efficiency Business Rebates, San Diego Gas and Electric, URL: 

https://www.sdge.com/rebates-finder/earn-rebates-your-improvements

8. “2013 – 2014 EERB Rebate Guide and Application”, Energy Efficiency Rebates for 

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