This page provides acquisition guidance for various boiler types. Boilers are subject to different efficiency requirements based on their size, output type (steam or hot water), and fuel input.
Federal laws and requirements mandate that agencies purchase either ENERGY STAR®-certified products or products that meet Federal Energy Management Program (FEMP)-designated efficiency levels except as specifically exempted by law. The FEMP-designated program covers boilers with an input rating greater than 2.5 million Btu/hr. EPA’s ENERGY STAR program covers smaller boilers, commonly referred to as residential and small commercial boilers.
High-pressure boilers (i.e., those used in industrial and cogeneration applications) and boilers meeting the definition of a “hot water supply boiler” are excluded from this definition. This aligns with the definition of boilers found in the Department of Energy minimum efficiency standards (10 CFR Part 430), with which all manufacturers need to comply.
This acquisition guidance was updated in September 2024.
How To Find Product Efficiency Requirements
For large commercial boilers covered by FEMP, federal purchases must meet or exceed the minimum efficiency requirements and thermal efficiencies listed in Table 1. These efficiency levels can be voluntarily adopted by non-federal organizations, institutions, and purchasers.
The U.S. Environmental Protection Agency (EPA) provides efficiency levels and product specification information for small commercial boilers and for residential boilers on its ENERGY STAR website. Manufacturers meeting these requirements are allowed to display the ENERGY STAR label on complying models. Federal buyers can use ENERGY STAR's list of certified small commercial boilers and list of residential boilers to identify or verify complying models.
Table 1. Efficiency Requirements for Boilers
| Boiler Type | Size (Input) | Output | Efficiency Requirementsa | |
|---|---|---|---|---|
| Gas-Fired | Oil-Fired | |||
| Residential | Less than 300,000 Btu/hr | Hot Water | ENERGY STAR-Certified Residential Boilers | |
| Packaged Boiler / Small Commercial | 300,000–2,500,000 Btu/hr | Hot Water | ENERGY STAR-Certified Commercial Boilers | |
| Large Commercial | 2,500,000–10,000,000 Btu/hr | Hot Water | Ec ≥ 96.0% | Ec ≥ 89.0% |
| Steam | Et ≥ 83.7% | Et ≥ 85.8% | ||
a Both thermal efficiency (Et) and combustion efficiency (Ec) are based on 10 CFR Part §431.86
- Uniform test method for the measurement of energy efficiency of commercial packaged boilers.
Note: There is an energy efficiency purchasing requirement for all covered product categories; current covered product categories for boilers include:
- All gas-fired boilers that produce hot water as an output
- Residential oil-fired boilers that produce hot water as an output
- Large commercial oil-fired boilers that produce hot water as an output
- Large commercial boilers whether gas-fired or oil-fired that produce steam as an output.
Boilers that are not in one of these covered product categories do not have a designated minimum efficiency level. While there is not a designated efficiency level, all purchases of energy consuming equipment must take into account life cycle cost, not just first cost, when selecting the efficiency requirement (FAR Part 23, 42 USC §8259b(b)(2)).
How To Determine Cost Effectiveness
An efficient product is cost effective when the lifetime energy savings exceed the up-front cost premium (if any) compared to a less efficient option. Find more information about determining life cycle cost effectiveness on FEMP’s general purchasing requirements webpage.
Tables 2-4 below each provide an example comparison of the life cycle energy cost savings of a base model (less efficient than the minimum required efficiency), a model meeting the ENERGY STAR or FEMP-designated efficiency level, and a model with the highest available efficiency. The examples use one of three efficiency metrics (annual fuel utilization efficiency [AFUE], thermal efficiency, and combustion efficiency) that set efficiency requirements for boilers. Note that the assumptions for each example may be slightly different depending when the calculation was last updated.
Example 1: ENERGY STAR Residential Boilers Meeting Annual Fuel Utilization Efficiency Requirements
FEMP has calculated that an ENERGY STAR-qualified gas boiler meeting the required 0.90 annual fuel utilization efficiency (AFUE) saves money if it costs no more than $1,150 more than the less efficient model with an AFUE of 0.84. The best available model shown below is cost effective if it costs no more than $1,824 above the less efficient model (or $674 above the required model).
Table 2. Lifetime Energy Cost Savings for Efficient Residential Gas Boiler Models
| Performance | High Efficiency Model | Required Efficiency Model | Lower Efficiency Model |
|---|---|---|---|
| AFUEa | 0.97 | 0.90 | 0.84 |
| Annual Energy Use (therms/yr) | 739 | 790 | 877 |
| Annual Energy Cost | $710 | $759 | $843 |
| Lifetime Energy Cost | $9,765 | $10,439 | $11,589 |
| Lifetime Energy Cost Savings | $1,824 | $1,150 | ====== |
a Annual Fuel Utilization Efficiency (AFUE) is a measure of how efficiently a boiler converts the energy in its fuel to heat over a typical year.
Energy Use and Cost Assumptions
Annual Energy Use: Assumed b oilers have a lifetime of 20 years and operating hours of 713, 1,600 and 1,517 for boilers with AFUE of 0.84, 0.90, and 0.97 respectively. Operating hours differ depending on efficiency because of differing heat outputs and the presence of modulating burner technology. The assumptions and calculation are based on the test method and Engineering Analysis for DOE’s Energy Conservation Standards for Consumer Boilers, referenced in 10 CFR Part 430.
Annual Energy Cost: The calculation used $0.961/therm for the cost of natural gas, which was the average price at federal facilities in the United States as of July 2024.
Lifetime Energy Cost: Calculated based on future natural gas price trends and a 3% discount rate from Energy Price Indices and Discount Factors for Life-Cycle Cost Analysis – 2024: Annual Supplement to NIST Handbook 135 and NBS Special Publication 709 (NISTIR 85-3273-39).
Lifetime Energy Cost Savings: The difference between the lifetime energy cost of the identified models.
Model Efficiency Levels
High Efficiency Model: Based on the most efficient model available in the December 2024 ENERGY STAR-Qualified Products List. More efficient models may have entered the market after FEMP's acquisition guidance was created.
Required Efficiency Model: Based on December 2024 ENERGY STAR efficiency levels. Federal agencies must purchase products that meet or exceed ENERGY STAR efficiency levels.
Lower Efficiency Model: Based on the least efficient product that meets the minimum efficiency required for products to be sold on the market (10 CFR Part 430), which is the minimum efficiency all manufacturers need to comply with. Note that energy savings will vary depending on actual usage.
Example 2: ENERGY STAR Small Commercial Boilers Meeting Thermal Efficiency Requirements
FEMP has calculated that a 500,000 Btu/hr ENERGY STAR-qualified boiler meeting the required 94% efficiency level saves money if it costs no more than $21,805 more than the less efficient model with a thermal efficiency of 80%. The best available model shown below is cost effective if it costs no more than $26,891 above the less efficient model (or $5,086 above the required model).
Table 3. Lifetime Energy Cost Savings for Efficient Small Commercial Boiler Models
| Performance | High Efficiency Model | Required Efficiency Model | Lower Efficiency Model |
|---|---|---|---|
| Thermal Efficiency (%) | 98 | 94 | 80 |
| Annual Energy Use (therms/yr) | 7,653 | 7,979 | 9,375 |
| Annual Energy Cost | $7,355 | $7,668 | $9,010 |
| Lifetime Energy Cost | $119,514 | $124,600 | $146,405 |
| Lifetime Energy Cost Savings | $26,891 | $21,805 | ====== |
Energy Use and Cost Assumptions
Annual Energy Use: Assumed boilers operate for 1,500 full-load hours per year and have a lifetime of 25 years.
Annual Energy Cost: The calculation used $0.961/therm for the cost of natural gas, which was the average price at federal facilities in the United States as of July 2024.
Lifetime Energy Cost: Calculated based on future natural gas price trends and a 3% discount rate from Energy Price Indices and Discount Factors for Life-Cycle Cost Analysis – 2024: Annual Supplement to NIST Handbook 135 and NBS Special Publication 709 (NISTIR 85-3273-39).
Lifetime Energy Cost Savings: The difference between the lifetime energy cost of the identified models.
Model Efficiency Levels
High Efficiency Model: Based on the most efficient model available in the September 2024 ENERGY STAR-Qualified Products List. More efficient models may have entered the market after FEMP's acquisition guidance was created.
Required Efficiency Model: Based on September 2024 ENERGY STAR efficiency levels. Federal agencies must purchase products that meet or exceed ENERGY STAR efficiency levels.
Lower Efficiency Model: Based on the least efficient product that meets the minimum efficiency required for products to be sold on the market (10 CFR Part 430), which is the minimum efficiency all manufacturers need to comply with. Note energy savings will vary depending on actual usage.
Example 3: FEMP-Designated Large Commercial Boilers Meeting Combustion Efficiency Requirements
FEMP has calculated that a 3,000,000 Btu/h gas-fired hot water commercial boiler meeting the required combustion efficiency level of 96.0% saves money if priced no more than $95,651 above the less efficient model with a combustion efficiency of 82.0%. The best available model shown below is cost effective if it costs no more than $107,085 above the less efficient model (or $11,434 above the required model).
Table 4. Lifetime Energy Cost Savings for Efficient Large Commercial Boiler Models
| Performance | High Efficiency Model | Required Efficiency Model | Lower Efficiency Model |
|---|---|---|---|
| Combustion Efficiency (%) | 98.0% | 96.0% | 82.0% |
| Annual Energy Use (therms/yr) | 35,143 | 35,875 | 42,000 |
| Annual Energy Cost | $33,773 | $34,476 | $40,363 |
| Lifetime Energy Cost | $548,809 | $560,242 | $655,893 |
| Lifetime Energy Cost Savings | $107,085 | $95,651 | ====== |
Energy Use and Cost Assumptions
Annual Energy Use: Assumed boilers operate for 1,400 full-load hours per year and have a lifetime of 25 years.
Annual Energy Cost: The calculation used $0.961/therm for the cost of natural gas, which was the average price at federal facilities in the United States as of July 2024.
Lifetime Energy Cost: Calculated based on future natural gas price trends and a 3% discount rate are from the Energy Price Indices and Discount Factors for Life-Cycle Cost Analysis – 2024: Annual Supplement to NIST Handbook 135 and NBS Special Publication 709 (NISTIR 85-3273-39).
Lifetime Energy Cost Savings: The difference between the lifetime energy cost of the identified models.
Model Efficiency Levels
High Efficiency Model: Based on the most efficient model identified in publicly provided manufacturer data as of July 2024. Note that more efficient models may have entered the market after FEMP's acquisition guidance was created.
Required Efficiency Model: Based on FEMP-designated efficiency requirements. Federal agencies must purchase products that meet or exceed FEMP-designated efficiency levels.
Lower Efficiency Model: Based on the least efficient product that meets the minimum efficiency required for products to be sold on the market (10 CFR Part 430), which is the minimum efficiency all manufacturers need to comply with. Note energy savings will vary depending on actual usage.
Where To Buy Compliant Products
Buyers can make sure the product they purchase will be compliant by incorporating federal acquisition regulation language into contracts. Compliant products can also be found using federal supply sources and product codes. See FEMP’s general federal purchasing requirements webpage for more details on buying compliant energy-using products.
Boiler Product Codes
The Defense Logistics Agency Environmental Attribute Code (ENAC) identifies items with energy characteristics that meet standards set by an approved third party, such as FEMP and ENERGY STAR. Purchasers can also use a United Nations Standard Products and Services Code (UNSPSC) to identify and buy products and to track purchases. In addition, the Unified Facilities Guide Specifications (UFGS) section 23 52 43.00 20 has information regarding low-pressure water heating boilers. These specifications are used in construction for the U.S. military services.
The UNSPSCs and DLA ENACs for boilers are listed in Table 5.
Table 5. Product Codes for Residential and Commercial Boilers
| Boiler Type | Size (Input) | DLA ENAC | UNSPSCs | ||
|---|---|---|---|---|---|
| Gas-Fired | Oil-Fired | Eithera | |||
| Residential | Less than 300,000 Btu/hr | LN | 40102004 and 40102005 | N/A | N/A |
| Packaged Boiler / Small Commercial | 300,000 – 2,500,000 Btu/hr | HF | 40102004 and 40102005 | 40102007 | 40102001 and 40102002 |
| Large Commercial | 2,500,000 – 10,000,000 Btu/hr | HF | 40102004 and 40102005 | 40102007 | 40102001 and 40102002 |
a Fire tube and water tube boilers can be either gas-fired or oil-fired.
Other Tips for Choosing and Using the Best Product Efficiently
Understand Factors Affecting Life Cycle Cost of Boilers
Before looking for specific boiler products, buyers and specifiers should consider the following factors that would affect how much a boiler costs over its lifetime.
Boiler Usage
If you live in a cold climate with significant heating needs, it usually makes sense to invest in a highest-efficiency boiler system. In milder climates with lower annual heating energy usage and costs, the extra investment required to go to an incrementally higher efficiency may be hard to justify.Building Energy Efficiency and Sizing
Before buying a new boiler or modifying an existing unit, agencies should first make every effort to improve the energy efficiency of the building, then have a heating contractor rightsize the boiler. Energy-efficiency improvements will save money on a new boiler because buyers can purchase a smaller unit. More importantly, a properly sized boiler will operate more efficiently, saving money over the lifetime of the boiler.Building Loads
The cost to purchase a boiler depends on selecting the right system with proper sizing. This requires knowledge of both the building’s peak heating demand and load profile. If building loads are highly variable, as is common in commercial buildings, designers should consider installing multiple small (modular) boilers in addition to boilers that have modulating burners. In periods of low demand, this would allow some of the boilers to be isolated from the other boilers and not incur any standby losses or cycling losses. The boilers can also be automatically staged such that each boiler is running at its most efficient operating point without incurring additional cycling. For guidance on boiler rightsizing and quality installation, consult the American National Standards Institute/Air Conditioning Contractors of America Standard 5: HVAC Quality Installations Specification (ANSI/ACCA 5 QI 2015).Local Rebates and Other Incentives
Many states and electric utilities offer rebates or other incentives for the purchase of products that are either ENERGY STAR certified or meet the FEMP designated efficiency level. Use the ENERGY STAR Rebate Finder to see if your local utility offers these incentives. Learn more about energy and water project incentives, demand response programs, and time-variable pricing. Look up state incentives for renewables and efficiency. Or, visit the National Association of State Energy Officials website to learn more about state energy offices.
Look for High Efficiency Features
Specifiers and purchasers should consider specifying boilers with the following features, which help the boiler to operate more efficiently.
Condensing
Hot water boilers include both condensing and non-condensing varieties. Condensing boilers are able to extract heat from water vapor in the combustion gases for use in producing hot water, and are typically more efficient than non-condensing models.There are some tradeoffs to consider along with the efficiency improvements. Condensing boilers must be made of corrosion resistant materials which can increase their manufacturing cost. Although more expensive, condensing boilers’ increased efficiency can significantly reduce energy costs to a point where savings exceed the cost premium reflected in the initial purchase price. Hybrid systems are useful in retrofit applications that integrate new condensing boilers and conventional boilers into an existing modular system.
Water Temperature Reset
Hot water boilers should have the capability for water temperature reset. When the heating load is reduced, the supply water is set to a lower temperature. This is typically based on the outdoor air temperature or the return water temperature.Modulating Burners
Most of the time boilers operate at part load. To prevent excessive cycling and losses, specify boilers that have modulating capability to vary their heating output with a modulating burner. This is particularly important in condensing boilers that run more efficiently at part load. A minimum turndown ratio of 5:1 is recommended for gas-fired, hot-water boilers.Low Mass
Because boilers cycle on and off and it takes time to bring a high-mass boiler up to operating temperature, using low-mass boilers will reduce energy consumption every time a boiler starts up. In addition, some boilers can be brought online quickly, therefore avoiding the need to keep a boiler on hot standby.Precise Air-Fuel Ratio Control
It is important to keep the air-fuel ratio at optimum levels at part-load operation as well as full-load operation. This is better accomplished by using sensor-driven servos rather than a mechanical linkage (e.g., jack shaft) between the gas input and the blower damper. Oxygen trim systems should be used on larger boilers. Oxygen trim systems monitor the oxygen in the flue gas and adjust the air-fuel ratio for optimum combustion efficiency.Other Enhancements
Other options to increase efficiency of the heating system include reusing heat from blow down and return condensate for steam boilers, using electronic ignition devices, and increasing boiler and piping insulation.System-Level Efficiency Features
Apart from the annual fuel utilization efficiency or AFUE (EPA’s measure of efficiency for residential boilers), buyers can also identify an overall efficient system using a residential boiler system’s other features. Mid-efficiency heating systems tend to have smaller diameter flue pipes, electronic ignition, more compact and lighter models, and exhaust fans compared to lower efficiency systems. The highest efficiency systems will have sealed combustion and condensing flue gases in a heat exchanger for extra efficiency.
Consider Other Boiler Features for Flexible Controls and Monitoring
Beyond efficiency, buyers and specifiers may want to consider the following features that make a boiler system easier to maintain and operate once installed.
Remote Monitoring Capability
Remote monitoring capability is useful to manage boiler operation and to detect any malfunctions in a timely manner.
Optimum Start Control
An optimum start control can allow users to fire up a boiler to heat up a building before it is occupied in the morning.
Network Connectivity
Many new energy consuming commercial boilers come equipped with Internet of Things (IoT) sensing components, and network connectivity. Connected boilers make it much easier to reduce loads on a signal from site management or the utility, enabling greater demand flexibility. For more information on how to build cybersecure networks of building technologies, consult FEMP's Energy and Cybersecurity Integration resources and Cyber-Securing Facility Related Control Systems fact sheet.
Tips for Using Boilers Efficiently
Several diagnostic and maintenance procedures are important to maintain efficient boiler operation. These procedures should be integrated into maintenance plans or contracts to increase boiler efficiency and extend the useful life of the boiler.
For details on specific procedures, the Boiler Efficiency Institute provides maintenance and operation manuals for boilers and boiler control systems. To encourage quality operations and maintenance, building engineers can also refer to ASHRAE/ACCA Standard 180: Standard Practice for Inspection and Maintenance of Commercial Building HVAC Systems. In addition, the FEMP O&M Best Practices Guide, Release 3.0, Chapter 9 provides valuable information on operation and maintenance of boiler systems.