The Federal Energy Management Program (FEMP) provides acquisition guidance for residential solar water heaters, a product category covered by ENERGY STAR efficiency requirements. Federal laws and requirements mandate that agencies purchase ENERGY STAR Certified products or FEMP-designated products in all product categories covered by these programs and in any acquisition actions that are not specifically exempted by law.

FEMP's acquisition guidance and associated ENERGY STAR efficiency requirements for residential solar water heaters are technology neutral, meaning that one technology is not favored over another.

This acquisition guidance was updated in June 2020.

Find Product Efficiency Requirements

The U.S. Environmental Protection Agency (EPA) provides residential solar water heater efficiency levels and product specification information 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 residential solar water heaters to identify or verify complying models. As of June 2020, the version 3.3 ENERGY STAR product specification for residential water heaters was not published. Please check the ENERGY STAR webpage on residential water heaters for updates on the version 3.3 specification.

Make a Cost-Effective Purchase: Save $1,428 or More by Buying ENERGY STAR

FEMP has calculated that the required ENERGY STAR Certified residential solar water heater saves money if priced no more than $1,428 above the less efficient model. The best available model saves up to $2,529. Tables 1 and 2 compare three types of product purchases and calculate the lifetime cost savings of purchasing efficient models for households with typical water use. Federal purchasers can assume products that meet ENERGY STAR efficiency requirements are life cycle cost-effective.

Table 1. Lifetime Cost Savings for Efficient Residential Solar Water Heater Models with Electric Backup
PerformanceBest AvailableENERGY STARLess Efficient
Solar Energy Factor4.71.81.0
Energy Factor (Backup)0.940.940.94
Annual Energy Use (kWh)7381,9283,470
Annual Energy Cost$64$168$303
Lifetime Energy Cost$683$1,785$3,212
Lifetime Cost Savings$2,529$1,428======

Note: Monetary and energy use values in this table are rounded to the nearest whole unit.

Table 2. Lifetime Cost Savings for Efficient Residential Solar Water Heater Models with Gas Backup
PerformanceBest AvailableENERGY STARLess Efficient
Solar Energy Factor1.91.21
Energy Factor (Backup)0.740.740.74
Annual Energy Use (therms)79125150
Annual Energy Cost$50$80$95
Lifetime Energy Cost$576$912$1,094
Lifetime Cost Savings$518$182======

Note: Monetary and energy use values in this table are rounded to the nearest whole unit.


View the Performance and Model Assumptions for Tables 1 and 2


Solar Energy Factor: Solar Energy Factor (SEF) refers to the energy delivered by the total system divided by the electrical or gas energy put into the system.

Energy Factor: A metric used to compare the energy conversion efficiency of residential water heaters; in this case describing the backup water heater.

Annual Energy Use: Based on the test method referenced in 10 Code of Federal Regulations (CFR) 430, Subpart B, Appendix E, for unit producing 20,075 gallons of hot water per year.

Annual Energy Cost: Calculated based on an assumed electricity price of $0.087/kWh for Table 1 and an assumed natural gas price of $0.63/therm for Table 2, which are the average prices at federal facilities.

The sum of the discounted values of annual energy cost with an assumed product life of 13 years. Future natural gas price trends and a 3% discount rate are from Energy Price Indices and Discount Factors for Life-Cycle Cost Analysis – 2020: Annual Supplement to NIST Handbook 135 and NBS Special Publication 709 (NISTIR 85-3273-35).

Lifetime Cost Savings: The difference between the lifetime energy cost of the less efficient model and the lifetime energy cost of the ENERGY STAR model or best available model.


Calculated based on the June 2020 ENERGY STAR Certified Products List. More efficient models may be introduced to the market after FEMP's acquisition guidance is posted.


Calculated based on June 2020 ENERGY STAR efficiency levels. Federal agencies must purchase products that meet or exceed ENERGY STAR efficiency levels.


Calculated based on typical products used in non-federal applications.

There are additional cost savings associated with waste heat recovery systems. Drain-water, or greywater, heat recovery systems capture the energy from waste hot water—such as showers and dishwashers—to preheat cold water entering the water heater or going to other water fixtures. Energy savings vary depending on individual household location and hot water consumption.

Determine When ENERGY STAR Products Are Cost-Effective

An efficient product is cost-effective when the lifetime energy savings (from avoided energy costs over the life of the product, discounted to present value) exceed the additional up-front cost (if any) compared to a less efficient option. ENERGY STAR considers up-front costs and lifetime energy savings when setting required efficiency levels. Federal purchasers can assume ENERGY STAR Certified products and products that meet FEMP-designated efficiency requirements are life cycle cost-effective. In high-use applications or when energy rates are above the federal average, purchasers may save more if they specify products that exceed federal efficiency requirements (e.g., the best available model).

Claim an Exception to Federal Purchasing Requirements

Products meeting ENERGY STAR or FEMP-designated efficiency requirements may not be life cycle cost-effective in certain low-use applications or in locations with very low rates for electricity or natural gas. However, for most applications, purchasers will find that energy-efficient products have the lowest life cycle cost.

Agencies may claim an exception to federal purchasing requirements through a written finding that no FEMP-designated or ENERGY STAR Certified product is available to meet functional requirements, or that no such product is life cycle cost-effective for the specific application. Learn more about federal product purchasing requirements.

Incorporate Federal Acquisition Regulation Language in Contracts

These mandatory requirements apply to all forms of procurement, including construction guide and project specifications; renovation, repair, energy service, and operation and maintenance (O&M) contracts; lease agreements; acquisitions made using purchase cards; and solicitations for offers. Federal Acquisition Regulation (FAR) Part 23.206 requires agencies to insert the clause at FAR section 52.223-15 into contracts and solicitations that deliver, acquire, furnish, or specify energy-consuming products for use in federal government facilities. To comply with FAR requirements, FEMP recommends that agencies incorporate efficiency requirements into technical specifications, the evaluation criteria of solicitations, and the evaluations of solicitation responses.

Find Federal Supply Sources

The federal supply sources for energy-efficient products are the General Services Administration (GSA) and the Defense Logistics Agency (DLA). GSA sells products through its Multiple Awards Schedules program and online shopping network, GSA Advantage!. DLA offers products through the Defense Supply Center Philadelphia and online through FedMall (formerly the U.S. Department of Defense eMALL). Products sold through DLA are codified with a 13-digit National Stock Number (NSN) and, in some cases, a two-letter Environmental Attribute Code (ENAC). The ENAC identifies items that have positive environmental characteristics and meet standards set by an approved third party, such as FEMP and ENERGY STAR.

The United Nations Standard Products and Services Code (UNSPSC) is a worldwide classification system for e-commerce. It contains more than 50,000 commodities, including many used in the federal sector, each with a unique eight-digit, four-level identification code. Manufacturers and vendors are beginning to adopt the UNSPSC classification convention and electronic procurement systems are beginning to include UNSPSC tracking in their software packages. UNSPSCs can help the federal acquisition community identify product categories covered by sustainable acquisition requirements, track purchases of products within those categories, and report on progress toward meeting sustainable acquisition goals. FEMP has developed a table of ENERGY STAR and FEMP-designated covered product categories and related UNSPSC numbers.

Residential Solar Water Heater Schedules and Product Codes

GSA offers residential solar water heaters through Schedule 51 V, Category 639 001 and Schedule 56, Category 206 3.

DLA's ENAC for residential solar water heaters is DS.

The UNSPSC for residential solar water heaters is 40101825.

Buyer Tips: Make Informed Product Purchases

Solar water heating systems usually cost more to purchase and install than conventional water heating systems. However, a solar water heater can usually save you money in the long run. How much money you save depends on the following:

  • The amount of hot water you use
  • Your system's performance
  • Your geographic location and solar resource
  • Available financing and incentives
  • The cost of conventional fuels (natural gas, oil, and electricity)
  • The cost of the fuel you use for your backup water heating system, if you have one.

On average, if you install a solar water heater, your water heating bills should drop 50%–80%. Additionally, you are protected from future fuel supply and price volatility by utilizing free solar thermal energy, increasing overall resilience.

When comparing solar water heating systems, consider installation and maintenance costs. Some systems might cost more to install and maintain. In addition, it is important to consider the household's anticipated water usage.

As shown in Tables 3 and 4, ENERGY STAR Certified products need substantially less power to heat water. Buyers can use these tables as a guide when replacing standard residential solar water heaters with more efficient residential solar water heaters.

Table 3. Comparison of Lifetime Cost Savings for Residential Solar Water Heater Models with Electric Backup at Different Water Use Levels
Water UsageVery SmallLowMediumHigh
Daily Water Usage (gal/day)10385584
Annual Energy Savings (kWh)2801,0661,5422,356
Annual Energy Cost Savings$24$93$135$206
Lifetime Cost Savings*$260$986$1,428$2,181

*Compared to less efficient models with the same draw.

Note: Monetary and energy use values in this table are rounded to the nearest whole unit.

Table 4. Comparison of Lifetime Cost Savings for Residential Solar Water Heater Models with Gas Backup at Different Water Use Levels
Water UsageVery SmallLowMediumHigh
Daily Water Usage (gal/day)10385584
Annual Energy Savings (therms)5172538
Annual Energy Cost Savings$3$11$16$24
Lifetime Cost Savings*$33$126$182$278

*Compared to less efficient models with the same draw.

Note: Monetary and energy use values in this table are rounded to the nearest whole unit.


Many states and electric utilities offer rebates or other incentives for the purchase of ENERGY STAR Certified products. Use the ENERGY STAR Rebate Finder to see if your local utility offers these incentives. FEMP's Energy Incentive Program helps federal agencies take advantage of these incentives by providing information about the funding-program opportunities available in each state.

Many new energy consuming solar water heaters come equipped with Internet of Things (IoT) sensing components and network connectivity. Making a new purchase or replacement represents a prime opportunity to evaluate the vulnerabilities of your network. All IoT-enabled devices introduce novel exposures to potential data breaches. Building controls and heating, ventilating, and air conditioning systems are no exception. Security can almost never be networked in after the fact, and so it is important to ensure that your networked devices are secure. Also, regularly testing for network vulnerabilities is key. For more information on how to build cybersecure networks of building technologies consult existing FEMP guidance and case studies.

User Tips: Use Products More Efficiently

When used and handled properly, energy-efficient residential solar water heater models provide years of safe and effective service. Federal users should be aware of the following user tips.

  • Install aerating, low-flow faucets and showerheads.
  • Repair leaky faucets promptly; a leaky faucet wastes gallons of water in a short period of time.
  • Set the thermostat on your water heater to 120°F to get comfortable hot water for most uses. Dishwashers require the hottest water of all household uses, typically 135°F to 140°F. However, they are usually equipped with booster heaters to raise the incoming water temperature by 15°F to 20°F. Setting the water heater between 120°F and 125°F and turning the dishwasher's booster on should provide sufficient hot water while saving energy and reducing the chances for scalding.
  • Insulate your natural gas or oil backup hot-water storage tank but be careful not to cover the water heater's top, bottom, thermostat, or burner compartment. Follow the manufacturer's recommendations; when in doubt, get professional help.
  • Insulate the first 6 feet of the hot and cold water pipes connected to the water heater.
  • Install heat traps on the hot and cold pipes at the water heater to prevent heat loss. All new water heaters have built-in heat traps.
  • Drain a quart of water from your water tank every 3 months to remove sediment that impedes heat transfer and lowers the efficiency of your heater. Follow the manufacturer's directions.

Lawrence Berkeley National Laboratory provided supporting analysis for this acquisition guidance.