Water Heater Key Product Criteria

Efficiency and performance for ENERGY STAR certified water heaters may be evaluated using two different methods. A water heater can be certified as ENERGY STAR by meeting Energy Factor (EF), Standby Loss, and/or Thermal Efficiency criteria or by meeting Uniform Energy Factor (UEF) criteria. Although these performance metrics are different, certification as ENERGY STAR by either method requires equivalent efficiency. Consumers should not directly compare EF values to UEF values.

Solar water heaters must meet minimum Solar Energy Factor criteria to be certified as ENERGY STAR.

ENERGY STAR Residential Water Heaters — Eligible Product Types
Storage Water Heaters Storage type units designed to heat and store water at a thermostatically controlled temperature, including: gas storage water heaters with a nominal input of 75,000 British thermal units (Btu) per hour or less, containing more than one gallon of water per 4,000 Btu per hour of input; electric heat pump water heaters with a maximum current rating of 24 amperes at an input voltage 250 volts or less.1
Instantaneous Water Heaters Instantaneous (or “tankless”) type units heat water, but contain no more than one gallon of water per 4,000 Btu per hour of input with an input less than 200,000 Btu per hour.2
Solar Water Heaters Solar water heaters include a collector and storage tank, and use the sun’s energy to heat water using one of the five basic types of solar water heating systems:
  1. forced circulation (includes both direct and indirect systems),
  2. integrated collector and storage,
  3. thermosiphon,
  4. self-pumped, or
  5. photovoltaic (PV).
High Capacity Storage Water Heaters Gas-fired storage units that are designed to deliver hot water at a temperature less than or equal to 180°F, with an input rate greater than 75,000 Btu/h but no greater than 105,000 Btu/h. These units are referred to as “Light Duty EPACT-covered” if they report thermal efficiency and standby loss as efficiency metrics and “Gas-fired Storage Residential-duty” if they report uniform energy factor as the efficiency metric.

ENERGY STAR Criteria – Energy Factor, Standby Loss, and Thermal Efficiency

A water heater model must meet all of the identified criteria to be labeled as ENERGY STAR. Water heaters that meet the criteria identified in this section report Uniform Energy Factor (UEF) but are not required to meet the UEF criteria.

Criteria for Certified Electric Storage Water Heaters

Criteria ENERGY STAR Requirements
Energy Factor ≤ 55 gallons EF ≥ 2.00
> 55 gallons EF ≥ 2.20
First Hour Rating FHR ≥ 50 gallons per hour at 135°F outlet temperature
Warranty Warranty ≥ 6 years on sealed system
Safety UL 174 and UL1995
Lower Compressor Cut-Off Temperature (Reporting Requirement Only) Report ambient temperature (°F) below which the compressor cuts off and electric resistance only operation begins

Criteria for Certified Gas Storage Water Heaters

Criteria ENERGY STAR Requirements
Energy Factor ≤ 55 gallons EF ≥ 0.67
> 55 gallons EF ≥ 0.77
First Hour Rating FHR ≥ 67 gallons per hour at 135°F outlet temperature
Warranty Warranty ≥ 6 years on system (including parts)
Safety ANSI Z21.10.1/CSA 4.1

Criteria for Certified Gas Instantaneous Water Heaters

Criteria ENERGY STAR Requirements
Energy Factor EF ≥ 0.90
Gallons-Per-Minute GPM ≥ 2.5 over a 77° rise
Warranty Warranty ≥ 6 years on heat exchanger and ≥ 5 years on parts
Safety ANSI Z21.10.3/CSA 4.3

Criteria for Certified High Capacity Storage (Light Duty EPACT-Covered) Gas Water Heaters

Criteria ENERGY STAR Requirements
Thermal Efficiency TE ≥ 0.90
Standby Loss Standby loss ≤ 1889 Btu/hr ×(TE–0.73)
Warranty Warranty ≥ 6 years on system
Safety ANSI Z21.10.3/CSA 4.3

ENERGY STAR Criteria – Uniform Energy Factor

A water heater model must meet all of the identified criteria to be labeled as ENERGY STAR. Water heaters that meet the criteria identified in this section are not required to meet Energy Factor, Thermal Efficiency, or Standby Loss criteria.

Criteria for Certified Electric Storage Water Heaters

Criteria ENERGY STAR Requirements
Uniform Energy Factor ≤ 55 gallons UEF ≥ 2.00
> 55 gallons UEF ≥ 2.20
First Hour Rating FHR ≥ 45 gallons per hour at 125°F outlet temperature
Warranty Warranty ≥ 6 years on sealed system
Safety UL 174 and UL1995
Lower Compressor Cut-Off Temperature (Reporting Requirement Only) Report ambient temperature (°F) below which the compressor cuts off and electric resistance only operation begins

Criteria for Certified Gas-fired Storage Water Heaters

Criteria ENERGY STAR Requirements
Uniform Energy Factor ≤ 55 gallons Medium Draw Pattern UEF ≥ 0.64

High Draw Pattern UEF ≥ 0.68
> 55 gallons Medium Draw Pattern UEF ≥ 0.78

High Draw Pattern UEF ≥ 0.80
First Hour Rating FHR ≥ 67 gallons per hour at 135°F outlet temperature
Warranty Warranty ≥ 6 years on system (including parts)
Safety ANSI Z21.10.1/CSA 4.1

Criteria for Certified Gas-fired Instantaneous Water Heaters

Criteria ENERGY STAR Requirements
Uniform Energy Factor UEF ≥ 0.87
Maximum Gallons Per Minute Max GPM ≥ 2.9 over a 67°F rise
Warranty Warranty ≥ 6 years on heat exchanger and ≥ 5 years on parts
Safety ANSI Z21.10.3/CSA 4.3

Criteria for Certified High Capacity Storage (Gas-fired Storage Residential-duty Commercial) Gas Water Heaters

Criteria ENERGY STAR Requirements
Uniform Energy Factor UEF ≥ 0.80
Warranty Warranty ≥ 6 years on system
Safety ANSI Z21.10.3/CSA 4.3

ENERGY STAR Criteria – Solar Energy Factor

Solar water heater models must meet all of the identified criteria to be labeled as ENERGY STAR.

Criteria for Certified Solar Water Heaters

Criteria ENERGY STAR Requirements
Solar Energy Factor SEF ≥ 1.8 for electric backup
SEF ≥ 1.2 for gas backup
Warranty ≥ 10 years on collector
≥ 6 years sealed system
≥ 2 years on controls
≥ 1 year on parts

Glossary

Energy Factor (EF): An older measure of water heater overall efficiency that is being phased out due to new test methods for water heaters. The higher the EF value is, the more efficient the water heater. EF is determined by the Department of Energy’s test method outlined in the 10 CFR parts 200 to 499 edition revised as of January 1, 2014.

First Hour Rating (FHR): An estimate of the maximum volume of hot water in gallons that a storage water heater can supply within an hour that begins with the water heater fully heated. The FHR is measured at a 135°F outlet temperature in the Energy Factor test method and at a 125°F outlet temperature in the Uniform Energy Factor test method.

Gallons per Minute (GPM): The amount of gallons per minute of hot water that can be supplied by an instantaneous water heater while maintaining a nominal temperature rise during steady state operation. The GPM is measured over a 77°F temperature rise in the Energy Factor test method and over a 67°F temperature rise in the Uniform Energy Factor test method.

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

Uniform Energy Factor (UEF): The newest measure of water heater overall efficiency. The higher the UEF value is, the more efficient the water heater. UEF is determined by the Department of Energy’s test method outlined in 10 CFR Part 430, Subpart B, Appendix E.


1 10 CFR Part 430, Subpart B, Appendix E

2 10 CFR Part 430, Subpart B, Appendix E and 10 CFR Part 430, Subpart A, § 430.2 Definitions