Water Heaters

Product Information 

Residential water heaters use oil, gas, or electricity to heat potable water to be used for such activities as bathing or washing dishes or clothes. Residential water heaters include storage type units that store heated water in an insulated tank and instantaneous type units that heat water on demand.

Water heating is typically the second largest energy use in a home, after heating and cooling, and can account for 14%-25% of household energy consumption. In the United States energy consumed by residential water heaters accounts for 11% of the electricity and 24% of the natural gas consumed in the residential sector. However, residential hot water use is variable and depends on the number of people in the household, the type of appliances, and the climate in which the house is located.

Current Standards

Gas-fired ( 75 kBtu/h input capacity), oil-fired ( 105 kBtu/h input capacity), electric ( 12 kW input capacity), and tabletop ( 12 kW input capacity) storage water heaters, as well as instantaneous gas-fired (<200 kBtu/h input capacity) and electric ( 12 kW input capacity) water heaters, manufactured and distributed in commerce must meet the energy conservation standards specified in Table 1 as of January 20, 2004.

Amended Standards

On March 31, 2010, the U.S. Department of Energy (DOE) completed the second rulemaking to amend energy conservation standards for residential water heaters, issuing a final rule. Residential water heaters must comply with the amended standards in Table 2 by April 16, 2015.

Table 1. Energy Conservation Standards for Residential Water Heaters
Product Class Rated Storage Volume Energy Factor
Gas-fired Water Heater 20 gal and 100 gal 0.67 - (0.0019*Vs)
Oil-fired Water Heater 50 gal 0.59 - (0.0019*Vs)
Electric Water Heater 20 gal and 120 gal 0.97 - (0.00132*Vs)
Tabletop Water Heater 20 gal and 100 gal 0.93 - (0.00132*Vs)
Instantaneous Gas-fired Water Heater < 2 gal 0.62 - (0.0019*Vs)
Instantaneous Electric Water Heater < 2 gal 0.93 - (0.00132*Vs)

Vs: Rated Storage Volume - the water storage capacity of a water heater (in gallons).

Table 2. Amended Energy Conservation Standards for Residential Water Heaters
Product Class Rated Storage Volume Energy Factor
Gas-fired Water Heater 20 gal and 55 gal 0.675 - (0.0015*Vs)
> 55 gal and 100 gal 0.8012 - (0.00078* Vs)
Oil-fired Water Heater 50 gal 0.68 - (0.0019*Vs)
Electric Water Heater 20 gal and 55 gal 0.960 - (0.0003*Vs)
> 55 gal and 120 gal 2.057 - (0.00113*Vs)
Tabletop Water Heater 20 gal and 100 gal 0.93 - (0.00132*Vs)
Instantaneous Gas-fired Water Heater < 2 gal 0.82 - (0.0019*Vs)
Instantaneous Electric Water Heater < 2 gal 0.93 - (0.00132*Vs)

Vs: Rated Storage Volume - the water storage capacity of a water heater (in gallons).

The efficiency metric for residential water heaters is the energy factor (EF), which indicates a water heater's overall energy efficiency based on the amount of hot water produced per unit of fuel consumed over a typical day. The EF accounts for the following:

  • Recovery efficiency - how efficiently the heat from the energy source is transferred to the water
  • Standby losses - the percentage of heat loss per hour from the stored water compared to the heat content of the water (for water heaters with storage tanks)
  • Cycling losses - the loss of heat as the water circulates through a water heater tank, and/or inlet and outlet pipes.