# Energy factor

> Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Energy_factor
> Markdown URL: https://mediated.wiki/source/Energy_factor.md
> Source: https://en.wikipedia.org/wiki/Energy_factor
> Source revision: 1288139637
> License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/)

An **energy factor** is a metric used in the [United States](/source/United_States) to compare the [energy conversion efficiency](/source/Energy_conversion_efficiency) of residential appliances and equipment. The energy factor is currently used for rating the efficiency of [water heaters](/source/Water_heating), [dishwashers](/source/Dishwasher), [clothes washers](/source/Washing_machine), and [clothes dryers](/source/Clothes_dryer).[1] The term is used by the [United States Department of Energy](/source/United_States_Department_of_Energy) to develop and enforce minimum energy conservation standards under the [Energy Conservation Program](/source/Energy_Policy_and_Conservation_Act#Energy_Conservation_Program).[2]

The higher the energy factor, the more efficient the appliance should be.[3]

Although the term energy factor is used to compare the relative efficiency of these appliances, the metric is defined differently for all four appliance categories. The energy factor is expressed in terms of site energy, which excludes losses through [energy conversion](/source/Energy_transformation). All of these efficiency metrics are defined by Department of Energy test procedures.[4]

## Water heaters

The energy factor metric only applies to residential water heaters, which are currently defined by fuel, type, and input capacity.[5] Generally, the EF number represents the [thermal efficiency](/source/Thermal_efficiency) of the water heater as a percentage, since it is an average of the ratio of the theoretical heat required to raise the temperature of water drawn to the amount of energy actually consumed by the water heater.

Residential water heaters Fuel Type Input capacity Natural Gas Storage ≤75 kBtu/h Fuel Oil Storage ≤105 kBtu/h Electric Storage ≤12 kW Tabletop Storage ≤12 kW Natural Gas Instantaneous <200 kBtu/hr Electric Instantaneous ≤12 kW

### Test procedure

The energy factor is determined using a stylized hot water use pattern. Hot water is drawn in six equal draws totaling 64.3 US gallons (243 L), and a standby period of 18 hours follows.

The energy factor for residential water heaters is determined using the results from the 24-hour simulated use test. During the test 64.3±1.0 gallons of water are drawn from the water heater in six equally spaced draws that begin one hour apart. The hot water flow rate for each draw is 3.0±0.25 gallons per minute. After the beginning of the last draw a standby period of 18 hours follows. During the test, the test conditions must be operated at a specified value and accuracy. [Heat pump](/source/Heat_pump) water heaters (HPWHs) have different values specified for ambient air temperature and relative humidity.[6]

Specified test conditions Measurement Required value and accuracy Inlet water temperature 58 °F±2 °F Outlet water temperature 135 °F±5 °F Ambient air temperature 67.5 °F±2.5 °F Ambient air temperature (HPWHs only) 67.5 °F±1 °F Ambient relative humidity (HPWHs only) 50%±1%

From the standard test procedure, the energy factor is defined as

- E F = ∑ i = 1 6 M i C p i ( 135 ∘ F − 58 ∘ F ) Q d m , {\displaystyle EF=\sum \limits _{i=1}^{6}{\frac {M_{i}C_{pi}\left(135^{\circ }F-58^{\circ }F\right)}{Q_{dm}}},}

where Q d m {\displaystyle Q_{dm}} is the modified daily water heating energy consumption (Btu), M i {\displaystyle M_{i}} is the mass withdrawn from the *i*th draw (lb), and C p i {\displaystyle C_{pi}} is the [specific heat](/source/Specific_heat) of the water of the *i*th draw Btu/lb°F, evaluated at the midpoint between 58 and 135 °F (14 and 57 °C).

### Uniform energy factor (UEF)

As of 2021[\[update\]](https://en.wikipedia.org/w/index.php?title=Energy_factor&action=edit) the Uniform Energy Factor (UEF) is newest measure of water heater overall efficiency according to the Department of Energy’s test method outlined in 10 CFR Part 430, Subpart B, Appendix E.

### Energy conservation standards

Minimum federal energy conservation standards are defined by fuel, type, and rated storage volume. All standards are calculated as a function of the rated storage volume *V* in gallons. The current conservation standards are less efficient than the standards that go into effect in 2015.[5][7][8]

Energy Conservation Standards Fuel Type Rated Storage Volume Energy Factor (Effective April 16, 2015) Energy Factor Natural Gas Storage ≥ 20 gal and ≤ 55 gal 0.675 − 0.0015V 0.67 − 0.0019V Natural Gas Storage > 55 gal and ≤ 100 gal 0.8012 − 0.00078V 0.67 − 0.0019V Fuel Oil Storage ≤ 50 gal 0.68 − 0.0019V 0.59 − 0.0019V Electric Storage ≥ 20 gal and ≤ 55 gal 0.960 − 0.0003V 0.97 − 0.00132V Electric Storage > 55 gal and ≤ 120 gal 2.057 − 0.00113V 0.97 − 0.00132V Tabletop Storage ≥ 20 gal and ≤ 100 gal 0.93 − 0.00132V 0.93 − 0.00132V Natural Gas Instantaneous < 2 gal 0.82 − 0.0019V 0.62 − 0.0019V Electric Instantaneous < 2 gal 0.93 − 0.00132V 0.93 − 0.00132V

## Dishwashers

This section needs expansion. You can help by adding missing information. (March 2013)

The energy factor for dishwashers is defined as "the number of cycles per kWh of input power [*[sic](/source/Sic)*]."[1]

## Clothes washers

This section needs expansion. You can help by adding missing information. (March 2013)

The energy factor for clothes washers, is defined as "the cubic foot capacity per kWh of input power per cycle."[1]

## Clothes dryers

This section needs expansion. You can help by adding missing information. (March 2013)

The energy factor for clothes dryers is defined as "the number of pounds of clothes dried per kWh of power consumed."[1]

## See also

- [Energy star](/source/Energy_star)

## References

1. ^ [***a***](#cite_ref-energy_star_def_1-0) [***b***](#cite_ref-energy_star_def_1-1) [***c***](#cite_ref-energy_star_def_1-2) [***d***](#cite_ref-energy_star_def_1-3) ["Federal Tax Credits for Consumer Energy Efficiency: Definitions"](https://web.archive.org/web/20130401155424/http://www.energystar.gov/index.cfm?c=tax_credits.tx_definitions&dts=mcs). *energystar.gov*. [U.S. Environmental Protection Agency](/source/U.S._Environmental_Protection_Agency). Archived from [the original](https://www.energystar.gov/index.cfm?c=tax_credits.tx_definitions&dts=mcs) on 1 April 2013. Retrieved 26 March 2013.

1. **[^](#cite_ref-stat_authority_2-0)** ["Statutory Authorities and Rules"](http://www1.eere.energy.gov/buildings/appliance_standards/statutory_authorities_and_rules.html). *eere.energy.gov*. [U.S. Department of Energy](/source/U.S._Department_of_Energy). Retrieved 26 March 2013.

1. **[^](#cite_ref-3)** ["ESTIMATING COSTS AND EFFICIENCY OF STORAGE, DEMAND, AND HEAT PUMP WATER HEATERS"](http://energy.gov/energysaver/estimating-costs-and-efficiency-storage-demand-and-heat-pump-water-heaters). *Energy.gov*. US Dept of Energy. Retrieved 2 June 2016.

1. **[^](#cite_ref-standards_4-0)** ["Standards and Test Procedures"](http://www1.eere.energy.gov/buildings/appliance_standards/standards_test_procedures.html). *eere.energy.gov*. U.S. Department of Energy. Retrieved 26 March 2013.

1. ^ [***a***](#cite_ref-waterheaters_5-0) [***b***](#cite_ref-waterheaters_5-1) ["Residential Water Heaters"](http://www1.eere.energy.gov/buildings/appliance_standards/product.aspx/productid/27). *eere.energy.gov*. U.S. Department of Energy. Retrieved 26 March 2013.

1. **[^](#cite_ref-test_proc_6-0)** ["10 CFR Part 430 Energy Conservation Program for Consumer Products: Test Procedure for Water Heaters; Final Rule"](https://www.gpo.gov/fdsys/pkg/FR-1998-05-11/pdf/98-12296.pdf) (PDF). *Federal Register*. **63** (90): 25995–26016. 11 May 1998. Retrieved 26 March 2013.

1. **[^](#cite_ref-7)** ["10 CFR Part 430 Energy Conservation Program: Energy Conservation Standards for Residential Water Heaters, Direct Heating Equipment, and Pool Heaters; Final Rule"](https://www.gpo.gov/fdsys/pkg/FR-2010-04-16/pdf/2010-7611.pdf) (PDF). *Federal Register*. **75** (73): 20112–21981 [20113]. 16 April 2010. Retrieved 26 March 2013.

1. **[^](#cite_ref-8)** ["10 CFR Part 430 Energy Conservation Program for Consumer Products: Energy Conservation Program for Consumer Products: Energy Conservation Standards for Water Heaters; Final Rule"](https://www.gpo.gov/fdsys/pkg/FR-2001-01-17/pdf/01-1081.pdf) (PDF). *Federal Register*. **66** (11): 4474–4497 [4497]. 17 January 2001. Retrieved 26 March 2013.

---
Adapted from the Wikipedia article [Energy factor](https://en.wikipedia.org/wiki/Energy_factor) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Energy_factor?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.