An '''energy factor''' is a metric used in the [[United States]] to compare the [[energy conversion efficiency]] of residential appliances and equipment. The energy factor is currently used for rating the efficiency of [[Water heating|water heaters]], [[dishwasher]]s, [[washing machine|clothes washers]], and [[clothes dryer]]s.<ref name="energy star def">{{cite web|title=Federal Tax Credits for Consumer Energy Efficiency: Definitions |url=http://www.energystar.gov/index.cfm?c=tax_credits.tx_definitions&dts=mcs |work=energystar.gov |publisher=[[U.S. Environmental Protection Agency]] |accessdate=26 March 2013 |url-status=dead |archiveurl=https://web.archive.org/web/20130401155424/http://www.energystar.gov/index.cfm?c=tax_credits.tx_definitions&dts=mcs |archivedate=1 April 2013 }}</ref> The term is used by the [[United States Department of Energy]] to develop and enforce minimum energy conservation standards under the [[Energy Policy and Conservation Act#Energy Conservation Program|Energy Conservation Program]].<ref name="stat authority">{{cite web|title=Statutory Authorities and Rules|url=http://www1.eere.energy.gov/buildings/appliance_standards/statutory_authorities_and_rules.html|work=eere.energy.gov|publisher=[[U.S. Department of Energy]]|accessdate=26 March 2013}}</ref>

The higher the energy factor, the more efficient the appliance should be.<ref>{{cite web|title=ESTIMATING COSTS AND EFFICIENCY OF STORAGE, DEMAND, AND HEAT PUMP WATER HEATERS|url=http://energy.gov/energysaver/estimating-costs-and-efficiency-storage-demand-and-heat-pump-water-heaters|website=Energy.gov|publisher=US Dept of Energy|accessdate=2 June 2016}}</ref>

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 transformation|energy conversion]]. All of these efficiency metrics are defined by Department of Energy test procedures.<ref name=standards>{{cite web|title=Standards and Test Procedures|url=http://www1.eere.energy.gov/buildings/appliance_standards/standards_test_procedures.html|work=eere.energy.gov|publisher=U.S. Department of Energy|accessdate=26 March 2013}}</ref>

==Water heaters== The energy factor metric only applies to residential water heaters, which are currently defined by fuel, type, and input capacity.<ref name=waterheaters>{{cite web|title=Residential Water Heaters|url=http://www1.eere.energy.gov/buildings/appliance_standards/product.aspx/productid/27|work=eere.energy.gov|publisher=U.S. Department of Energy|accessdate=26 March 2013}}</ref> Generally, the EF number represents the [[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.

{| class="wikitable" |+ Residential water heaters ! Fuel !! Type !! Input capacity |- | [[Natural Gas]] || Storage || ≤75 kBtu/h |- | [[Fuel Oil]] || Storage || ≤105 kBtu/h |- | [[Electric]] || Storage || ≤12&nbsp;kW |- | Tabletop || Storage || ≤12&nbsp;kW |- | Natural Gas || Instantaneous || <200 kBtu/hr |- | Electric || Instantaneous || ≤12&nbsp;kW |}

===Test procedure=== [[File:Energy Factor Draw Patter Water Heaters.svg|thumb|upright=1.6|The energy factor is determined using a stylized hot water use pattern. Hot water is drawn in six equal draws totaling {{convert|64.3|USgal|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]] water heaters (HPWHs) have different values specified for ambient air temperature and relative humidity.<ref name="test proc">{{cite journal|title=10 CFR Part 430 Energy Conservation Program for Consumer Products: Test Procedure for Water Heaters; Final Rule|journal=Federal Register|date=11 May 1998|volume=63|issue=90|pages=25995–26016|url=http://www.gpo.gov/fdsys/pkg/FR-1998-05-11/pdf/98-12296.pdf|accessdate=26 March 2013}}</ref>

{| class="wikitable" |+ Specified test conditions ! Measurement !! Required value and accuracy |- | Inlet water temperature || 58&nbsp;°F±2&nbsp;°F |- | Outlet water temperature || 135&nbsp;°F±5&nbsp;°F |- | Ambient air temperature || 67.5&nbsp;°F±2.5&nbsp;°F |- | Ambient air temperature (HPWHs only) || 67.5&nbsp;°F±1&nbsp;°F |- | Ambient relative humidity (HPWHs only) || 50%±1% |}

From the standard test procedure, the energy factor is defined as :<math> EF=\sum\limits_{i=1}^6 \frac{M_i C_{pi}\left( 135^\circ F-58^\circ F\right)}{Q_{dm}},</math> where <math>Q_{dm}</math> is the modified daily water heating energy consumption (Btu), <math>M_i</math> is the mass withdrawn from the ''i''<sup>th</sup> draw (lb), and <math>C_{pi}</math> is the [[specific heat]] of the water of the ''i''<sup>th</sup> draw Btu/lb°F, evaluated at the midpoint between {{cvt|58|and|135|F}}.

<!-- FOLLOWING SAYS IT IS THE EQUATION FOR Qdm, BUT IT IS NOT. IT IS THE EQUATION FOR Qhw, which is only a component of Qdm: The modified daily water heating energy consumption is defined as :<math> Q_{dm}=\sum\limits_{i=1}^6 \frac{M_i C_{pi}\left( \overline{T}_{del,i}-\overline{T}_{in,i}\right)}{\eta_r},</math> where <math>\overline{T}_{del,i}</math> is the average delivery temperature of the ''i''<sup>th</sup> draw (°F) as measured during the test, <math>\overline{T}_{in,i}</math> is the average inlet temperature of the ''i''<sup>th</sup> draw (°F) as measured during the test, and <math>\eta_r</math> is the recovery efficiency of the water heater. -->

===Uniform energy factor (UEF)=== {{asof|2021}} 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.<ref name=waterheaters /><ref>{{cite journal|journal=Federal Register|date=16 April 2010|title=10 CFR Part 430 Energy Conservation Program: Energy Conservation Standards for Residential Water Heaters, Direct Heating Equipment, and Pool Heaters; Final Rule|volume=75|issue=73|pages=20112–21981 [20113]|url=http://www.gpo.gov/fdsys/pkg/FR-2010-04-16/pdf/2010-7611.pdf|accessdate=26 March 2013}}</ref><ref>{{cite journal|title=10 CFR Part 430 Energy Conservation Program for Consumer Products: Energy Conservation Program for Consumer Products: Energy Conservation Standards for Water Heaters; Final Rule|journal=Federal Register|date=17 January 2001|volume=66|issue=11|pages=4474–4497 [4497]|url=http://www.gpo.gov/fdsys/pkg/FR-2001-01-17/pdf/01-1081.pdf|accessdate=26 March 2013}}</ref>

{| class="wikitable" |+ 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== {{expand section|date=March 2013}} The energy factor for dishwashers is defined as "the number of cycles per kWh of input power {{sic}}."<ref name="energy star def" />

==Clothes washers== {{expand section|date=March 2013}} The energy factor for clothes washers, is defined as "the cubic foot capacity per kWh of input power per cycle."<ref name="energy star def" />

==Clothes dryers== {{expand section|date=March 2013}} The energy factor for clothes dryers is defined as "the number of pounds of clothes dried per kWh of power consumed."<ref name="energy star def" />

==See also== * [[Energy star]]

==References== {{Reflist}}

[[Category:Energy conversion]]