RESNET Board of Directors Adopts National Home Energy Rating Standards Interpretation on Domestic Hot Water Equipment That Does Not Have an Energy Factor

August 24th, 2010 - Posted by RESNET under Energy Efficiency, Heating & Cooling, RESNET News, RESNET Notes, RESNET Notes - August 2010

To provide guidance to Home Energy Raters for domestic hot water equipment that does not have an Energy Factor the RESNET Board of Directors have adopted an interpretation to the Mortgage Industry National Home Energy Rating Standards.  The interpretation was recommended by the RESNET Technical Committee.

The interpretation states that In situations where a manufacturer provided or an AHRI published Energy Factor can not be found, the rater shall use the following guidance to determine the Energy Factor of the water heater:

1. For conventional (oil, gas and electric) water heaters or heat pump, use default Energy Factor values described in RESNET Mortgage Industry National HERS Standards Chapter 3 Table 303.7.1.(3) for aged based efficiency or Table 303.7.1.(4) for non age-based Efficiency Factor values.

2. For commercial water heaters used in residential applications, one of the following approaches shall be followed to determine the Energy Factor for a particular piece of equipment:

  • a. Use the calculator attached – Commercial Hot Water EF Calculator.xls.
  • b. Use table 504.2 Minimum Performance of Water Heating Equipment in the 2009 International Energy Conservation Code to find the current minimum requirement for most types of water heater.

The interpretation is posted on RESNET’s web site at

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