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County-Level Design Temperature Limits for
ENERGY STAR Certified Homes

Welcome

Are you an HVAC designer, builder, or Rater working on a home that will be ENERGY STAR certified? If so, this page will explain one key requirement of the program – the outdoor design temperatures that must be used to calculate the room-by-room heating and cooling loads.

Outdoor Design Temperature Limits

To meet the requirements of the program, the outdoor design temperatures used must not exceed the maximum cooling season temperature and minimum heating season temperature listed in the ENERGY STAR Certified Homes, v3, County-Level Design Temperature Reference Guide PDF (4MB) for the state and county in which the home is to be certified.

For example, a home will be certified in Travis County, TX. By consulting the reference guide, we find that the cooling season outdoor design temperature limit is 98 F and the heating season outdoor design temperature limit is 30 F.

This means that the designer must:

  • Use a cooling season design temperature that is less than or equal to 98 F.
  • Use a heating season design temperature that is equal to or greater than 30 F.
  • Not use the cooling sizing limit for a Condition B Climate because the HDD/CDD Ratio is 0.2, which is < 2.0.

Only two exceptions apply:

  1. Jurisdiction-Specified Temperatures: If the outdoor design temperatures to be used in load calculations are specified by the jurisdiction where the home will be certified, then these specified temperatures shall be used.
  2. Temperature Exception Request: In rare cases, the designer may believe that an exception to the limits in the reference guide are warranted for a particular state and county. If so, the designer must complete and submit a Design Temperature Exception Request PDF (120KB), including a justification for the exception, to energystarhomes@energystar.gov for review and approval prior to the home’s certification.

To obtain the most accurate load calculations, EPA recommends that designers always use the ACCA Manual J, 8th edition, 1% cooling season design temperature and 99% heating season design temperature for the weather station that’s geographically closest to the home to be certified.

The state, county, and corresponding outdoor design temperatures selected by the designer will be documented in the HVAC Design Report. And the Home Energy Rater will verify that the selected temperatures are within the limits in the reference guide, or per an allowance, prior to certification. Visit the ENERGY STAR Certified Homes Program Requirements page to download the HVAC Design Report and visit the ENERGY STAR Certified Homes Policy Changes and Clarifications page to learn more about recent program changes