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RESNET Board Extends Use of Seasonal Based HERS® Software Until 1/1/21

Oct 6, 2020

Based upon the recommendation of the RESNET Software Consistency Committee (SCC), the RESNET Board of Directors has voted to extend the use of the seasonal calculation engine version of the REM/Rate HERS software for homes that are permitted before January 1, 2021. Additionally, the RESNET Standard Management Board has moved the Mandatory Compliance Date for Standards ANSI/RESNET/ICC 301-2019 and ANSI/RESNET/ICC 380-2019 to January 1, 2021.

The RESNET Board of Directors had set a policy that all accredited HERS Software programs need to be based on hourly calculations by January 1, 2020. The objective of this policy was to improve consistency and among all RESNET accredited software tools and to improve the rigor of the underlying calculations. REM/Rate 16.0 was released with an accredited hourly calculation capability on December 19, 2019, in compliance with RESNET policy.  The accredited version also allows seasonal calculations.

The SCC (of which all the software vendors are active members) investigated the impact of the policy and found the hourly calculation requirement has served to increase the rigor of the underlying calculations of HERS indices, but also resulted in significantly different HERS Index Scores.

The SCC is working to better understand the source of the HERS differences and find a resolution. It is not yet clear whether the difference in HERS Index Scores is related to the increased rigor in its underlying building physics calculations, or inconsistencies in the application of RESNET standards.

In the meantime, the SCC has established a much more rigorous approach to testing software that will better allow the committee to determine the impact of policy changes before affected software is accredited and released.

The SCC also recommended that the Mandatory Compliance Date for the change from the 2014 edition to the 2019 edition of Standard ANSI/RESNET/ICC 301 should be delayed in order that impacts on ratings due to the implementation of hourly calculations coincide with impacts due to the updates to Standard 301. The RESNET Standards Management Board has approved moving the Mandatory Compliance Date to January 1, 2021.

RESNET recognizes the 2019 edition of Standard 301 is beneficial for rating certain dwelling units and also may be required for rating dwelling units for non-RESNET programs that rely on HERS ratings. The Standards Management Board authorized voluntary use of Standard 301-2019 as of October 1, 2019 and its voluntary use remains authorized. RESNET still anticipates all software vendors will release versions compliant with Standard 301-2019 before the original Mandatory Compliance Date of July 1, 2020.

RESNET understands that changes to software can be disruptive to the work of many of its constituents. We appreciate your patience as we work towards improving the consistency of HERS Index calculations, recognizing that the end product will be a more reliable and accurate assessment of home energy.