Ekotrope Version 5.1: Overview and Impact

Ekotrope Version 5.1.0, currently in beta since April 17, 2025, introduces key changes driven by ANSI 301-2022 Addenda C & E and updates to DOE ZERH and ENERGY STAR programs. The full release date is forthcoming.

Impact on Results:

A comparison of approximately 2,000 homes registered in 2025 between Version 5.1.0 and 5.0.2 shows the following:

• HERS: 

• Average change:

Major updates affecting HERS scores include:

1. CFIS System: Addendum E significantly improves the accuracy of ventilation calculations for CFIS systems by considering the ventilation strategy for more accurate predictions of hourly ventilation rate, consumption, and duct losses. Refer to this help article for accurate modeling.

2. Infiltration: Addendum C replaces ACH Natural with ACH 4 Pa as the infiltration measurement unit, impacting single-family homes with less than 0.3 ACH 4 Pa and without mechanical or exhaust-only ventilation. It also accounts for additional infiltration due to duct leakage imbalance in buffer and conditioned spaces.

• The change in HERS score varies based on CFIS system presence, infiltration rate, duct location, climate, and other building factors. For roughly 75.2% of projects, the HERS score remains the same or varies by 1 point. Here’s a breakdown of changes in HERS score for homes with CFIS system and without CFIS system:

IECC Performance Compliance:

This slight positive change indicates it is marginally easier to meet the Performance Path due to updates in hourly profiles for end-use loads and improved duct load calculations for CFIS and infiltration from unbalanced duct leakage. These algorithm changes affect both proposed and reference homes, resulting in minor differences based on home configuration and location.

DOE ZERH and ENERGY STAR: 

• Target scores generally decrease by less than one point in Version 5.1.0 compared to 5.0.2.

Improvements in Algorithm:

1. Updates for ANSI 301-2022 (Addenda C & E):

• Addendum C: Introduces ACH 4 Pa, affecting single-family homes with whole house infiltration less than 0.3 ACH 4 Pa and no or exhaust only mechanical ventilation. It also addresses infiltration from duct leakage imbalance and updates criteria for default Distribution System Efficiency (DSE) and duct insulation R-values. Hourly profiles for end-use loads are introduced for consistency across RESNET-accredited software, with minimal impact on results.

• Addendum E: Enhances CFIS ventilation system calculations by incorporating ventilation strategy and operating conditions. New inputs are added in Ekotrope, and energy calculations are updated accordingly. See the CFIS modeling help article for details.

2. Updates to ENERGY STAR and DOE ZERH programs: 

• ENERGY STAR programs are updated to Revision 14 (Single Family New Homes) and Revision 5 (Multifamily New Construction), and DOE ZERH Single and Multifamily V2 programs are updated to Revision 1 in Version 5.1.0.

3. Miscellaneous Bug Fixes:

• The update includes fixes for:

1. Incorrect accounting of adiabatic walls in Maryland Code 2021 (R402.1.3.1).

2. A minor bug in solar gain calculation through glazing.

We really appreciate it when you let us know about any problems you find – it helps us make Ekotrope RATER better for everyone. So, if you have any thoughts or run into anything weird with the new version, shoot us an email at support@ekotrope.com. For all the details about what's changed, you can check out the full release notes here: Version Release Notes.