Ekotrope Version 5.2: Overview and Impact
Ekotrope Version 5.2.0, released in beta on Aug 27, 2025 was developed to resolve a bug in the calculation of insulation values in reference homes’ foundation walls that was present in versions 4.2.0 through 5.1.0. The bug affected the IECC Performance pathway, ENERGY STAR Single Family (SF) target home calculations, and programs and codes that are derived from either of those for homes with conditioned basements and crawlspaces. The bug did not affect HERS Index calculations.
Version 5.2 also fixes a bug in the Iowa 2012 Performance reference home: it corrects the infiltration to 3 ACH50 from 4 ACH50.
This blog will explain which homes see the biggest impacts, which see no impacts, and the average impact of this new version.
What type of home is impacted?
The new version will only impact the performance of the calculations related to the IECC Performance Pathway, ENERGY STAR target home calculations, and programs and codes that use either of those programs for homes with conditioned basements and crawlspaces.
This new version does not impact the HERS Index so there is no change in HERS Index when switching from version 5.1.0 to this new version.
It also does not impact homes without conditioned basements or conditioned crawlspaces, with the exception of homes analyzed for the Iowa 2012 Performance path, so those homes see no change to any results between Version 5.1.0 and 5.2.0.
We analyzed ~5,000 homes with foundation walls to understand the impact of this new version on IECC Performance and ENERGY STAR Target Indexes. These homes were predominantly in climate zones 4 and 5.
IECC Impact
We analyzed the sample of homes’ performance with IECC 2012, IECC 2018, and IECC 2021. This bug does not impact ERI or Total UA calculations, so we only measured the change in Performance compliance buffer. The performance compliance buffer is measured as a percentage above or below the compliance target (so +2% means the home performs 2% better than the target and passes the code; -2% means the opposite).
Using version 4.1.0 (the latest minor version before the bug was introduced), these sample homes on average passed IECC 2012 with a compliance buffer of 3.9%, passed IECC 2018 by 4.4%, and failed the IECC 2021 by -2.4%. Analyzing these same homes in version 5.2.0, they had a compliance buffer for IECC 2012 of 3.8% (a 0.1% point drop), IECC 2018 of 4.5% (a 0.1% increase), and failed IECC 2021 by -2.3% (a 0.1% increase).
This shows that Version 5.2 brings the average IECC performance compliance for these affected sample homes to within a close margin of version 4.1.0, before the foundation wall bug was introduced.
The change between Ekotrope Version 5.1.0 and 5.2.0, which represents the resolution of this issue, is shown below:
| Version | IECC 2012 Performance Buffer | IECC 2018 Performance Buffer | IECC 2021 Performance Buffer |
|---|---|---|---|
| 4.1.0 | 3.9% | 4.4% | -2.4% |
| 4.2.0 | 7.7% | 8.0% | 1.2% |
| 5.1.0 | 8.8% | 9.3% | 3.1% |
| 5.2.0 (Beta) | 3.8% | 4.6% | -2.3% |
Above data includes only the affected homes (with conditioned foundation walls). Overall average deltas including all homes are significantly lower.
ENERGY STAR Target Index Impact
We analyzed the sample of affected homes’ performance with ENERGY STAR for Homes Single Family v3.1, v3.2, and v3.3. This version will impact ENERGY STAR Target Index for homes with conditioned basements and crawlspaces.
Using v5.1.0, these sample homes’ average Target HERS Index for v3.1 was 60.8, v3.2 was 51.7, and v3.3 was 50.4. Analyzing these homes in version 5.2.0 they had Target Indexes of 59.5 (a -1.3 point decrease) for v3.1, 49.9 (a -1.8 point decrease) in v3.2, and a 48.8 (a -1.9 point decrease) in v3.3.
The change between Ekotrope Version 5.1.0 and 5.2.0, is shown below:
| Version | ENERGY STAR v3.1 HERS Target | ENERGY STAR v3.2 HERS Target | ENERGY STAR v3.3 HERS Target |
|---|---|---|---|
| 5.1.0 | 60.8 | 51.7 | 50.4 |
| 5.2.0 (Beta) | 59.5 | 49.9 | 48.8 |
Above data includes only the affected homes (with conditioned foundation walls). Overall average deltas including all homes are significantly lower.
How did this bug occur?
This bug was introduced to the software when updating to an improved ground heat transfer model in version 4.2. The IECC performance reference home and ENERGY STAR SF target home’s foundation wall U-factors include concrete and soil. To work with the new model it was necessary to calculate the reference home foundation wall insulation-only R value based on the overall wall + ground U Factor, which is a multi-step process, one step of which was implemented incorrectly.
Summary
We encourage you to use v5.2 for your performance code compliance calculations and ENERGY STAR SF certifications for newly permitted homes with conditioned crawlspaces and basements.
Version 5.2 will be accredited with RESNET in the coming weeks and we will notify our network when that is complete.
If you have any questions, please contact support@ekotrope.com. Please let us know if you would like any additional support or information. For all the details about what's changed in this and historical versions, you can read the full release notes here: Version Release Notes.
