Below is a list of Ekotrope algorithm versions along with some highlights of the changes in each version.  The list may not include every change in each version, but generally includes the changes that will have a significant impact.  If you have specific questions about a certain version please Contact Support.

Version 3.3.0

Released in Beta on June 28, 2019.

This version includes the following algorithm changes:

  • Improves heat pump algorithm to determine efficiency hourly based on weather conditions, heat pump specifications, and hourly required heat output.

Version 3.2.0

Released on July 17, 2019.

This version includes updates to support ANSI/RESNET 301 Addendum L duct leakage exemption logic.


This version also includes the following algorithm changes:

  • Adjusts hourly lighting & appliance and internal gains load profiles to be more accurate.

  • Minor adjustments to kWh unit conversion factor in reports.

  • Improve estimation of solar flux in design load calculation.

  • Correct minor bug in ASHRAE 152 duct system efficiency algorithm.

  • Improve roof area calculation in roof temperature algorithm.

  • Improve home initial starting temperature for first hour of annual simulation.

  • Support thermal breaks in slab on grade modeling.

  • Fix bug in Mississippi and Michigan federal minimum air conditioner SEER rating.

  • Update DOE ZER envelope requirements to check against IECC 2015 UA instead of IECC 2012 UA without fenestrations.

  • Update DOE ZER wall U factor based on DOE ZER February 2019 amendment.

  • Change ENERGY STAR 3 & 3.1 ventilation check from warning to failure.

  • Update Michigan and Illinois 2015 federal minimum equipment reference homes to use the most recent federal minimum equipment standards.

  • Update Duke program HERO reference homes to use rated home slab covering R value in the reference homes.

  • Fix bug with tankless water heaters in Austin energy code.

  • Update and improve cooling equipment logic in the Mass Save R&A reference home

Version 3.1.1 

Released on December 22, 2018.  Note: this includes many changes that were on previously on version 3.2.0 from July to December 2018 and were ported over to 3.1.1.

This version includes the following algorithm changes:

  • Adjusts DOE ZER target home electric water heater efficiency to EF = 1.5 for multifamily dwellings according to November 2018 DOE ZER update.

  • Updates IECC ventilation efficacy warning to be a requirement.

  • Updates Reference Home for Duke HERO 2012 calculations to use the worse performance between 4 ACH50 and 0.24 SFSA, rather than always using 4 ACH50.

  • Updates IECC reference homes to use mass wall values when the home specifies a high mass wall.

  • Removes radiant barrier for ducting in the North Carolina 2012 Reference Home.



Version 3.1.0

Released July 1, 2018.  Approved for RENET registry submissions starting July 1, after which a 6 month transition period will be allowed.  This version is identical to Version 3.0.0 except that it fixes a fairly significant bug dealing with the wall area of the IECC reference home used for compliance with the IECC Performance Path and other reference homes derived from IECC codes.  The affects of this bug fix will be to make IECC Performance Path compliance more difficult for most homes.  It is not mandatory to update to this version until January 1, 2019, so please take the time to prepare accordingly.


Version 3.0.0

Released July 1, 2018.  Approved for RENET registry submissions starting July 1, after which a 6 month transition period will be allowed.  This version and subsequent versions include the House Size Index Adjustment Factor from Addendum E and LED lighting support from Addendum G of RESNET/ANSI 301.  It also includes a few other minor fixes:

  • Updates water usage calculation for DOE ZER home and ENERGY STAR reference home to use HERS Reference water usage.
  • Fixes bug where doors on adiabatic walls would get treated as exterior doors.
  • Changes ENERGY STAR reference home logic for ceilings to leave the location of the ceiling in the reference home the same as the rated home.
  • Add QA check for R6 duct insulation for ENERGY STAR.
  • Update window calculation for reference home of IECC 2015 performance path to include Footnote (h), which was left out in the original version of IECC 2015.
  • Update federal minimum equipment for IECC 2006 - 2015 w/ Federal Minimum Equipment reference home.  2018 and later iterations of the IECC use updated equipment even if the version is before 3.0.0.
  • Update lighting CFL % in IECC 2006 - 2015 w/ Federal Minimum Equipment reference home to equal the mandatory lighting requirements.  2018 and later iterations of the IECC do this even if the version is before 3.0.0.
  • Fix infiltration zone for n factor calculation for Colorado to be Zone 4 instead of Zone 1.
  • Update MassSave reference home duct R value to use proper parallel path R value calculation.


Version 2.2.5

Released April 10, 2018.  Only affects MassSave incentive results.  

  • Updates MassSave water usage calculations to use RESNET water usage equations rather than IECC equations.


Version 2.2.4

Released February 6, 2018.  Only affects North Carolina code compliance and MassSave incentive results.  

  • Fixes a bug with interior window shading coefficients by setting them to 0.9 in the Proposed and Reference homes for North Carolina energy code.
  • Updates reference home electric water heater EF from 2.16 to 2.08 and reference home air source heat pump HSPF from 10.05 to 9.63.


Version 2.2.3

Released Jan 17, 2018.  Small change to how the HERS reference home's mechanical ventilation system's watts are calculated when ACH Natural is selected.  May increase HERS scores slightly for some houses only if ACH Natural is used.

Version 2.2.2

(Does not affect HERS score) Released Jan 5, 2018.  The same as Version 2.2.1 with some updates for ENERGY STAR (see the list of updates below).  When version 2.2.2 was added, we chose to remove Version 2.2.1 from the normally visible list of versions and switched users' preferred version from 2.2.1 to 2.2.2.  This is our policy for minor version updates to reduce the number of options in the version list.

  • Eliminates Size Adjustment Factor for ENERGY STAR Version 3.1

  • Changes furnace AFUE from 90 to 80 for the ENERGY STAR v3.1 reference home in Climate Zone 3.

  • Changes tank size of water heaters for the ENERGY STAR target home when the rated home has a non-electric tankless water heater from 40g to 50g.


If you have questions about this or would like to switch a project back to version 2.2.1, please email us at support@ekotrope.com.


Version 2.2.1

(Does not affect HERS score) Released early November, 2017.  The same as Version 2.2.0, except for some relatively minor changes (see below).  When version 2.2.1 was added, we chose to remove Version 2.2.0 from the normally visible list of versions and switched users' preferred version from 2.2.0 to 2.2.1.  This is our policy for minor version updates to reduce the number of options in the version list.

  • For the Massachusetts MassSave program, if the proposed house uses a ductless distribution system, the reference house will now use a ducted system with ducts in the attic, insulated to R-8 with the proper reference home leakage.

  • For homes in North Carolina, the air sealing of the NC Code Reference Home has changed to use North Carolina specific logic rather than IECC logic.  This should generally make it easier for homes to pass code compared to v2.2.0.
  • For homes in climate zone 4, the North Carolina prescriptive SHGC has been corrected from N/A to 0.3.
  • For IECC 2009, if a tankless water heater is specified, the reference house will now get a tank water heater with current federal minimum efficiency.


If you have questions about this or would like to switch a project back to version 2.2.0, please email us at support@ekotrope.com.

Version 2.2.0

Released August 29, 2017.  The same as Version 2.1.0, with the following changes:

  • Fixes bug with ENERGY STAR target home.  These fixes will reduce target HERS scores making ENERGY STAR more difficult to meet.
    • Fixes % high efficacy lighting for target home.
    • Fixes distribution system efficiency for homes with multiple distribution systems.
    • Remove radiant barrier from target home.
    • Switches floor covering R value to 1.23 from 2.
    • Floor area used in the size adjustment factor calculation now excludes conditioned basement area where at least half of the wall area is below grade.
  • Smooths anomaly for duct losses for low capacity heating and cooling equipment.  Should reduce consumption for some homes.
  • Updates water heater tank loss temperature to use hourly indoor house temperature rather than 75F.
  • Uses a more accurate water heater energy consumption simulation.
  • Minor change to basement wall UA calculation for partially insulated walls.
  • Removes crawlspace walls from HERS and IECC reference home window calculations.
  • Removes radiant barrier from IECC reference homes.  Also, minor correction to duct losses in attics with radiant barriers which will slightly reduce consumption in those cases.
  • Fixes a bug where Dishwasher EF was used for water consumption calculation even if Dishwasher kWh was inputted.
  • Uses a more accurate estimate of crawl-space buffer temperature.  In general, this change will reduce energy consumption for houses with crawlspaces.
  • Improves heating and cooling fan and pump consumption so that they now depend on total heating/cooling load and equipment capacity.
  • IECC Specific Changes:
    • Updates IECC reference mechanical equipment to be sized according to the design load
    • Uses sq feet served per distribution system rather than total CFA to calculate duct leakage for IECC reference homes.
    • If a proposed house has a non-storage water heater it will now get a storage water heater, the same as the reference house.
  • Include adiabatic area in shell area calculations.  This affects load due to infiltration if Effective Leakage Area or ELA / 100 sq. ft. are used.
  • Excludes the ASHRAE 62.2-2013 infiltration credit for multi-family homes

Version 2.1.0

Released September 13, 2016.  The same as Version 2.0.0, with the following changes:

  • Fix bug with HERS Index rounding.  HERS Index scores are now rounded to the nearest whole number.
  • Update IECC cost compliance path to use EIA state-average energy prices from 2014 rather than user-entered utility rates.
  • Update combined infiltration and ventilation load algorithm to use ASHRAE HOF Ch. 16 Eq. 51.
  • Adjacent and overhang shading now also reduces diffuse solar gains using proper view-factor equations.

Version 2.0.0

Released June 1, 2016 (Note that RESNET allowed using earlier versions on new projects until Jan 1 2017).  Update algorithm to comply with RESNET/ANSI 301 - 2014.  Major changes include:

  • Significant changes to hot water calculations according to ANSI/RESNET 301 Addendum A.  These changes include, but are not limited to, support for Low-flow fixtures, Drain Water Heat Recovery and Re-circulation systems.  These changes can both increase or decrease HERS scores.
  • Reduced the reference home specific leakage area (used for infiltration calculation) from 0.00048 to 0.00036.  This causes an increase in HERS scores across the board.
  • Updates to calculations of energy and water consumption for clothes washers.  

Unrelated to ANSI:

  • Adjacent and overhang shading only reduces direct solar gains, not reflected or diffuse.

Version 1.9.0

Released September 13, 2016.  The same as Version 1.8.0 with the following changes:
  • Fix bug with HERS Index rounding.  HERS Index scores are now rounded to the nearest whole number.
  • Update IECC cost compliance path to use EIA state-average energy prices from 2014 rather than user-entered utility rates.
  • Update combined infiltration and ventilation load algorithm to use ASHRAE HOF Ch. 16 Eq. 51.
  • Fix HERS Reference Home SHGC for climate zones 4 - 8 to be 0.55
  • Adjacent and overhang shading only reduces direct solar gains, not reflected or diffuse.
  • Fixed bug where HERS Rated home was not being re-simulated if combined mechanical ventilation and infiltration was below minimum.

Version 1.8.0

Original Ekotrope release.