ERI pre-check
Test proposed assemblies and systems against an Energy Rating Index target before the house goes to the rater. Uses the ANSI/RESNET/ICC 301 scoring equations and Reference Home; the load engine is simplified, so treat results as ±3–5 points.
How this compares to Ekotrope
The scoring side follows ANSI/RESNET/ICC 301 directly: the 2006 IECC–based Reference Home (envelope U-factors by climate zone, window area at 18% of floor area, SHGC 0.40, Reference air leakage at SLA 0.00036, 78% AFUE furnace or 7.7 HSPF heat pump, 13 SEER cooling, 0.80 distribution efficiency), the normalized Modified End Use Load equation with the Table 4.1.1 a/b coefficients, Reference lighting and appliance equations, and PEfrac for on-site power.
The load side is where this differs. Ekotrope runs its own hourly simulation on TMY weather. This tool runs an hourly thermal-mass model on representative cool, typical and warm days for each month using approximate local monthly normals. Because the Rated and Reference homes go through the same engine, much of the modeling error cancels in the ratio. Cold-climate heat pump derating also cancels, since 301 normalizes by rated efficiency.
Known simplifications: no duct leakage test inputs (use the distribution setting), no dual-fuel or multiple systems, no dehumidifiers, no attic/roof solar gains, hot water use from the older 301 gallons-per-day equation, and site-to-source factors for PEfrac. Keep about a 3–5 point cushion under your target, then have your rater confirm in Ekotrope.
Location data: climate zones are the 2021 IECC county designations, which the 2024 IECC kept unchanged and which New York’s 2025 ECCCNYS table matches (Tompkins, Schuyler and Seneca are 5A). They come from PNNL-33270, the DOE guide to climate zones by county. Monthly temperatures are 1991–2019 averages of NOAA nClimDiv county data; solar on windows and PV yield are calculated from latitude and a statewide clearness index. If your jurisdiction is still on a code older than the 2021 IECC, about 1 in 9 counties used a different zone, so use the override.
References: ANSI/RESNET/ICC 301-2014 (RESNET); ANSI/RESNET/ICC 301-2022 sample chapter (ICC).