Both are free tools from the Department of Energy's Building Energy Codes Program. Both produce a compliance certificate that gets submitted with a building permit. And both exist to prove a building meets minimum energy code requirements. But COMcheck and REScheck are built for different building types, and using the wrong one — or being unsure which applies to a borderline project — is a common source of permit delays.
REScheck is designed for residential buildings, generally defined as single-family homes, townhomes, and low-rise multifamily buildings up to three stories. COMcheck handles commercial buildings and taller multifamily structures — generally four stories and above, though the exact threshold and classification can depend on the specific energy code edition and jurisdiction.
This isn't an arbitrary software limitation — it reflects a genuine split in how energy codes are structured. The IECC itself has separate residential (Chapter 11 in some editions, R-chapters in others) and commercial provisions, with meaningfully different requirements, compliance methods, and baseline assumptions. REScheck and COMcheck each implement the compliance methodology for their respective code chapters.
REScheck focuses primarily on building envelope: wall, ceiling, floor, and foundation insulation, window and door performance, and air leakage. It's a relatively narrow, envelope-focused compliance check, since residential energy code has historically concentrated most heavily on envelope performance (with mechanical equipment efficiency governed by separate federal appliance standards rather than the building energy code itself in many cases).
COMcheck checks three separate areas: building envelope, lighting power allowances, and in some cases mechanical system requirements. Commercial energy code puts significantly more emphasis on lighting power density than residential code does, reflecting how much energy commercial buildings typically use for lighting relative to homes.
The trickiest classification questions usually come up around:
When in doubt, the local building department's plan review staff can confirm which classification applies before compliance documentation is prepared — a much cheaper conversation than discovering the wrong tool was used after submission.
It's worth remembering that REScheck and COMcheck are the national baseline tools tied to the IECC. Several states run their own compliance software and forms instead of, or in addition to, the national tools — California's Title 24 compliance uses its own CBECC modeling software, Florida's residential code uses R402/R405 forms rather than REScheck directly, and Washington's WSEC uses its own state-specific compliance documentation. In those states, understanding whether the project needs REScheck/COMcheck, a state-specific tool, or both depends entirely on what the local jurisdiction has adopted.
Beyond choosing between REScheck and COMcheck, both tools support multiple compliance paths — prescriptive (component-by-component minimums) versus trade-off or performance-based approaches that allow flexibility by comparing overall performance rather than requiring every individual component to meet its own minimum. Which path makes sense depends on the specific design — conventional, straightforward layouts often comply prescriptively without issue, while designs with larger glazing areas or unconventional assemblies often need the trade-off or performance path to comply at all.
Submitting the wrong compliance tool's report — REScheck for what's actually a commercial-classified building, or vice versa — typically results in a straightforward rejection and resubmission requirement, adding delay to the permitting timeline. Confirming building classification and the applicable compliance path before generating the report avoids this entirely.
Can a project need both REScheck and COMcheck?
In mixed-use buildings with clearly separated residential and commercial portions, yes — each portion may need its own compliance documentation using the appropriate tool for its classification.
Is there a hard rule for "three stories or fewer" being residential?
Generally that's the common threshold, but exact classification depends on the specific code edition adopted and how the jurisdiction defines building height/story count for energy code purposes — always confirm locally rather than assuming.
Do REScheck and COMcheck cost anything?
No, both are free tools provided by the DOE's Building Energy Codes Program.
If my state has its own energy code (like California or Florida), do I still need REScheck or COMcheck?
Not necessarily — states with their own compliance software and forms (Title 24's CBECC, Florida's R402/R405) typically use those instead of the national tools, though some jurisdictions within those states may still reference REScheck/COMcheck for specific project types. Confirm what's required locally.
Whether your project needs REScheck, COMcheck, or a state-specific compliance path, Psychro.Pro helps keep your documentation aligned with Manual J, S, and D. Learn more.
