Alternatives to the WSU C3 Calculator for Washington State

Why are people looking for alternatives to the WSU C3 calculator?

The official WSU Code Compliance Calculator (C3) is a macro-enabled Excel spreadsheet. It works for many projects, but it has known limitations that send builders looking elsewhere:

• It requires Excel for Windows. There is no supported Mac version and no web version.
• Modern antivirus software flags the macros and often blocks the file from opening.
• The spreadsheet does not save or sync — every project starts from a blank file.
• Plan reviewers in some jurisdictions request additional documentation that the C3 output does not include.

Builders, designers, and owner-builders facing those issues typically consider three options.

What are the three main C3 alternatives, side by side?

Can I use REScheck for Washington State energy code compliance?

REScheck cannot be used as a complete C3 replacement in Washington. It calculates the IECC Total UA portion of WSEC-R compliance but does not calculate Washington’s mandatory R406 energy credits. Every new dwelling unit in Washington must earn between 5.0 and 9.0 R406 credits depending on size, and REScheck does not include the R406 menu, point values, or option-conflict logic.

REScheck is a free national tool published by the Pacific Northwest National Laboratory (PNNL) for the U.S. Department of Energy. It is fully capable of running the Total UA Alternative calculation defined in WSEC-R Section R402.1.5, and it is correct on that single piece. But a builder who relies on REScheck alone for Washington compliance still needs to manually fill out the R406 portion of the WSU C3 spreadsheet or an equivalent form before plan review. That defeats the purpose of using an automated tool.

REScheck is a useful supplement for the UA portion of compliance. It is not a complete C3 replacement.

Why is WSEC.ai a complete C3 alternative?

WSEC.ai was built specifically to solve the C3 spreadsheet’s two biggest problems for Washington builders: it does not run on Mac, and it does not save your work. It does everything the C3 does — prescriptive path, UA trade-off path, full R406 credit selection — plus what the C3 does not: it runs in any browser, saves projects to your account, and produces a downloadable PDF with a QR code your AHJ can use to verify the math.

It is built and maintained by a licensed Washington contractor (Property Matters LLC, contractor license PROPEML811MR). The calculation engine has been verified against the WSU C3 spreadsheet and the 2021 WSEC-R WAC text, including the R406.3 credit table and the R402.1.5 Total UA Alternative percentages.

Frequently asked questions

Does the WSU C3 calculator work on Mac?

No. The WSU C3 calculator is a macro-enabled Excel for Windows spreadsheet. WSU’s official documentation states it is not supported on Mac. WSEC.ai runs natively in any modern browser, including Safari on Mac.

Is WSEC.ai approved by Washington jurisdictions?

WSEC.ai produces a PDF in the same format as the official WSU C3 output and uses the same underlying code citations from WAC 51-11R. The PDF includes a QR code for AHJ verification. Plan reviewers across Washington accept compliance documentation that matches the WSEC-R requirements, regardless of which tool produced it. If your AHJ has a specific question about a WSEC.ai submittal, contact us at hello@wsec.ai.

How much does WSEC.ai cost?

WSEC.ai has three tiers. The online C3 calculator — the spreadsheet replacement that runs on Mac, mobile, and any browser without macros — is $19. The full guided wizard with chatbot help and saved projects is $99. An uploaded plan review (you email or upload your plan set, we run it through our calculation engine and double-check key items, then email you back a written PDF report with notes — no phone calls or live discussion) is $499.

Can I use REScheck for the R406 credits portion?

No. REScheck does not calculate R406 credits. R406 is a Washington-specific amendment to the IECC and is not part of the national REScheck tool. You must use the WSU C3 spreadsheet, WSEC.ai, or an equivalent Washington-specific tool to calculate R406 credits.

Is the WSU C3 calculator free?

Yes. The WSU C3 calculator is published free by the WSU Energy Program. The cost is in the time it takes to work around the spreadsheet’s macros, antivirus blocks, and lack of Mac support. Tools like WSEC.ai charge a small fee ($19 for the online C3 replacement, $99 for the full guided wizard) in exchange for a tool that actually runs on Mac and mobile and saves your projects.