WSU C3 Calculator: Check Your Numbers Before You Submit
What is the WSU C3 calculator?
The C3 — short for code compliance calculator — is the WSU Energy Program's official spreadsheet for documenting 2021 WSEC-R energy credit compliance. Most Washington jurisdictions direct residential applicants straight to it: pick your dwelling's size tier, select options across the seven R406.3 credit categories plus your R406.2 fuel-normalization credit, and the sheet totals what you've earned against what's required.
It's a real, working spreadsheet used across the state every day. The macros, Mac compatibility, and crash issues that come with a large Excel workbook are covered separately in our guide to common WSU C3 calculator problems. This page is about a different question: you got the file to open, you filled it in, the numbers look fine — how do you know they're actually right?
How do I know if I did the C3 right?
This is the question that actually matters once the spreadsheet opens and behaves itself. A filled C3 can look completely normal — every cell has a number in it, the banner at the top says something, nothing is red — and still be wrong in ways that are easy to miss on a read-through, because the worksheet doesn't check its own arithmetic against the WAC the way a second, independent tool would.
The honest answer is: you don't know, not by looking. Building departments themselves recognize this — energy code documentation is a named, standing correction category at plan review, not a rare edge case. The only reliable way to know is to recompute your numbers independently and compare.
Four ways a filled C3 goes wrong without telling you
1. The printed total doesn't match the option rows
The C3's summary cell is supposed to sum every selected option across all seven R406.3 categories plus R406.2. If a formula reference shifted, a row got pasted over, or a cell was edited out of order, the printed total can drift from what the option rows underneath actually add up to. Add the visible line items by hand and compare the sum to the printed total — they should match exactly.
2. A required-credit figure keyed to the wrong size tier
Washington's required credit total depends on your dwelling's conditioned floor area and fenestration area — small (5.0), medium (8.0), or large (9.0), with a reduced 2.0 for small additions. If the wrong tier gets selected, or the tier selection doesn't update after you revise the floor plan, the worksheet compares your earned credits against the wrong target and can print a passing result against a requirement that no longer applies to your project. See our guide to how many energy credits you need for the full tier table.
3. An orphaned entry that earns nothing
This is the quiet one. Say you type an estimated annual renewable production figure — 3,000 kWh, for example — into the renewable-energy input cell, but never select the corresponding R406.3 Option 6.1 checkbox. The kWh value sits there, looking filled-in. But the credit only gets counted when the option is selected, at a rate of 0.5 credits per 600 kWh. A 3,000 kWh entry left unselected is 2.5 credits sitting on the page that never made it into the total — and nothing about the row tells you it didn't. The same pattern shows up anywhere a worksheet separates “enter the value” from “claim the option” as two different actions.
4. A PASS or FAIL banner that's stale
Excel recalculates on its own schedule, and the C3's many inter-tab formulas mean a manual-calculation setting or a slow recalculation can leave the top-of-sheet result banner reflecting an earlier state of the workbook — not the numbers currently sitting in the option rows. A banner is a cached conclusion, not a live check. Confirm it against the arithmetic underneath before you trust it, particularly after any late edit.
What checking actually means
Checking a filled worksheet means recomputing the same WAC math independently — from your project's inputs, not from the C3's own formulas — and then comparing the two sets of numbers side by side. Where they agree, you have real confirmation. Where they disagree, you've found something worth a second look before it reaches your building department. And where a figure can't be checked from what's on the page — an unclear entry, a value with no clear source — that gets flagged as needing your eyes, not silently assumed either way.
That's the shape of the check inside wsec.ai's $19 C3 calculator: upload your filled worksheet, and see line by line where it agrees, disagrees, or needs your eyes against an independent recomputation under the WAC. It doesn't decide pass or fail for you — it shows you where the two sets of numbers line up and where they don't, so you're the one deciding what to fix before you submit.
Check your worksheet against the code for $19
Get started →Frequently asked questions
How do I know if I did the C3 right?
The C3 will let you submit a worksheet with silent mistakes in it — a printed total that doesn't match the option rows underneath, a credit awarded to the wrong dwelling-size tier, or an entry that never actually counted. The spreadsheet itself won't flag these. The only way to know is to re-check the numbers against the code, line by line, separately from the tool that produced them.
What is the WSU C3 calculator?
The C3 (code compliance calculator) is the WSU Energy Program's macro-enabled Excel worksheet for documenting 2021 WSEC-R energy credit compliance. It's the tool most Washington jurisdictions point applicants to for the R406 credit tables.
Can a filled C3 look correct but still have an error?
Yes. The most common silent errors: a printed total that doesn't match the sum of the selected option rows, a required-credit figure keyed to the wrong dwelling-size tier, an entry with a value typed in but the corresponding option box left unchecked (which awards zero credit for that entry), and a PASS or FAIL banner that was calculated before a later edit and never recalculated.
What's an example of an entry that silently earns zero credit?
Entering an estimated annual renewable production figure — say 3,000 kWh — without selecting the corresponding R406.3 renewable-energy option. The kWh value sits in its cell, but with the option unchecked, the worksheet awards none of the 2.5 credits that figure should be worth at 0.5 credits per 600 kWh. Nothing on the sheet says this happened.
Does wsec.ai replace the WSU C3 spreadsheet?
wsec.ai's $19 C3 calculator is a web-based tool that runs the same 2021 WSEC-R credit math independently, plus a check that compares a filled worksheet's printed numbers against its own recomputation under the WAC and shows you where they agree, disagree, or need your eyes. It doesn't rely on the WSU spreadsheet to do that — it's an independent calculation, run separately, that you can compare your own numbers against.
It's built and reviewed by an ICC-Certified Residential Plans Examiner — the same certification your building department's plan reviewer holds.