Serving Washington since 2020 · 7+ years of experience
ACCA Manual J, S & D Reports in Washington
ACCA-compliant Manual J load calculations, Manual S equipment selection, and Manual D duct design for Washington homes and small commercial projects.
Seattle · Spokane · Tacoma · Vancouver & beyond
HVAC Design for Washington Building Codes
Washington enforces some of the most demanding energy requirements in the country through the Washington State Energy Code (WSEC), layered on top of the state's amended Residential Code. Accurate, well-documented HVAC sizing is essential here — equipment must be selected with ACCA Manual S from a Manual J load calculation, and reviewers expect it. That's exactly the documentation we deliver.
Washington's climate divides at the Cascades. The Puget Sound corridor — Seattle, Tacoma, Bellevue — sits in the mild, humid marine Climate Zone 4C, where tight, efficient envelopes and heating loads drive the design. East of the mountains — Spokane, Yakima — is colder and drier Zone 5B. In IECC terms the letter marks moisture: the “C” is marine and the “B” is dry. Pairing the right design conditions with WSEC's strict envelope assumptions is where a careful Manual J pays off.
From Puget Sound new construction to Spokane remodels, we produce a complete Manual J, S & D package your local Authority Having Jurisdiction (AHJ) can accept — typically within three business days.
Washington Climate Zones & County Design Temperatures
The Puget Sound corridor sits in the mild marine Climate Zone 4C, while east of the Cascades turns colder and drier into Zone 5B — in IECC terms the “C” marks a marine climate and the “B” a dry one. Design temperatures below are the 1% cooling and 99% heating values for each county, per the ENERGY STAR County-Level Design Temperature Reference Guide (ASHRAE-based).
| County | Cities Served | 1% Cooling | 99% Heating |
|---|---|---|---|
| King | Seattle, Bellevue, Kent, Renton | 82°F | 27°F |
| Pierce | Tacoma | 83°F | 24°F |
| Snohomish | Everett | 79°F | 25°F |
| Clark | Vancouver | 88°F | 28°F |
| Thurston | Olympia | 83°F | 24°F |
| Whatcom | Bellingham | 76°F | 23°F |
| Spokane | Spokane | 91°F | 9°F |
| Yakima | Yakima | 93°F | 12°F |
| Benton | Kennewick | 97°F | 11°F |
We serve projects statewide — these are just a sample of Washington counties. We use the recognized design conditions for your specific county and elevation when we run your Manual J.
Washington HVAC Design FAQ
Does Washington require a Manual J for a permit?
Yes. Under the Washington State Energy Code and amended Residential Code, HVAC equipment must be sized using ACCA Manual S based on a Manual J load calculation. Washington reviewers routinely expect this documentation — we provide the complete Manual J, S & D package.
What climate zone is my Washington project in?
The Puget Sound region (Seattle, Tacoma, Bellevue) is marine Climate Zone 4C. East of the Cascades (Spokane, Yakima) is Zone 5B. We use the correct design conditions for your specific city.
Will my local building department accept your report?
Yes. We produce a complete, ACCA-compliant Manual J, S & D report formatted for your Authority Having Jurisdiction (AHJ) and consistent with WSEC requirements. If your reviewer requests a small change, we handle minor revisions free of charge.
What do you need to get started?
Building plans, insulation and window values, equipment locations, and preferred model numbers. See the full What We Need for a Complete Report checklist.
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Have a Washington project? Let's talk about working together and answer any questions you have. Send us a note and we'll reach out within 24 hours. Fields marked * are required.
Business hours: Mon–Fri, 7:00 AM – 4:00 PM PT.