Oak Harbor, WA: Climate Zone, Risk and Window Requirements
Oak Harbor sits in IECC climate zone 5C, which sets the energy-performance bar for any window installed here. Below that, a short list of Oak Harbor's longest-licensed window contractors can turn a spec into an actual installed window.
Licenses checked · Washington State Department of Labor & Industries
5CIECC climate zone · ENERGY STAR Northern zone
Oak Harbor's climate zone, in plain terms
Oak Harbor, WA runs a January average near 44°F and climbs to about 62°F by July, a swing that adds up to roughly 4,727 heating degree days most winters, with 25 on the summer cooling side of the ledger.
That load is the actual argument for paying up for a better U-factor in Oak Harbor, separate from anything a brochure claims.
Zone 5C's requirement is the floor; Oak Harbor's specific load is what tells you whether beating that floor is worth the extra cost.
Data: U.S. EPA / DOE, ENERGY STAR, ENERGY STAR Version 7.0 Climate Zones by County/ZIP (Windows, Doors, and Skylights) (V7.0); Pacific Northwest National Laboratory (DOE Building America), Guide to Determining Climate Zone by County: Building America and IECC 2021 Updates (PNNL-33270) (2021 IECC), from the nearest NOAA station 4.3 mi away.
What FEMA's risk data says about Oak Harbor
FEMA scores Island County's winter-weather risk as Relatively Low and its flood risk as Relatively Low.
Winter risk in Oak Harbor weighs on U-factor and condensation resistance; flood risk weighs more on sill height and drainage detailing than on the glass package.
Treat these as two separate conversations with a Oak Harbor contractor, not one.
- Strong wind
- Very Low
- Winter weather
- Relatively Low
Data: FEMA, National Risk Index for Natural Hazards - County-level table, v1.20 (v1.20, December 2025).
Guides to finish before Oak Harbor window bids come in
- How to Read an NFRC Window Label Four numbers on one sticker decide most of a window's real-world performance. Here's what each one means.
- ENERGY STAR Window Criteria by Climate Zone ENERGY STAR splits the country into four zones, each with its own numbers. Here they are, and why the Northern zone works backward from the other three.
- Impact Windows vs. Shutters in Florida's Hurricane Zones Florida gives homeowners two paths to a protected opening. Here's how each one is tested, and where the HVHZ raises the bar further.
Oak Harbor's longest-licensed window installers
Oldest license first, newest last, pulled directly from the state's file. This list isn't for sale.
- Lang Glass LLCVerify license
- Island Glass COVerify license
- Window Pains LLCVerify license