Air conditioning in Washington: climate, SEER2 rules and real costs
In Washington, Seattle long held the lowest AC ownership of any major US metro; the 2021 heat dome’s 108 °F reading changed that in one week, and heat pump installs have run hot ever since. That is the terrain — here is what it means for choosing and sizing cooling.
| DOE climate zone | 4C–5B (marine to dry) |
|---|---|
| Cooling degree days | ≈ 350 per year (approx.) |
| Summer humidity | mixed humid/dry |
| SEER2 region | North — minimum 13.4 SEER2 |
| Cooling demand | minimal |
The Washington cooling climate
Cooling in Washington is minimal on average (≈ 350 CDD) but the mixed humid/dry climate splits the state: check whether your summers are muggy or arid before choosing between dehumidification-focused equipment and high-EER2 dry-heat hardware. DOE zone: 4C–5B (marine to dry).
Efficiency rules that apply here
Washington sits in the DOE North efficiency region: new central air conditioners must meet 13.4 SEER2, and heat pumps 14.3 SEER2 / 7.5 HSPF2 nationwide. Northern rules apply at manufacture, so pre-2023 stock could be sold through. Our SEER2 guide does the savings math.
Indicative costs in Washington
| System | Typical use | Indicative installed range |
|---|---|---|
| Central AC (replacement) | existing ducts, like-for-like swap | $4,300–$8,100 |
| Ducted heat pump | electrification at replacement | $5,700–$10,500 |
| Ductless mini-split | per zone, no ducts | $2,900–$5,200 / zone |
Reference ranges, not bids: labor markets and duct condition swing real prices widely. See the replacement cost guide for what moves a quote.
Go deeper: heat pump guide, ductless options, BTU sizing by square footage, and the 25C credit and rebates.
Frequently asked questions
How much does central AC or a heat pump cost in Washington?
Market reference ranges in Washington (2026, installed): central AC $4,300–$8,100, heat pump $5,700–$10,500, mini-split $2,900–$5,200 per zone. Labor markets, duct condition and equipment tier move real quotes well outside these bands in either direction.
Does a heat pump make sense in Washington?
Yes, increasingly: cold-climate heat pumps hold capacity well below freezing, and in Washington the cooling side comes almost free with the heating investment. The federal 25C credit (up to $2,000) plus state and utility rebates apply; see our heat pump vs AC guide.
Other states in the same SEER2 region: Alaska · Colorado · Connecticut · Idaho · Illinois.