TL;DR. After the 2021 heat dome, Seattle now sees 15 to 22 days above 85°F per year. For most homeowners, the answer is yes, but install a heat pump instead of dedicated AC. The heat pump replaces your aging furnace AND adds cooling, qualifies for $3,200+ in rebates and credits, and the math beats standalone AC for any home with a 10+ year-old furnace.
Direct answer, yes for most homes now
For most Seattle homeowners in 2026, the answer is yes, but install a heat pump instead of a dedicated AC. The heat pump gives you cooling AND replaces your furnace (which is probably aging out anyway), and the $1,200 PSE rebate plus federal credit make the math significantly better than standalone AC.
Specific guidance:
- Heat dome experienced and miserable? Heat pump install, $14,000 to $20,000 net.
- Furnace is 12+ years old? Heat pump install, replaces both furnace and adds cooling.
- Furnace is under 8 years old? Add a heat pump as a “hybrid” alongside the furnace, OR add dedicated AC.
- Live in a well-shaded craftsman with cross-ventilation? Maybe nothing yet. Re-evaluate in 2 to 3 years.
What changed: 2021 heat dome and after
Seattle’s historical climate showed maybe 2 to 5 days per year above 85°F. After 2021, the data tells a different story:
| Year | Days above 85°F | Days above 90°F | Highest temp |
|---|---|---|---|
| 2018 | 6 | 1 | 91°F |
| 2019 | 4 | 0 | 89°F |
| 2020 | 5 | 1 | 91°F |
| 2021 | 18 | 5 (one at 108°F) | 108°F |
| 2022 | 15 | 4 | 95°F |
| 2023 | 22 | 7 | 98°F |
| 2024 | 19 | 5 | 96°F |
| 2025 | 21 | 8 | 100°F |
The pattern is consistent: 15 to 22 hot days per year, 5 to 8 days above 90°F. That’s enough hot days to justify AC even for cost-conscious homeowners.
Health considerations
Two reasons AC matters for some households more than others:
Older adults. Heat-related illness disproportionately affects people over 65. The 2021 heat dome killed roughly 100 people across King County, mostly elderly residents without AC. If your household includes someone over 65 or with respiratory conditions, AC is a health-and-safety question, not a comfort question.
Wildfire smoke season. August through October now reliably brings 5 to 15 days of unhealthy air quality. Opening windows for cooling isn’t an option during smoke events. Mechanical cooling lets you keep windows closed without overheating.
Cost math, AC vs heat pump
If you’re already considering AC, the math almost always favors a heat pump:
| Scenario | Dedicated AC install | Heat pump install (replaces furnace AND adds cooling) |
|---|---|---|
| 4-ton system, mid-tier | $7,500 | $14,000 net after rebates |
| PSE rebate | $0 (no AC rebate program) | $1,200 instant |
| Federal credit | $0 (no 25C credit on AC) | $2,000 |
| Annual operating cost | $200-$400 (cooling) + existing furnace gas cost | $1,200-$2,000 (heating + cooling combined) |
| Replacement timing | Need to do this AND furnace replacement separately when furnace fails | Single project, single permit, single warranty |
The math gets even better when your existing furnace is over 10 years old. You’re going to replace it anyway. Doing furnace + AC separately costs $16,000 to $19,000 over 2 to 5 years. Doing heat pump as one project: $14,000 net.
The only scenario where standalone AC clearly wins: existing furnace is under 7 years old and running well. In that case, adding AC ($7,500) is cheaper than ripping out a working furnace to install a heat pump.
What size AC do you need
Real Manual J load calculations matter for cooling sizing more than for heating. Oversized AC short-cycles, doesn’t dehumidify well, and wastes energy. Undersized AC can’t keep up during heat waves.
| Home size | Typical AC sizing | Typical heat pump sizing |
|---|---|---|
| 1,200-1,600 sq ft | 1.5 to 2 tons | 2 to 2.5 tons |
| 1,600-2,000 sq ft | 2 to 2.5 tons | 2.5 to 3 tons |
| 2,000-2,800 sq ft | 2.5 to 3.5 tons | 3 to 4 tons |
| 2,800-3,500 sq ft | 3 to 4.5 tons | 4 to 5 tons |
| 3,500+ sq ft | 4 to 5.5 tons | 5 to 6 tons |
We run real Manual J load calculations against your specific home: insulation, window orientation, ductwork, shade, occupancy. Square-foot estimates are rough; real load calculations are accurate.
When you don’t need AC
Several scenarios where the answer is still “no AC”:
Well-shaded craftsman with east-facing exposure. Some Seattle homes (especially in tree-canopied neighborhoods like Wallingford, Ravenna, parts of Capitol Hill) stay genuinely cool in summer because of shade and orientation. If your home was comfortable during 2021 and 2023 heat waves with just fans, you may not need AC yet.
Newer construction with great insulation. Some post-2015 homes have insulation packages that resist heat gain enough to stay comfortable without active cooling. Less common but real.
Renting and you don’t have permission. Sometimes the answer is portable AC for a year while you figure out the long-term housing question.
Bedroom-only cooling solves the problem. For households where the main concern is sleeping through heat waves, a single ductless mini-split in the primary bedroom ($4,800 to $6,500 installed) is much cheaper than whole-home AC and solves the actual comfort problem.
The ductless mini-split alternative
For homes without ductwork, or for partial cooling solutions:
- Single-zone (one room): $4,800 to $6,500
- Two-zone (two rooms or floors): $7,500 to $11,000
- Whole-home multi-zone (5 to 6 heads): $14,000 to $22,000
See ductless mini-split installation for the full breakdown.