Seattle, WA: the heat pump payback math
In Seattle, the math is close enough that it comes down to how long you plan to stay. Against a like-for-like gas furnace and AC swap, going electric costs $3,500 more up front here (already netting out a $2,000 tax credit). Lower bills claw that back: about $311 saved annually, for a payback of roughly 11.2 years. It's a genuine toss-up here — Seattle's numbers don't point clearly either way.
Seattle's weather, in the numbers that matter
4232 heating degree days pile up here every year, so Seattle has a real but manageable winter; the cooling side runs to 365 cooling degree days, where summers add a moderate cooling load. 18°F is the figure equipment gets sized against here — the 99th-percentile cold snap, not an average day — with a record low of 14°F on file. Worked through the model, that's a seasonal COP of 3.13 on the cold-climate unit fit for this climate. Seattle needs the cold-climate class of unit: past a 25°F design temperature a standard heat pump falls back on resistance backup often enough to eat the savings. Climate figures trace to the nearest NOAA station, BOEING FLD/KING CO INTL AP, 6.6 miles from Seattle.
What it actually costs to run, year to year
A 2000-square-foot house here would pull roughly 3,424 heating kilowatt-hours annually on top of cooling, totalling about $533 a year on electricity. That compares with roughly 44 Mcf a year of gas at Seattle's 17.62 per-Mcf rate — about $844 a year — against a local electricity rate of 14.27¢/kWh. Priced as a standalone purchase rather than against a like-for-like replacement, equipment payback runs about 43.4 years, for a 15-year net position $1,167 ahead.
If your home heats with electric baseboard instead of gas
Gas isn't universal in Seattle — many houses run on electric heat already. Compared with baseboard or electric-furnace resistance heat, the numbers shift in the heat pump’s favor. About $1,064 a year comes back this way, enough that the 7.5-year payback clears the $8,000 premium comfortably within the equipment's life.
Seattle against the rest of the country
Among 3206 cities, Seattle's winter puts it at rank 1387 for severity, while its size puts it at rank 18 for population — 1 in both cases being the extreme. That's the middle third for winter severity among the cities covered here.
Next step for 780,995 people in Seattle
Seattle, Washington is home to about 780,995 people, and the figures above are the same ones a local HVAC contractor uses to size and quote a system — this site doesn't guess where a real quote would land, it just tells you whether it's worth asking for one. In Seattle, nothing is lost by holding off until the current equipment genuinely fails.
Line up a few local HVAC quotes before you decide.
Where Seattle's figure comes from
Every constant behind this page — the 3.13 seasonal COP, the degree-day corrections, the equipment costs — is documented in the methodology guide. At a 18°F design temperature, Seattle sits in cold-climate territory; the guide to that class of unit explains why.