Answers
Do heat pumps work in the Pacific Northwest?
Yes, and western Whatcom County is close to an ideal heat pump climate.
The short answer
Yes. Western Whatcom County is one of the better heat pump climates in the country. We sit in IECC zone 4C, marine: long cool shoulder seasons, a heating-dominated load, and a winter design temperature of 19°F. A heat pump spends nearly all of its annual runtime in the range where it is most efficient.
What zone 4C, marine means for the equipment you buy
Zone 4C is the I-5 corridor west of the Cascades, and it is heating-dominated: the annual load is mostly heating hours with very little cooling demand. So heating performance, not cooling capacity, should drive equipment selection here. A system chosen for a Phoenix cooling load and a system chosen for a Bellingham heating load are not the same machine, even at the same tonnage.
The 19°F number, and why we use it instead of “Pacific Northwest”
Washington’s energy code publishes an outdoor heating design temperature for each station, and the Bellingham 2 N station is 19°F (WAC 51-11C-80100, Table C-1). Sea-Tac is 24°F, so Bellingham is genuinely colder than Seattle, and a Seattle-based rule of thumb starts five degrees off. Blaine is 17°F and Glacier is 13°F, which is why a foothills cabin is not sized like a house in town.
Where the marine climate is actually hard on a heat pump
The problem here is not deep cold, it is wet cold. Outdoor coils near 32°F in high humidity ice up and force frequent defrost cycles, which is normal operation and not a fault. Salt air is the other one: Christianson’s Heating reports that coastal exposure can shorten equipment life by two to four years without corrosion protection. That matters on any lot within reach of salt spray.
When we tell people not to do it
If your house is uninsulated and leaky, a heat pump is the second thing to buy, not the first. Air sealing and attic insulation shrink the load, so we can install smaller equipment that runs at a lower speed for longer. PSE pays instant weatherization rebates, which makes that order of operations cheap to follow. We would rather size to a tightened house than sell you tonnage to overcome a draft.
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