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Sizing a furnace for this house means sizing it for what the burner is actually going to do here. Homes in Wahkiakum County, WA run heat about ten months a year, from September through June. The heat exchanger and ignition system cycle through that entire stretch, and a unit that is undersized works harder each cycle to hold temperature, which moves wear forward. A contractor doing the load calculation has to account for the house envelope, the ductwork already in place, and the depth of the heating demand before settling on equipment. Get that wrong and the mismatch shows up in component fatigue, not in the first winter but in the ones that follow.
Existing ductwork in a house built for an earlier generation of equipment rarely lines up with what a modern furnace needs from it. The runs, the sizing, the return placement: all of it was designed around something else. Half the homes in Wahkiakum County, Washington were built in 1978 or earlier (2020-2024 ACS 5-year). A contractor installing a new furnace here has to work out whether those ducts move enough air for the new unit, and where they do not, the ductwork becomes part of the job before the furnace itself is ever priced.
What a Furnace Installation Covers
The furnace itself sits in a utility space, basement, or closet and is the piece that generates heat. A flue or vent pipe runs from the furnace to an exterior wall or through the roof, carrying combustion exhaust out of the house. These are the two pieces a homeowner notices first once the work is done.
The air handler or blower compartment, which moves conditioned air through the home, is built into or attached to the furnace cabinet. A filter housing sits at the return-air intake, and a thermostat mounts on an interior wall to give the system its operating instructions. Each of these has a specific location a contractor determines based on the existing layout.
The drawing shows a typical layout, and a licensed contractor determines what applies to this particular house.
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5 severe weather events were recorded in Wahkiakum County, Washington between 2015 and 2024.
NOAA National Centers for Environmental Information, Storm Events Database, bulk CSV export, events 2015-01-01 through 2024-12-31.Half the homes in Wahkiakum County, Washington were built in 1978 or earlier (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesWahkiakum County, Washington holds 2,250 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 83.2% of the occupied homes in Wahkiakum County, Washington (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesFurnace & HVAC Installation Rules for Wahkiakum County, Washington5 sourced standards and codes
What the installation actually looks like
Non-weatherized gas furnaces manufactured on or after November 19, 2015 must reach 80.0 percent AFUE.
Non-weatherized oil-fired furnaces manufactured on or after November 19, 2015 must reach 83.0 percent AFUE.
Mobile home gas furnaces manufactured on or after November 19, 2015 must reach 80.0 percent AFUE.
Non-weatherized gas furnaces manufactured on or after December 18, 2028 must reach 95.0 percent AFUE, up from the 80.0 percent minimum that applies to units manufactured before that date.
What Wahkiakum County, Washington Requires for HVAC Installation
Washington requires contractor registration rather than an HVAC licence: every contractor must register with the Department of Labor and Industries, and advertising, bidding or working as a contractor without that registration is a gross misdemeanour.