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Sizing a furnace for this county starts with understanding what the burner and heat exchanger are actually being asked to carry. Homes in Thurston County, WA run heat about ten months a year, from September through June. A system that is undersized cycles harder and more often than it should, and the ignition system and heat exchanger absorb that extra stress across a season that leaves almost no idle time for the equipment. A contractor quoting a replacement here has to run a proper load calculation for the house, not pull a number from the old unit's nameplate, because an install that looks adequate on paper can run short when the heating demand never really lets up.
Ductwork laid in for an older furnace was sized for that furnace's airflow, and a new unit running at different volumes and pressures will expose every joint, every undersized run, and every trunk line that no longer fits the load. Half the homes in Thurston County, Washington were built in 1991 or earlier (2020-2024 ACS 5-year). That distribution of age means a contractor quoting a furnace replacement spends real time on what is already in the walls before settling on the unit itself. Getting the ductwork right is what determines whether the new system performs or just runs.
What a Furnace Installation Covers
The furnace itself sits in a basement, utility room, or closet and is the piece a contractor replaces at the center of the job. It draws in air, heats it with a gas burner and heat exchanger, and moves it through the house. The flue pipe runs from the furnace to an exterior wall or the roof, carrying combustion gases out.
The air handler or blower sits inside the furnace cabinet and pushes conditioned air into the supply side of the system. Alongside it, the thermostat mounts on an interior wall and is the control point a contractor wires to the new unit. The condensate drain, where present, runs from the furnace to a floor drain or utility sink.
The drawing shows a general layout of these components, and a licensed contractor determines exactly what applies to this house.
Find a contractor in Thurston CountyThurston County, by the numbers
2 severe weather events were recorded in Thurston 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 Thurston County, Washington were built in 1991 or earlier (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesThurston County, Washington holds 125,163 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 67.7% of the occupied homes in Thurston County, Washington (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesFurnace Installation Rules on the Books in Thurston County, Washington5 sourced standards and codes
What the installation 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 Thurston 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.