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A contractor quoting central AC installation in Thurston County has to work out what the homeowner is actually buying, because the answer here is different from what it would be elsewhere. Homes in Thurston County, WA have essentially no cooling season — no month of the year is warm enough to call for it. A compressor that sits idle every month of the year accumulates no cycling wear, but it does sit, and a system parked indefinitely can develop refrigerant migration, seized contactor points, and capacitor degradation before it ever runs a single cooling cycle. That changes what the install conversation is about: getting the equipment right matters, because what the system does from day one is essentially what it will always do.
Ductwork sized for an older system and a service panel never designed around a modern cooling load are what shape a central AC installation here, often more than the equipment choice itself. Half the homes in Thurston County, Washington were built in 1991 or earlier (2020-2024 ACS 5-year). A contractor quoting the work has to measure what the existing ducts can actually deliver and what the electrical service will carry before a unit can be matched to the house. Those two answers decide the scope.
What Gets Installed With a New Central AC
The outdoor condenser unit sits on a concrete pad beside the house and holds the compressor and condenser coil, the hardware that does the heaviest mechanical work in the system. Inside, the air handler mounts in a utility space, basement, or attic and contains the evaporator coil and blower that move conditioned air through the home.
The thermostat goes on an interior wall where it reads the living space and tells the system when to run. A refrigerant line set connects the outdoor and indoor units, running through the wall or along the structure, and a condensate drain line carries moisture the evaporator coil pulls from the air out of the house.
The drawing shows a typical layout, and a licensed contractor determines exactly how these components are configured in your home.
Get matched 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 EstimatesCodes & Standards Governing Central AC Installation in Thurston County, Washington9 sourced rules and standards
What the installation looks like
Split-system central air conditioners rated below 45,000 Btu/h manufactured on or after January 1, 2023 must meet a federal minimum of 13.4 SEER2.
Split-system central air conditioners rated at or above 45,000 Btu/h manufactured on or after January 1, 2023 must meet a federal minimum of 13.4 SEER2.
Split-system central air conditioners manufactured between January 1, 2015 and December 31, 2022 had to meet 13 SEER, the metric that preceded SEER2.
Single-package central air conditioners manufactured on or after January 1, 2023 must meet a federal minimum of 13.4 SEER2.
Space-constrained central air conditioners manufactured on or after January 1, 2023 must meet a federal minimum of 11.7 SEER2.
Federal efficiency standards for split-system central air conditioners and heat pumps are set on each certified combination of outdoor unit and indoor coil rather than on the outdoor unit alone.
Residential and light commercial air conditioning and heat pump systems assembled in the field, including mini-splits and unitary systems, may not be installed on or after January 1, 2025 using a refrigerant with a global warming potential above 700.
A field-assembled system whose specified components were all manufactured or imported before January 1, 2025 carries no installation compliance date under the refrigerant restrictions and may still be installed.
What Thurston County and Washington Require 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.