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A contractor quoting central AC in King County has to size a system for a load that almost never arrives. Homes in King County, WA have essentially no cooling season — no month of the year is warm enough to call for it. Compressor contacts corrode during long idle periods, refrigerant charge shifts without cycling to reveal it, and capacitors degrade on the shelf as readily as under load. The first genuine hot stretch is when every dormant fault surfaces at once, which is the worst possible moment to discover the install was undersized or the electrical connections were never quite right.
Ductwork laid down for one generation of equipment does not automatically carry the next. Half the homes in King County, Washington were built in 1983 or earlier (2020-2024 ACS 5-year). A contractor installing central AC in this county has to assess what those ducts will actually move before anything else on the job can be priced or planned, because routing and sizing decisions made for an earlier system can limit what a new one delivers, regardless of how capable the new unit is. The electrical service gets the same look: a panel configured for a smaller load will stop an installation before the equipment question ever comes up.
What Gets Installed With a New Central AC
The outdoor condenser unit sits outside the house, usually on a concrete pad beside the foundation, and holds the compressor and condenser coil. Inside, the air handler or furnace-mounted evaporator coil sits in a utility space, basement, or closet and is the indoor half of the system. Together these two units are what a homeowner is buying.
The refrigerant line set runs between the two units, typically along an exterior wall or through a small penetration in the structure, and connects the indoor and outdoor sides. A thermostat goes on an interior wall where it reads the living space and tells the system when to run.
The drawing shows the general layout of these components, and a licensed contractor determines exactly how each one is positioned and connected in your specific house.
Get matched in King CountyKing County, by the numbers
1 severe weather event was recorded in King 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 King County, Washington were built in 1983 or earlier (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesKing County, Washington holds 1,003,284 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 55.4% of the occupied homes in King County, Washington (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesRules & Standards Behind Central AC Installation in King County, Washington9 sourced rules and standards
What the installation actually 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.
Licensing and Legal Requirements in King County, Washington
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.