Plumbing and HVAC rules in Washington

What the state says about plumbing and heating and cooling work, with the page each rule comes from. It's a summary of the published rules, not legal advice, and your city or county can have rules of its own.

Checked September 23, 2026

Plumbing licensing

In Washington, a plumbing business holds a plumbing contractor license from the Department of Labor and Industries, and plumbers hold plumber certificates.^{1, 2}

Heating and cooling licensing

Heating and cooling contractors in Washington register as specialty contractors with the Department of Labor and Industries under the HVAC/R code. That's a registration, not a competency license.^{1, 2}

Plumbing and mechanical codes

Washington's State Plumbing Code is the 2021 Uniform Plumbing Code with amendments.³ Washington's State Mechanical Code is the 2021 International Mechanical Code with amendments.⁴

Permits to replace a water heater, furnace or AC

Ask your local building department whether replacing a water heater, furnace or AC needs a permit where you live.

Backflow testing

Washington requires backflow assemblies to be tested when they're installed and every year after by a certified backflow assembly tester.⁵

Sources

What plumbing and HVAC work costs in Washington

Published national ranges for plumbing, water heater, sewer, AC, heat pump and furnace jobs, and a planning estimate for your own job.

Plumbing, heating and cooling costs in Washington

Contractors in Washington

3,543 plumbers and heating and cooling contractors are listed in Washington. 321 hold an active USDOT registration. Browse them by county, or ask for quotes and we'll pass your job to contractors near you.

Cite this page

“Plumbing and HVAC rules in Washington.” PlumbingInformationSite.com, updated September 27, 2026. https://plumbinginformationsite.com/wa/rules/