King County Water Heater Permit — What Changed in 2026

For years, replacing a water heater with the same type and size in King County was one of the few plumbing jobs that did not require a permit. That changed when King County migrated to its new Public Health Permit Center system on December 10, 2025. As of January 1, 2026, like-for-like water heater replacements now require a plumbing permit in King County and unincorporated areas.

What the New Rule Covers

The permit requirement applies to replacing an existing water heater with one of the same fuel type (gas, electric, or heat pump), same location, and same capacity. This is a "like-for-like" swap — no new gas lines, no additional electrical circuits, no relocation within the building.

Previously, this type of replacement was considered routine maintenance and was exempt from the permitting process. The new Permit Center system includes it as one of 25 distinct permit types, closing the historical exemption.

Who Can Pull the Permit

Under RCW 18.106.440, plumbing permits in King County can only be issued to licensed plumbing contractors. Not general contractors, not handymen, not the homeowner's general contractor acting on their behalf. The plumbing contractor must hold an active L&I plumbing contractor registration with a current bond, insurance, and designated plumber assignment.

The narrow homeowner exemption still applies: an owner-occupant of a single-family residence can pull their own plumbing permit for work on their primary home. But the exemption does not extend to rental properties, multi-family buildings, or homes built for sale.

The Inspection Process

The permit triggers a code inspection from King County's Public Health department. An inspector verifies that the replacement water heater meets current Uniform Plumbing Code requirements for clearances, temperature and pressure relief valve discharge, seismic strapping (in earthquake zones), and — for gas units — combustion air and venting.

If you are replacing a decades-old unit, the new installation may need to meet current code standards that the original unit predated. This can mean adding a drip pan, upgrading the T&P discharge line, or adjusting gas venting — work that goes beyond a simple swap and may require additional permit scope.

Cost Impact

The legacy billing grace period ended January 1, 2026, which also increased plan review costs across the board. The exact permit fee depends on the scope of work, but plumbing contractors should factor in both the permit application fee and the time required for the inspection scheduling cycle.

For plumbing contractors working in King County, the Washington Plumber License Guide covers local permit requirements alongside the state licensing framework.

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