What Washington code requires for a water heater installation

Yes. Washington's plumbing code requires a permit for water heater installation and replacement, and jurisdictions enforce it — Public Health – Seattle & King County, historically the one outlier that skipped like-for-like replacements, requires a permit for every replacement water heater as of July 1, 2026. Most are quick over-the-counter permits, and a licensed contractor pulls it as part of the job. Adding or modifying an electrical circuit triggers a separate electrical permit, and venting changes can trigger a mechanical permit.

Yes — Washington is earthquake country, and the state plumbing code (WAC 51-56-0500, UPC 507.2) requires storage water heaters to be anchored against horizontal displacement with two straps: one in the upper third of the tank and one in the lower third, keeping at least 4 inches of clearance above the controls. Wall-mounted tankless units are considered anchored by their mounting.

Whenever a check valve, pressure-reducing valve, or backflow preventer creates a closed plumbing system — which describes most modern Puget Sound water services. Under UPC 608.2–608.3 as adopted in WAC 51-56, thermal expansion control is required in a closed system, because heated water has nowhere to expand except against your pipes, fittings, and the T&P valve.

The temperature-and-pressure relief valve's discharge pipe must be full-size (no reduction), rigid or approved material, sloped to drain, and terminate within 6 inches of the floor or at an approved receptor — with an unthreaded end, no valve, and no trap, so nothing can ever cap or block a discharge (UPC 608.5). It's one of the most common corrections on DIY and handyman installs.

If it's a non-FVIR unit, yes — the ignition source must sit at least 18 inches above the garage floor, where gasoline vapors pool (WAC 51-51 Chapter 24 / IFGC). Modern FVIR (flammable-vapor-ignition-resistant) tanks are the standard exception, and electric units have no ignition source, so the platform rule doesn't apply to them. Any unit in a vehicle path also needs a bollard.

A dedicated branch circuit sized to the load — a typical 4,500 W / 240 V element needs a properly rated circuit and conductors (NEC Article 422, with the circuit sized at 125% for a storage unit per 422.13) — plus a disconnecting means within sight of the unit or a lockable, identified breaker (NEC 422.31(B)). Washington adopts these under WAC 296-46B, and the circuit work needs an electrical permit.

Electric is the simpler code path: no venting, no combustion air, no gas train, no garage platform — just the plumbing items every tank needs plus a dedicated circuit and disconnect. Gas adds the vent connector to the exterior, combustion air, and the sediment trap. The right choice still depends on your gas-line sizing, electrical service capacity, and hot-water demand — our water heater comparison guide walks the decision.