What's Required in Washington
- Manual J load calculations for new installations.
- Exterior unit placement must comply with noise and setback codes.
- Condensate drainage must be properly piped to a drain or outdoors.
- A mechanical permit is required for furnace or AC replacement.
- Electrical sub-permit required for the power connection.
- Gas piping permit required if switching from electric to gas heat.
Do You Need a Permit to Replace an AC or Furnace in Washington?
Yes. Washington treats HVAC replacement as permit-required work, and that includes the common case people hope is exempt: a like-for-like swap of a furnace, AC condenser, or heat pump in the same location. Permit fees typically run $150–$350, and the permit is issued by the Department of Buildings. In practice your HVAC contractor pulls it as part of the job — if a bid doesn't mention the permit, ask why, because unpermitted mechanical work surfaces at home sale time and in insurance claims.
HVAC Repairs vs. Replacement: Where the Permit Line Falls
The line falls at equipment, not maintenance. Repairs that keep an existing system running — a blower motor, capacitor, control board, or a thermostat swap on existing wiring — generally don't need a permit. Replacing the equipment itself, adding or reworking ductwork, or running new gas or electrical almost always does. Refrigerant-line and coil replacements sit in the gray zone and vary by city. When the scope is unclear, describe the exact job to the Department of Buildings before work starts; it's a five-minute call.
How to Get a HVAC Permit in Washington
Step 1: Load Calc
Ensure the system is correctly sized for the square footage of the home.
Step 2: Contractor Filing
A licensed mechanical contractor must apply through Access DC.
Step 3: System Install
The unit is installed, including ductwork and venting.
Step 4: Electrical Hookup
An electrician completes the final wiring to the panel.
Step 5: Final Inspection
Mechanical inspector verifies refrigerant lines, venting, and safety switches.