Permit Required? Required
Typical Fee Range $100–$300 Standard flat fee for residential system replacement.
Fee Method Flat fee
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What's Required in St. Louis

  • Mechanical permit required for all HVAC unit replacements.
  • Manual J load calculations required for new system sizing.
  • Electrical permit required for power connections to the unit.
  • Proper venting and condensate drainage must be installed.
  • Exterior unit must meet property line setbacks.
  • Gas piping permit required if switching from electric to gas heat.

Do You Need a Permit to Replace an AC or Furnace in St. Louis?

Yes. St. Louis 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 $100–$300, and the permit is issued by the Building Division. 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 Building Division before work starts; it's a five-minute call.

How to Get a HVAC Permit in St. Louis

1

Step 1: System Sizing

Perform load calculations to select the correct unit size.

2

Step 2: Submit Application

Apply for mechanical and electrical permits online.

3

Step 3: Installation

Replace the unit and ductwork according to code.

4

Step 4: Safety Check

Ensure all gas and electrical connections are secure.

5

Step 5: Final Inspection

Inspector checks venting, drainage, and safety switches.

Frequently Asked Questions

Yes, any permanent mechanical heating or cooling system requires one.
Yes, but some components may require a licensed technician for safety.
A standard residential replacement permit is roughly $100–$150.
Yes — furnace and AC replacements require a mechanical permit in St. Louis, even like-for-like swaps. Fees typically run $100–$300; your contractor normally pulls the permit.
Adding or altering ductwork is mechanical work that typically requires a permit in St. Louis. Confirm the scope with the Building Division before starting.