Do I Need a Permit to Replace My Furnace in Wisconsin?

Replacing a furnace in Wisconsin requires a mechanical permit in virtually every municipality. This applies to gas furnaces, propane furnaces, oil furnaces, and boilers — regardless of whether you are installing the same type and size of equipment. The permit triggers an inspection that verifies safe installation, proper venting, adequate combustion air supply, gas line integrity, and correct thermostat and control wiring. Permit fees for furnace replacement typically range from $50 to $200. In Milwaukee, a mechanical permit for furnace replacement costs approximately $75 to $125. Madison charges similar fees. Most municipalities offer expedited processing for straightforward equipment replacements, with permits issued in 1 to 5 business days. The inspection is typically scheduled after installation is complete and usually takes 30 to 60 minutes. When a furnace replacement triggers additional requirements, the project becomes more complex. If you are switching from a standard-efficiency furnace (80% AFUE) to a high-efficiency condensing furnace (90%+ AFUE), the venting must change from a metal chimney liner to PVC through-wall venting, which may require a building permit for the wall penetration. If you are switching fuel types (oil to gas, electric to gas), a gas line installation or modification requires a separate plumbing or gas permit. Adding or replacing ductwork may also require additional plan review. Wisconsin homeowners can replace their own furnace in an owner-occupied single-family home, but this is strongly discouraged due to the safety risks of improper gas furnace installation. Carbon monoxide poisoning from improper venting is a leading cause of accidental death in residential settings. Licensed HVAC contractors carry insurance and are trained to identify issues that a homeowner might miss, such as cracked heat exchangers, undersized gas lines, or inadequate combustion air.

Check Your Municipality

Permit requirements, fees, and exemptions vary by municipality. Verify the specifics for your location.