Do I Need a Permit to Replace a Furnace in Montana?
Furnace replacement permit requirements. Even same-model swaps need a mechanical permit. What inspectors check.
Yes — even a like-for-like furnace swap requires a mechanical permit.
Why Even a Swap Needs a Permit
Furnace replacements involve gas connections, venting, and combustion air — all safety-critical systems. Most jurisdictions require a mechanical permit to verify the new furnace is properly vented, has adequate combustion air, and the gas connections are leak-free. This is true even for exact same-model replacements.
High-Efficiency Conversions
Upgrading from a standard-efficiency (80%) to high-efficiency (90%+) furnace changes the venting requirements: standard units use metal B-vent, high-efficiency units use PVC/CPVC. The old metal vent chase may need to be sealed. A condensate drain line is also required for high-efficiency units.
What Inspectors Check
The final inspection covers: gas piping and drip leg, venting type and clearances, combustion air supply (especially in confined spaces), condensate drain (high-efficiency units), thermostat operation, and CO detector presence on every level.
Bundled with AC?
If you're replacing both the furnace and AC unit at the same time, one mechanical permit typically covers both. The inspector will check the AC refrigerant lines, electrical disconnect, and condenser pad in addition to the furnace items.
Yes, always. The permit is $40-$75 and your HVAC contractor handles it. One final inspection. Don't skip it — CO poisoning from bad venting is real.
Permit fees by city in Montana
Verified from each city’s published fee schedule. Where a city has no separate fee listed for this project, open the city page for the current requirements and amount.
| City | Permit fee | Source |
|---|---|---|
| Anaconda-Deer Lodge | $48 for the first $1,000 plus $14 for each additional $1,000 or fraction thereofVerified | Mechanical / HVAC Permit → |
| Belgrade | $48 up to $1,000, plus $14 for each additional $1,000Verified | Mechanical / HVAC Permit → |
| Billings | $15.00Verified | Mechanical / HVAC Permit → |
| Bozeman | Determined based on contractor valuation of the project, subject to Building Division approval of the valuation, applied against Table CVerified | Mechanical Only Permit → |
| Butte-Silver Bow | $75.00 per hour, one-hour minimumVerified | Mechanical / HVAC Permit → |
| Choteau | See city page for the current Residential Building Permit (New Construction / Addition / Alteration) fee | Residential Building Permit (New Construction / Addition / Alteration) → |
| City of Deer Lodge | $48 for the first $1,000 plus $14 for each additional $1,000 or fraction thereofVerified | Mechanical / HVAC Permit → |
| Colstrip | See city page for the current Residential Building Permit (New Construction / Addition / Alteration / Repair / Move) fee | Residential Building Permit (New Construction / Addition / Alteration / Repair / Move) → |
| Columbia Falls | $48.00 for the first $1,000 plus $14.00 for each additional $1,000 or fraction thereof, to and including $10,000Verified | Mechanical / HVAC Permit → |
| Conrad | See city page for the current Zoning and Building Permit (New Construction / Addition / Alteration / Repair) fee | Zoning and Building Permit (New Construction / Addition / Alteration / Repair) → |
| Cut Bank | $23.50 (subject to the $100.00 minimum permit fee)Verifiedvia Residential Building Permit (New Construction / Addition / Alteration) | Residential Building Permit (New Construction / Addition / Alteration) → |
| Darby | $75 for the first $1,000 plus 2.0% of the balance of construction valueVerified | Mechanical / HVAC Permit → |
| East Helena | $48 for the first $1,000, plus $14 for each additional $1,000 or fraction thereofVerified | Mechanical / HVAC Permit — State-Issued → |
| Forsyth | See city page for the current Residential Building Permit (New Construction / Addition / Alteration) fee | Residential Building Permit (New Construction / Addition / Alteration) → |
| Glasgow | See city page for the current Residential Building Permit (New Construction / Addition / Alteration) fee | Residential Building Permit (New Construction / Addition / Alteration) → |
| Great Falls | $34.39Verified | Mechanical / HVAC Permit → |
| Hamilton | $48 for the first $1,000 plus $14 per additional $1,000, up to $10,000Verified | Mechanical / HVAC Permit → |
| Hardin | See city page for the current Residential Building Permit (New Construction / Addition / Alteration / Re-Roof) fee | Residential Building Permit (New Construction / Addition / Alteration / Re-Roof) → |
| Havre | $48 for the first $1,000, plus $14 for each additional $1,000 or fraction thereofVerified | Residential Mechanical / HVAC Permit → |
| Helena | $42.00Verified | Mechanical / HVAC Permit → |
| Kalispell | $30.00Verified | Mechanical / HVAC Permit → |
| Laurel | $48 for the first $1,000, plus $14 for each additional $1,000 or fraction thereofVerified | Residential Mechanical / HVAC Permit (State-Issued) → |
| Lewistown | See city page for the current Residential Building Permit (New Construction / Additions) fee | Residential Building Permit (New Construction / Additions) → |
| Libby | $24Verifiedvia Residential Building Permit (New Construction / Addition / Alteration / Repair) | Residential Building Permit (New Construction / Addition / Alteration / Repair) → |
| Livingston | $48 for the first $1,000, plus $14 for each additional $1,000 or fraction thereofVerified | Mechanical / HVAC Permit (State-Issued) → |
| Manhattan | See city page for the current Mechanical / HVAC Permit fee | Mechanical / HVAC Permit → |
| Miles City | $48 for the first $1,000, plus $14 for each additional $1,000 or fraction thereofVerified | Mechanical / HVAC Permit (State-Administered) → |
| Missoula | $43.00Verified | Residential Mechanical / HVAC Permit → |
| Missoula County (Unincorporated) | $44.00Verified | Mechanical / HVAC Permit (MM) → |
| Polson | $48 for the first $1,000 plus $14 for each additional $1,000 or fraction thereofVerified | Mechanical / HVAC Permit → |
| Red Lodge | See city page for the current Residential Building Permit (New Construction / Addition / Alteration) fee | Residential Building Permit (New Construction / Addition / Alteration) → |
| Ronan | $35.00 for up to $1,999Verifiedvia Building Permit (New Construction / Addition / Alteration / Repair) | Building Permit (New Construction / Addition / Alteration / Repair) → |
| Shelby | $23.50Verifiedvia Building Permit (New Construction / Addition / Structural Alteration) | Building Permit (New Construction / Addition / Structural Alteration) → |
| Sidney | $48 for the first $1,000 plus $14 for each additional $1,000 or fraction thereofVerified | Mechanical / HVAC Permit → |
| Stevensville | $50.00 for the first $1,000 plus $15.00 for each additional $1,000 or fraction thereof above $1,000Verified | Mechanical / HVAC Permit → |
| Townsend | $48 for the first $1,000, plus $14 for each additional $1,000 or fraction thereofVerified | Mechanical / HVAC Permit — State-Issued → |
| Troy | $24Verifiedvia Residential Building Permit (New Construction / Addition / Alteration / Repair) | Residential Building Permit (New Construction / Addition / Alteration / Repair) → |
| Unincorporated Yellowstone County | $48 for the first $1,000 + $14 for each additional $1,000 or fraction thereofVerified | Mechanical / HVAC Permit → |
| West Yellowstone | See city page for the current Residential Building Permit (New Construction / Addition / Alteration / Repair) fee | Residential Building Permit (New Construction / Addition / Alteration / Repair) → |
| Whitefish | Based on a percentage of the estimated project cost/valuation, consistent with the City's general building-permit valuation-based fee methodology; a deposit is required at time of permit submittalVerified | Mechanical / HVAC Permit (Trade Permit) → |