Two answers, decided by where you live
Scroll the drawing sideways to see all of it.
Inside Caldwell city limits, the city's own Building Safety Division issues the mechanical permit and sends a city inspector. The office is at 205 South 6th Avenue. Their published rule is that an inspection request has to be in by 7:00 am to be scheduled for that working day, which matters when a job is waiting on a sign-off.
In unincorporated Canyon County, the State of Idaho took this over. The county's own building department page says it plainly:
With the exception of built-in solid fuel burning appliances (such as wood stoves and pellet stoves), all Mechanical, Electrical and Plumbing permits and inspections are handled by the State of Idaho, Division of Occupational and Professional Licenses.
The county dates the change to 1 September 2023. Canyon County Development Services is at 111 N. 11th Ave, Room 310, in Caldwell, and built-in wood and pellet stoves still go through them.
What a state HVAC permit costs
These come from the Idaho administrative rule governing HVAC installation, and every clause in it is dated 28 March 2023. They are fixed published figures rather than anybody's estimate.
| What | Fee |
|---|---|
| Base permit | $100 |
| First furnace, AC, heat pump, evaporative cooler, mini-split, boiler or similar appliance | plus $30 |
| Each additional appliance | plus $15 |
| First exhaust or ventilation duct, including dryer, range hood and bath fan vents | plus $15 |
| Each additional duct | plus $5 |
| Fuel gas piping | plus $5 per appliance outlet |
| Hydronic systems | plus $5 per zone |
| Requested inspection | $65 per hour or part hour |
| Mobile or manufactured home | $65 per inspection |
| Plan check or technical service | $65 per hour or part hour |
The per-appliance fee covers the ducts, vents and flues attached to that appliance, so those are not charged twice.
A permit expires 365 days after it is bought or after the last inspection, whichever is later, and renewing it for another year costs $65. Transferring one to somebody else costs $45.
Does a repair need a permit?
Not under state law. Idaho Code requires a permit before any heating, ventilation or air conditioning system is installed, extended or altered, "except that no permit shall be required to perform work related to repair or maintenance of an existing HVAC system". Nampa is the exception to watch: its Building Department says permits are required for all plumbing, electrical or mechanical work inside city limits. Installing or replacing an appliance is where permits come in everywhere.
The line is a judgment for whoever is doing the work, and a reasonable contractor will tell you which side of it a job falls on without being pushed. If someone says a repair needs a permit, it is fair to ask which office issues it and what it will cost, and to expect a straight answer.
You can pull your own permit
The rule provides for it. Homeowners making HVAC installations on their own premises secure a permit by applying to the Division directly, under sections 54-5002(1)(a) and 54-5016 of the Idaho Code.
That is worth knowing, and it is worth being realistic about: gas appliances, combustion venting and the electrical supply that goes with them are not a forgiving place to learn. Pulling your own permit does not make the work safe, and the inspection is not a tutorial.
Where to apply, by address
The state's own lookup, Where do I apply for an Electrical, HVAC or Plumbing Permit?, sends Caldwell and Nampa addresses inside city limits to the city, Middleton addresses to the City of Middleton, and Parma and unincorporated Canyon County addresses to the state Division of Occupational and Professional Licenses.
Which codes apply
Idaho adopts, as the Idaho Mechanical Code:
- The 2018 International Mechanical Code, including appendix A.
- The 2018 International Fuel Gas Code, including appendices A, B, C and D.
- For one and two-family dwellings, Part V (Mechanical) and Part VI (Fuel Gas) of the 2018 International Residential Code, with appendices A to D.
Each with Idaho amendments.
The venting test
Idaho's amendments to the fuel gas code add a test that matters on a high-efficiency furnace: all plastic pipe within a dwelling used for venting flue gases must be tested at five psi for fifteen minutes. It is part of an inspected installation, and a fair thing to ask about on a replacement quote.
The amendment worth knowing as a homeowner
One of those Idaho amendments adds a requirement most people have never heard of:
Where work requiring a permit occurs in existing dwellings, an approved carbon monoxide alarm must be installed outside of each separate sleeping area in the immediate vicinity of the bedrooms in dwelling units where a fuel fired appliance is installed.
So if you are having permitted work done on a house with a gas furnace, gas water heater, fireplace or any other fuel-burning appliance, carbon monoxide alarms outside the bedrooms are part of the job. If a quote does not mention them, ask.
Sources
- Canyon County Development Services, building department, read 25 September 2026.
- City of Caldwell, Building Safety Division, read 25 September 2026.
- IDAPA 24.39.70, rules governing installation of heating, ventilation and air conditioning systems, clauses dated 28 March 2023, read 25 September 2026.
No heat? Tell us what the furnace is doing.
Gas, electric and high-efficiency furnaces across Caldwell, Nampa, Middleton and Parma. Start with the symptom and your ZIP code.
You'll be asked for your ZIP code first, so your call reaches a technician who covers your area.