HVAC Permit Guide: Furnace, AC & Heat Pump Mechanical Permits

Short answer: replacing a furnace, air conditioner, or heat pump usually needs a mechanical permit, even for a like-for-like swap. Only minor parts are typically exempt. Adding ducts, moving outdoor equipment, or switching fuel adds load calculations, a site plan, and often electrical or gas permits.

Furnaces fail on the coldest weekend. Condensers quit during a heat advisory. Someone on the crew says a “like-for-like” swap does not need a mechanical permit, and someone in a neighborhood group swears their cousin never pulled one. Meanwhile your city portal lists furnaces, heat pumps, and Manual J uploads on the same page.

This guide explains when HVAC, furnace, and AC work needs a mechanical permit, what “one-for-one” really means, and how gas, electrical, and zoning setbacks stack onto the job. Every city example is a public illustration—not a quote for your address. Confirm with your AHJ.

Related: Do I need a building permit? · How to apply · Permit cost patterns · Who pulls the permit? · Water heater permits

This cluster: Roof / re-roof · HVAC / mechanical · Electrical · Solar PV · Garage / ADU · Inspection prep

What mechanical permits usually cover

Mechanical permits typically cover furnaces, boilers under local BTU limits, heat pumps, air conditioners, duct systems, certain range hoods, fuel-oil or LP tank and piping segments regulated by fuel-gas or mechanical codes, and related ventilation equipment. Montgomery County, Maryland’s Department of Permitting Services states a mechanical permit is required to erect, install, enlarge, alter, repair, remove, convert, or replace a mechanical HVAC system regulated by the IMC, IFGC, or IRC—and the county explicitly lists furnaces, heat pumps, AC units, range hoods, and certain tanks and boilers. A clothes dryer exhaust is a smaller mechanical job with its own duct rules; our dryer vent replacement permit guide covers it.

Exemptions are narrow. Montgomery County’s published list includes portable cooling units, replacement of minor parts that do not alter equipment approval, self-contained refrigeration systems at or below 12,000 BTUs, and swapping internal components such as compressors or burners. Replacing the entire furnace or condenser is not a “minor part.” Our Do I need a permit? checker gives a quick first answer for HVAC and other trade work.

Michigan’s public statewide framing

Michigan’s Bureau of Construction Codes is blunt in its mechanical FAQs: except for replacement of minor parts, mechanical work shall not start until a permit is issued. An owner who occupies a single-family dwelling may perform the work without a mechanical contractor license—but must still obtain the permit and the inspection before covering or operating equipment. Dearborn and Detroit mechanical applications include homeowner affidavits that repeat that duty.

Michigan also flags plan review when residential heating input exceeds 375,000 BTU/H. That threshold rarely hits a single house furnace, but it shows how “equipment room” projects leave the simple swap lane.

Verify locally: Owner-occupant privileges, gas licensing, and refrigerant handling rules vary. Rentals are often treated differently than your primary home.

For the rest of the Detroit permit picture, from the eLAPS portal to decks and sheds, see our Detroit building permits guide.

Like-for-like vs new ducts or relocated equipment

Montgomery County notes that electronic applications for one-for-one replacements can be issued immediately, while applications needing plan review are generally issued within about three business days. When ducts are installed or added, ACCA Manual J (Eighth Edition) calculations aligned with IRC equipment-sizing sections are required—and the county says applications without required Manual J will not be processed. New or relocated outdoor equipment typically needs a marked site plan for zoning setbacks.

• Same location, similar capacity, same fuel — often the fastest mechanical permit.
• Upsizing tonnage, moving the condenser, adding duct runs — expect calculations and possible zoning review.
• Fuel switching (oil→gas, gas→heat pump) — new venting, combustion air, electrical load, and sometimes utility rebates with their own paperwork. If the old oil tank is coming out as part of the switch, see heating oil tank removal permits.

If your contractor’s quote only says “install new 3-ton unit” without stating whether ducts, pads, electrical disconnects, or gas piping change, ask them to spell out the permit scope in writing before you sign.

How the scope changes the mechanical permit

Sources: Montgomery County DPS.

Gas furnaces and the second agency

In Montgomery County, installing or replacing a gas furnace requires inspection by both DPS and WSSC (the regional utility that also handles certain gas-related inspections). All-electric heat pumps follow the DPS inspection path without that dual stop. Your metro may pair the building department with a gas utility or fire marshal instead. Ask who signs the gas piping and who signs the appliance.

Detroit’s mechanical fee materials have historically noted that an electrical permit is required for new furnace and air conditioner installations—another common stack. Budget trade permits as a set. Fee patterns (not national averages) are covered in our building permit cost guide.

What inspectors commonly check

Who should pull the permit?

Best practice: the licensed HVAC contractor pulls the mechanical permit so corrections land on the party who controls the install. Homeowner-pulled permits for contractor work create ugly disputes when something fails—Dearborn’s materials discourage homeowners from obtaining permits on behalf of contractors. Read Who Pulls the Building Permit? before you sign anything titled “owner-builder.”

Hoods, basements, and combo remodels

High-CFM range hoods can trigger makeup-air rules (Michigan’s FAQ cites capability exceeding 400 CFM as a makeup-air threshold in their framing). Finishing a basement with new supply runs often combines building and mechanical scope—see finishing a basement. A kitchen remodel that moves gas or adds a new hood pairs with kitchen remodel permits.

If the swap already happened

Unpermitted HVAC replacements show up in home inspections, utility red-tags, and insurance reviews. Legalizing after the fact usually means an after-the-fact mechanical permit, possible uncovering of concealed connections, and fees that are not a bargain. Start with after-the-fact permits and keep the permit alive until final—see expired or open permits.

Also remember that a heat pump or new AC circuit may tip an electrical service conversation—especially if you are adding load alongside EV charging. That is a good moment to skim the electrical permit guide and the solar permit guide if rooftop PV is part of the energy plan.

Heat pumps, dual-fuel systems, and outdoor clearances

Heat pump installations blur the old “furnace permit” mental model. You may need a mechanical permit for the outdoor unit and air handler, an electrical permit for the new circuits or disconnects, and—if you keep a gas furnace as backup in a dual-fuel setup—fuel-gas inspection for the furnace side. Outdoor units also invite zoning questions: setbacks from lot lines, noise ordinances, and platform heights in flood-prone areas. Montgomery County’s requirement for a marked site plan when outdoor equipment is new or relocated is a useful mental checklist even if your city phrases it differently.

Ask your contractor to state, in the proposal, which permits they will pull, which inspections they will schedule, and whether Manual J / Manual S / Manual D documentation is included when ducts change. Vague “permits as required” language is how homeowners discover mid-job that the mechanical card was never opened.

The federal heat pump credit is gone, so check the math again

A lot of heat pump quotes written in 2024 and 2025 leaned on the federal Energy Efficient Home Improvement Credit. The IRS now says plainly that the credit covers improvements made through December 31, 2025. Before that date it was worth up to $2,000 a year for qualifying heat pumps (IRS: Energy Efficient Home Improvement Credit). If your system goes in during 2026, that money is not part of the deal, no matter what an old brochure says.

That changes the real comparison. A homeowner weighing "replace the furnace like-for-like" against "switch to a heat pump" should price both jobs with permit fees, any electrical work, and any duct changes, and leave the federal credit out. Utility or state programs may still exist where you live, but they come with their own forms and deadlines. Ask the installer to name the exact program, and check it on the program's own website before you sign.

The permit side does not change. A heat pump swap is still mechanical work, often with an electrical permit for a new circuit or disconnect, and the inspector still looks at the outdoor unit's clearances, the condensate line, and the electrical connection.

FAQ

Can I still claim the heat pump tax credit for a 2026 install?

Not the federal one. The IRS lists December 31, 2025 as the end date for improvements under the Energy Efficient Home Improvement Credit. If your contractor's quote still shows it, ask them to update the numbers.

Do I need a permit if the new unit is the same size as the old one?

In most places, yes. A like-for-like swap usually still needs a mechanical permit, but it is often a simpler, over-the-counter one. What adds review is moving equipment, adding ducts, or changing fuel type.

Can a homeowner pull an HVAC permit?

In Michigan, an owner who occupies a single-family home may do mechanical work without a contractor license but must still get the permit and inspection. Rules vary, and rentals are often treated differently.

Does replacing a compressor need a permit?

In Montgomery County, swapping internal components such as compressors or burners is on the exempt list; replacing the whole condenser or furnace is not (Montgomery County).

Practical takeaways

1. Assume a mechanical permit for furnace/AC/heat pump replacement unless a written AHJ exemption clearly fits.
2. Like-for-like is faster; duct changes and outdoor moves add Manual J / site plan.
3. Gas appliances may need a second agency inspection.
4. Electrical and fuel permits often stack—ask for the full list in the contractor quote.
5. Close the permit. An unfinaled HVAC swap becomes permit history when you sell.

More in this cluster: roof permits · electrical · solar · garage / ADU.

PermitCove is not a government agency and does not provide legal advice. Always verify mechanical permit rules with your local building department.

Official sources

Official pages for further reading. Rules change and vary by address, so always confirm with your own local building department.

• Montgomery County, MD: Residential mechanical permit process
• City of San Diego: Mechanical permit
• IRS: Energy Efficient Home Improvement Credit

Related guides

• Mini-split permits: electrical and mechanical requirements
• Do you need a permit to replace a dryer vent?

Edited by Ahmed Khalifa, founder of PermitCove. Sources are linked inline; see our Editorial Policy.