Short answerIn Michigan, replacing a furnace, air conditioner, heat pump or water heater requires a mechanical permit and a follow-up inspection. The City of Ypsilanti and Ypsilanti Township each issue their own; the Washtenaw County Building Department handles most other townships; Ann Arbor has its own office. A licensed contractor normally pulls the permit, and some jurisdictions let homeowners pull their own.
What the Michigan Mechanical Code requires
Michigan adopts the International Mechanical Code with state amendments, administered under the Stille-DeRossett-Hale Single State Construction Code Act. Under that code, installing or replacing a furnace, boiler, air conditioner, heat pump, water heater, or any gas piping requires a mechanical permit, and the work has to be inspected. The same applies to a new flue or chimney liner, a significant ductwork replacement, and gas line extensions for a range or a generator. Swapping a thermostat, replacing a capacitor, changing a filter or cleaning a coil does not; those are repairs, not installations.
Water heaters catch people off guard. A like-for-like 40-gallon atmospheric unit still needs a permit, because the inspection confirms the gas connection, venting, TPR discharge and, in many jurisdictions, the expansion tank and seismic strapping requirements that apply to the new installation even though the old one predates them.
Which office issues your permit
This is where Southeast Michigan gets confusing, because the answer depends on exactly which municipality the house is in, and street addresses do not always make that obvious. Ypsilanti mailing addresses cover the City of Ypsilanti, Ypsilanti Township, parts of Superior Township and a corner of Pittsfield Township, and each of those answers to a different building department.
- City of Ypsilanti. Addresses inside the city limits, roughly the area around Michigan Avenue, Cross Street, Depot Town and the Normal Park and Historic East Side neighborhoods, go through the City's building department.
- Ypsilanti Township. Everything south and east of the city, including the big 1950s to 70s subdivisions off Grove Road, Textile Road and Whittaker Road, and our own shop on Lakeridge Drive, is Ypsilanti Township, which has its own building department and inspectors.
- Washtenaw County Building Department. The county handles permitting and inspection for most of the townships that do not run their own department: Superior, Pittsfield, York, Augusta, Lodi, Scio, Ann Arbor Township, Salem, Webster, Lyndon, Sylvan, Lima, Freedom, Bridgewater, Sharon and Manchester Township, plus some villages. If you are in a Saline, Dexter, Chelsea or Milan mailing address but outside the city limits, this is probably your office.
- City of Ann Arbor. The city has its own planning and development services department and its own inspectors.
- Cities of Saline, Milan, Chelsea and Dexter. Each incorporated city handles its own, though some contract portions to the county.
- Wayne County side. Canton, Van Buren, Sumpter and Plymouth Townships and the cities of Westland, Wayne, Garden City, Inkster, Romulus, Belleville, Livonia, Plymouth and Northville each run their own building department. There is no county-level mechanical permit in Wayne County the way there is in Washtenaw.
If you are not sure which jurisdiction a house falls in, the property tax bill tells you. Any HVAC contractor who works the area regularly will know from the address.
Who pulls the permit
In the normal course of a replacement, the contractor pulls the permit, pays the fee, schedules the inspection and meets the inspector. The permit is issued against the contractor's state mechanical license. That is how we handle every furnace installation, AC installation and water heater installation we do, and the permit cost is built into the quote.
Michigan law allows a homeowner to pull a permit for work on their own owner-occupied residence in most jurisdictions, and some people do this for a water heater swap. The homeowner then takes on the responsibility for the work meeting code and for passing the inspection. We do not recommend it for gas equipment, not because of the paperwork but because of what the inspection checks: gas-tight connections, correct venting, proper combustion air. An error there is a carbon monoxide or fire risk, not a cosmetic one.
What you should be wary of is a contractor who offers a lower price "if we skip the permit." That tells you the work is not going to be inspected, and it often means the installer is not licensed. Skipping the permit also creates a problem at resale: a buyer's inspector or title company that finds a 2019 furnace with no permit on file can hold up closing, and some municipalities assess a penalty for after-the-fact permits.
What the inspection covers
The inspector comes out after the installation is complete, usually within a few business days of the request, and the visit typically takes 15 to 30 minutes. On a furnace replacement they look at the gas connection and shutoff valve, the drip leg, the flue or PVC venting and its pitch and support, the combustion air supply, the condensate drain on a high-efficiency unit, electrical disconnect and bonding, clearances to combustibles, and that the furnace is level and secured. On an AC they check the disconnect within sight of the condenser, the pad and clearances, the line set routing and insulation, and the refrigerant labeling, which since 2025 includes the A2L markings on R-454B equipment. On a water heater they look at the TPR valve and its discharge pipe terminating near the floor, the gas connection, the venting and draft hood, and in many jurisdictions the expansion tank.
They are not there to judge the brand or the efficiency choice; they are confirming the installation is safe. A failed inspection is corrected and reinspected, and a good contractor rarely fails one. The most common corrections we hear about from other jobs are a missing drip leg on the gas line, PVC exhaust terminated too close to a window or the gas meter, and a TPR discharge pipe that was reduced in size or run uphill. All are quick to fix and all are things a careful installer gets right the first time.
Why it matters beyond compliance
A permit record is a documented history of the house. When you sell, the buyer's agent can look up that the furnace was replaced in a given year by a licensed contractor and inspected, which makes it a selling point instead of a question. The same record matters for insurance claims; a fire traced to an unpermitted gas appliance is a claim that gets a hard look.
And the inspection is a free second set of eyes on work that affects your safety. We have seen unpermitted installs around Ypsilanti and Westland with flue connectors sloped the wrong way, PVC exhaust terminated under a deck, and gas flex connectors run through the furnace cabinet. An inspector would have caught every one.
Permits and the pre-purchase inspection
If you are buying a house in Washtenaw County, pull the permit history on the property; most offices will provide it on request and some have it searchable online. A furnace listed as "new in 2016" with no corresponding permit is worth a question. We talk more about using this in a purchase in HVAC inspection before buying a home.