Does a like-for-like AC or furnace replacement need a permit?

Under the model code adopted in most US jurisdictions (2021 IRC R105.1), yes: a permit is required to "erect, install, enlarge, alter, repair, remove, convert or replace any electrical, gas, mechanical or plumbing system." Replacement is explicitly on that list. Major jurisdictions confirm it — Los Angeles issues same-size AC replacements as express permits (permit required, no plan check), and Houston requires a mechanical permit and inspection for residential A/C replacement. Local amendments vary; your building department is the final word.

What mechanical work is exempt from a permit?

The model code (2021 IRC R105.2) exempts: portable heating, ventilation, and cooling appliances; portable evaporative coolers; steam/hot- or chilled-water piping within regulated equipment; replacement of minor parts that do not alter the equipment's approval; self-contained refrigeration systems with 10 pounds or less of refrigerant driven by motors of 1 horsepower or less; and portable fuel-cell appliances. Everything fixed — condensers, furnaces, air handlers, ductwork — is permit work.

How long is a building permit valid once issued?

The model code runs two 180-day clocks: work must commence within 180 days of issuance, and the permit expires if work is suspended or abandoned for 180 days after starting. Big variations exist: California allows 12 months to commence (AB 2913), Florida permits stay active only 180 days from each passing inspection (FBC 105.4.1), and Washington DC uses one-year windows. Extensions must be requested in writing and filed before expiration.

What happens if a permit expires without a final inspection?

It becomes an "open permit," and it resurfaces at the worst time: when the property sells. Title companies run permit searches, and an open or expired permit becomes the buyer's objection or the seller's repair bill. Florida statute (F.S. 553.79) lets agencies close permits after six years absent safety hazards and protects arms-length purchasers — most states offer no such cleanup path, so the practical rule is simple: never let a job close without its final inspection.

Can the homeowner pull the permit instead of the contractor?

Usually legal, usually a mistake. Owner-builder permits shift the legal and financial risk from the contractor to the homeowner — California's CSLB warns explicitly that a contractor asking the homeowner to pull the permit "is trying to put their legal and financial risk on your shoulders," and license-bond protections can evaporate. In Florida, the owner must personally appear, sign the application, and sign a statutory disclosure. The contractor of record should pull the permit.

Free check · model-code sourced

Replacing the AC? That needs a permit.

The model code most US jurisdictions adopt (2021 IRC R105.1) requires a permit to “erect, install, enlarge, alter, repair, remove, convert or replace any electrical, gas, mechanical or plumbing system” — like-for-like included. Check your job below; the checker answers only what the code answers, and says so when it can’t.

Describe the job in plain words

Verdicts answer only what the model building code answers (2021 IRC R105.1 / R105.2) — local amendments vary, and no national permit-requirement database exists from any government source. When in doubt, the answer is always your local building department.

The two clocks that expire permits

Model code: 180 days to start work, 180 days of inactivity kills it (IRC/IBC 105.5). California: 12 months to commence (AB 2913). Florida: alive only 180 days from each passing inspection (FBC 105.4.1) — expired means a new permit. Extensions exist, but only requested in writing, filed before expiration.

The open-permit resale trap

A permit that never got its final inspection stays open — and title companies find it when the property sells, years later, as the buyer’s objection or the seller’s bill. The rule that avoids all of it: no job is finished until the final inspection passes.

Sources — and the honest limit

2021 International Residential Code R105.1/R105.2 and IRC/IBC 105.5 (model text) · California AB 2913 (2018) · Florida Building Code 105.4.1 and F.S. 553.79 · LADBS express-permit bulletin P/GI 2026-003 · Houston Permitting Center · CSLB owner-builder guidance. The limit: permitting is local — no national government database of requirements exists, local amendments override model text, and unincorporated areas (notably in Texas) may have no mechanical permit requirement at all. Your building department is always the final word.

We track these clocks so nobody has to remember them

Morthn runs the back office for service businesses. Our platform tracks every job’s permit against its jurisdiction’s actual clock — commencement, inactivity, Florida’s inspection-reset — chases the renewals before the deadlines, and refuses to let a job archive without its final inspection, because the open permit is always found eventually.

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