Key takeaways
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Most HVAC replacements need mechanical + electrical permits; skipping risks fines/failed inspections.
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Inspectors flag venting, sizing/placement, duct sealing, electrical safety, filter access (MERV 8+).
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Timelines: few days to 2 weeks; plan for weather and materials.
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Pass first inspection: prep site, coordinate early, pick right-sized/code-compliant equipment.
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More help: HVAC Tips blog, Sizing Guide, R-32 heat pumps & air handlers.
Why permits are the small step that prevents big problems
Here’s a simple picture: an AC is swapped in with no permit. The vent isn’t sized correctly, a wire is undersized, and the new filter slot is buried. It “works” at first, but the unit struggles, bills climb, and the home fails an appraisal later. Permits help you avoid that spiral. They trigger inspections that verify basics like venting, drain lines, and electrical safety. They also ensure the equipment size matches your home, which protects comfort and humidity control. In 2025, many homes are moving to R-32 or R-454B refrigerants; code checks confirm safe use. If you’re curious how an inspection actually unfolds, this walk-through is useful: What happens during an HVAC inspection or diagnosis.
The common mistake: skipping permits or leaving it to chance
Many homeowners assume the contractor “probably” pulled the permit. That guess can cost you. If your locality requires a mechanical or electrical permit and it’s missing, an inspector can force tear-outs, apply fines, or block utility service changes. Insurance and future buyers may also ask for proof that work was permitted. A strong habit is to ask for the permit number and the scheduled inspection date before install day. If you bought equipment online, make sure your installer is licensed and familiar with local codes. Using a pro protects warranties and ensures code-level workmanship—more on this in finding the right installer after buying online. Keep documents together: permit application, approved drawings (if any), equipment spec sheets, and the final inspection sign-off. Store digital copies with your home records so they’re easy to share during refinance or resale.
The permits you’ll likely need (mechanical + electrical)
For a straight HVAC replacement, the mechanical permit is standard. It covers the equipment swap, venting, condensate disposal, drain pans, and refrigerant line work. You’ll often also need an electrical permit if the job touches a service disconnect, breaker size, or wiring to the air handler, furnace, or heat pump. Some jurisdictions add a refrigerant change or fuel-gas check when moving to A2L refrigerants (like R-32) or when reconnecting gas furnaces. Ask your contractor to confirm which department issues each permit (building vs. mechanical vs. electrical) and who schedules the inspection. If you’re still evaluating equipment, the Design Center
Code items inspectors flag most (what they look for first)
Inspectors tend to check the same “gotchas” because they affect safety and performance. Venting and combustion air must be correct to avoid carbon monoxide risks. Equipment sizing and clearances matter so the unit can breathe and be serviced. Duct changes should be sealed with mastic or UL-listed foil tape, and returns must be airtight to stop dust and attic air from sneaking in. Electrical work needs proper breakers, wire gauge, and a visible service disconnect. Finally, many areas now expect MERV 8 or higher filters with easy access for changes. If you’re deciding between filter ratings, this explainer helps: MERV 8 vs. MERV 13: what should I use?..
How inspections work and typical timelines
After you or your contractor submit permits, the inspection date is usually set within a few days to two weeks, depending on your city’s workload and the season. Expect at least one inspection after installation; some areas require a rough-in check if ducts, electrical, or condensate lines are run inside walls or attics before they’re sealed. On site, inspectors verify model numbers, breaker and wire sizing, refrigerant line routing, drain safety (like float switches), smoke/CO alarms near fuel-burning equipment, and outdoor clearances. If something is off, they’ll list corrections; once those are fixed, you can request a re-inspection. To prepare, clear a 36-inch pathway to indoor units and electrical panels, label the new disconnect, and keep manufacturer manuals handy. If your job includes a packaged unit, this buyer’s guide outlines unique install checks: Installing a package HVAC unit: what to know.
Plan the job to pass the first time
Good planning turns inspection day into a quick thumbs-up. Start by walking the site with your contractor: confirm equipment location, pad size, line-set path, and any duct changes. Share photos of your electrical panel and attic/basement ahead of time. Order parts early, especially drain safety switches, line-set covers, and filter racks, to avoid last-minute “fails.” Schedule work when weather won’t block roof or pad access. If you’re switching to an A2L (R-32/R-454B) system, confirm clearances and ventilation; this guide covers safety and permit steps: Preparing your home for A2L equipment. Keep the home tidy: move stored items away from the furnace closet, attic hatch, and returns. Finally, review the permit card together and verify who will be present for inspection, so any small fixes (like labeling or securing a whip) can be handled on the spot.
Choose right-sized, code-ready equipment
Right size = right comfort. Oversized units short-cycle, miss humidity targets, and can fail inspection if ducts and airflow can’t support the blower. Undersized units run hot, wear faster, and leave rooms uneven. Use a load calculation (Manual-J style) to pick the tonnage, then match coil and blower (Manual-S/D) so the system meets airflow requirements. A practical place to start is the Sizing Guide and this step-by-step article: Central AC sizing checklist.
Quick homeowner checklist (step by step)
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Confirm permits: Get the mechanical permit number; ask if an electrical permit is included.
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Pick equipment: Use a load calc, then choose a matched system; see R-32 AC/handler systems.
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Plan duct updates: Seal leaks and set return placement; stock mastic/tape and proper filter rack (MERV 8+).
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Prep the site: Clear 3 feet around units, open access to panels/attic, and protect floors.
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Verify electrical: Breaker size, wire gauge, service disconnect location.
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Set inspection date: Ensure someone can meet the inspector.
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Keep docs handy: Manuals, spec sheets, and permit card.
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After approval: Log serial numbers, thermostat settings, and filter change schedule; follow up with the Help Center if questions come up.
FAQs
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Do I really need a permit to replace my AC or furnace?
In most U.S. areas, yes. A mechanical permit is typical, and an electrical permit is common when wiring is updated. -
How long do inspections take to schedule?
Often a few days to two weeks after the permit is submitted, depending on season and workload. -
What causes most inspection failures?
Incorrect venting, wrong unit size, poor duct sealing, missing disconnects, and hard-to-reach filters. -
What MERV rating should I use?
MERV 8–13 works for most homes; check system airflow before jumping to higher ratings. -
Can I pass inspection with old, leaky ducts?
Maybe, but leaks hurt efficiency and comfort. Sealing ducts makes passing easier and lowers bills. -
What if I bought my system online?
Hire a licensed installer who will pull permits, follow code, and keep warranties valid.