Do you need a permit for an AC unit, heat pump, or generator in Montgomery County, MD?
It depends on the details of your project.
Even replacing a heating unit needs a permit in Montgomery County.
AC units and similar equipment may project up to 5 ft into a front or rear setback.
Equipment noise is capped at 65 dBA by day and 55 dBA at night at the property line.
A person last checked these rules on October 20, 2026. This is guidance only, so confirm with Montgomery County before you build.
Check your exact lot
Your zoning district sets the setbacks, and a flood zone can change the permit answer. Enter your address to see both.
Permits a AC unit, heat pump, or generator can need in Montgomery County
| Permit | When it applies |
|---|---|
| Mechanical permit | DPS lists HVAC heating, including replacement, as work that needs a permit. |
| Electrical permit | A generator's transfer switch or a new unit's circuit needs an electrical permit.Medium confidence |
| Gas permit (WSSC) | Gas piping is permitted by WSSC Water in Montgomery County.Medium confidence |
| Historic Area Work Permit (HPC) | On a Master Plan historic site or in a historic district, exterior changes need a Historic Area Work Permit from the Historic Preservation Commission before DPS issues other permits. |
Limits that apply citywide
| Setback encroachment | Residential mechanical equipment may project up to 5 ft into a front or rear setbackMedium confidence |
|---|
Local details
- Call 811 at least a few days before you dig footings or post holes. Utility locating is free.
- HOA covenants and deed restrictions can be stricter than city rules. Check yours before you build.
How to apply
- DPS eServices
- Department of Permitting Services
- MCAtlas zoning map
- Phone: 311 (240-777-0311)
Common questions
- When does an AC unit, heat pump, or generator need a mechanical permit in Montgomery County?
- DPS lists HVAC heating, including replacement, as work that needs a permit. Generators are permitted under electrical.
- Where do I apply for an AC unit, heat pump, or generator permit in Montgomery County?
- Apply through DPS eServices, or call 311 (240-777-0311).
Sources
- Montgomery County DPS, Permits Required / No Permits Required (2024). Checked 2026-10-21
[Likely requires a permit:] Accessory Structure; Deck; Driveway (apron only); Electrical Work; Exterior Work on Historic Property; Fence; Garage; Hot Tub; HVAC Heating (replacing); Land Disturbance (greater than 5,000 square feet or 100 cubic yards or more …
- Montgomery Planning, Historic Area Work Permits. Checked 2026-10-21
Work requiring a HAWP includes but is not limited to the following: [new construction, additions, removing porches and other exterior work on Master Plan historic sites and properties in Master Plan historic districts, reviewed by the Historic Preservation …
- Montgomery County Zoning Ordinance (Chapter 59), Articles 59-3, 59-4 and 59-6 (Zoneomics copy of the official American Legal text). Checked 2026-10-21
[6.4.3.C] Fences, walls and other visual obstructions [on corner lots in Residential zones] are limited to 3 feet above curb level for 15 feet from the intersection of the front and side street lines... [4.1.7.B.5] Residential mechanical equipment, includin…