First question: what else uses this chimney?
Go to the basement and follow the metal vent pipe from the top of the furnace, boiler or water heater. If it runs into the brick near the fireplace's chimney, that chimney is still working, even if you never light a fire.
Philadelphia's residential code covers this setup. When an appliance connects to a flue that also serves a fireplace, the code calls for a noncombustible seal below the connection so room air can't get into the flue, plus a way to reach the flue for inspection and cleaning. It also says the space around a liner inside a masonry chimney can't be used to vent a second appliance. In practice, closing the fireplace may be the right move, but the appliance's vent path has to stay open, lined and accessible.
If an appliance is involved, ask whoever services it to check the vent, not just the fireplace company. The city's mechanical permit page says a licensed contractor must do permitted heating and venting work. Our guide on furnace and air conditioner permits in Philadelphia explains when that applies.
Get the flue inspected before it disappears behind a wall
The U.S. Fire Administration recommends a professional chimney inspection and cleaning every year. Years without a fire don't mean the flue is in good shape, and once the opening is covered, problems are much harder to see. Ask the inspector for written findings on:
- the damper and firebox, and whether the flue liner is cracked, missing or partly blocked
- any other appliance connected to the chimney, and whether its flue is separate
- water entry at the crown, cap or roof flashing
- what has to be fixed before the opening is closed
Water stains around the hearth or on the chimney breast are a separate problem from drafts. A cover inside the room won't stop rain coming in at the top. Our guide on why a chimney can leak after a new roof covers the usual entry points.
You can help by taking photos of stains, fallen debris and cracks from inside the room, and noting when you get drafts or smells. Leave the roof and the flue to the inspector.
Removable seal or permanent closure
These are different jobs, so be clear about which one you're paying for.
A removable seal fits a fireplace you might use again. The Building America Solution Center, a Department of Energy program, explains that fireplace dampers rarely close tightly, and it shows how to make a removable chimney pillow for long stretches without fires. Whatever you use, leave a visible tag on the fireplace saying the flue is blocked and the seal must come out before anyone lights a fire.
A permanent closure, such as a framed and drywalled opening, changes the room. Philadelphia's building permit page says you need a permit for any project that changes the interior or exterior of an existing structure, so ask L&I about a full enclosure before work starts. In Bucks or Montgomery County, ask your township, since permit rules differ from one township to the next.
For a permanent job, ask the contractor three things:
- Where exactly is the air seal, and how are the edges sealed? Fiberglass stuffed into the throat isn't an air seal.
- What materials go next to the chimney? The Department of Energy's weatherization job aids call for high-temperature caulk and sheet metal around chimneys and flues, and at least 3 inches of clearance from combustible material where the chimney passes through the attic.
- How will the closed flue stay dry, and will there be an access panel for later inspection?
Test for backdrafting after the work
Sealing a home tighter can change how natural-draft appliances vent. The Building America air-sealing checklist calls for a combustion safety test after air sealing whenever natural-draft equipment remains in the home, to make sure exhaust isn't spilling back inside. Ask who will run that test, and get the result in writing.
Keep carbon monoxide alarms working. EPA advises an alarm on every level of the home, including the basement, at least 15 feet from any fuel-burning appliance, tested monthly. If one goes off after the closure, our guide on when a CO alarm means leave the house explains what to do.
Keep the inspection report, the contractor's closure details, any permit and the backdraft test result with your house records. The next owner or chimney inspector will need to know what's behind that wall.