How do I stop cold air coming down my fireplace?

First close the damper fully and feel for a draft on a cold, windy day. If cold air still spills into the room, the damper is probably leaky or missing. For an unused fireplace, a magnetic cover on an iron or steel frame is the simplest fix. If magnets will not stick, or the damper is wide open, use a wool or felt flue plug or an inflatable chimney balloon sized to the flue above the damper. Remove any blocker before lighting a fire. If you burn often, fix or replace the damper instead of relying on a seasonal plug.

Will a fireplace draft stopper lower my heating bill?

It can when an unused fireplace has a leaky or open damper and you feel a cold downdraft at the hearth. Warm indoor air rises and escapes up the flue, and your furnace or heat pump works harder to replace it. How much you save depends on how open the damper was, flue size, climate, your rates, and other leaks in the house. A damper that already seats tightly with no draft usually means you do not need a product yet.

Magnetic cover, wool flue plug, or chimney balloon—which should I buy?

Buy a magnetic cover if a fridge magnet sticks firmly to a continuous iron or steel surround—it seals the opening from the room and stays visible so you will not forget it. Buy a wool or felt plug or an inflatable chimney balloon when you need a seal inside the flue, usually above a broken or missing damper, and you can measure that opening. Magnets will not stick to bare brick, stone, tile, wood, or many stainless surrounds.

Can I leave a chimney balloon or flue plug in with gas logs?

No for any active fire, and never with operable vented gas logs still connected. Remove covers, plugs, and balloons completely before any flame. A vented gas log set must be disabled or removed before you use an in-flue blocker. Keep carbon monoxide alarms working on every floor, and pull the blocker before chimney sweeps or inspections. Unvented gas appliances have their own code and CO rules—do not block those openings without a qualified technician.

How do I measure for a fireplace draft stopper?

Confirm the fireplace will stay unused. Check whether the damper seats. Magnet-test the surround for ferrous metal. For magnetic covers, measure the opening width and height (common retail size is about 39 by 32 inches). For plugs and balloons, measure the flue length and depth, or diameter, where the product will sit—often one to two feet above the firebox, above the damper if one is present. Photograph the opening with a tape in the frame, and plan where any reminder tag will hang.

Why is my fireplace still drafty after installing a blocker?

Common causes are magnets on a non-ferrous surround, a cover that does not span the opening, the wrong balloon or plug size, a balloon that deflated, sealing only the face while leaving a wide-open damper behind a loose panel, or bigger envelope leaks elsewhere. Recheck fit after the first cold, windy week. Pair the fireplace fix with door weatherstripping and other air sealing if the room is still cold.

Is a top-sealing damper better than a chimney balloon?

For a fireplace you will burn again, yes—a properly installed top-sealing damper is a longer-term fix than stacking seasonal plugs. A removable cover, wool plug, or balloon is a good winter bridge when the fireplace stays idle and you are not ready for a pro damper job. Do not burn with any seasonal blocker still in place.

Do magnetic fireplace covers work on brick?

Not by themselves. Magnets need iron or steel. Bare brick, stone, tile, and many stainless surrounds will not hold a magnetic cover safely. Some covers include hook-and-loop tape or hooks for non-metal frames—read the listing carefully and follow the maker’s instructions. Otherwise use a flue-level wool plug or chimney balloon sized to your measured opening.

What should I do before I install a chimney balloon or flue plug?

Make sure nobody will light the fireplace while the blocker is in. Hang the bright reminder tag if the product includes one, and tell everyone in the house. Measure the flue at the install height, not the decorative face trim. Never install an in-flue blocker with operable vented gas logs still connected. If you smell gas, see heavy creosote, animal nests, or structural chimney damage, call a pro before you plug anything.

Should I seal the fireplace or fix other drafts first?

Do both if you can feel cold air at the hearth—an unused flue is often one of the largest single leaks in a living room. Also handle free and cheap wins: a closed damper check, door weatherstripping, and obvious gaps. An empty attic or leaky attic stairs can dump more heat than one fireplace, so do not stop at the hearth if those are wide open.

How to Stop Cold Air From a Fireplace (Draft Stoppers)

If cold air spills out of your fireplace on a windy winter night, you are not imagining it. Warm indoor air rises, finds an unused flue, and dumps out the chimney like a vertical hole open to outdoors. A leaky or missing damper makes that path worse. The fix for an idle fireplace is usually a removable draft stopper—a magnetic cover across the opening, a wool or felt plug in the flue, or an inflatable chimney balloon—never something you leave in place for a live fire.

The short version

Close the damper fully first. If it seats tightly and you feel no hearth draft, you may not need a product.
Magnetic cover for an iron or steel surround: fast, visible, and hard to forget before someone lights a fire.
Wool or felt flue plug, or a chimney balloon, when you need a seal inside the flue above a broken damper—and you have measured that opening.
Never block a flue you still use. Remove every cover, plug, and balloon before any flame. Never use an in-flue blocker with operable vented gas logs still connected.
Damper repair or a pro top-sealing damper beats stacking seasonal products if you will burn again next year.

Why the hearth feels cold

Warm air rises. A chimney is a tall, cold shaft open (or poorly closed) to outdoors, so stack effect pulls conditioned air up the flue and replaces it with outdoor air through every other leak in the house. Even with the damper “closed,” many older dampers warp, do not seat, or leave large gaps. An open damper on a fireplace you never use is a continuous exhaust you did not ask for.

A blocker helps most when you feel cold air or chimney odor at the hearth with the damper shut, the fireplace sits unused all winter, the damper is missing or will not latch, and the opening faces a room you use every evening.

It helps less when the damper already seals, the real problem is an empty attic or major duct leaks, you only drape a loose panel over the face while leaving the damper wide open, you still need the fireplace for heat this season, or the chimney has structural damage, heavy creosote, or animal nests that need a sweep or mason first.

A sealed idle flue can cut a noticeable draft and ease HVAC runtime in leaky older homes—especially on cold, windy nights. Treat the downdraft as a reason to inspect and choose the right removable seal, not a promise for your address.

Product types at a glance

Type	Best when	Limitations
Magnetic fireplace cover (fabric or panel with magnets)	Iron or steel surround; you want a room-facing seal without climbing into the flue	Magnets need ferrous metal—will not stick to bare brick, stone, tile, or non-magnetic stainless; seals the opening face, not deep in the flue
Wool / felt flue plug (pressure-fit pad)	You can reach the flue tile above the firebox; you want a puncture-proof plug	Must match flue size; trim only as the maker allows; remove before any fire or sweep
Inflatable chimney balloon (Chimney Balloon / pillow)	Measured rectangular or square flue; damper missing or leaky; seasonal seal	Must inflate to fit; can deflate if punctured; size-critical; never with active vented gas logs

Rule of thumb: magnetic cover for a ferrous surround face seal; wool plug or balloon for a seal in the flue above a broken damper. Fix the damper (or hire a top-sealing damper) if you will burn regularly.

What to do first

Confirm the fireplace will stay unused for the season (or permanently). Blockers are for idle openings only.
Open and close the damper fully. If it seats and you feel no draft on a cold windy day, stop shopping. If it will not close, will not latch, or daylight shows through gaps, plan a removable blocker—and eventually a damper repair.
Magnet-test the surround. Hold a fridge magnet where the cover would cling. Continuous iron or steel → magnetic cover is on the table. Bare brick, stone, tile, wood mantel, or non-magnetic stainless → skip magnets; plan a flue-level wool plug or balloon.
Measure the opening for magnetic covers (width × height of the face or metal frame). Common retail size is about 39″ × 32″—verify magnets will reach continuous metal, not only thin trim.
Measure the flue for plugs and balloons (inside dimensions where the product will sit, often 1–2 feet above the firebox). Length × depth for rectangular flues; diameter for round. Match the manufacturer’s fit range—balloons usually want an opening slightly smaller than the labeled maximum.
Photograph the opening and damper hardware so you do not order a plug that cannot clear the damper flap or smoke shelf.
Plan the reminder tag. Hang it where everyone sees it so nobody lights a fire with the blocker still in.

What not to do

Read this before installing anything in or over a fireplace.

Never with an active fire. Remove the cover, wool plug, or balloon completely before lighting wood, pellets, or any flame.
Never with operable vented gas logs still connected. Disable or remove vented gas logs before any in-flue plug or balloon. Unvented (“vent-free”) gas appliances have their own code and CO rules—do not DIY-block those without a qualified tech.
Keep carbon monoxide alarms working on every floor. If you smell combustion odors, get pilot outages, or CO alarms sound after sealing, remove the blocker and call a pro.
Magnets only on ferrous frames. Bare masonry and many stainless surrounds will not hold a magnetic cover.
Measure the flue for in-flue products. A too-small balloon can fall; a forced oversized plug can damage tile.
Remove for chimney sweeps and inspections. Tell your sweep the product is there.
Do not plug over structural damage, heavy creosote, or nests. A draft stopper is not a chimney repair.
Do not seal a chimney that still vents an appliance without a qualified tech confirming the path and code.

If you smell gas, see scorched dampers, or suspect CO or combustion-air problems, stop and call a pro.

Which one should you buy?

You will burn this fireplace during heating season? Skip the seasonal product. Fix or replace the damper.
Operable vented gas logs still connected? Do not install an in-flue plug or balloon until a tech disables or removes them.
Damper already seats tightly and no hearth draft? Put the budget into doors, attic stairs, or attic depth instead (checklist, weatherstripping, attic stair covers).
Iron or steel surround that holds a magnet across the frame? Magnetic fireplace cover sized to the opening (often ~39×32—verify your width and height).
Bare masonry, tile, stone, or non-magnetic stainless? Skip magnets. Use a wool plug or chimney balloon sized to the flue.
You can reach the flue and want puncture-proof? Wool or felt flue plug matched to the measured flue (for example a ~12×12 class when that matches).
Measured rectangular or square flue in a balloon fit range? Inflatable chimney balloon matched to the listing min/max. Inflate until snug; keep the reminder handle visible.
You will burn again next season and the damper is the real failure? Removable blocker as a winter bridge only; plan a pro damper or top-seal.
Empty attic or attic stairs dump more heat than this flue? Block the fireplace and prioritize attic stair covers, attic insulation, and air sealing.

Our picks

We earn a commission if you buy through these Amazon links, at no extra cost to you. Check size and fit on the listing before you order. Stock rotates—confirm the size chart on the product page.

Best everyday magnetic cover (~39×32)magnetic fireplace blanket

Best for: Unused fireplaces with a continuous iron or steel frame—fast room-facing seal without reaching into the flue.

Watch-outs: Do the fridge-magnet test first. Measure against the published 39×32 coverage. Not for bare masonry unless the listing includes a non-magnetic mounting method you will actually use. Remove before any fire.

Magnetic Fireplace Cover 39×32 (12 built-in magnets) Check price on Amazon

Best alternate magnetic shortlistMODIGT 39×32

Best for: Comparison shopping on the common 39×32 magnetic size—check recent reviews for magnet strength on your frame type.

Watch-outs: Needs continuous ferrous metal. Do not assume every “39×32” seals your surround equally.

MODIGT 39×32 Magnet Fireplace Cover Check price on Amazon

Best magnetic pick with hook-and-loop optionCADARA

Best for: Iron frames when you also want hook-and-loop tape as a backup (read the listing for brick or non-metal installs).

Watch-outs: Magnets still need metal where you rely on them. Follow the maker’s mounting instructions; remove before any fire.

CADARA Magnetic Fireplace Draft Stopper 39×32 Check price on Amazon

Best wool flue plug (square ~12×12)Flueblocker

Best for: Reachable square or near-square flue tiles when you want a puncture-proof pressure-fit pad that does not need re-inflation.

Watch-outs: Measure the flue; trim only as allowed. Same gas-log and active-fire rules as balloons. Remove for sweeps.

Flueblocker 12″×12″ wool chimney draft stopper Check price on Amazon

Best rectangular wool plug (~11×19)Flueblocker

Best for: Rectangular flues that match the 11×19 class better than a square 12×12.

Watch-outs: Match listing size to your measured flue at install height, not the decorative face opening.

Flueblocker 11″×19″ wool chimney draft stopper Check price on Amazon

Best small rectangular chimney balloon15×9

Best for: Measured flues in the small Chimney Balloon / 15×9 class with a missing or leaky damper.

Watch-outs: Inflate snug; hang the reminder; remove before fire or sweep. Never with operable vented gas logs. Match the listing min/max to the flue, not face trim.

Chimney Balloon 15×9 Check price on Amazon

Best mid-size square balloon14×14

Best for: Near-square flues that fit a 14×14 draught stopper better than a 12×12 or 15×9.

Watch-outs: Same inflate, reminder, and remove-before-fire rules. Confirm your measured opening against the listing.

Chimney Balloon draught stopper 14×14 Check price on Amazon

Best large-flue balloon14×38 class

Best for: Wide rectangular flues that match a large Chimney Balloon range (verify measured opening vs listing min/max—often roughly mid-teens by mid-30s up to about 14×38).

Watch-outs: Size-critical; dry-fit past the damper bar before committing. Never leave inflated for a season you still burn.

Chimney Balloon large 14×38 Check price on Amazon

Amazon links may earn us a commission as an Amazon Associate at no extra cost to you (disclosure).

Install habits that keep blockers working

Idle confirm first—leave the reminder tag where everyone sees it.
Magnetic covers—wipe the frame; seat on continuous ferrous metal; feel the perimeter for gaps.
Wool plugs—seat at the measured flue tile above the damper when present; do not force an oversized pad.
Chimney balloons—inflate until snug; keep the retrieval handle and reminder accessible from the firebox.
Never “test” with a fire—fully remove the blocker before any flame, every time.
Tell your chimney sweep and pull the product before brush or camera work.
Revisit after the first cold windy week—feel for hearth drafts; reseat magnets or re-inflate before assuming failure.
Pair with other envelope work—weatherstripping, air sealing, attic stair covers.

Troubleshooting

Symptom	Likely cause	Fix
Magnetic cover will not stick / falls overnight	Non-ferrous surround (brick, stone, tile, stainless); magnets only on thin trim	Fridge-magnet test; switch to wool plug or chimney balloon sized to the flue
Cover sticks but hearth still drafty	Opening larger than panel; gaps at corners; damper wide open behind a loose face seal	Remeasure width × height; reseat on continuous metal; add a flue-level plug or balloon if the face seal is not enough
Balloon will not stay inflated / drops	Puncture, under-inflation, wrong size, sharp damper edge	Inspect for holes; inflate to a snug fit; size-match listing min/max; protect from sharp damper bars
Wool plug will not seat / falls	Wrong size; damper bar blocking; install height wrong	Remeasure flue at install height; clear the damper path; do not force oversized pads
Still smell chimney odor after install	Incomplete seal; other house leaks; need for sweep / creosote	Reseat the product; check air sealing and doors; schedule a sweep if odor persists
Condensation or damp smell near hearth	Moisture or ventilation issue the blocker did not create	Fix chimney moisture and ventilation; do not seal in a wet, damaged flue—call a pro
Kids or guests almost lit a fire with blocker in	No household habit / reminder invisible	Hang a bright reminder tag; label the mantel: remove blocker before lighting
CO alarm or combustion odor after sealing	Make-up air or appliance draft affected	Remove blocker immediately; ventilate; call a qualified pro; keep CO alarms working
Want to return but product is sooty	Wrong size bought without measuring flue	Measure first next time; photograph listing charts against your tape before ordering
Living room still cold despite sealed flue	Attic stairs, empty attic, door drafts, or HVAC dominate	Keep the blocker; add attic stair covers, attic insulation, weatherstripping
Damper repair needed but winter is here	Broken damper; temporary bridge only	Use a removable blocker for an idle season; plan a pro damper or top-seal for next burn season—do not burn with the blocker in

What a fireplace blocker will not replace

A working damper if you burn regularly—seasonal seals are for unused openings.
Chimney structural, creosote, or animal problems—need a sweep or mason.
Other stack-effect holes—attic stair covers, attic insulation, air sealing.
Door, window, and garage drafts—weatherstripping, window kits, thermal curtains, garage seals.
Dirty filters, wild setpoints, failing HVAC, or CO issues—priority checklist; CO needs a pro.

Longer-term fixes when you will burn again

Seasonal blockers are for idle fireplaces. If you want fires next winter, plan a real damper solution:

Damper repair or replacement when the existing throat damper warps, sticks, or will not seat. A chimney pro can tell you whether the hardware is salvageable.
Top-sealing (chimney-top) damper mounted at the crown, often with a cable you pull from the firebox. These usually seal better than old throat dampers because they close at the top of the flue instead of halfway down a warped throat. Installation is a roof job—budget for a pro.
Glass fireplace doors that latch can cut room air exchange at the opening, but they do not replace a working damper, and poorly fitted doors still leak. They are a comfort upgrade, not a substitute for flue sealing when the damper is gone.
Chimney cap keeps rain, animals, and some downdrafts out. It does not replace a closed damper or a plug when the flue is otherwise open to the house.

Use a magnetic cover, wool plug, or balloon as a winter bridge on an unused opening. Schedule damper work before the next burn season rather than lighting fires around a forgotten plug.

Bottom line

Treat an unused fireplace as a hole to outdoors. Close and check the damper, magnet-test the surround, measure the opening or flue, then pick a magnetic cover, wool plug, chimney balloon, or a real damper repair. Follow the safety list—especially remove-before-fire and never with operable vented gas logs—install for a continuous removable seal, and keep going with weatherstripping and attic work rather than stopping at one product. For order of operations, return to Start Here and the priority checklist. Amazon links may earn a commission as an Associate (disclosure).

Some links on this page go to Amazon, and we earn a commission if you buy, at no extra cost to you. Prices and savings vary by home and utility rate. More in our disclosure.

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