Install a Fireplace Draft Stopper in 20 Minutes for $25
An unused fireplace is basically a hole in your roof, and whether it keeps stealing your heated air comes down to one simple seal.
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Every fall I'd crank the thermostat and still feel a cold draft near the living room, and it took me years to realize the culprit was my never-used fireplace. Chimneys are basically vertical wind tunnels, and if the damper doesn't seal perfectly (most don't, after years of rust and warping), warm indoor air keeps rising straight up and out. The fix isn't sealing the damper shut permanently — it's installing an inflatable chimney balloon or a rigid foam draft stopper above the damper that you can remove anytime you actually want a fire. This whole project takes about 20 minutes and costs around $25, and the difference in that room is immediate. The key variable is getting a snug, gap-free fit against the flue walls — a loose fit still lets air leak past and defeats the entire point.
What You'll Need
- Materials (~$25 total):
- 1 inflatable chimney balloon or rigid foam draft stopper sized to your flue (~$20)
- 1 tube of removable weatherstrip caulk for gap edges, optional (~$3)
- 1 bright tag or ribbon to hang from the balloon's inflation tube as a reminder (~$1)
- Tools:
- Flashlight for inspecting the flue opening
- Tape measure for confirming flue dimensions before ordering
- Small hand pump if your balloon didn't include one
How to Do It
- Measure the width and depth of your flue opening just above the damper with a tape measure — an undersized stopper leaves gaps that let air slip right past it, so accuracy here matters more than anything else.
- Inspect the damper and flue walls with a flashlight for creosote buildup or debris, since you want a clean surface for a proper seal and want to confirm there's no active animal nest up there first.
- Open the damper fully so the balloon or foam stopper can be positioned above it rather than getting wedged awkwardly against a half-closed plate.
- Position the deflated balloon or the foam block into the flue opening, centering it so it will expand evenly against all four sides rather than lopsided against one wall.
- Inflate the balloon slowly using the hand pump, checking every few pumps that it's expanding symmetrically and not pushing itself crooked or too far up the flue.
- Test the seal by holding a lit incense stick or a tissue near the closed damper — if smoke or the tissue gets pulled upward, you've still got a leak and need more inflation or repositioning.
- Label the inflation tube clearly with a bright tag hanging into the firebox so nobody accidentally lights a fire with the balloon still installed — this is the single most important safety step in the whole project.
- Remove the stopper completely before ever using the fireplace, and get in the habit of checking for it every time you plan to build a fire this winter.
Chimney sweeps often recommend pairing the balloon with a magnetic damper cover rated for your flue size, since the two-layer approach catches any leaks the balloon alone might miss around warped damper edges. They also suggest re-checking balloon inflation monthly, since flue temperature swings can cause slow air loss over the season.
