Chimney Balloons: Stopping Fireplace Drafts Safely

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An open masonry fireplace looks inviting, but for most of the year it is simply a large hole in the house. When there is no fire, warm indoor air can rise up the flue in winter, cold air can tumble down it, and in summer the chimney can bring in hot air, odors and the smell of old creosote. Many fireplace dampers, especially older cast-iron throat dampers, close poorly or have warped, rusted or broken parts. Some fireplaces have no working damper at all. A chimney balloon is an inflatable draft stopper that is pushed up into the flue and inflated to seal it. It is inexpensive and can noticeably reduce drafts, but it carries one firm rule: it must be removed before anyone lights a fire. This guide explains how chimney balloons work, how they compare with dampers and other options, the fire and carbon monoxide safety issues, and what a home inspector looks for at the fireplace and chimney.

Part of our Heating, Cooling & Ventilation guide — start there for the full picture →

What a Chimney Balloon Is and How It Works

A chimney balloon, also called a flue plug, fireplace plug or chimney pillow, is a pillow-shaped bladder made of durable laminated plastic or similar material. It is inserted through the firebox into the flue, typically just above the damper or in the smoke chamber, and inflated, usually by mouth or with a small pump, until it presses against the flue walls. A short inflation tube or a reminder tag commonly hangs down into the firebox so occupants can see the balloon is in place and can deflate it for removal.

Balloons come in a range of rectangular and round sizes, and fit matters. Sizing guidance from manufacturers usually asks for the flue or throat dimensions measured where the balloon will sit, often recommending a size slightly larger than the opening so it can conform. An undersized balloon leaves gaps; an oversized one may not inflate fully and can leave wrinkles that leak.

The idea is not new. An EPA guide on energy for older and historic homes lists, among simple ways to reduce drafts, closing the fireplace damper and/or using an inflatable device that fills the flue opening when the fireplace is not being used in winter.

Why fireplace drafts matter

A chimney is designed to move air upward, and it keeps doing so even when there is no fire. In cold weather, the stack effect that draws warm air up and out of the top of a house acts strongly on an open flue. In some houses, especially tightly sealed ones with powerful exhaust fans, the flow can reverse and the chimney can pull cold outdoor air, along with soot odors, into the room. ENERGY STAR’s home energy quiz notes that hidden gaps and cracks in a home can add up to as much airflow as an open window, recommends sealing leaks as one of the most cost-effective improvements, and advises keeping the fireplace damper closed unless a fire is going.

Chimney Balloon vs Closing the Damper

Where the damper works well, closing it is the first and simplest step. A chimney balloon is most useful when the damper does not seal well or is used only rarely.

• Throat dampers. These metal plates sit at the top of the firebox. Even when closed, many leak around the edges, and older ones often rust, warp or seize. A balloon placed above a leaky throat damper can reduce air movement considerably.
• Top-sealing dampers. Installed at the top of the chimney and operated by a cable from the firebox, these typically seal with a gasket and also act as a rain and animal barrier. They usually seal better than throat dampers, which can make a balloon unnecessary.
• Missing or broken dampers. Some older or modified fireplaces have no damper at all, or one that has been removed. In these, a balloon may be the only thing standing between the living room and the outdoors.
• Fireplaces that are never used. Owners who do not burn wood at all may prefer a more permanent solution, discussed below, rather than a balloon.

A balloon also adds a layer of insulation, since it fills the flue rather than leaving a thin metal plate as the only barrier. Some owners use both: damper closed and balloon in place for the off season.

The Critical Rule: Remove It Before Any Fire

A chimney balloon is not heat-resistant and is not designed to withstand a fire. Manufacturers commonly warn that the balloon must be deflated and removed before lighting a fire, and many products include a visible reminder tag for exactly this reason. If someone lights a fire with a balloon in place, smoke cannot escape properly and can spill into the room, the balloon can melt, deform or fall into the firebox, and burning plastic adds its own smoke and fumes. Some manufacturers describe their balloons as designed to deflate or drop away if heated, but that should never be treated as a safety feature to rely on.

Practical habits that reduce the risk:

• Keep the reminder tag visible and hanging into the firebox, not tucked up out of sight.
• Tell everyone in the household, including guests, house sitters and anyone renting the home, that a balloon is installed.
• Store matches, lighters and fire starters away from the fireplace during the off season.
• Put a note on the fireplace tools or screen as a second reminder.
• Remove the balloon well ahead of a planned fire, not at the last minute.

Gas fireplaces and gas logs

Gas fireplaces and vented gas log sets need their venting path open whenever the burner or pilot is lit, and many gas log installations require the damper to be fixed partially open. Manufacturers of chimney balloons commonly warn against using them in fireplaces with gas logs or a standing pilot unless the gas is shut off, and a balloon should never be installed in a sealed direct-vent gas fireplace or in the flue of any gas appliance. When there is any doubt, the gas appliance’s installation manual and a qualified gas technician should be consulted before anything is placed in the flue.

Carbon Monoxide and Fire Safety

Any wood or gas fire produces carbon monoxide, and blocking the flue while combustion is happening is dangerous. CDC describes carbon monoxide as an odorless, colorless gas that can cause sudden illness and death, lists fireplaces among the sources of fumes that contain it, and states that more than 400 Americans die each year from unintentional CO poisoning not linked to fires. CDC also advises having chimneys checked or cleaned every year, noting that chimneys can be blocked by debris that causes CO to build up inside a home, and recommends battery-operated or battery-backup CO detectors near every sleeping area.

NFPA’s public education messages address the related question of when the flue must be open. Before using a fireplace, the damper should be opened for proper ventilation, and when the fire is finished the damper should be left open until the fire is completely extinguished, so that smoke and gases from smoldering embers do not enter the home. That guidance applies equally to a balloon: it should not go back into the flue until the fire and embers are completely out and the firebox is cold, which can be many hours after the last flames.

Heating equipment is also a leading source of home fires. The U.S. Fire Administration reports an estimated 32,200 home heating fires in 2021, causing an estimated 190 deaths, 625 injuries and $442 million in property loss. USFA advises keeping anything that can burn at least 3 feet from heat sources including fireplaces and wood stoves, and having heating equipment and chimneys cleaned and inspected each year by a professional.

Things a balloon cannot fix

A balloon stops drafts. It does not address creosote buildup, cracked flue tiles, a deteriorated crown, missing mortar, animal nests or water entry. Some of those problems can make a fireplace unsafe to use at all. A chimney with damaged or missing flue tiles may need a new liner; see our guide to chimney liners for when that comes up.

Signs a Fireplace Is Leaking Air

Not every fireplace needs a draft stopper. A few simple observations help show whether the flue is a meaningful source of air leakage:

• Cold air felt at the firebox opening on a cold, windy day with the damper closed.
• Movement of smoke from an incense stick or a lit match held briefly near the opening (only with no fire in the fireplace), which shows whether air is flowing up or down the flue.
• Soot or creosote odors in the room, especially in summer or on humid days, which often indicate air flowing down the chimney.
• Ash moving in the firebox or a whistling sound in high winds.
• Light visible from above when looking up past a closed damper, which means the damper is not sealing.
• A room near the fireplace that is consistently colder than the rest of the house in winter.

A blower door test performed during a professional energy assessment can quantify how much the chimney contributes to overall air leakage, and it often identifies other leaks worth sealing at the same time.

Front Range considerations

Colorado’s Front Range brings strong downslope winds, large day-to-night temperature swings and frequent periods of wildfire smoke drifting in from regional fires. Wind blowing across a chimney top can cause gusty downdrafts through a leaky damper, while a closed and sealed flue helps keep outdoor smoke and odors from entering through the fireplace on poor air quality days. Many Front Range communities also have burning restrictions on high-pollution days, so owners who rarely burn may find a seasonal balloon or a top-sealing damper a practical way to keep the flue closed for long stretches. Animals such as birds and raccoons seek out uncapped chimneys, and a balloon is no substitute for a proper cap to keep them out.

Alternatives and Longer-Term Fixes

A chimney balloon is a low-cost, temporary measure. Depending on how often the fireplace is used and its condition, other options may make more sense:

• Glass fireplace doors. Tight-fitting doors reduce drafts into the room when there is no fire and can limit heated room air lost up the chimney while a fire dies down. Our fireplace doors guide covers how they work and their limits.
• A top-sealing damper or chimney cap. A cap keeps rain, snow, debris and animals out, and some combine a cap with a sealing damper. See our chimney cap guide.
• A fireplace insert. For owners who want heat from the fireplace, an insert with its own liner turns an inefficient open fireplace into a closed heating appliance and eliminates most open-flue drafts. The fireplace insert guide explains wood, gas and electric options.
• A freestanding stove. Some owners replace the open fireplace with a wood stove vented through a lined chimney.
• Permanent decommissioning. For fireplaces that will never be used, a chimney professional can seal and cap the flue so it cannot be used, with clear labeling so a future owner does not light a fire in it.

Comparing those options with the cost of heating the house with a leaky chimney over several winters often shows that a modest permanent fix pays for itself, while a balloon remains a reasonable bridge.

Installing and Maintaining a Chimney Balloon

Installation instructions vary by product, but the general sequence is consistent:

1. Confirm the fireplace is cold and has not been used for at least a day.
2. Open the damper and measure the opening where the balloon will sit, using a flashlight to see past the damper.
3. Clean loose soot from the area if needed, wearing gloves and eye protection.
4. Partially inflate, position and finish inflating until the balloon is snug against the flue walls without being overinflated.
5. Leave the inflation tube or reminder tag clearly visible in the firebox.

Balloons slowly lose air, especially over a long winter with large temperature swings, and may need topping up. Inspect them each season for punctures, abrasion from rough masonry and sticky creosote residue. A balloon that will not hold air should be replaced, not patched with tape.

Typical Costs

As a rough 2026 guide, with variation by size and brand:

• Chimney balloons commonly cost in the range of a few tens of dollars, with larger or specialty sizes costing more.
• Glass fireplace doors typically range from a few hundred dollars for standard sizes to considerably more for custom units.
• Top-sealing dampers are often several hundred dollars installed, depending on chimney height and access.
• Chimney inspection and sweeping are separate services, commonly priced per visit, with more detailed camera inspections costing more.
• Inserts and liners are larger investments, often several thousand dollars installed.

What a Home Inspector Looks For

The ASHI Standard of Practice and similar standards ask home inspectors to inspect fireplaces, chimneys and vent systems that are readily accessible, but not interiors of flues that are not readily accessible or the draft characteristics of a chimney. In practice, inspectors look at the firebox, damper operation, visible flue sections, hearth extension, clearance to combustibles, the exterior chimney structure, crown and cap, and signs of water entry or smoke staining. If a chimney balloon is installed, an inspector may note it and may not remove it. Many inspectors recommend a Level 2 chimney inspection by a certified chimney sweep during a home purchase, particularly when the fireplace’s history is unknown.

Fireplace and heating findings are covered in our heating and cooling inspections section, and the main guide to hiring a home inspector explains what to expect from an inspection overall.

References

• Energy Advice for Owners of Older and Historic Homes — U.S. Environmental Protection Agency
• Home Energy Quiz — ENERGY STAR
• Educational Messages Desk Reference — National Fire Protection Association
• Carbon Monoxide Poisoning Basics — Centers for Disease Control and Prevention
• Heating Fire Safety — U.S. Fire Administration

Not sure whether the fireplace in a home you are considering is sound, sealed or safe to use? Ask us to connect you with a Front Range inspector who looks closely at fireplaces, chimneys and heating systems.