The most practical way to seal an unused fireplace is to close its damper and use a removable, correctly sized fireplace plug below it. A masonry-fireplace draft stopper is best for a quick, adjustable fit; a rectangular felt plug is better when its stated dimensions match the flue. Gasket tape and sealants are for specific repair jobs, not for blocking a chimney opening. Never leave a plug in place when using the fireplace.
| Product | Best For | Important Fit Or Use Note |
|---|---|---|
| Fireplace draft stopper | Many masonry fireplaces with rectangular dampers | Listed for dampers up to 38 x 16 inches |
| Rectangular felt flue plug | Unused rectangular flues | Opening must be no larger than 27 x 13 inches |
| 3M Fire Block Sealant | Small, appropriate gaps around building materials | Not a removable flue plug |
| Flat gasket tape | Replacing a gasket between flat surfaces | Not intended to cover a fireplace opening |
| CloudBuyer foam weather stripping | General-purpose draft sealing away from hot surfaces | Not identified as a fireplace or high-temperature product |
Fireplace Draft Stopper For Masonry Fireplaces
This inflatable plug is designed for brick or masonry fireplaces with a rectangular damper. The product listing says it fits most such fireplaces with dampers up to 38 by 16 inches. It installs below the damper, and its telescoping pole supports the pillow for positioning and removal.
Best for: People seeking a removable draft barrier for an unused masonry fireplace and who need a product with a relatively large stated fit range. The listing says the plug can help reduce energy loss, downdrafts, odors, toxins, noise, and insects.
Why it was selected: It is specifically described as a fireplace draft stopper, rather than a general-purpose caulk, tape, or weather strip. Its below-damper placement makes it a direct option for temporarily sealing an unused fireplace.
Limitation: Measure the opening and check its shape before ordering; “fits most” does not mean it fits every fireplace. Remove the plug before lighting a fire, and do not use it while the fireplace is active.
Rectangular Felt Fireplace Flue Plug
This double-layer felt plug measures 28 by 14 inches and is designed for rectangular flue openings up to 27 by 13 inches. The listing describes its compressed fit as a way to help reduce drafts, outdoor odors, dust, and debris. It also includes a telescopic removal rod.
Best for: Owners of unused fireplaces with a rectangular flue opening within the stated size limit. Choose this if you want a felt barrier and can measure the inside of the flue accurately.
Why it was selected: Its dimensions and intended use are clearly specified, making it easier to compare with a measured rectangular opening. The double-layer felt is described as helping limit air movement and unwanted material entering through the flue.
Limitation: This product is for unused fireplaces only. The listing excludes round flues, active fire conditions, and actively vented gas fireplaces. Remove it before lighting a fire, and only install it once the fireplace is fully out and cool.
3M Fire Block Sealant For Suitable Gaps
This single-component, cementitious sealant comes in a 10.1-fluid-ounce cartridge. Its listed features include adhesion to concrete, metal, wood, plastic, and cable jacketing, plus heat resistance up to 2,000°F. Those details may make it relevant to certain small sealing or repair tasks around compatible building materials.
Best for: A buyer addressing a suitable gap or joint where a sealant is appropriate and the product’s materials and application instructions match the job.
Why it was selected: It offers a high stated heat-resistance limit and adhesion to several material types, which distinguishes it from ordinary foam weather stripping. It can be considered for a repair around a fireplace only when the specific joint and application are appropriate.
Limitation: The listing does not describe this as a removable fireplace flue plug. Do not use sealant to close a chimney opening, obstruct required ventilation, or make a fireplace unusable without checking the appliance and local requirements. Follow the product label for approved applications.
Flat Gasket Tape For Fireplace Repairs
This self-adhesive flat gasket tape measures 5/8 inch by 1/8 inch and is 72 inches long. It is made from graphite-impregnated fiberglass, and the listing states that it can withstand temperatures up to 1,100°F. Its stated purpose is sealing two flat surfaces or protecting parts from damage.
Best for: Someone replacing or adding a gasket between compatible flat surfaces on a stove or fireplace component, where the product’s size and application fit the repair.
Why it was selected: The listing explicitly identifies it for stoves and fireplaces and describes a high-temperature adhesive backing. It may be a more relevant repair material than general-purpose adhesive foam when a gasket is actually needed.
Limitation: Gasket tape is not a flue plug and should not be used to cover the chimney opening. Check the equipment instructions and the dimensions of the existing gasket area before applying it.
CloudBuyer Foam Weather Stripping
This package is described as two adhesive foam weather-stripping rolls, each 1 inch wide and 3/4 inch thick, for 13 feet total. The product name lists doors, automotive use, and air conditioners as intended applications.
Best for: General draft-sealing jobs on surfaces for which this type of foam strip is appropriate, such as a door or another listed application. It may help address a gap around a fireplace surround only if that location stays cool and the material is suitable.
Why it was selected: It provides adhesive-backed foam in a defined width, thickness, and total length, giving buyers a general-purpose option for non-hot gaps near—but not inside—the fireplace area.
Limitation: The provided product information does not identify this foam as heat-resistant or designed for fireplace use. Do not place it inside the firebox, flue, or anywhere exposed to heat or flame, and do not treat it as a chimney plug.
Buying Guide: How To Seal An Unused Fireplace
Start by identifying what you need to seal. A removable plug blocks airflow through an unused flue. Gasket tape repairs a gasket joint, while sealant and foam weather stripping address certain gaps in building materials. These products are not interchangeable. For most buyers trying to stop a chimney draft, a purpose-made removable flue plug is the relevant category.
What Should You Measure Before Buying?
Measure the inside opening where the plug will sit, not just the visible fireplace opening. Record the shape and both dimensions, then compare them with the product’s stated maximum opening. The rectangular felt plug in this list is for openings up to 27 by 13 inches. The inflatable model is listed for masonry fireplaces with rectangular dampers up to 38 by 16 inches.
Check whether the measurement refers to the damper or the flue opening. The product descriptions specify different fit references, so do not assume one size range applies to every part of the chimney. If the opening is irregular, damaged, round, or outside the listed dimensions, choose a product specifically made for that situation or seek professional advice.
Should You Choose An Inflatable Plug Or Felt Plug?
Choose an inflatable draft stopper if its stated size and masonry-fireplace application match your setup. Its listing describes quick installation below the damper and a telescoping support pole. Choose the felt plug if you have an unused rectangular flue within its specific maximum dimensions and prefer a double-layer felt barrier.
Neither should be installed as a permanent obstruction in a fireplace that will be used. A removable plug must be taken out before lighting a fire. Keep track of the plug so it is not forgotten, and follow all product instructions.
Is It Safe To Seal A Fireplace Permanently?
Do not permanently block a chimney or fireplace based only on a draft problem. The fireplace may be used in the future, and fuel-burning appliances may rely on venting. A plug product is intended for an unused fireplace and must be removed before use. For a permanently abandoned chimney, ask a qualified chimney professional about appropriate closure, ventilation, and moisture control for the specific structure.
Before installing any plug, make sure the fireplace is fully out and cool. Do not use a flue plug with an active fire or an actively vented gas fireplace unless the appliance instructions specifically allow the arrangement. Never obstruct a vent required for safe operation.
When Are Tape, Sealant, Or Foam Appropriate?
Use gasket tape only where a gasket is required and its dimensions and temperature rating suit the equipment. It is not a substitute for a removable flue plug. Use sealant only for the type of joint and materials allowed by its instructions; a high heat-resistance statement does not make it suitable for every fireplace application.
General-purpose adhesive foam weather stripping is not a chimney-sealing material unless its manufacturer specifically says it is appropriate for the exact location. Keep foam away from fire, hot surfaces, and the inside of the flue. If you are unsure whether a gap is part of a venting path, do not seal it until its purpose is confirmed.
What Else Can Cause A Fireplace Draft?
A draft may relate to an open or poorly fitting damper, air pressure in the home, chimney condition, or other factors. A removable plug can reduce airflow through an unused flue, but it does not repair a damaged chimney or correct every source of odor and draft. If smoke, persistent odors, visible damage, or unexplained airflow continues, have the fireplace and chimney inspected by a qualified professional.
Frequently Asked Questions
Can I leave a fireplace plug in year-round?
A removable plug can remain in place while the fireplace is unused if the product instructions permit it and it does not block required ventilation. Remove it before using the fireplace, and check it periodically for proper placement.
Should I close the damper before installing a draft stopper?
Follow the plug’s instructions and your fireplace’s operating guidance. A plug is generally positioned below the damper in the products listed here, but the correct placement depends on the fireplace design and the product.
Can I use a fireplace plug in a gas fireplace?
Do not use a plug in an actively vented gas fireplace unless the appliance manufacturer explicitly permits it. The rectangular felt plug listed here specifically excludes actively vented gas fireplaces.
Can foam weather stripping seal the chimney opening?
No. The listed foam strip is general-purpose weather stripping and is not described as a fireplace flue plug or heat-resistant material. Use a purpose-made removable fireplace plug for an unused flue.
What if my fireplace opening is round?
Do not choose a product specified only for rectangular openings. Find a plug explicitly designed for the measured round opening, or consult a chimney professional.
Do fireplace plugs stop all odors and drafts?
A plug may help reduce drafts and odors, but results depend on fit and the source of the problem. It does not repair chimney damage or guarantee that all airflow or odors will stop.