How to Seal an Unused Fireplace and Save Money on Heating Bills

Updated on December 12, 2017

If you have one or more masonry fireplaces in your home, you can save big money on your heating bills by sealing them off when not in use. This article explains why fireplaces are so inefficient, how much money might be going up your chimney, and a variety of methods of sealing your fireplace.

Masonry Fireplaces are Notoriously Inefficient

While radiant heat from the fire emanates into your room creating that feeling of warmth, heated air, pollutants and gasses from the burning fire rise up the chimney and into the atmosphere. Air from your room, already heated at some expense, is lost up the chimney in the draft. As the fire burns down and out, heated room air continues to be drawn up the chimney.

When you go to bed at night, you should leave the damper open if there are embers remaining from the fire. That is to protect you from deadly carbon monoxide, but it also allows even more heated air to escape up the chimney.

If you forget to close the flue when you're not using the fireplace, the loss of heated air continues. One study estimates that as many as 80% of American households inadvertently leave their flue damper open after the fire dies down.

Even When the Damper Is Closed, Flue Dampers Are Inefficient

Even with the fireplace damper closed, there are air leaks around the edges of the damper. Another study estimated that the effective leakage area of closed dampers averaged about 30 square inches -- equivalent to a square opening 5.5" x 5.5" in size allow continual flow of heated air.to the outside.

In the heating season, with the flue damper closed, some of your valuable warm heated air is escaping up the chimney. The reason for this is the "chimney" or "stack" effect. Warm air in your house rises drawing cold air inside through cracks around windows, doors, vents and other places. This leads to a slight difference in air pressure between the higher and lower zones in your house. In between the higher and lower pressure zones there is a "neutral" pressure zone.

Your fireplace chimney works the same way. Near the top of the chimney the pressure is higher, near the bottom it is lower, and in between is the "neutral" zone. If your chimney top is higher that the top of your house (as it should be) the "neutral zone" is higher that the "neutral zone" in your house. This difference causes an upward draft in the chimney, sucking warm room air around the edges of the closed flue damper.

According to the U.S. Department of Energy, by sealing and weatherstripping fireplaces, a typical home owner can reduce air leaks by up to 14% and save as much as $275 a year. If you seal up more than one fireplace, you can save even more.

For more info on how this works, see a white paper by Mark Tyrol, P.E., White Paper - Seal Fireplace Dampers With Weatherstripping to Conserve Energy.

Air Conditioned Air Also Escapes up Your Chimney

Now think about the cooling season. It's hot outside and you turn on your air conditioner. You closed all windows and doors to make the system work better and save energy.

But there are still air leaks around ducts and cracks around windows. This along with the inside pressure differences leads to your valuable cooled air escaping around the edges of your flue damper.

How to Seal You Masonry Fireplace

There are several products that you can buy that are designed specifically as fireplace seals. You can (1) purchase one that fits your needs and install it yourself. Or you can (2) make one yourself.

-- 1. Purchase a Fireplace Sealer

Here are three types of masonry fireplace draft sealers that you can buy through Amazon:

  • (a) a balloon-shaped balloon that comes in many sizes, depending on your flue size,
  • (b) a rectangular-shaped balloon that presses up against your damper, and
  • (c) a fitted decorative cover over the fireplace opening
    .

-- (a) The Chimney Balloon is an inflatable balloon-type seal. It should be installed just above the damper, or in the bottom of the smoke shelf.

The one shown here is 12" x 12" and and fits many chimney flues. It is also available in many sizes so that it can fit every type of fireplace opening.

-- (b) Another fireplace draftstopper by Battic Doors, the Large Fireplace Plug, is an rectangular inflatable pillow 38" x 16" that is pressed up against the damper with an adjustable height pole to keep the pillow pressed tight.

It fits most any masonry fireplace,

-- 2. Make Your Own Fireplace Damper Sealer

If you do not want to purchase an inflatable pillow, you can make one yourself.

Look up into the fireplace opening and note the shape of the opening just below the damper. That is where your damper seal will be installed. Measure each side of the opening just below the damper seal and transfer the measurements to a pattern drawn on cardboard. Cut out the pattern and put it in place to see if it fits. Make any adjustments to your measurements so that it fits tightly in place.

  • Insulating foamboard seal. Transfer the final pattern to a piece of insulating foamboard and cut out. Press the foamboard seal firmly in place just under the damper. You can use steel insulation springs to help hold it in place.
  • Plywood and insulating foamboard seal. Transfer the pattern onto a piece of plywood and cut out. Insert foam pipe insulation over the edges of the plywood. The pipe insulation will press against the bricks and provide a good seal. You can also glue rigid foam insulation on the plywood, providing even more insulation.

-- 3. Fitted Decorative Cover over the Fireplace Opening

If you have a metal fireplace screen you can but a cover fitted with magnets that attach the cover to the metal screen. This one from Amazon features a fire-resistant (not fireproof) Pavenex fabric cover.

If you do not have a metal screen you will have to improvise.

Or, go to Fireplace Fashion by Beverly for a custom-made fashion cover for any fireplace type.

Cautionary Reminder . . .

Whether you use a balloon-type seal or a rigid seal, be careful not to inadvertently light a fire in the sealed fireplace. I think it is a good idea to place a small label on the fireplace noting that it is sealed.

Questions & Answers

    Do you know of other ways to seal off a masonry fireplace?

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      • profile image

        dave lund 

        7 years ago

        I stuffed some batting from insulation up into the fireplace as we don't use it..also installed glass doors. However there still is some drafts.

      • profile image

        Mark Tyrol 

        8 years ago

        How To Reduce Your Energy Bills / Energy Conservation Begins at Home

        Imagine leaving a window open all winter long -- the heat loss, cold drafts and wasted energy! If your home has a folding attic stair, a whole house fan or AC Return, a fireplace or a clothes dryer, that may be just what is occurring in your home every day.

        These often overlooked sources of energy loss and air leakage can cause heat and AC to pour out and the outside air to rush in -- costing you higher energy bills.

        But what can you do about the four largest “holes” in your home -- the folding attic stair, the whole house fan or AC return, the fireplace, and the clothes dryer?

        To learn more visit www.batticdoor.com

        Mark D. Tyrol is a Professional Engineer specializing in cause and origin of construction defects. He developed several residential energy conservation products including an attic stair cover and an attic access door. Battic Door is the US distributor of the fireplace plug.

      • minnow profile image

        minnow 

        8 years ago from Seattle

        great hub! I never thought of sealing off our fireplace but I'll look into it for this winter

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