Chimney heat loss (is there a better way to temporarily close it up)


My chimney, circa 1985, lets a lot of heated air out of the top floor causing the "fireplace room" to be ten degrees colder than the rest of the house even though I never have used it as a "fireplace".
The chimney metal valve is shut (you can't "see" daylight looking up the chimney) but the chimney still has a breeze going through it (and it makes a lot of metallic noise in the wind). The chimney on the outside is concrete looking but it kind of looks metallic on the insides plus it has a metal covering around it at the top for about 2 feet above the chimney concrete.
I thought about putting a temporary fiberglass or styrofoam cover in the bottom shaft of the chimney but, of course, if someone were to start a flame, that would be a bad idea (even though it has never been used).
I ask you here if there is a standard solution to putting a temporary plug in the chimney from the bottom so that all the heat isn't lost going up it.
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Joseph Donner wrote:

Make your plug, and hold it in place with a stick between it and the bottom/center of the fireplace. Anyone building a fire will have to remove it first.
Or, get a really good sealing glass fireplace door.
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wrote:

Google for "chimney pillow". It's what you're looking for.
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My gradnparents had covers for all the fireplaces, their house was built in the 20's and had a fireplace in every room. Make a cover out of ply and paint it. Some foam weather striping on the backside will help seal it against an irregular surface like brike.
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Joseph Donner wrote:

Just because you can't see daylight doesn't mean the damper is actually shut. Many chimneys have an off-set to prevent, say, rain from dropping straight down and putting out the fire.
A more thorough inspection might be called for.
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I took 3/4" steel L channel and screwed it into the brick in my fireplace opening all around, then I got 4 " of R 7.2" foilfaced foamboard and put magnetic tape on the foamboard and painted it a near flat black so it cant be noticed behind the screen. Its R 28, it pulls right of when I want a fire and my room is about 6f warmer when its in place. I looked for doors but none sealed that I saw and I was told 1000$ would get me a sealing door, and it would have no real R value, but this seals and insulates better keeping cold fireplace air from entering my living room.
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The foam plugs is what weatherization use to do as kind of the old school method of dealing with fireplace draft like what you are describing, but the trouble was trying to cut it to a tight fit took time and you couldn't caulk it in place so you had to prop it with a stick (as described). We kind of dropped that method because of the liability of someone lighting a fire under it as well. I know... you wouldn't THINK someone would do that, but sometimes people are a few wine glasses gone by the time the stoke a fire I guess. And if they burn a place down it gets traced back to the person who put the plug in.
You can go with a chimney balloon to plug it and they will put you back about $50, but if someone lights a fire under it then it bursts and falls out so there is less liability. There are different sizes and types on ones out there and i am sure you can find one to fit your fireplace. This is mostly what weatherization has moved to, but we buy them in bulk because we are in a lot of homes that are "cookie cutter" neighborhoods.
You could go the glass door set route and that would start at about $400 or so. The more expensive ones are tighter, but i have never really found one that is as tight as a standard exterior window because they are mostly glass on glass or metal on metal connections with no weatherstripping and they have plenty of seams.
The trick is as with anything you have to air seal and insulate to stop the cold (just like an attic) if you only do one then you will still have a problem.
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Never bought one but had info. one time that there was/is a UK device like a blow up football bladder, that you poke up the flue and inflate via a tube. Recall it was somewhat expensive.
Right now, however, our fireplace chimney, it's 'damper' having rusted away years ago is blocked by a garbage bag full of paper/cardboard rammed up the flue from below. Seems to work OK.
Been looking for a football bladder. Or even an old tyre inner tube, but so far no luck.
Other ideas have been/are to make wooden plug to fit in or on top of the flue where it projects above the brick by an inch or two; means of securing could include clamps, or screws. Or holding it in place by either an old sash weight or a chain down the now unused chimney.
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Sealing at the flue still leaves the firebox open, that is where the cold transfers from uninsulated brick. Seal it at the inside inside opening, the foam plug is best
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With magnetic tape its airproof-draftproof, it sticks to the metal L channel.
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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.
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