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Discussion Starter #1
We bought a house that has a wood burning fireplace insert where a regular fireplace used to be. There is a strong cold draft that flows into the room around the insert. I believe most of the cold air is flowing down the chimney around the stainless steel exhaust tube running up the shaft. I want to try and seal the void around the exhaust tube. There is no live flame associated with the insert outside its chamber just the smoke and some heat. Can I use Roxul around the stainless exhaust pipe to pack and seal the void between the chimney and the tube?
 

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Yes you can Roxul or any mineral wool type insulation will be fine. Don't use fiberglass home insulation.
Ron
 

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I have used fiberglass for this type thing.

To get a perfect answer,, you probably should ask Roxul.

I have two fireplace chimneys' that are no longer used.
I fabbed a cap for both of them from metal roofing,,


The sealing helped keep the house cooleer in the summer,,,
and warmer in the winter.

With the metal roofing in place, the chimneys are no longer weather degrading,,
another plus.
 

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Discussion Starter #4
I use the insert from time to time during the winter to heat the first floor additionally. I did cap the rest of the chimney at the top around the exhaust pipe, but the chimney is about 25' tall and exterior to the house. So a lot of cold still infiltrates down on all that exterior exposed brick.
 

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Fiberglass home insulation is NOT considered an acceptable fire safeing product. Its density is not high enough and its binder breaks down at less than 400 degrees F. Mineral wools are an approved fire safeing product and are used for this all the time. This void should have been sealed when the unit was installed for fire safety reasons and being a draft stop is a result. I was in the commercial and industrial insulations business for 40 years.
Ron
 

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Discussion Starter #6
Thanks Ron,

I figured as much by reading a lot of information, but you know it is never spelled out exactly in black and white for the purpose you want to use it in. I wanted to check with people that are more knowledgeable in this area just in case. The great knowledge bowl of GTT.
 

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The temp rating of Roxul is up to 2150 deg. F. I work for them in Mississippi and can tell you by their demonstrations, that temperature rating is true. There are several videos on YouTube that show the manufacturing and demonstrations. The place that I would put the insulation is at the exit (the top) of the chimney, under the rain cap. The insulation is waterproof as well as fireproof. Even though I work there, I still find it fascinating on the manufacturing process. It is very good temp, waterproof and sound deadening insulation. I even have a BBQ smoker that has Roxul insulation in every square inch of the sidewalks, even including the firebox. The smoker is painted with automotive paint, and it is not tarnished one bit.
 

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it also sounds like the damper has not been sealed. There are kits to seal the damper location when converting to a wood stove insert.. You may want to investigate that also.. As an inspector we look for the sealing of the damper as part of the approval. The damper (moving part) itself should have been removed, The other good advice you have received is to cap the top of the chimney. Watch for condensation in the chimney too, it's always a good idea to insulate the stove pipe all the way to the exit, most do not do this because of the expense but good installers do recommend this as part of their price/install.. Jeff
 

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Just wanted to add my 2 cents. When we had out fireplace insert installed, they sealed the top of the chimney around the liner (good advice), removed the damper plate and had to cut a bit of the damper to fit the 6" liner. They put all the pieces inside/above the damper area "just in case someone decides to change back to a working fireplace", but they didn't seal the damper area with a block-off plate just stuffed some type of insulation around the liner and terracotta flue liner at the bottom. We've had no drafty issues.

In addition, whoever built my fireplace, installed an outside air intake under the firebox with a damper flap to control the air. That was sealed shut during the installation.

I guess it depends on where your air leak is coming from, top, leaky chimney between the firebox and top, cold air intake (if you have one)? Sealing all areas would help your problem.

Regarding insulation on your liner, IMO, it's not necessary on the fireplace insert, I guess you'd be expected to run it long enough and hot enough that condensation shouldn't be an issue. In addition, there may not be enough room in your flue to have insulation. My fireplace flue has a 6" X 9" terracotta liner and I needed a 6" SS liner. I installed a SS liner for my oil furnace, and I did put insulation around it. 6" X 6" terracotta and 5" SS liner with 1/2" insulation. Tight fit but I got it in. My oil burner fires on and off for short periods, especially when just making hot water, and sometimes doesn't run enough to really heat up the entire chimney, so condensation would be a concern.

So ... back to your original question, I don't know about Roxul, but I will say that I have thermocouples on my fireplace insert and the flue pipe several inches above the fire box. The hottest I've run my fireplace insert is well over 800F, never hit 900F, but I'm sure it can go that high or above. Let that be your guide for the insulation you choose.

Again, just my 2 cents.

BTW, don't forget to sweep your fireplace chimney at least once per year, creosote builds up and can cause chimney fires.
 
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