Insulating fireplace cavity

[petemoss]

Hey all, we recently had opened up our fireplace cavity to stop some air leaks and have noticed
fiberglass insulation stuffed up the outside of a class A double wall chimney (air gap). The insulation
was unfaced. I removed a portion and immediately noticed a lot of cold air rushing down the outside
portion of the chimney, Is it ok to leave? Does it need cold air coming down or just the air gap?

 

[begreen]

The fiberglass should not be there.

Wind coming down double wall chimney

We have a zero clearance fireplace and we had to make some repairs inside our chimney chase. I noticed there is a ton of air coming down outside part of the double wall chimney where it connects to the fireplace. Is this normal?

www.hearth.com

 

[petemoss]

The fiberglass should not be there.

Wind coming down double wall chimney

We have a zero clearance fireplace and we had to make some repairs inside our chimney chase. I noticed there is a ton of air coming down outside part of the double wall chimney where it connects to the fireplace. Is this normal?

www.hearth.com

So take it completely out and seal the cavity as well as i can?

 

[begreen]

Yes, for this style ZC, the chimney needs free air passage to cool it.

 

[webby3650]

There should be a draft stop or ceiling above the fireplace with a metal plate the pipe passes through. The exterior walls also should be insulated around the fireplace. These areas are both overlooked often.

 

[petemoss]

Thanks for the help guys. Another question, this fireplace has an outside air kit with no damper to control it when the fire is not lit. How much draft can this create? I was wondering if I could unhook the OAK and have it use air from the house. This house is not a tight house.

 

[begreen]

It might be better to put a controllable damper on the outside air supply.

 

[petemoss]

It might be better to put a controllable damper on the outside air supply.

Thanks, that is a good idea

 

[webby3650]

Are the exterior walls insulated? As well as an insulated draft stop above the fireplace?

 

[petemoss]

Are the exterior walls insulated? As well as an insulated draft stop above the fireplace?

The walls are log and we just sealed last night. Do you mean where the chimney exits the roof?

 

[webby3650]

The walls are log and we just sealed last night. Do you mean where the chimney exits the roof?

When you look up above the fireplace you shouldn’t see the roof deck. There should be a sealed off flat ceiling above the fireplace and the pipe going through a metal fire stop. If that’s not in place cold air will always fall down from the soffit into that cavity. In some instances you will see the roof but typically not.