Cold air from chimney

qwertyjjj · Oct 4, 2015

This is a fireplace insert, the flue goes up in the old chimney.
There is cold air coming down.
I'm going to block up the holes on the left and right of the fireplace as they link to the old chimney but if I take a picture upwards, it seems there is a small gap where the flue goes up. Should this have been blocked off? I can't access it easily.
I also can't have a damper on the outside due to ice in winter.
How do I stop the cold air?

https://drive.google.com/folder/d/0BwSNadx1dbgxU25hYlRpSmstR00/edit

begreen · Oct 4, 2015

A block-off plate with insulation behind it sealing off the damper area should help.

Grisu · Oct 4, 2015

Here is the link on how to make one: https://www.hearth.com/talk/wiki/make-a-damper-sealing-block-off-plate/
You could also add some Roxul insulation behind the insert for further heat retention: https://www.hearth.com/talk/threads/finally-got-around-to-insulating-my-fireplace.75755/

qwertyjjj · Oct 4, 2015

It looks like (from limited view with a camera) that there is a block off plate but they badly sealed it so there's a gap around the flue.
Fireplace seems heavy to pull out.
With roxul, won't it be difficult to cut to shape?

Swedishchef · Oct 4, 2015

qwertyjjj said:
With roxul, won't it be difficult to cut to shape?

Roxul is the easiest thing to shape! Simply use a serrated knife, like a bread knife, and cut away the shape you need to remove. It's 10 times easier to work with than fiberglass batts.

Andrew

qwertyjjj · Oct 4, 2015

Yeah but I can't see what I'm doing there !
I can barely hey my hands in over the top of the fireplace.
To remove it I'd have to disconnect the flue somehow? Then 2 people to lift it out?

begreen · Oct 4, 2015

I see no sign of a block-off plate. Roxul is available in batt form. You can just stuff it up around the liner in the damper area. That may be sufficient for your purposes. If not, to put in a block-off plate the insert liner would need to be disconnected at the stove, then the insert slid out, pack the insulation, the block-off fitted and then attached, then reinstall the insert.

qwertyjjj · Oct 5, 2015

Around where the flue goes into a hole in the pictures? Is that not a metal insert? It seems appropriately sized (even though) badly cut to fit the flue through it?

I read about some flues needing a 1" cold clearance - why would that be necessary?

begreen · Oct 5, 2015

No, that is part of the damper area. It looks like you have have a metal firebox, perhaps a Heatform unit.

TradEddie · Oct 5, 2015

begreen said:
It looks like you have have a metal firebox, perhaps a Heatform unit.

You can see the vent holes in the bricks and OP mentions them in his post. I found that mine was acting in reverse, with a perfect cooling convection loop. I stuffed the entire space full of Roxul and sealed the vents. The OP may not be able to do the same, but sealing the flue might be only part of the problem.

TE

qwertyjjj · Oct 10, 2015

I'm blocking the old holes with mortar.
I can probably fit a metal plate but I'll have to remove the fireplace, which is very heavy.
Is there any moisture risk by closing it off?

Lastly, once that is all done i think cold air will still come down the inserted flue itself into the fireplace? Even if it's blocked off in the old brick chimney?

qwertyjjj · Oct 13, 2015

Will a block plate do the same thing as a top damper?
Would a top damper be worth it instead? I'm worried about it freezing up in the winter and not being able to open it, plus the chain/lever would have to go through 3 storeys.

begreen · Oct 13, 2015

No a top damper has a completely different function. I don't think you can have one with an insert.

TradEddie · Oct 15, 2015

qwertyjjj said:
Lastly, once that is all done i think cold air will still come down the inserted flue itself into the fireplace?

If you are thinking that when the insert is not in use, cold air could come down the flue into the insert and out of the air supply holes into the room, then it's possible, mine certainly does, but from responses here, it seems rare. Most people do not have that problem. In any case, just remember to leave your air supply fully closed when the insert is not in use (but realize that on modern stoves/inserts, the fully closed position is designed to never completely close the air supply.

Block those old "heatilator" vents and install a block off plate and you'll have solved 90%+ of the cold air problems.

TE

Grisu · Oct 15, 2015

When air comes down the flue/liner it should smell smokey. If it is simply cold it is more likely coming down beside it.

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Cold air from chimney

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