Attic/chimney question

[Steve]

Hello, I have been wrestling with this question for quite some time. I have a two story house with a concrete block chimney with clay tile liner. I have a oil fired forced air furnace with an add on wood stove piped into the same chimney. I have been heating my home with this set up for close to 30 years so I am not a wood burning greenhorn. I have never had a chimney fire or at least one that I was aware of. I keep the chimney clean and burn only seasoned hardwood. My question is that my chimney has about a 3 inch air space which goes up all the way into the attic and adds alot of warm air into the attic which I think causes ice to form at the eaves. Would I be making a big mistake to insulate around the chimney where the chimney extends into the attic? What about insulating around the whole chimney inside the attic? I would guess the outer block temp gets pretty warm but not over 200 degrees F. Although, a chimney fire, if one did occur, could approach or exceed that temp..... Or should I just leave well enough alone and put up with the ice buildup at the eaves?

Thanks, Steve

ps I have about a foot of fiberglass batt insulation in the attic floor.

[Colbyt]

Unfaced fiberglass insulation will not burn. If you hold it in a direct blue flame (like a gas stove burner) it will melt but will not catch fire.

As long a your chimney has a proper draft I see no reason why you can not insulate any gaps. Modern construction actually requires a non-combustible firestop around all chimneys to retard the spread of a fire.

Colbyt

[crumbbuma]

Isn't it the other way around?

[EXT]

Isn't it the other way around?

------------------------------------------------------------- It really isn't the warm air that causes the ice to form, but the humid warm air that will rise up through any opening and carry the moisture with it. This moisture will for the ice.

[Bob F]

I thought warm air heats the roof deck, melting the snow, causing water to flow and re-freeze at the eaves.

[Boden]

Could you flash around the chimney to cover the 3" gap using stainless steel? Most stainless steel alloys do not conduct heat well at all well.

[Steve]

l.- Hide quoted text -

This is what I was thinking of doing. Thanks! Steve

[hallerb]

all well.- Hide quoted text -

I BELIEVE THE AIRSPACE IS A CODE REQUIREMENT, so that a chimney fire cant conduct heat back to framining to start a fire,''

you might call your local building inspector and ask?

[Boden]

Hide quoted text -

The reason for using stainless steel is so that heat is not conducted back to the framing.

[PerryOne]

The air rising through your ceilings, light fittings etc and loft trapdoor carries lots of water vapour. Each of us produces around 2.5 litres of water vapour each 24 hours. During the night we sweat 330 ml of water keeping our temperatures steady. Children and animals produce more, as they tend to be more active. Drying things on radiators, leaving bathroom and kitchen doors open adds to the total. All this humidity rises as wet air is lighter than dry air. Once in the loft space it condenses onto or into the nearest cold thing. Hot always moves to cold. This action creates the ice in your loft. And of course it also makes an uninsulated roof warmer than the roof overhang which melts the snow on the roof makes an ice dam and floods into the home. The solution is to stop the warm air rising into the loft space by inserting a almost vapour proof barrier between your comfort zone and the outside. This is usually a plastic waterproof sheet that covers the whole of the ceiling area throughout the home. Insulation is a separate thing designed to keep the heat inside the home, most insulation is not water vapour proof -so, does not help. Perry

[Steve]

Maybe I should just check with the building inspector to see what answers he (or she) might have. Thanks!

Steve