Chimney Lining - Single Vs Double Wall

[CAS8100]

Question about chimney lining.... The project is a combination category I furnace and natural draft WH currently venting into a masonry chimney with 7 x 7 clay flue tiles. I'll be putting in a 5" (appropriate for BTU) liner and am deciding between single wall and type b venting. There's obviously a cost premium for the type b.

The chimney is an "exterior" chimney for code purposes. Any thoughts on using type B over single wall vent material? The home is located in WI and I was thinking the type B might offer some insulation advantages over the single wall. Any thoughts?

Thanks,

Carl

[BaldLoonie]

Should be an approved liner kit or double wall. The latter would be better BUT if there are any offsets, it won't go.

[CAS8100]

Thanks.

[khc95]

If you can get a b-vent down it would be better with a exterior chimmeny. Less chance on condesation....

[CAS8100]

I'm hearing conflicting views that type b is not allowed for use as a chimney liner because of the inability to inspect the joints. Can anyone add some clarification to this?

To be specific, this is an "exterior" chimney with existing clay tile liners. The B vent would be inside the existing liners.

[genduct]

The liner needs to "approved" for the purpose, but if the "dead air space is created by another sheet metal pipe OR your existing clay liner, I don't see a difference in outcomes.

The main issues are the amount of heat it takes to warm up the clay so it can actually do it's job and VENT and the larger size is not conducive to quickly warming up and Venting, so you are also reducing the size as per code. The min BTU size thing was not always on the books and understood til about 10 years ago, maybe a little longer, it's a little fuzzy

[khc95]

Air space in b-vent keeps temperature of fue gas better less heatt absorbed by clay liner. If moisture gets into liner or worse the bricks of the chimmeny it will freeze and pop. Have seen this many times with a 4" liner in a 8 by 8 liner. Had to pull liner and insulate with "approved" sleeve. Fixes it every time.

[genduct]

Isn't there some poured, loose insulation that is approved for this?
again the point is the single wall liner heats up pretty quick and then can do it's job. Right?

[khc95]

The only product I know about is vermiculate and well we all know about that now... I agree that a single wall will do he job, I just think under certain conditions a b vent is a better option for the house.

[genduct]

Good post, I think the HO has enough good info to help make an informed choice