Chimney / Flue Question..

[johnrbek]

Here's a question for you guys out there that know a little about chimney's.. being down in S. Fla., we're a little out of touch when it comes to code / rules related to chimney design, etc...

The front landing of my oven will be under a covered patio and I'll be running my flue on a diagonal back up over the dome into a masonry chimney at the rear of my stand in order to get around my patio over hang... the oven enclosure will be a gable design with the upper portion built of 4x8x16 concrete block (block is standard down here in hurricane country) that will be filled with loose perlite insulation.

My question is this... can I use a flexible single wall chimney liner from my vent running through the loose perlite insulation over to the masonry chimney at the rear or do I need to use the double wall stuff (e.g., the duravent product sold here on Forno Bravo).

With the flexible liner, I don't think I'd need the 30 degree angle connectors and the multiple pieces of 8" wide x 48" pipe need to traverse the span between the vent at the front of the oven back to the chimney...

Here's the flexible liner I've been looking at: eBay: 8" X 20' Stainless 316Ti Steel Chimney Liner Free S&H (item 290023034911 end time Feb-21-07 07:17:25 PST)

I guess to be really specific, I know the building code for an internal structure will require a triple insulated product, but this structure being outside and filled with loose perlite insulation, can I get away with the single wall flexible stuff?

Thanks guys...

JB

[CanuckJim]

John,

First off, this is an unusual request in my experience, but here goes. The flexible stuff you're looking at is really meant as a reliner for existing masonry chimneys, and I've used it that way in the past for masonry chimneys with problems not easily fixed. It's important to realize that this material is thin, will radiate considerable heat into your perlite and keep the enclosure quite warm. This will obviate using combustible materials anywhere near it, and you'd have to be careful about venting the enclosure. In a Florida summer, heat radiation could be a real issue, and I doubt loose perlite would be sufficient.

Perlite is fireproof, true, but I wouldn't run the pipe through loose material. What you might want to do is make up a perlite/portland mix (6:1 by volume)and coat the pipe with about six inches of the stuff once you had it routed, then use loose perlite in the other open areas. Alternately, you could wrap the pipe in Insulfrax, then follow the same procedure.

Personally, I'd use the double-walled stainless insulated pipe, just for peace of mind. You won't be able to see what's going on with the pipe, and I'd be a lot happier knowing I'd gone the double-walled route.

Hope that's some help, and maybe other members will have other ideas.

Jim