Flue vent & chimney pipe questions...

[angelboy]

My vent is basically two bricks wide by half a brick deep - it's not fancy, no sweeping bricks to guide the smoke, just plain old rectangular vent.



I've gone for a single wall 6" stove pipe which is slightly bigger than the flue opening (see the pictures).



The chimney parts I've bought I'm assuming go together like, the steel tube with the lip should rest on a course of bricks, the steel plate then goes over the top which is fixed to the bricks, then the stove pip slots over the steel tube and then the brackets fix the pipe to the tube.



Does this sound about right?

I've read that the chimney should be separate from the bricks/sealant as it will expand and crack it so how do you fix it so it's safe and won't move?

Do I drill the plate onto the bricks and then use some high temp silicon? - or do I use fire cement to fix it in place with no silicon?

I was going to put the bracket ears down a touch to fit inside the brickwork.

I think the lip of the steel tube could rest on a course of bricks but then the plate be attached to the next course above with the brackets being under that course so they're not visible.

[Sixto]

I am a new builder like yourself, so all I "know" is from reading other posts and my intuition as a former architect. Your proposed plan is different from any I've come across in my research, so i may be way-off the mark, butI'll take a shot at responding anyways.

My vent is basically two bricks wide by half a brick deep - it's not fancy, no sweeping bricks to guide the smoke, just plain old rectangular vent.

You probably know this, but I'll mention it anyways-The abrupt transition between square and round will cause turbulence and slow down your draft....you could reduce the risk of smoke coming out the front arch by shaping the top course of bricks with a grinder to streamline the smoke path.

I've gone for a single wall 6" stove pipe which is slightly bigger than the flue opening (see the pictures).

Typically, The area of your brick flue should be larger than your metal chimney, to act as a funnel and guide the smoke up to the metal chimeney The concern here is that your brick flue may be too small for the oven, but I don't know the size of your oven, so I'll assume it has a 32" or smaller inside diameter. If it is 36" or larger, then your brick flue opening may be too small and you will get smoke coming out of your front arch regardless of how smooth you make the transition between brick and metal.

The chimney parts I've bought I'm assuming go together like, the steel tube with the lip should rest on a course of bricks, the steel plate then goes over the top which is fixed to the bricks, then the stove pip slots over the steel tube and then the brackets fix the pipe to the tube.

that sounds about right from what the photos show.

I've read that the chimney should be separate from the bricks/sealant as it will expand and crack it so how do you fix it so it's safe and won't move?
Do I drill the plate onto the bricks and then use some high temp silicon? - or do I use fire cement to fix it in place with no silicon?
I was going to put the bracket ears down a touch to fit inside the brickwork.
I think the lip of the steel tube could rest on a course of bricks but then the plate be attached to the next course above with the brackets being under that course so they're not visible.

Some people drill holes into the metal flange to allow the grout to bind the metal to the brickwork. Others drill the bricks below and use 4 expandable anchors or through-bolts to secure the flange. Still others use high temp sealants to prevent smoke and moisture from getting between parts. Ive not read any reports of failure so far, but most use stainless steel and the flange is typically welded to the first round section thus providing a secure base for the taller chimney sections above. You have a lot of separate parts that may move independently, whether due to heat or corrosion, but that may take a while (years) to become a problem. I think you have a sound plan of action for the parts you have, I would recommend using high-temp sealant between every separate metal component, and drilling the flange with at least three holes at each corner of 1/2" diameter each hole to allow the grout to securely bed the flange between brick courses.. I don't think you need to use sealant between the flange and the bricks. The problem I see with drilling galvanized is that the holes will eventually start to rust, so maybe adding a touch of sealant to the hole edges will prevent that.

Enjoy the process and please do report back on what you end up doing and how it worked! Sixto

[david s]

The flue pipe and anchor plate should be stainless (usually 304). Galvanised will corrode in one to two years. Also any fixings (bolts screws or masonry anchors should be stainless for the same reason. High temperature silicone will not cope in an area close to flame. A vermicrete or perlcrete mix packed around the anchor plate is more suitable. A fabricated stainless funnel between brick and flue pipe is a good solution, which transitions from a narrow rectangular area to the circular area of the pipe. Alternatively, a similar form can be easily cast using castable refractory or homebrew castable.