36" x 18" High. Pompeii with centered chimney. Will this work?

[MeBeMarc3]

One challenge with doing it that way is that you want to create a nice cavity for the smoke to go into as it goes up the flu. If you don't do it large enough, you will have black soot all over your masterpiece at the opening. If you can design it in a way that you have a nice opening and travel space for the smoke it will stay clean on the front side and draw nicely. Try not to simply expect that all smoke will go into a small flu area because it likely won't.

That is what I've been trying to make work. I'm trying to design for an 8" flue for the chimney, which is roughly 50 square inches. The the flue will need to be wide and low profile along the oven from the opening and then once it gets to the top of the oven it will open up into the round flue. I'm hoping that the change in shape is ok, as long as the opening never gets smaller along the way.???

[UtahBeehiver]

A squirrel tail build will be interesting to watch. Smoke will take the path of least resistance so minimize large angle changes or restrictions. I seem to have read somewhere that 50 sq inches in a round chimney is not the same as 50 sq inches in the rectangular or square chimney in terms of venting efficiency, maybe I was dreaming this but worth checking out. BTW, nice brick and granite work.

[MeBeMarc3]

A squirrel tail build will be interesting to watch. Smoke will take the path of least resistance so minimize large angle changes or restrictions. I seem to have read somewhere that 50 sq inches in a round chimney is not the same as 50 sq inches in the rectangular or square chimney in terms of venting efficiency, maybe I was dreaming this but worth checking out. BTW, nice brick and granite work.

I still have the option to make it square. So if there is a better eason to make it that way I will! Thank you!

[MeBeMarc3]

[UtahBeehiver]

Actually I remember round seemed to be more effective than square or rectangular but you will need to research farther, just something I read somewhere.

[Gulf]

You are right Russell, It was a big discussion on this forum some time back. Square and rectangular flus will still work, but the corners aren't figured into what is called the effective flu area when sizing.

Sizing fireplace openings and flues.

[MeBeMarc3]

You are right Russell, It was a big discussion on this forum some time back. Square and rectangular flus will still work, but the corners aren't figured into what is called the effective flu area when sizing.

Sizing fireplace openings and flues.

Thank you for the link! Any suggestions for material to use for the sides of my flue? I was going to do them with a 5:1 ratio of vermiculite to portland cement. Will this be strong enough to support the weight of the chimney? I am pouring 3" wide.

[Gulf]

That question is probably above my pay grade. But, if I understand you correctly, my honest answer would be no. The sides made of vcrete would need to be much wider and also parged smooth inside imo. I don't think that you want exposed vecrete inside the flue. It will continually shed and fall a little at a time into your landing and possibly on to food. I have seen pics of masonry squirrel tails flues done with brick and with clay tile. If you don't go with metal piping, I think that those materials would be your best bet.

[MeBeMarc3]

That question is probably above my pay grade. But, if I understand you correctly, my honest answer would be no. The sides made of vcrete would need to be much wider and also parged smooth inside imo. I don't think that you want exposed vecrete inside the flue. It will continually shed and fall a little at a time into your landing and possibly on to food. I have seen pics of masonry squirrel tails flues done with brick and with clay tile. If you don't go with metal piping, I think that those materials would be your best bet.

I went ahead and poured concrete already this afternoon. I wasn't feeling too confident with the vermi-crete. I hadn't thought of the pieces falling down into the oven. Good thinking. How thick is clay tile? I'm limited with space. Do you think I can get away with a concrete flu? It sounds like you think I should line it.

[MeBeMarc3]

[MeBeMarc3]

[deejayoh]

The inside of the flue is still super hot, and goes through a lot of heat/cool cycling. This may be too late - but I don't think I would trust concrete. I would worry about it cracking and spalling. The flue is going to be 700-800 degrees. I think the stuff you want is called Ciment Fondu. High-temp concrete.

[MeBeMarc3]

The inside of the flue is still super hot, and goes through a lot of heat/cool cycling. This may be too late - but I don't think I would trust concrete. I would worry about it cracking and spalling. The flue is going to be 700-800 degrees. I think the stuff you want is called Ciment Fondu. High-temp concrete.

I knew I should have waited. Should I line it with metal or add a thin layer of high temp mortar or are those bad ideas?

[deejayoh]

Others might chime in here, maybe it's ok and I am overreacting but I don't think concrete is great with heat/cool over time.

If you line it, it would need to be with stainless - other metals are going to break down from the smoke. A thin layer of mortar doesn't really insulate the concrete so I am not sure that helps.

Is it a real pain to cut out the concrete? If it were me I would just lay it up with firebrick.

[MeBeMarc3]

Others might chime in here, maybe it's ok and I am overreacting but I don't think concrete is great with heat/cool over time.

If you line it, it would need to be with stainless - other metals are going to break down from the smoke. A thin layer of mortar doesn't really insulate the concrete so I am not sure that helps.

Is it a real pain to cut out the concrete? If it were me I would just lay it up with firebrick.

Originally I was going to use firebrick but between gravity, the pain in the butt of cutting all the angles and the finicky nature of the fire mortar, I decided to form it and pour it. What do you think about if I cut away the inner half of the concrete that I poured? Then I could line the inside with 1.5" of firebrick while using the concrete as a guide and for stability. Sorry, just trying to think of easier ways to get out of trouble.