Chimney Size and Design

[lcripe]

This my first post at this Forum although I used it a lot during my oven building adventure. I want to thank you all for the plans, the great information and help that this forum gave me. I used the Pompeii Plans and built a 36" oven. I followed the plans carefully with the exception of the flue size. I live in the tropical highlands of Chiriqui, Panama and do not have easy access to many of things that you can easily buy at a HomeDepot. I cannot buy stove pipe here. I had some extra 5" Simpson Dura that I brought down in 2006 for another project so I decided to use the bird in hand. I only had enough for about 30 inches of chimney. I figured this would be too short. The rectangular flu opening from the entry is 2.5" x 22". I cast a concrete transition to the pipe. The oven works great but sends a lot of smoke out the entry especially with heavy firing. I positioned the stove on our patio so I can run the stove pipe up through the ceiling and out the roof. I have ordered 8 more feet of pipe and will try this extension as it will be the easiest fix. What do you think? Will this work? The worst case scenario is that it doesn't and I will have to rebuild the chimney section. You highly experienced guys, please take a look at the photos at this link and let me know what you think and recommend: Wood Fired Oven Chimney
Best, Lloyd

[BurntFingers]

I would guess that for sure additional rise on the chimney would increase its draw once it heats up. I had to add an additional length of chimney tile to my oven and the draft up the chimney increased beautifully. No more smoke in the face or out the opening. Up and out would do it. Good luck.
Bill

[lcripe]

Thanks for your reply. Do you think I can get by with the 5" pipe? Lloyd

[BurntFingers]

I believe that there is a formula for the door opening height ratio to the inside height of the dome to allow for the correct draw. I remember something around 60% of the height of the dome would allow for the best proportion. The diameter of the flue pipe is important too. I am not sure what would work best. My terra cotta chimney tile is 8"X8" and it is two lengths high, ending close to 5 feet above the top of the door. Once it gets warm (just from the kindling) it draws well in all types of weather. There are some photos at: Bill P.'s Page - My Wood Oven
Bill

[dmun]

First of all, I like your flue transition. That's a nice design.



A five inch flue pipe is marginal. FB recommends a six inch round flue unit for the 36 inch oven. A five inch circle has an area of 19.63 sq in, and a six inch 28.27 sq in. You can see that it's like one third bigger. That said, more length will absolutely help. It will get that smoke out of your patio area, too. Why not do a test with cheap galvanized stove pipe to see if it has the draw you want before you spring for the expensive duravent unit?

[lcripe]

Thanks for appreciating the work I put into the transition casting.

I already ordered the dura vent and it is on the way. Should be here in a couple of weeks and I can't stop the process now. I will give it a try and am sure the draw will improve, but whether it will completely solve the problem is unknown. Unfortunately there is no simple galvanized pipe here in Panama.

I did the same calculations on the area differences between 5" and 6" pipe ans saw that the difference in area is considerable. I took a risk with the 5" piece I had in hand. This is why I am concerned.

I grew up around wood burning stoves and know that well cured wood is essential. I have seen stoves with 5" and 4" pipes function very well, but they didn't have such large intake areas. If the experiment doesn't work, I will simply have to rebuild the flue.

[johnter]

I spent a week last spring in David, Boquete seemed like a nice place for an oven

[lcripe]

Yes, a wood-fired oven is perfect in Paradise! Checkout my weather web site: Boquete Weather Home to learn more about the weather and climate here.

[Eli Rogosa]

Does any have thoughts on placing the chimney on the BACK BOTTOM of the oven?
Wouldn't this vent the cooler air to maintain more heat in the oven??
Eli Rogosa

[brickie in oz]

The rule of thumb when building an open fireplace is, flue size should be 10% or more than opening size