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Venting a reverse flow smoker

post #1 of 13
Thread Starter 

Hello - I am ready to install the vent portion of the cook chamber and have a couple of questions.

I was thinking of using a 90 degree duct that they use in home construction that goes from a 8" round to a 4 x 12 rectangular opening - like for a floor register. Any opinions using this vs using a 8" round 90 degree fitting?

 

Also I was thinking of placing the vent just above the cooking grate vs the top corner of the smoker above the fire box. Any opinion on which is better?

 

thanks Jeff

post #2 of 13
Smokers are sensitive to friction in their design.... When designing intakes, FB/CC openings, RF plates and the area under them, opening at the end of the RF plate and exhaust stack and design..... the fewer restrictions the better...
Redesigning a perfectly good smoker can cause poor design performance......
A straight through 8" exhaust, with no elbows, or the installation of an exhaust plenum, is the least restrictive exhaust.... other designs may work OK, but the possibility of screwing up a good design is always there.......
post #3 of 13

Hey Jeff, what Dave said is great advice, I have never been a fan of elbows . If you want or need more cooking area I would go with a plenum. Also you are talking 8" stack how big is your smoker ?

 

Gary S

post #4 of 13
Thread Starter 

I understand the concepts of restrictions. Do you not want to keep the smoke and heat in the cooking chamber for a certain period of time and still maintain the 'draw' of the heat and smoke from the fire box? That is the purpose of the original question. I am adhearing by Fledons Calculator on sizing. Where is the best location of the cooking chamber vent opening? I haved seen several variations.

 

thanks

Jeff

post #5 of 13
Exhaust........ Some say near the top of the CC...... others near the food grate......

Feldon's has a calculation problem, In My Opinion, when it comes to Reverse Flow smokers....

Smokers, IMO, need continuous flow of air and smoke to provide good smoke flavor.... If you have smoke, it will follow the air flow... Creating stagnant air conditions will adversely affect the flavor... IMO....
post #6 of 13
I am 100% in agreement with Dave on this. Especially in a reverse flow, the key to even temperatures and nice tasting THIN BLUE smoke is good flow. Good flow also helps the food cook, like a convection oven, by reducing cold zones or boundary layers near the meat.
post #7 of 13
Thread Starter 

Thanks for the replies to all.

 

What problems do you see with the Feldon calculations on the reverse flow? I respect everyones opinion and since this is my first reverse flow build would like to consider all options.

 

I used a 275 gal fuel oil tank for the reverse flow cooking chamber and have the first set of removable shelves 3.5" above the reverse flow plate and the second set of shelves 10" above the first. There is 10" above the second set of shelves to the top of the door opening of the tank. This leaves alot of 'dead air space' above the door opening--- what is your opinion of welding in a 'ceiling' to lower the smoke and heat closer to the cooking surface?

 

What is the advantages / disadvantages of the cooking chamber chimney placement on top versus near the food grate?

 

According to the Feldon calculator I have made the firebox that is 114% of the recommended size. I have two adjustable air intakes - one on the bottom (below the grate) and one on the side - both sized according to the calculator. My thinking was to use the bottom air intake for starting the fire and getting the temperature up, then close the bottom vent and open the side air intake for drawing the air across the fire into the cook chamber.

 

The firebox opening to the area under the reverse flow plate is 116% of the recommended size. The opening at the end of the of the reverse plate into the cook chamber is the same as the firebox opening.

post #8 of 13
Quote:
Originally Posted by jcweis1 View Post

Thanks for the replies to all.

What problems do you see with the Feldon calculations on the reverse flow? I respect everyones opinion and since this is my first reverse flow build would like to consider all options.

I used a 275 gal fuel oil tank for the reverse flow cooking chamber and have the first set of removable shelves 3.5" above the reverse flow plate and the second set of shelves 10" above the first. There is 10" above the second set of shelves to the top of the door opening of the tank. This leaves alot of 'dead air space' above the door opening--- what is your opinion of welding in a 'ceiling' to lower the smoke and heat closer to the cooking surface?

Cut down the tank or get a smaller Cook Chamber.... or use it as is....

What is the advantages / disadvantages of the cooking chamber chimney placement on top versus near the food grate?

Read up on what folks think....

According to the Feldon calculator I have made the firebox that is 114% of the recommended size. I have two adjustable air intakes - one on the bottom (below the grate) and one on the side - both sized according to the calculator. My thinking was to use the bottom air intake for starting the fire and getting the temperature up, then close the bottom vent and open the side air intake for drawing the air across the fire into the cook chamber.

Re calculate Feldon's and make the FB 100%..... use those numbers for the exhaust... Add 50% for the FB/CC opening, area under and at the end of the RF plate..... Then make the FB as big as you want...
Intakes for the FB.... Lower controls how much heat the fire puts out... adjust as necessary.... Upper air inlet moves heat throughout the CC for even heating, and adjusting the heat as necessary...


The firebox opening to the area under the reverse flow plate is 116% of the recommended size. The opening at the end of the of the reverse plate into the cook chamber is the same as the firebox opening.

Make them 150% of recommended.... Chimney height is above the CC... extend it into the CC as far as you want....
post #9 of 13
Quote:
Originally Posted by jcweis1 View Post
 

I understand the concepts of restrictions. Do you not want to keep the smoke and heat in the cooking chamber for a certain period of time and still maintain the 'draw' of the heat and smoke from the fire box? That is the purpose of the original question. I am adhearing by Fledons Calculator on sizing. Where is the best location of the cooking chamber vent opening? I haved seen several variations.

 

thanks

Jeff

 

 

Quote:
Originally Posted by DaveOmak View Post

Exhaust........ Some say near the top of the CC...... others near the food grate......

Feldon's has a calculation problem, In My Opinion, when it comes to Reverse Flow smokers....

Smokers, IMO, need continuous flow of air and smoke to provide good smoke flavor.... If you have smoke, it will follow the air flow... Creating stagnant air conditions will adversely affect the flavor... IMO....

 

 

 

OR

 

post #10 of 13
Thread Starter 

I like the concept of the exhaust in the pictures.... can you explain how you did the tube inside the pipe vent?

 

thanks

Jeff

post #11 of 13

Jeff its a 22 oz can IIRC with both ends removed of course, it fits perfectly inside a 4" black pipe.

Some guys will use flashing and roll it up, place inside and let it unravel, this will hold it in place and is adjustable.

post #12 of 13
Thread Starter 

Good ideas... How do you use it in your smoking process?

 

thanks

Jeff

post #13 of 13

To be quite honest I don't, it really makes no difference on my pit, I believe this is because my cooking chamber Diameter is only 20"

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