# Reverse Flow smokers

Discussion in 'Reverse Flow' started by doug kiser, Dec 23, 2014.

1. ### doug kiserFire Starter

To DaveOmak,Think I found the site. My pipe is 26" dia by 50 by 3/8 for cc.fb is22" dia.by 24" both 3/8 wall. Flat end caps.What will the football cut out be. That will determine hieght for rf plate.Also dia. And length of exhaust pipe. Thanks,Do

Last edited: Dec 23, 2014

3. ### daveomakSmoking GuruOTBS MemberSMF Premier Member

Here you go...... Dave

Calculations for a standard design, reverse flow smoker..

Volume of the Cook Chamber.... Use the Inside Diameter of the tank...

Diameter X Diameter X 0.7854 X Length = Volume in cubic inches / 231 = Volume in gallons 25.25x25.25x.7854x50=25037 cu. in.

Volume in cubic inches X 0.004 = FB/CC opening in square inches...100
Volume in cubic inches X 0.004 = Area under the RF plate in square inches....100
Volume in cubic inches X 0.004 = Area required at the end of the RF plate in square inches....100

The above areas are necessary for great air/heat/smoke flow.... using less may cause an overheated FB.... Narrow / Long CC may require an increase in those numbers due to increased surface area friction to volume... Wide/Fat Short CC may use smaller numbers due to reduced surface area friction to volume...

Volume in cubic inches X 0.001 = FB air inlets in square inches... 25037x.001= 25
Recommended upper and lower air inlets... Upper air inlet directly across from the FB/CC opening to facilitate moving heat from the FB to the CC, and insuring good air flow through the CC.. The lower air inlet should be situated at or below the fuel grate.... The two air inlets can share the designated square inches of opening....

Volume in cubic inches X 0.017 = Exhaust Stack Volume in cubic inches, above the CC.... (ESV)25037x.017= 425

Exhaust Calculation..

ESV in cubic inches_____425_______________ ... = Stack Length in inches (36" +/-) = 34" stack up to 40" is fine
0.7854 X 4" Stack Diameter X 4" Stack Diameter

Adjust the diameter of the stack, until the proper length is achieved... be sure to measure the actual internal diameter of the pipe used..
this is for round stacks only..

4. ### daveomakSmoking GuruOTBS MemberSMF Premier Member

OK..... now for the football shaped opening......

Segment height has to be figured so the SEGMENT AREA is 1/2 of the FB/CC opening...

4" figures a SEGMENT AREA of 50.975 sq. in. double that and we've go 102.... close enough....

So with the height of the football 8"..... we have 2 halves... 8" inside measure...

5. ### doug kiserFire Starter

Thanks DaveOmak, I guess I was pretty close on my layout. Gonna burn some plate and wire. I'll send pics as the build goes on.

6. ### daveomakSmoking GuruOTBS MemberSMF Premier Member

Holey [email protected] I forgot the width of the RF plate.....

Sooooo, back to the circle calculator..... Set the radius at 12.625" and the segment height at 8"...... Then Chord AB calculates 23.5".... That should be the distance across the smoker at the top of the football..... If the RF plate stops 5" from the end of the smoker, 5 X 23.5 = 118".... perfect for the end of the RF plate for good air flow... Remember, the air has to take a 180 degree turn down there...

Sooooooooo, now that your smoker calculations woke me up, because I had a brain lapse earlier, I think I will go say good morning to my chickens..... (I should probably add that tricky part, about the football shaped opening, in the calculation)

7. ### doug kiserFire Starter

That's what rocked my world, THE FOOTBALL!!!!!! Thanks again!

8. ### doug kiserFire Starter

Yes Dave ,l build Towboats,The football had me baffled. If liked to think I know the angle of the dangle!

Dave

10. ### doug kiserFire Starter

Dave,you told me I need 25 sq. In. of vents in my fb. www.kck.com/BBQ_air_damper has 5,6,&7" round dampers . The dampers have 2 triangle shaped openings.Don't know how to figure sq. in. On triangles. Could you help me out. Appreciated!!

11. ### daveomakSmoking GuruOTBS MemberSMF Premier Member

Last edited: Jan 10, 2015
12. ### doug kiserFire Starter

DaveOmak,so 2 4" pie vents .One below the fire grate and one across from the CC will be 24" . Adequate for draft?

13. ### daveomakSmoking GuruOTBS MemberSMF Premier Member

No...... You will need 3 below the fire grate and one across from the FB/CC opening...

14. ### doug kiserFire Starter

DaveOmak,I need some suggestions for intake air vents. Fb is 22" dia.x 24". Feldons calc says I need 25 sq.in.

15. ### doug kiserFire Starter

DaveOmak,Smokingunny, Here's the start of my rf.

17. ### doug kiserFire Starter

DaveOmak,Ribwizzard. Any suggestions on how to keep the door cutout from springing open. .375 wall gas pipe

18. ### smokejumperSmoking Fanatic

Whether or not the door springs depends on the amount of stress in the pipe.

How you cut it makes no difference.

Best way to deal with it is to always expect it to spring, and have a plan to straighten the door when it does.

On those occasions where the stress in the pipe is low and it does not spring, consider yourself lucky and have a beer in celebration.

On those occasions where the stress in the pipe is high and it springs greatly, straighten it per the plan and have a beer in celebration.

19. ### doug kiserFire Starter

Well Smoke, I know the stress is high cause I cut out 6 x14 for channel iron vent in fb and that little piece went bong

20. ### doug kiserFire Starter

Smoke, You suggest a press break in small increments?