RF smoker build, firebox size and location

dcrook84 · Post by **dcrook84** » July 28th, 2015, 12:48 pm

I'm attempting to build a reverse flow smoker. I have most of the materials needed. Just working on getting the design figured out. The cook chamber tank is a 115 gallon propane tank. Outside measurement is approx 30"x44" I need to figure out how big of a hole "height from bottom of tank"i need to cut for the firebox. And how big the fire box needs to be. Any other input will be appreciated. Hoping to get started on it this weekend. Thanks

mp4 · Post by **mp4** » July 28th, 2015, 1:06 pm

My barrel is 30" wide and I made my baffle plate 29" wide so I cut the mouth of my tank out to match that. If your firebox is 29" wide you can make it 18" long and 18" tall and your firebox will be at 106% of recommended (which from reading here is the sweet spot for firebox sizing. You can look at viewtopic.php?f=11&t=4558 to see how mine worked out.

The calculator is http://www.smokerbuilder.com/pitcalc/ It took me a little bit to figure out the calculator, but once I started plugging in numbers it all started to make sense.

I would suggest verifying the volume of your cylinder just to make sure you're starting with the right numbers.

forty_creek · Post by **forty_creek** » July 28th, 2015, 3:05 pm

Ditto MP4! Plus consider buying plans from the site. They are very reasonable IMO

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dcrook84 · Post by **dcrook84** » July 28th, 2015, 3:11 pm

Thanks, but not wanting to use someone else's plans. I have my materials and just would like some insight on the size of firebox and how far down it should sit. I have my own ideas on the inside setup and everything else.

dcrook84 · Post by **dcrook84** » July 28th, 2015, 3:53 pm

And mp4, that's a sweet setup

Post by **Pete Mazz** » July 28th, 2015, 4:49 pm

You can use this calc to figure out your throat cut-out.

http://planetcalc.com/4581/

Or if you prefer a trapezoidal throat shape:

http://planetcalc.com/4628/

You'll need a ~76" throat.

dcrook84 · Post by **dcrook84** » July 28th, 2015, 5:22 pm

Ok thanks KS so according to that calculator and a 76" throat. Says the cut out is 4.9" tall and 22" across. So using that, how.do I determine size of the firebox. I'm assuming it would be 22" wide, but how deep/tall ?

Thanks again

forty_creek · Post by **forty_creek** » July 28th, 2015, 10:34 pm

I first used the Feldon Pit Calculator before I found this site. To me it was more user friendly starting out for myself. Then I started using the site calculator. I checked my measurements by both. They were dead on.
Your FB height on the CC is determined by your throat height. Bottom of the throat at the bottom of CC.
The pit calculators help you determine your FB dimensions.
With your 30x44 CC. I'm getting roughly 20Tx30Wx20L for your FB which puts you on the high end of the sweet spot of 105-115% recommended.

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Post by **Pete Mazz** » July 29th, 2015, 5:35 am

I used the 29w x 18 x 18 that yielded 106% but those sizes can be anything that yields the desired cubic inches, as long as it's wide enough to cover the opening into the tank.

Post by **Rodcrafter** » July 29th, 2015, 10:06 am

I like to make my FB taller than wider, it seems to allow the fire room to do it's thing.

jm2cw

forty_creek · Post by **forty_creek** » July 29th, 2015, 2:25 pm

RC always has some good wisdom for his 2cw!

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dcrook84 · Post by **dcrook84** » July 29th, 2015, 4:47 pm

This sites calculator and the feldon one are giving me different numbers on the throat height and width. One says 22" wide throat, the other says 15". That's quite a bit of difference for whatever reason.

Post by **Pete Mazz** » July 29th, 2015, 5:39 pm

Feldon's uses a half circle. Mine uses the full diameter of the tank to minimize the height of the throat cut-out. Doesn't matter what shape you use as long as the area is the same.

forty_creek · Post by **forty_creek** » July 29th, 2015, 9:03 pm

Pete has some great tools/calculators.

Someone on here gave me this link when I started:
http://www.handymath.com/cgi-bin/arc18.cgi?submit=Entry

dcrook84 · Post by **dcrook84** » July 30th, 2015, 9:21 am

I think I have the firebox figured out as far as size goes. I cut out the plate last night. Still not sure on how big the opening should be. I'm going to have the firebox at the lowest point of the cook chamber rather than putting in a false floor. Thanks for the info so far

forty_creek · Post by **forty_creek** » July 30th, 2015, 10:31 pm

I'm just trying to pay it forward!

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Post by **Rodcrafter** » July 31st, 2015, 2:44 pm

I guess I should have said

to the crew! first

Pete is giving you some good info on the size of the opening. I also would recommend making the top of the FB be the same as the top of the opening. Some folks make that cut lower than the top of the FB causing turbulence in the air flow leaving the FB.

jm2cw

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