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# RF Design / Build question

All,

I am starting to draw out my new RF build that I am planning.  I have read a lot of useful stuff on this forum regarding the calculations for openings, CC size, FB size, etc.  Is there any advantage to cutting down on my CC size by insulating the walls and roof?

Thanks,

Fr. Deacon James

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Still no answer on my insulation question, so I am going to go with 1.5" hard insulation sandwiched between two 1/4" steel plates.  I am working on designing the CC first as that for me is the driving factor.  I would appreciate it if one of the master builders on this site could check my math and assumptions.

Based on the trailer that I have, I have a working area of 76" x 36" for my platform to build the CC on.  I will hang the FB off the rear edge of the trailer.  I plan on using a rectangular design rather than a cylinder.  Assuming that I want to have the CC at least 36" of exterior height, and I am losing 2" on sides and top, I come up with an overall volume of 72x34x34=83,232 Sq. Inches.

Using Dave Omak's calculator:

FB/CC Opening = 333 Sq. Inches = 9.8 inches tall by 34" wide

Area under RF plate = 333 Sq. Inches so RF plate has to be 9.8 inches off bottom

Area required at end of RF plate = same as above, but I read that it should be 1.5 larger so 14.7 inches from end wall (total RF plate = 57.3 inches

Minimum volume FB = 27,467 Cu. Inches = 36" outside width (35.5" inside) x 31" outside length (30.5" inside) x 26" outside height (25.5" inside) = 27,610 Cu. Inches

FB Air Inlets = 83.25 Sq. Inches

ESV = 1831 Cu. inches

Stack Length = (assuming dual 6" stacks equally spaced) = 1831 / 2x(.7854x5.875x5.875) = 2 stacks at 34" each

I just have the following questions:

1.  My trailer only has 24" clearance from the bottom of CC box to ground.  Can I raise the FB so the FB/CC aperture is below the top of the FB?  Otherwise I will have to shorten my FB height and lengthen the FB to account for volume.

2.  How much of a lip is standard for the RF plate when using it as a drip pan / water holder?

3.  Are there any preferences as to where to place the RF pan drain?  Middle or end near the smoke turn around?

4.  If I do go with the insulation, do you think I could get away with using a 1/8" steel plate for the exterior?

Any assistance will be greatly appreciated.

Thanks,

FrDcnJim

I put my drain on the side opposite of the FB with a 1" lip.
Quote:
Originally Posted by frdcnjim

..... Is there any advantage to cutting down on my CC size by insulating the walls and roof?

Yes, insulating the CC will reduce the amount of BTUs needed to maintain temps, reducing fuel usage.

Quote:
Originally Posted by frdcnjim

....Area required at end of RF plate = same as above, but I read that it should be 1.5 larger so 14.7 inches from end wall (total RF plate = 57.3 inches......

The area at the end of the RF plate should be at least as big as the FB/CC opening. It does not need to be 1.5 larger.

I just have the following questions:

1.  ... Can I raise the FB so the FB/CC aperture is below the top of the FB?

Yes you can, but it is not ideal and will cause your FB to get hotter than it needs to. If you go this route, use an angled plate to make the transition from top of FB to the RF plate, similar to the way many traditional offsets use to transition from the top of the FB down to the tuning plates.

2.  How much of a lip is standard for the RF plate when using it as a drip pan / water holder?

No standard really. I like 1.5"

3.  Are there any preferences as to where to place the RF pan drain?  Middle or end near the smoke turn around?

Personal preference; both have been used with great success.

4.  If I do go with the insulation, do you think I could get away with using a 1/8" steel plate for the exterior?

Absolutely. I am using 14ga outer skin on mine.

You may also want to reconsider the depth of your CC. At 34" it will be quite a reach to the back of the racks.

Check out my build for ideas and answers to some of your questions:

http://www.smokingmeatforums.com/t/142872/my-rf-vision

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