Firebox and RF plate questions

[radioguy]

I have some general questions about FB size and RF plate size / placement.  I have a "build" thread already started but need some advice before going forward. 

I would like to make my FB a bit taller to accommodate an ash pan at the bottom.  My FB grate will be placed at a point where it is 100- 110% of what the calculator recommends.  The total volume of the FB would be about 120% of what the calculator recommends (2-3 inches taller).  Do I use the original numbers (smaller FB) for the CC to FB opening, intake vents? or the larger numbers?   Some of the FB volume will be taken by grate, door seals etc.  Or am I over thinking this? 

I am a bit confused on RF plate dimensions and placement.   From what I have read that the RF plate opening to CC (opposite FB) should be 1.5 times the area of the CC to FB opening.  Is there a recommended area for RF plate as well?  I am planing on setting my FB into the CC by 1/3 of the FB length.  What about RF plate height?   Is there a recommended min/max RF plate dimension to cooking grate?  or does it just sit on top of FB top.  Doing this would place my cooking grate about 6" above the RF plate. 

Thanks in advance,

Tom aka RadioGuy

 

[daveomak]

Question 1  Firebox size, I want to make room below the grate for a slide out ash pan, do I include this additional space in FB calculation? 

Not necessary to include but a good idea....

Question 2   RF plate,  I am planning on putting FB under cook chamber by about 1/3 its length.  About the RF plate, should that be welded in?  Or can I just place it on some angled brackets?  I was thinking it may be better to have it removable for cleaning.  I would take it that I want this plate to be heavy, 1/4" or thicker.  I do have some stainless stock, but it is only .120" 

Setting the RF plate on angle brackets is fine...  I would use mild steel sheet and save the stainless for another project... 

Question 3  I haven't been able to find much detail on drains, any help would be appreciated.

With a removable RF plate, a drain in it is very tricky....  You could just go with a drain in the cook chamber....  I would go with a 1" dia. pipe nipple and a cap or a ball valve...

 I would like to make my FB a bit taller to accommodate an ash pan at the bottom.  My FB grate will be placed at a point where it is 100- 110% of what the calculator recommends.  The total volume of the FB would be about 120% of what the calculator recommends (2-3 inches taller).  Do I use the original numbers (smaller FB) for the CC to FB opening, intake vents? or the larger numbers?   Some of the FB volume will be taken by grate, door seals etc.  Or am I over thinking this? 

Either volume is OK.... I would use the larger volume.....

I am a bit confused on RF plate dimensions and placement.   From what I have read that the RF plate opening to CC (opposite FB) should be 1.5 times the area of the CC to FB opening.  Is there a recommended area for RF plate as well?  I am planing on setting my FB into the CC by 1/3 of the FB length.  What about RF plate height?   Is there a recommended min/max RF plate dimension to cooking grate?  or does it just sit on top of FB top.  Doing this would place my cooking grate about 6" above the RF plate. 

Does this make sense ????   I'm here to answer any questions you may have....   Dave

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• daveomak
• Mar 25, 2013

The numbers I used for the calculations....

http://feldoncentral.com/bbqcalcula...36.69&fi=5,3,0,15.55,1.04&fc=7.27,10.28,41.47

 

[ribwizzard]

RadioGuy,

Most of my fireboxes are way bigger than what the calculator reccomends, just for that reason. I want plenty of room under the firegrate for ash build up and plenty of height for the fire to "breath". 

It should not give you any problem, just make sure it seals up good and your vents are the right size and located where they should be.

 

[radioguy]

Dave and RW,

Thanks very much for the clarification.  Things are now clearer.  For whatever reason I was taking the 1.5 times RF plate area figure as the total RF plate surface area and not the cross-sectional or air flow (vertical) area.   I am going ahead with the larger FB and using those numbers for the calculator.   

Thanks ever so much,

Tom  aka RadioGuy

 

[daveomak]

RG, morning.....  All this calculation stuff can get confusing trying to put it all together....     It's not cast in stone but a very good guideline...

Dave

 

[navarre]

Thanks for the info. You are right, it is easy to overthink. Why are you radioguy? are you a ham radio operator?

 

[radioguy]

Yes don't over think it,  the calculators are a very good guideline but are not hard fast rules.  The circle math doesn't' lie.

This forum is a very good place to get answers.  Just post you questions / progress and you'll get great advice.  

I did CB radio when I was 10 years old, amateur radio operator since my teens, cellular radio tech for many, many years. 

God and radio have been quite good to me!

 

[daveomak]

Thanks for the info. You are right, it is easy to overthink. 

navarre, afternoon......  The folks at this forum have seen many many smokers built that don't work correctly...  A frustrated member trying to get his smoker to work is depressing to us....   We want our members to light it, throw the grub in, sit back and relax.....   A poorly built / designed smoker will drive you to letting the kenmore oven cook your food when a properly designed and built smoker is heaven....   You can't put too much thought into a build...  get it right on paper before you make the first cut or lay the first stone or brick.....  

Then you won't have to do this...

.....

 

[doodleq]

As Dave said, a drain with a reversible plate would be tricky. Mine is in a gutter with a slope in both directions towards it, but my plate is welded in. 1" like Dave said with a simple ball valve . Keeping a fair bit of distance will keep the seals from melting.

 

[navarre]

In looking at the firebox/warming box, I am thinking of building a firebox and not cut the end off the tank. If I build the firebox and tuck it under the tank and vent straight up, it should give me enough room to have a decent warming chamber without making it 5 feet tall. I want to build a charcoal holder that will hold at least a bag of charcoal, and have it slide out to fill it, start, etc. What gap should I have between the bottom of the FB and the charcoal holder? I was thinking about 3 inches or so. 

I have a stick of 3 inch exhaust pipe. Would that work for the chimney,or should I look for something larger?

 

[urbotrimmm]

Exhaust pipe:  Plug your numbers into the calculator and it will be specific on length of your 3" pipe.  It should calculate to let you know if 3" is big enough.  The guys are right, after a smoker is built is the wrong time to find a mistake.  And 6" from RF plate to cook area in my opinion is perfect because it allows for pans of water if you so desire to use.  My last comment is, weld your rf plate in solid.  I had a grease fire in my little brickman gas smoker a couple of weekends ago and it was a big fire for such a little smoker.  Allowing grease to drip down where it can ignite is anything but good.  If that happens you will have a fire.