First off all sorry if the below info is difficult to read, didn't know how to transfer it the correct way!!! Anyway I just picked up a 500 gallon propane tank with the dimensions of 119 inch long and 37 inches wide and plan on transforming it into the best rf smoker in my neck of the woods. This is my first ever build and want to do it right, so I have been checking out all the info on here. I uploaded my number on the fire box calculator and that info is listed below, not sure if I understand everything correctly so I figured I would just tell everyone what I want to do and maybe get some feed back. I hope to build a 24 x 24 x 37 inch fire box and have my rf plate sit about 13.5 inches off the bottom of the tank. This would have about a 2.5 inch drop in heights from the fire box to the other end of the tank for grease disposal. Question 1 I don't know if the plate should be going up hill or down hill from the fire box or if it even matters considering it would only be 2.5 inches difference in heights from one end to the next. Question 2 looking at my numbers I think Im ok for the open space from the fire box to the smoke chamber but I don't know if Im looking at it right? Question 3 Looking again at my numbers I think Im ok for the space from the smoke chamber to the cooking area but again not sure if I am looking at the right number, don't know all the terminology. Smoker Ratio Calculations For Square or Rectangular Firebox NOTE: Rule of thumb, firebox volume should be 1/3 the size of the cooking section Cooker chamber size Enter your tank size below. The green cell will show the volume you will need your firebox to be. Diameter Length Tank volume in gallons Height Width Length 37.00 119.00 42628.38 or 500.00 38500.00 or 0.00 cubic in. cubic in. cubic in. Fire box size (square or rectangular) Enter the dimensions that you would like for your firebox. If the green cells match your firebox is 1/3 the size of your cooking chamber. Disregard if you want a firebox laeger or smaller than 1/3. Height Width Length The rest of the calculator will work for whatever size you choose. 24.00 37.00 24.00 21312.00 cubic in. Exhaust chimney volume needed Size of pipe for chimney Length of chimney needed in inches 1065.60 Dia 6.00 37.71 cubic in. Enter the size pipe you want to use to see how long it will need to be. Firebox air inlet opening Air inlet opening area needed Enter the opening size you want to use to see how many you will need. 63.94 Sq. in. Square or rectangular Area Number of openings needed to match area listed above. 13.50 by 37.00 = 499.50 0.13 Sq.in. Note: number above should be 1 or more. Circular Number of openings needed to match area listed above. = 0.00 #DIV/0! Sq. in. Note: number above should be 1 or more. Fire box to cook chamber opening Firebox to cook chamber opening area needed Enter the opening size you want to use to see how many you will need. 170.50 Sq. in. Square or rectangular Area Number of openings needed to match area listed above. 11.00 by 37.00 = 407.00 0.42 Sq. in. Note: number above should be 1 or more. Circular Number of openings needed to match area listed above. = 0.00 #DIV/0! Sq. in. Note: number above should be 1 or more. NOTE:On a reverse flow smoker, the opening on the side opposite the firebox should be no smaller than the opening from the firebox to the cooking section.