Is this a home built or store bought. Either way, I'd check everything is built to work for a start. There's a nice excel calculator in this post to quickly check.
http://www.smokingmeatforums.com/t/246198/rf-calculator
Used the calculator from this site. Have spoken with Paul Shirley about the calculators...while he didn't come right out and say it he made mention of using an online calculator.....from what I know he is not a member here so he must be using Feldons. The guy that helped me from the other site suggested that when I build,my next one that I use Feldons...I ran my numbers for the next one on both Daves calculator and Feldons,
if I remember right Feldons called for more air intake...hmm....
Ink, evening.... I'm sorry you posted that... You are wrong.... dead wrong....
Smoker Calculator reasoning
The concept for the changes is below.... Alien and his associates, did an amazing job putting the original calculator together...
100% of my numbers are based on his original numbers... small changes were made for the improvements due to design changes in smokers.....
The original measurements were taken from SFB smokers with tuning plates I do believe.... The advent of the RF smoker did not make any changes to the calculator... Now the exhaust has to travel twice as far as before, and the original FB/CC opening restricted the air flow from the FB, causing the FB to over heat... Some would get up to 450 deg and higher while the CC wouldn't get over 250.... And then there is the increased friction from the steel.... When using natural draft, any restriction/friction is very detrimental to the flow....
So, on a whim, the FB/CC opening was enlarged, the area under the RF plate was increased and the area at the end of the RF plate was increased... all by 50%.... That solved ALL the problems.... fuel consumption was reduced.... folks were happy....
I personally experienced members improvements and fuel usage by the letters/PMs they wrote me on their improvements...... One additional modification was suggested.... members here, tested a second air inlet to the FB.... directly across from the FB/CC opening... That was a significant improvement of some/most smokers.... If the FB was too hot, it could be cooled by opening the upper air inlet.... Also, the fire had a separate air inlet to adjust it's heat output.... It should be installed at or below the wood fire grate....
All of this has been tested and proven by members building smoker on this forum.... The only place you will find using these numbers... or it used to be... I'm sure many builders are now using these ideas for their builds.... this process has been going for at least 2 years....
Volume in cubic inches X 0.001 = FB air inlets in square inches... 57,750 cu. in FB needs 57.8 sq. in FB air inlets..
Link to BBQ Pit Calculator
Feldon's uses the FB for it's calculations... Dave's uses the CC for it's calculations...
Shirley Fabrications has had some problems, over the years, with some of their smokers not flowing air and smoke too well..... It was documented on here...