Too big

[MedicMike]

Is it possible to have a Firebox too big. For the size smoker I am wanting to build a 20x20x20 is rated to be 110.52%. Would it be too big of a Firebox to make it 24x24x24? The formula, if I remember correct, shows that size (24x24x24) being around 197%.

Thanks,
Michael

[dacolson]

For sure. Why would you want to go that big? 115% to 120% is about as much over as you should go. That big and you’ll have a hard time controlling temps. Small fire in a big open pit. If you want a 24” FB, consider making it insulated with the interior at 20”. You would have 2” gap that you could fill w rock wool. Or leave empty for partial insulation.

[MedicMike]

It's not that I am wanting to go that big, just more curious how it would effect the smoker. Just more of curiosity I guess.

[dacolson]

Airflow is what all the calculations in the sizing calculators are geared toward optimizing. It's all about keeping temp as even as possible. Make your FB bigger and you have to make your throat, stack, vents bigger. Too big and you waste heat warming the FB, the stack may need to be bigger to draw hard enough to pull smoke/air from the FB into the CC. Then the vents and throat need to be expanded to accommodate a larger draw. Small changes on large volumes equal larger heat fluctuations. I think i've seen a few times that 106 to 112% is the sweet spot on FB volume. I'm sure other guys can share some specific examples but this is the design thought process.

[Dirtytires]

Just keep it less than 110%.....