Is There a Calculation to Figure Required BTU's For a Pan?

[holey_bucket]

This is a hard topic to search for here on MT. BTU is too short of a search term, and Heat is too generic.

I am building a small 2x4 propane evaporator with a homemade syrup pan. Actually, it will only be a flat pan, and the whole thing will only be used for maybe two years.

My struggle is how to determine what size burner to get. The burners all have BTU/hrs charts, but I just don't know what to pick. The biggest would work, I'm sure, but the propane usage gets astronomical and I'd have to handle freeze up issues.

2x4 flat pan, continuous flow with preheaters

Thank you for any info you may have.

[maple flats]

A finishing pan in 2x4 size comes with a 160,000 BTU tube burner. A 16" x 24" canning unit comes with a 40,000 BTU, that is 1/3 the size of your 2x4. The canners will boil but not as violently as a finisher. My guess is about 150-160,000 BTU based on these comparisons..