I know that is what most guys figure, but these numbers are false. Might as well throw out an hour each day and pretend you didn't boil on a wood fired evaporator, just like the time didn't exist by the time you get it warmed up to full potential and then shut it down, you have an hour that you are not evaporating off very much. Oil fired, probably about 10 minutes. I have a meter and I take the total gallon boiled down for entire day divided by total time spent boiling from time I light match until I am done with evaporator and that is true gph.
There have been hours I have probably boiled off aprox 75 gph with my evpaorator, but I am not going to say it boils off 75 gph because it won't do that for an entire day.