How should the question about the “percent of heating potential utilized” be answered when 60% of this heat is used to power the digester and 40% is used to heat domestic hot water and some rooms?

You should enter 40%. The 60% that is used to power the digester does not count toward the heating potential utilized. When we think about ‘heat potential’ and ‘energy potential’ used we should always think of the digester and its processes as something that can fit in an envelope. Anything we add to the envelope (electricity for example) needs to be included as an input and anything that leaves the digester unit can be included as an output. Therefore, if electricity (or heat) is created by the digester but goes back to running the digester, it should still be considered ‘in the envelope’ and therefore not included as an output. For the question at hand, only the heat used to warm the water for use in the farm can be counted as heat potential used.