Horse manure to heat hot tub

[Bob]

Yes, without knowing more about specific details, I would say that your idea is quite feasible.

You should be able to burn biogas in a natural gas heater without modification, and in a propane burner, with only a simple modification (changing the orifice size).

Do you have an idea of the daily quantity of manure that your animals produce? (Or, more importantly maybe, the quantity that you would be willing to collect and transport to the digester on a daily basis...)