Diesel_John
I am impressed on your energy return from a pond, does the surface not freeze in the winter? Water is least dense at 4C and so the colder denser water goes to the bottom. I have to admit I don't fully understand how these things work but I thought 1 or 2C water and -5C air temps wouldn't be very good for pumping heat around. But what do I know? I'm just a neandertal wood burner
Neil,
I would love to see the specifics of how they are heating for $68 a winter, spread over 5 months, thats $13.60 a month, I don't think a forced air furnace fan for a large house can be run for that much. Plus how can they even see that on their electric bill? especially for a variable usage business.
Maybe if they went from an old crappy forced air system with the fan on all the time, to a new hydronic system with on demand circulator pumps, I might believe there bill only went up $68, but thats different than $68 outright.
Using Diesel_john's figures of 4 to 1 return on input, assuming electric heat costs $200/month(this is dreaming in my area, realistically $400-600 or more) for a house, that still gets us down to $50/month, which is a fantastic deal for sure.
Really, to compare systems we need to see cost per btu at specific temperatures. Even my woodstove becomes less efficient in cold temps as I'm drawing in air from somewhere to make up what's going out the chimney.
Ian