That is cool. How are you heating your home? Is the water running thru the core and the fan is blowing the heat?
Have you tried or thought about heat in your flooring? Passing the water in pipes under your floor? The heat then rises constantly.
What would be cool is to heat the water to a high temp, store it for the evening in a large container then cycle it through a radiator or floor type system in the evening.
I've been giving this a lot of thought because heat is my biggest bill as well. I'm trying to figure a way to cycle engine oil thru something similar to your water heater. I figure engine oil could store the heat for several hours into the night and would absorb heat quickly in the sun.
The main issue is night time for me. My house faces south, so on a sunny day my house is pretty warm even on a January day with low the heat set low. It's the evenings without sunshine that make my heat bill high.
