Odd, our geothermal heat pump puts waste heat in the water tank. Our is electric and only runs on days we have the windows open. The heat pump generally keeps the water temps at 131*f.Yup - got insulated and got the geo-thermal heat pump thing going, got new windows, got new sliders, and guess what, I'm broke!This place is so tight, that we don't eat chili without a window open.
The gas wh is the last big ticket thing to do. Weird, it isn't expensive to run over all, but it's the CO2, one last gasp and we'll turn off the gas at the meter, which also eliminates an earthquake hazard.