Our Aquatherm feeds our house with a HX in the forced air furnace. I just noticed after about 5 years of use that I don't remember the "high" fan ever kicking in with the boiler thermostat that is mounted above our propane thermostat. With the propane when it needs to use the high fan it works but not with the wood thermostat. Before I call an electrician friend of mine I was just curious if this is possible or is it my cheapo thermostat that I have for the wood? It works but I think the high fan would be better for pumping the heat from the basement to our 3rd and 4th floors of our house. To me I would rather have it wired to high all the time.