[Daox]

If I might poke around your business a bit, I think the best way to turn it on/off would be to setup a small controller for it. Perhaps we should start a new thread since its not on topic for this thread, but I'll outline the idea. Basically, you want two temperature sensors. One goes in a colder area of the house, and one in a known warm area. When the cold temperature sensor is X degrees cooler than the warm sensor, you turn the fan on to equalize the heat. Once it is within a degree or so, you turn it back off. Basically a thermal differential controller for your furnace blower. Something like this wouldn't be hard to setup or even buy for a relatively cheap amount, and would pay for itself very quickly.