I am curious about this as well. I have a six inch vortex that blows my air through a carbon filter. My night time temps are super low and I just bought a space heater. Obviously having the room flushed of its air all the time is a bit counter productive to trying to heat the damn thing! I am considering turning the fan off for 10 mins every half hour so the heat will be used more effeciently. Or would it be better to do 20 mins off-->40 mins on type thing?