I recently had a heating contractor over to give estimates on a new forced air gas furnace. He wanted to upgrade me to a higher end model that has a DC blower motor, rather than the usual AC blower. He said that because it is DC, it will use way less electricity, I think he said 1/8th or 1/10th of what a comparable AC blower would use. So you could therefore leave it running continuously, circulating air in the house, without driving electricity bills way up.
Somehow I have trouble believing this.