I have the GMVM80K furnace and the comfortnet stat. According to the manual, if the room temp is 2 deg below setpoint it will run on high fire to catch up. If only one degree below, it will run on a lower fire unless it can't get caught up in a reasonable amount of time. So, in playing around with heating programs and set-backs, I have found that if I only bump up the program temp 1 degree at a time, then it never runs on high fire... so it runs a lot on a lower fire and brings my room temp up gradually. To me this seems more economical.. But is this the best way to run this furnace? Is there any harm in the fact that I expect it to not run on high fire unless it is very cold outside? thanks, Mike