First of all, thanks to all of you who post here. I've been reading this board for over a year and have learned so much. Here's my situation: We have a gas fireplace (probably 10-20 years old, with glass doors and blower) in our main living area. The room heats up nicely with it on. Our furnace is also natural gas (about 45 years old). Do you think it's cheaper to run the gas fireplace to heat the main living area rather than using the furnace to heat the whole house? I normally keep the thermostat at 64 during the day, but am thinking I could set it lower and use the fireplace when we are feeling cold. Our house is well-insulated and the programmable thermostat is located near enough to the fireplace that it is affected by the heat produced there. Does anyone have experience using their gas fireplace as a main source of heat?