[cercis]

It could have been their memory, but thinking back, I think I do remember them showing the thermometer and the drop.

They don't go into why the temp dropped. Just that those rooms were a certain temp and then they were 3 degrees cooler. If the thermostat was in the room with the fire, then the heater wouldnt' have kicked on and that could just be a function of bad insulation.

I figure it's only 3 degrees and it took a while to happen. So, if you want to have a roaring fire and you plan to be in that room for several hours, it could save heating bills, especially if you heat with central heat and turn it off while you're in the room with the fire.