"Tony Hwang" wrote in message
Hi,
Or house has poor insulation, or it could be as simple as dirty air fiter
if it is force air furnace. Here, it's been -30C with windchill of -40C
or so last two weeks. Our furnace has been running more than usual but
keeping indoor temp. at constant 21C.

I've only ever seen it get close to that once in 27 years here in CT but the
house was still comfy. Tomorrow my new boiler is being installed and
tomorrow night will be a good test. Prediction is 5F (-15C) overnight.