I actually live on the same latitude as Ontario so -40F/C is not unusual. Add in windchill, and it gets even more common, given my windy location.

Yeah, I understand I'm probably an outlier at 66F. I was using the numbers more to point out how little a house temperature will drop with good windows and insulation.

What year was your house built? Do you have a whole-house humidifier?

My house was built in the late 1980s. It has decent insulation but not amazing. It still needs a lot of heating when temperatures plunge below -15C. I do not have a whole-house humidifier. I had one with my previous furnace but it had issues with mold in the filter and clogging of the condensate pump.