Crappy foundations without insulation, roofs and walls with poor insulation, front door directly opening into the house instead of a separate space, almost all of them freestanding (especially rural ones) and relatively large for the number of people living there. Heating in Canada is an interesting problem. -40 Celsius on the other side of a 4" barrier is nothing to take lightly. One elderly couple that I'm aware of had begun to dismantle their house on the inside and they were burning it all up bit-by-bit to stay warm, the two of them sitting around a shitty old pot bellied stove that moved the bulk of the heat generated straight out the chimney. Stuff like that breaks your heart.
My post was a little too quick… one of my good friends was an energy efficiency expert and when I asked him for advice on replacing a boiler in our “new to me” home and he goes “don’t!”.
We did an audit and spent about $4000 on efficiency retrofit - it cut our heating bill about 25%. That was 10 years ago, and we’ll probably start looking at replacement boilers when incentives ramp up for new tech.
A few years later I got another report and fixed a few more things. House cold spots mostly went away, bills went down, less outside noise, and have the same windows and furnace.