Our house is wood framed, but built to beyond R2000 specifications and passive solar heated. We do not have a furnace,
but do sometimes use a wood stove.
The building includes concrete floors and exposed aggregate structural and feature walls
that provide a heat sink. There is a large solarium on the southern side, to make the most of the solar gain.
The design is quite open so that the heat can circulate, with a fan to blow the warm air down in the winter, and high clerestory
windows, that create a thermal siphon, so that the hot air can escape in the summer. The house is well insulated, and was airtight at the time of construction.
We have a heat exchanger to keep fresh air circulating, without losing any heat. Originally, we did not need the wood stove,
but with the years (ours and the house's) it is sometimes welcome now.