"You draw to the curtain
And one thing's for certain
You're cozy in your little room"
-- Elton John
Plaster and lath doesn't make good insulation. I live in an 84 year old house that's undergone numerous transformations - conversion to and from a duplex, moved staircases, and some interesting examples of period construction ("I can't construct a damn thing. Period!"). Just about everything has been remodeled or redone except for the exterior walls and windows. (Slated for replacement when the owners return.)
I've gas baseboard heating, which ever-so-conveniently lines the outer walls, so in a typical Maryland winter, I've a 2500 square foot cold sink. Set the thermostat at the recommended 68F? The heating system can't keep up, and the gas bills top $300 a month. I've set it at 58F, and my gas bills still approach $150 a month. I do have a couple space heaters, but the ones that really pump out the heat aren't safe to leave unattended, and the saftey heaters don't generate enough to heat a room. That can make for some pretty chilly nights.
So I've taken to sleeping in my computer room. I've usually two computers running full-time, but sometimes as many as five, with the appropriate complement of monitors, switches, and other electronic gizmos. I've got enough green LEDs lit to rival any nightlight, enough fans whirring to rival any white-noise machine, and the room is consistently several degrees warmer that the rest of the house. (As an aside, I lost a couple of degrees when I switched my main monitor from a CRT to an LCD.) The electricity cost of running my lab? About $38.
Open Source development as an alternate heat source.