Heating update: Yesterday's low was really 34°F, and this morning's was 33. The forced air didn't start coming on until the wee hours; by 7am it was running a few minutes at a time at 15 to 20 minute intervals. That's considerably less energy used than the night before.
And it wasn't that bad, sleeping at 55. To help get people out of bed, though, I've turned it back up to 65. It's supposed to be below 40 again tonight (maybe I'll turn the heat off altogether).