In the meantime, kf4vkp, a recent joiner of this journal, suggested boiling water on the stove top. "It adds humidity to the air that holds the warmth it also adds to the air," she said. And yep, I got a few more degrees of warmth in my kitchen doing that. (I could've pretended to be sweaty, too, with the extra humidity in the room, but I didn't. ...I have odd ideas sometimes.)
We've had worse heater-less cold spells in this building before, where I even started having problems drying my towels overnight, and like those times we toughed it out. But honestly, I toyed with the idea that, if the heater hadn't been fixed by tonight, driving the 30 miles to Dundee to stay the night in my parents' house.