Oh, there's an 80% efficient forced air gas furnace in the crawl. I turned it on in early November, cranked it up to 68 for the afternoon/evenings, lower at night and during day. However by Christmas I had rediscovered my sweater/pullover collection and now the stat is set to 66F, and I feel just fine... most of the time...
What brand furnace? I forget, and I'm not about to go spelunking to find out again. Let's just say it's about 37 years old, and going strong. Yah, I have CO detector in bedroom, it never goes off.
About R45 in the attic (added about 15 years ago) helps keep the warm in (and the hot out in the summer). Have about R20 under most of the flooring, but ran out of it halfway through and don't think I'll be adding more any time soon. I did add extra insulation to the forced air ducting, including the return duct, which helped to quiet it down. And of course I sealed off as many drafts as I could. Major draft was from the kitchen cooktop hood - it had no damper whatsoever. Easy and cheap fix for that. You do what you can.
This was a fairly hot summer in the greater SF Bay Area, and it was quite a transition from short sleeves and shorts, having to button up the house with shades drawn during the days to keep the heat out, to all windows open and fans blasting (hopefully) cool night air through the house at night, to securing all doors and windows all the time and drawing the shades/curtains at night. I only had to run the portable A/C unit for about a week total. It's got a heating mode but it fills up its drain tray after about an hour in that mode, so I don't bother trying to use it to heat.
At least it's not snowing. Some rain would be nice, though.
All things considered, life is beautiful.