The most common thermostat recommendation for sleeping adults is 60-67F:
https://www.theatlantic.com/health/archive/2019/12/sleep-cold/604111/
https://health.clevelandclinic.org/what-is-the-ideal-sleeping-temperature-for-my-bedroom/
https://www.sleep.org/articles/temperature-for-sleep/
Open window. Heat off. Upper forties outside. You calculate the temp. 
Fireplace gets flipped on just before we crawl out of the bed. Heater kicks in at 6 am.
Window has to be open, no matter what the outside temperature is. When the heat kicks on about 6 am it wakes me up. I can’t sleep with the window closed.
Well, I find 60-67F too cold, personally. We are not at that temp ever at home—hotter.
When we are in HI, we turn off the AC and sleep with the ceiling fan going and window open. 
60-64 year round. Low humidity.
In winter, we keep our house at 68 during the day and 55 at night.
We like the cool sleeping temps…and we have warm blankets and PJs.
Used to use heavy AC to keep it cool in our room in summer. Then one night our AC conked out. I thought I’d never be able to sleep but DH brought up an old box fan from our basement. Changed my life. With the air blowing at me I could slept easily with a much higher temperature. Saved a bundle in electricity costs. And the white noise made me sleep better too.
I keep temp around 68-70 F DĂĽring the day and around 65 F at night.
I used to need flannel sheets at night during winter and a warm duvet.
But now that I’m in menopause, I just use cotton bedding and need to keep my arms uncovered or I get too hot.
It was too hot the other night when H forgot to turn down the heat. I tossed and turned until 3am when I got up. Checked the thermostat and it was 68!
@maya54, I love sleeping with the fan on instead of AC.
I need cold too. H is generally freezing on his side and I’m too warm. We keep it around 63 at night for sleeping. I’d go much cooler if he’d let me.
Same as someone upthread - we keep the heat at 68 during the day and while people are at home, drops to 64 while people are at work/school, and 55 at night. Have done this my entire married life. The programmable thermostats have certainly made our lives much easier! We used to wake up to a COLD bathroom/house and the first person up would run downstairs and turn up the heat. Now it is all controlled. I also have the same experience as others who have forgotten to reset the heat (holiday, party) and sleep fitfully or wake up in the middle of the night because the heat was on hold at 68.
This is all my children have ever known. I have one that sleeps hot and in addition to the 55 nightly temp, will also sleep with the ceiling fan on high all night. It is an adjustment when they live in very close quarters like a dorm or apartment with someone who was raised in a different environment. I think it should be part of the roommate survey! My DD17 had her own room in a suite while rooming on campus and it was a good thing! Her southern roommates were used to sleeping/living in very, very warm rooms.
Just confirmed that our thermostat thinks our house is warmer than it is. It turns down to what it thinks is 65 at night, but is actually 63. We have a thin but superwarm silk duvet from China.
We are in a drafty old house but I still keep the heat register shut in my bedroom so it is even cooler.
Wow, lots of penguins on CC! Brrr!
72 all day in the winter, and 76 in the summer. Perfect.
Definitely prefer sleeping when it’s cooler. 60-61 is ideal for me which I can achieve in the winter; not so much in the summer. DH tolerates the cooler conditions, but it’s not his preference.
I also prefer coolness to sleep. And probably 9 months of the year, the ceiling fan as well.
We have radiator heat so it can be a little less convenient to let the temp go up and down (night) too much. For sleeping it is important to me NOT to near the radiator which can really “radiate” heat out.
We keep the house about 67ish during the day. No can do an open window this time of year in Northern Ohio but anytime I can open the window I do it. This is a bone of contention between me and my H who as he has got older seems to want to close the bedroom like a box at night with no fan going or anything. I find myself sometimes just heading off to a spare bedroom where I can open the window or turn on the fan to my content! (I get claustrophobic otherwise!)
We have heat pumps so extreme drops in temperature setting are inefficient. In the winter, I keep the thermostat at 68 during the day as I’m in and out during the day. At night, it goes down to 65. Anything cooler than that would mean raising the temp in increments and since we get up early, it doesn’t make sense. If I get too hot I just kick one leg out from the comforter. I don’t get horrible heat flashes, but if I get too uncomfortable, I turn our ceiling fan on.
We just had to fully replace both of our heat pump units after the outside fans were crushed by a tree limb during a recent storm-insurance covered top of the line units. Heat pumps have greatly improved in the last 10-15 years - I actually feel warm in my house now whereas before there were days my hands would be freezing.
AC in the summer is set around 78 during the day and b/w 73-75 at night, plus ceiling fans.
Don’t open windows (allergies) but keep the temp low year round and run the ceiling fan so it’s cold in there. Heavy comforter feels good as does the heated floor in the bathroom!
During heating season I set it for 65 when we are home/awake and 58 at night and during the day while at work.
I’m impressed with @thumper - maybe I will try 55 instead of 58!