They often begin ~9:30, which is about an hour before I retire for the night. I don’t know why I begin to experience heat surges around that time, but they have been occurring fairly regularly recently and can last for hours.
It is difficult to know how to deal with them. Yes, I can and do open windows, as I did, even when outdoor temperatures dropped to -18C/-1F on two consecutive nights. (By the way, those are the only two nights that caused the furnace to kick in. We have the nighttime thermostat set to only activate at 15C/59F, and up until those nights, the indoor temperature had remained above 15, and therefore, the furnace had remained asleep.)
The heat waves are difficult for me to deal with, for the heat is internal and not reliant on the ambient temperature. But one tries regardless, so I open the windows and remain as uncovered as possible. But my reality is that I do have to stay lightly covered even in simmer, for air on my skin at night is an unpleasant sensation for me. This is partly because I have some sensitive cold spots on my shoulders and shins and partly because I am weird.
Anyway, the point is that when I open the windows to cool the house, my bodily stupidity is such that I still have to keep myself covered to some degree.
I did that last night and fell asleep in my chair just in my clothes and sans covers. even though the windows were a little bit open on a frigid night. When I moved to the bed an hour later, I pulled up the sheet but kicked aside the two blankets. A few hours later, I pulled up one blanket, and by morning, I had both of them over me, for the surges tend to subside as the night wears on. It's a very fine balance between warm and cool.
So far, I have just described heat surges, but night sweats can also be a problem, and it is not unusual for me to have to fumble about in the darkness to change my shirt in the middle of the night. This was happening so consistently, that, for the last week or so, I have made it a point to really cut back snacks and sugar intake. I have also abstained from evening munching. That seems to have helped the sweats: not entirely but largely. However, the heat surges remain.
Look up night sweats in men online, and you will find andropause as a probable cause. But really, I am 75, so my andro has surely been pausing for quite some time, and this problem is relatively recent — at least to the extent that I have been experiencing it recently. However, I don’t know what else it can be because it is, apparently, not as connected to diet as I had supposed.
It is different during the day. Yesterday afternoon, I decided to give myself the opportunity to nap. It didn't work, but the point is the house was at a warmer daytime temperature; the windows were shut; and, I was also more covered than I had been the night before. There were no waves or sweats; there was only a very pleasant warmth.
If you have made it here to the end, I congratulate you for your dedication. I really shouldn’t have inflicted my personal problem on you, but, partly at least, one hopes that writing will lead to clarity and, perhaps, a solution. Alas! It doesn't seem to have worked.