Room temperature | Dementia Support Forum
If I were to get up a few hours later, I wouldn't like the room to be stone cold, so perhaps the heating could be left on in his room, but at a lower temperature, say 60 degrees? That takes the chill off, and he might not feel any difference when he gets back to bed.
I understand that Down duvets are much better at adjusting to body temperature. They cost more, but may be worth it. You can also get electric blankets that can be used all night (and even electric duvets - which might be safer if he is likely to wet the bed), so that when he gets up in the night he goes back to a warm bed.
But if he's happy with sweating and it doesn't make him uncomfortable, I'd just accept it. Perhaps check with the medics if overheating poses a physical problem.
Hope you find a solution.
Margaret