It has been unseasonably cold here and this is one of my favorites tips to quickly warm up.

put towels or something in front of all doors at the floor and in the windows where ever you feel a draft

vent your dryer inside and do your wash before going to bed and stick it in the dryer first thing in the morning

When it is really cold out lock or block off all exterior doors except for one and do whatever is needed at once so you don’t need to keep going in and out. I have noticed our inside temp drops when folks start going in and out a lot.