Even at around zero F they keep my house warm enough during the day, but the interior temp does drift down a bit when it’s colder at night. And it’s not a state of the art energy efficient house, either. Built in 1968.
Well I went around my apartment and discovered the outside brick mortar was dry and loose. The landlord had a fellow come out and refill all that and it stopped all the drafts.
Before he did that I bought the rolls of silver covered thermal bubble wrap and tapped it to the one wall in the winter. Worked great even though I didn’t like the look...better to be warm than pretty! LOL I think the whole roll was like $20 and I had plenty left over.