When I left my parents’ home, I moved into an apartment built in the 1920s. It had many of the original windows and even when they were closed, if the wind blew outside, my bedroom curtains moved. Until I learned to plug the leaks and keep the cold air out.
Because I was a renter, I couldn’t make permanent improvements like new windows. So each fall when the temperatures started dropping, I dug out packing material and old towels and used them to fill the space between the windows and the frames where the cold air was entering.
This cut back on the icy drafts, making my rooms warmer, requiring my furnace to work less to keep them that way and reducing my monthly natural-gas bill.
The house I bought has much newer and energy efficient windows but a couple of 1920s doors. When walking past one of them, I noticed a cool draft and realized it was coming from the original old-fashioned keyhole. Since I have a more modern lock on the door, I was able to plug up the old keyhole and keep the cold air out in winter, which helps me keep my heating costs from getting too high.