Covered over my window air conditioner.
I have a piece of 2" thick styrofoam I put in the bay window in my living room at night or really dark/snowy days when there is no significant sunlight, and almost finished the annual task of converting my lawn tractor into a snow thrower.
If you recall I got sick last winter and pretty much changed my life. It lead to a finding of a poor heart not to exclude the pneumonia I was having that got to this point. Well, to make a long story short I hope to improve the home to better weather the winter.
I've already got a replacement 500gal. propane tank(great deal) and now installing more insulation. The ad-hoc insulation is being replaced with R-25 rated insulation. In some areas, rolled over the better older insulation. New windows were already put in 3yrs. ago but now they can really work better as i plan to add curtains that better insulate or block-out the in/out of heat transfer. I already have a good furnace, but the ducting needs to be replaced(funds?) when I can but not now. Also, I have a wood pile that mucks any past piles of yrs. ago. I hope also to replace the wood burner fireplace with a more efficient model, but since the house is so small all those fancy burners actually would roast me out so I look for a model that puts out btus at smaller levels(I know). Oh yeah, I've darned my socks and long johns to be 100%. -----Willy brrrrr!