Low Cost Heating
If you just want to heat a small area or room, you can use a space heater. There are all kinds of newer, safer, and cheaper-to-use space heaters available today. Always turn them off when you leave the room to prevent fire hazards, and never place close to flammable items, like curtains. Keeping a space heater on a metal "lunch" tray is a great added safety precaution - and never keep a space heater where pets or small children can reach or knock it over!
Window Air Conditioners That Can't Be Removed?
To prevent cold air from coming into your home and raising your heating bill, cover them with a large plastic bag sealed tightly with duct tape. There are also products desgined specifically for this need available for sale at places like home improvement stores and big box retailers, if you prefer the more polished look.
Windows Drafty?
Some windows, especially older windows, may be drafty. One easy way to tell if your windows have a draft is to light a candle, then blow it out and quickly hold the candle in front of the windows and along the edges. If the smoke moves, it's because drafts are coming in! You can add caulk or weather stripping around the edges to seal them up tight and prevent cold air from invading your home by windows. You can also sew fabric pieces together - or use old tube socks, doubling them so that one is inside the other for extra sturdiness - and fill with rice, sand (or kitty litter works great!), and seal shut with tape or sew the end if you're handy with a needle and thread.