Here’s a simple way to get more heat out of your old cast-iron radiators without spending one cent more on your gas or oil bill: Make a heat reflector to put behind them. Tape heavy-duty aluminum foil to cardboard with the shiny side of the foil facing out. The radiant heat waves will bounce off the foil into the room instead of being absorbed by the wall behind the radiator. If your radiators have covers, it also helps to attach a piece of foil under the cover’s top.