One of the best ways to save energy in your home this winter is by caulking the gaps and cracks around windows and doors. This prevents the transfer of air between heated and unheated spaces, so your furnace doesn’t have to work as hard.
The problem is that caulk alone is only effective in narrow cracks, which are about a quarter-inch-wide or smaller, because it shrinks as it dries. To give the caulk some help in larger gaps, try using a foam backer rod first.
These flexible foam tubes are available at building supply stores in several diameters. You simply push them into the gap with a putty knife or painter’s tool until they’re just below the surface, then you can apply the caulk on top of them.