Installing exterior storm windows is a cost-effective, easy way to make your home more energy-efficient.

Step 1: Calculate the proper storm window size by measuring the exterior height and width of the existing window. Measure the height in three spots, once in each corner and once down the middle of the window. Use the smallest of these three measurements to determine the height of the storm window. Repeat the process for the width of the window.

Step 2: Clean the existing window glass, as well as the exterior trim around the window.

Step 3: Once you have your storm windows, identify the top and exterior side by determining which direction the window and screen operate. Some manufacturers install a sill expander on the top of the window for shipping purposes. If this is the case, remove the expander and install it on the bottom of the window.

Step 4: If the storm window does not have pre-drilled screw holes for installation, drill 1/8-inch diameter holes, spaced 12 inches apart along the top and sides of the storm window flange. Check the fit of the storm window before drilling holes to ensure the screws will hit the trim or blind stop of the existing window.

Step 5: Set the storm window into place. Use shims and a level to ensure it is square and plumb within the window frame.

Step 6: Once the storm window is plumb, screw it into place with aluminum or stainless steel sheet-metal screws. Do not over-tighten the screws.

Step 7: Adjust the sill expander so it lies even along the bottom of the sill and screw it into place. Make sure the placement of the expander allows for proper water drainage.

Step 8: Fill in the gaps along the top and sides of the storm window with a smooth bead of premium quality latex or butyl caulk. If possible, caulk around both the interior and exterior of the storm window. Do not apply caulk along the bottom edge, as this will impede water drainage.

Step 9: Test the operation of the storm window and screen. Pack up your tools, wipe off the glass and shut the window on another job well done.