How to Insulate Your Old Double Hung Windows
If you have old double hung windows and you have already installed storm windows, weatherized the sashes and do
ne everything that you can think of to make them energy efficient, there may be one more thing that you can do. Older windows have ropes attached to the sashes that run up the jambs and over pulleys and are attached to counterweights concealed in the walls.
The downside to storm windows is that they make your double hung windows much less effective in the summer time. By raising the lower sashes on the cooler side of the house and lowering the upper sashes on the warm side of the house, the warm air in the house will exit through the open upper sashes and draw cooler air in through the open lower sashes.
You can remove the counterweights for the upper sashes and insulate the concealed spaces in the walls.
First, secure the upper sash in place by driving a screw diagonally up through the bottom of the sash and into the jamb. You may not need 
to do this since many old sashes have already been painted in place.
Next, carefully remove the casing around the window. Run a utility knife around the perimeter between the casing and the wall in order to cut any paint or caulk that might be connecting the casing to the wall. Insert putty knives in between the casing and the wall and between the casing and the window jamb in order to begin to remove the casing. Continue this process with a pry bar, being careful not to damage the wall. This will expose the counterweight pockets next to the window.
After removing the casing, cut the cords for the counterweights for the upper sash and remove the counterweights. A great way to remove the nails from the casing without causing any damage is to clamp on to the nail on the back side of the casing with a vice grips. Pry the nail out a little. Straighten the nail and re-clamp the vice grips tight to the wood. Repeat this until the nail comes all of the way out of the back. This process will not mar the finish on the good side of the casing.
There are a couple of ways to insulate the counterweight spaces.
- Measure the width and height of the pocket. Cut rigid polyisocyanurate insulation to fit snugly into the pocket. Polyiso has one of the highest R-values available. Install two layers of ¾” insulation and push tight to the outside of the pocket.
- Get some PVC that has an inside diameter at least ½” larger than the diameter of the counter weight. Cut it to length – 1” less than the distance from the bottom of the pocket to the pulley. Insert the counterweight into the pipe. Secure the pipe to the window jamb. Stuff batt insulation into the remaining space in the pocket.
Replace the casing. Drill pilot holes for the finish nails to help prevent splitting the wood. Set the nails and fill the divots with wood putty. Lightly sand smooth, and finish to match the rest of the trim.
Tools: Drill, drill bits, screwdriver bit, putty knives, pry-bar, hammer, scissors, vice grips, utility knife, tape measure, finish nails, sandpaper and nail set.
Materials: 2” screws, wood putty, and rigid insulation or batt insulation & PVC pipe.
Dan Bossenbroek
February 2, 2010
Tags: Energy Conservation, Insulation, Windows Posted in: Energy Conservation, Insulation, Weatherize
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