If your double hung window is not pulling up smoothly, one of the problems could be a deteriorating sash cord. Over time, the sash cords can suffer from wear and tear. Instead of replacing with another sash cord, you can replace it with something that would be more durable and long lasting. A window spring, also known as a spring-loaded counterbalance, is a better alternative than a sash cord because it is made of metal and not plastic. It operates like a tape measure, it actually even looks like one. This project is something a homeowner can do from one to two hours per window.
Remove the stop bead, which is the thin wood frame that covers the window sash. Score the paint along the stop bead using a utility knife to prevent the paint from chipping. Then, remove the screws and lift the stop bead gently.
Cut-off the sash cords located on the side jambs using a utility knife.
Remove the sash window by pulling it out gently, and then set it aside.
Unscrew the sash cord pulleys from each of the side jamb.
Check the weight of the sash window by using a weighing scale to determine if the retractable spring-loaded counterbalance can handle the weight. Each counterbalance should have a corresponding weight inscribed on the faceplate. The weight of the window sash should not exceed that weight. If it does, you can always exchange the spring-loaded counterbalance or window spring with a higher weight capacity.
Adjust the size of the old pulley holes on the side jambs to lengthen the opening to accommodate the spring-loaded counterbalance. Use a Forstner bit and a drilling guide made of wood shingle to keep the Forstner bit from wandering off, which can damage the side jamb.
Place the window spring or spring-loaded counterbalance into position and mark the outline of the faceplate on the side jamb where the old sash cord pulley used to be. Drill a recess or groove, a process known as mortising, on the side jambs using a Forstner bit to allow the faceplate of the window spring to sit flush into position. Screw the spring-loaded counter balance into position on each side jamb.
Remove the old cords from the window sash, and then screw in the metal hooks for the window spring. Apply paste wax along the side jambs to lubricate the wood for a smoother glide.
Pull out the retractable springs from the counterbalance and then connect it to the metal hooks on the window sash.
Set the window sash back into position and test by operating the window sash up and down. Reconnect the stop bead into place and seal the seams with caulk. Touch up with paint.
One person can do one window provided it is not too wide. You may need a helping hand if you need to replace the window spring on windows wider than 1.2 m (48 inches).
Keep spring-loaded counterbalance free from paint to prevent interference with free action of moving parts.