Tom Shafer

Stuck window sash? Suspect busted balance

June 29, 2012

If your double- or single-hung window sash is hard to raise and lower, a broken window balance is usually the culprit. The balance system counterbalances the weight of the sash, making it easier to lift the heavy sash and to open and close the window. When the balance is busted, the window is hard to move. You can take out the broken balance and replace it, but you have to know what type to get.

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Which type of window balance do you have?

1. Weights and pulleys. The oldest window balances were weights and pulleys. The sash was attached to a rope or a chain that wrapped around the pulley in the jamb. Behind the jamb a lead weight countered the weight of the sash. Many of these balances are still in use today. They were dependable: the parts were large and heavy, and they lasted seemingly forever.

Rope pulley window balance

Rope/pulley weight balance

Although the rope/pulley-weight balance system is still made for some windows in old house rehab applications, three types of balances are used in newer homes: spiral, block and tackle, and constant force. Each of these balances is made to accommodate a specific sash weight and size. An insulated glass window (multiple panes) needs a heavier balance than a single-glazed window, and a large window requires a stronger balance than a small or short one.

2. Spiral. The spiral balance is a tube, either metal or plastic, with a metal helix (spiral) inside. Tension, which is achieved by turning the spiral a specified number times, holds the correct weight. The spiral balance, however, was phased out of residential use in the early 2000s, but is still in use for many commercial applications.

3. Block and tackle. The block and tackle mechanism is housed inside a square, three-sided tube. A string attached to the top of the jamb is the only part visible. These balances are very dependable and especially good in new buildings because they can still function properly after being exposed to construction dust.

4. Constant force. Most vinyl replacement windows use a constant force balance. This is simply a coiled piece of spring steel attached to the window frame and the sash by means of a bracket, called a "shoe," and a metal pin that holds the shoe to the window sash. This type of balance is not recommended for use in a new construction environment because it requires lubrication, which, in turn, attracts dust. Drywall dust is particularly hostile to a constant force balance and can hamper its operation.

If you have a jamb liner…

Many newer wood windows have a vinyl or aluminum jamb liner system that compresses when pushed, allowing the sash to tilt in for cleaning. These balances have a spring attached to a shoe/pin assembly (see photo below). The shoe can become brittle over time and break. In this case the entire jamb liner must be replaced.

Window sash balance with jamb liner

Jamb liner

If double- or single-hung sashes are too heavy to open, check to see if one of these balances may be at fault. With a little effort you can replace it, and your window can work "as good as new" again.

About the Author

Tom Shafer has decades of experience in window sales, marketing and product development. He's worked closely with window design engineers in testing, design, and building code interpretation. Past employers include United Windows and Doors and Norandex, MI Windows. He currently works at a home improvement retailer.

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