window spring

Sounds like you need a new balance spring. They haven't made this kind of spring in many decades, so we can't supply you with an exact match, but I think you can use our 9/16" diameter Series 500 spiral as a replacement option, along with a 17-012 bracket. Just make sure you have enough room to install the 9/16" tube and you should be okay.

To determine size, you want to measure the height of the visible glass and add 3". So if the visible glass is 20" high, you want a 23" long balance. This is for the bottom sash. If you're repairing the top sash (assuming it even uses a balance) then you only add 1" instead.

To determine weight calibration, you'll have to weigh your sash on a scale. We have a weight char ton each Series 500 store page that tells you precisely how much weight that particular length carries.

Please feel free to reach out if you had any other questions.