Need a stronger spring for the S350 balance

A home owner says:
On my previous order I purchased 3 S350-30 Balances that were for my stamped "2920" balances~ I Installed a pair on 1 window, but when I open the window all the way up, it slides down 6 inches.
Is it possible I can purchase for another window a pair of Balances with a "stronger spring"
Profile picture of Donna
Donna from SWISCO responded:
Hi Joe,
Please remove the window sash and place it on a scale.
You need the weight of the window sash in pounds to determine the proper stamp option.

2910 will carry a window sash weight range of 7 through 12 pounds
2920 will carry a window sash weight range of 12 through 16 pounds
2930 will carry a window sash weight range of 16 through 23 pounds
2940 will carry a window sash weight range of 23 through 28 pounds

This information is based on 2 balances per sash. Balances are designed assuming friction in the jamb weather-strip will carry a portion of the sash weight. Suggested sash weights are approximate.

IF your window sash weighs 29 lbs or heavier let us know, you will need a custom balance.
Reply to Thread
Use this form to ask a follow-up question or to share your experience regarding this subject.
(your email address will be kept private and is only used to inform you when a response has been made)
Current wait time is 4-7 business days
We promise that one of our experts will personally get back to you as soon as they are able. Thank you very much for your patience and understanding. If your inquiry is time-sensitive, please feel free to reach us at 856-317-6263 or at