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"
Joe
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.
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