Coil balance continues to break do I need heavier size coil?

Let's get some information together...

When you installed the S190-740 coil springs, did the numbers match the ones from the old coil springs? When installed, did the window operate okay, or was there difficulty in closing the sash? We can try to sort this out once we're clued in a little more.

Thanks for getting back to us. We usually recommend sticking with the old stamps when it comes to these balances, but I actually think your old stamps weren't right to begin with. Two 7 pound springs are made for a 14 pound sash, which is too strong for your 11 pound sash. That may be why they broke. Our S190-640 may be a better option; these are 6 pounds each, so using one on each side will support a 12 pound sash. It's still a little strong but should prove to work much better.