Window balance assembly

I see you were looking at our S390-30. Is this what you have? If so, can you confirm the weight of the sashes these balances support? I think it might be 42 pounds. Refer to the chart on the S390-30 store page. As you can see, there are two possible options that could work for a 42 pound sash: the 2970, which can carry a sash weight of 39 through 42 pounds, and the 2975, which can carry a sash weight of 42 through 45 pounds. I highly recommend getting an exact sash weight just to see if it leans more one way over the other.

I don't believe the S390-30 has a double spring, but the 2975 can carry a sash weight of 42 through 45 pounds. That perfectly covers your sash weight of 43 pounds.