Coil series 152

It does look like you have the 15-177 shoe in there, which uses our Series 152 Coil Balances--I do advise you double-check the shoe's identity to be safe. Now, I am afraid dimensions don't tell us the window's weight as there is too much variation. What you should do is obtain the exact weight of the window sash, perhaps on a bathroom scale. Give me that exact weight, and I can tell you the spring weights you'll need.

Yes, that's indeed the 15-177 Shoe. If the bottom window sash weighs exactly 10.2 pounds, you can use one of the S152-5 5 pound springs on both sides of the sash. This equals 10 pounds of support overall, close enough to the exact 10.2 pound weight. Let me know if you have further questions.