Coil Balance

A home owner from Temperance MI says:

Need some advise. The current coil balance on my window has 2 springs each side (see picture). Using your calculation, window size = 20.75" x 33.5", double insulated, the window sash calculation comes out to 8lb per side. This means i can go with a single 8lb spring each side.Correct or should i upsize it?

The product code for the 8lb replacement is S140-8.
User submitted photos of a coil window balance.
Profile picture of Paul
Paul from SWISCO responded:
Thank you for posting! I agree, the Series 140 looks like a good match. As for the weight of the sash, your best bet would be to weigh it on a scale. Alternatively, you can check the coil springs themselves for any stamps.

I would not go for a stronger spring than what is required to lift the sash. You don't want them to be too strong.
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