Balance Question

A home owner from WEST ORANGE NJ says:
Good day, While in the process of replacing the thermopane glass of my single hung windows, I find that the spring balances are not able to support the weight of the new, heavier sash (the replacement glass weighs considerably more than the original). The original hardware used the 540 S190 Coil Balance Springs (I previously purchased these from you, and they were an exact match), how do I determine what size Coil Balance Spring the replacements need be? thank you gary f
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Paul from SWISCO responded:
Can you tell me the weight of your sash? Can you also tell me how many springs are used on each side of the window? That will allow us to come up with a solution. Thanks!
A home owner from West orange ,NJ says:
The weight of the sash unit is 24lbs. There are 2 springs on each side
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Tom from SWISCO responded:
Thanks! That explains it. The S190-540 springs can only hold 5 pounds, individually. I would recommend our S190-640, which holds up 6 pounds individually. Four of these altogether should be able to hold up your 24 pound sash.
A quick learner from West orange, nj says:
Rather than replace all 4 springs on the window, can I accomplish the same thing by changing one one spring on ech side to the S190-740? I have more than 12 windows with this problem, and am simply looking to save some cash.

Thank you
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Paul from SWISCO responded:
Two S190-740 would only carry a 14 pound sash, and two S190-840 springs would only carry a 16 pound sash. I don't think going down to two springs on each side are going to work for a 24 pound sash. It is simply too heavy.
A quick learner from West orange,nj says:
Please let me clarify. I propose only changing two springs (one on each side) to the S190-740, while keeping in place one S190-540 on each side.
The sash would be supported by two S190-740 and two S190-540
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Paul from SWISCO responded:
Ah, I'm sorry I misunderstood. I think that can work, yes. As long as the combination of springs is symmetrical and as long as it can hold up the sash weight.
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