Advice needed for length of 400 series spiral balance.

A handy person from California says:
March 17, 2022

Hi! I really hope you can help me a bit. I'm needing to add some sash balances to these windows I want to retrofit which have nothing and no easy way. 

I can cut 1/2 or 9/16 dado in the side of the sash to fit your series 400 spiral balance. As you can see the window measures ~22" and the total available length above the sash is 19.75". I was guessing that a 21 inch balance would work best and I'll either cut a spot on the bottom for Bracket, #14 17-031 or on the side for Bracket #S 32 17-026. I could use the side bracket as I'll probably need to remove the sash completely each time I needed to replace the spiral balance anyway. 

Also the side mount might be less prone to rain water than the bottom mount..?? With S32 bracket I would probably drill another hole in the bracket and use two screws. The sash weighs 9 lbs so will try to buy red balance. Unfortunately it says 21" red 400 series is out of stock. It seems 22" would work and might even be better as I don't know the total length of the balance when extended. Anyway it seems an inch longer would be okay even if the window didn't go all the way up? 

Also I would install one balance on each side unless you think a single balance on one side would work ok?

Thank you for any information you can provide!

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Tom from SWISCO responded:
March 18, 2022

Hello! You're definitely on the right track. For length, the rule of thumb for wood windows is to measure the height of the visible glass and then add 3" if it's for the bottom sash and 1" if it's for the top sash. For example, if the visible glass is 15" high, then you want an 18" long balance (bottom sash) and 16" long balance (top sash).

I would also absolutely opt for the 17-031 bracket. The 17-026 may not install properly because of the groove in the side of the sash. The 17-031 just cradles it from underneath, which is a lot easier to repair and deal with.

Finally, you always want 2 balances for a single sash (1 on each side). The weight ranges you see are calibrated specifically under the assumption that two balances are holding that load. If you only use one balance for a sash then it won't work properly and will likely fail.
Bracket, #S 32
Bracket, #S 32
17-026
$0.92
Bracket, #14
Bracket, #14
17-031
$1.35
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