Window channel balance, doesnt use your shoes

A quick learner from Seattle says:
September 11, 2014
I need help deciding whether my existing window channel balance is a series 351 or series 390. The channel balance is 22 inches long and 0.5 inch wide. The problem is the bottom shoe. It measures 1 1/16 inch and its shape does not seem to match either 15-001 or 15-002 shoe. I included picture of the top and bottom shoe with this post.

I see the word "C21" on the channel balance.
User submitted photos of a window balance.
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Paul from SWISCO responded:
September 11, 2014
The shape may be a little different, but I still think either our 15-001 or 15-002 will work. I'm just not sure which one. Between these two shoes, which is closer to your own measurements? Personally, I think it's closer to the 15-001, but you should measure yours just to be sure. Keep in mind your measurements may not be identical due to wear, so use your best judgement.
A quick learner from Seattle says:
September 28, 2014
Thanks for your reply. I purchased the 15-001 and it fits fine. The problem I have now is that after installing the new channel balances, the window slides up on its own. Could it be due to the spring being too strong? Any suggestions?
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Tom from SWISCO responded:
September 29, 2014
Yeah, it sounds like the spring strength might be mismatched. What is the weight of your sash and what option did you select when you purchased your balance?
A quick learner from Seattle says:
September 29, 2014
I bought the 2140. My window was right around 15 lbs.
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Tom from SWISCO responded:
September 29, 2014
Hmm... 2140 should be able to support that weight, though I admit that 15 pounds is right on the cusp.

You mentioned that the original stamp is C21. That may be something like a 21C stamp, which corresponds to our 2130 option. Weighing the sash itself is usually better than relying on the stamp, but in this case I think maybe going down to the original 2130 spring strength is your best bet. Also triple check your sash weight just to make sure its not a less than 15 pounds.
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