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Channel Balance Confirmation

A handy person from Trabuco Canyon says:
I have a single hung, non-tilt window with one of two channel balances that has broken. The broken channel balance has the marking "27DS B.S.I. BM 33". The matching channel balance (still functioning) has the marking "2740 EH B.S.I". It is a nominal 28" length channel with just over a half inch width. The window includes sash stops but does not include take out clips. Take out clips were not necessary to remove either the broken or the functioning channel balance. Please advise 1) if the S351-28 Option 2740 is suitable for both channel balances, and 2) whether a takeout clip will be necessary to install the new channel balances. Thanks.
A handy person from Trabuco Canyon says:
Just realized that the broken channel balance with the DS (double spring?) marking has two springs, one smaller diameter inside a larger diameter spring. The larger diameter spring appears to be about the same diameter as the 2740 marked balance. Not sure why the mismatch and whether two S351-28 Option 2740's are the right solution or not. Thanks in advance for the help.
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Tom from SWISCO responded:
Thank you for posting! I'm actually not sure if our S351-28 will work for you without seeing what the attachments on your balance look like. Unfortunately, that's not something I can determine based on just the stamp. You can send a few pictures for me to look at, to start.

I'm also not totally sure about the double spring. Does the other balance in the same window (marked 2740 EH B.S.I.) also have a double spring? Also, what is the weight of your sash? It may be possible that a regular balance would work for you.

As for the take out clip, it is necessary to install new balances. Then again, I would also say that its necessary to take the old ones out. How did you remove them without it? Check out the video below to see the proper method of replacing this type of channel balance.

A handy person from Trabuco Canyon says:
Attached are pictures of the two channel balances from the same window. As you are facing the window, the right hand balance is the one that broke. This balance has the DS marking and does indeed have two springs (one inside of the other). The balance from the left hand side of the window is marked 2740 and contains only one spring. Each balance has the same type shoe and top. Any reason why the balances would not be identical?

The sash weight is approximately 18 lbs.

None of the windows in the house have takeout clips. When the sash stops are removed, the sash can be lifted beyond the point where there is any tension on the balance, hence not needing a takeout clip.
User submitted photos of a window balance.
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Tom from SWISCO responded:
Great, thanks for the pictures. I'm not sure why one balance has a double spring, but a sash weight of 18 pounds isn't out of the ordinary.

Are you sure that 18 pounds accurate though? It's important to get a weight that's as exact as possible. The reason I ask is because two balances with a 2740 option can carry a window sash weight of 19 through 26 pounds, which would be too strong for your window. If your sash weight is definitely 18 pounds exactly, then I would go with the 2730 option instead. This can carry 13 through 19 pounds.

I would also double check the depth of your shoe. It looks a little bigger than the 15-002 that comes with our Series 351 balance. You might be looking at a Series 390 instead, which uses the 15-001 shoe. Check out the dimensions below to see which is closer.

I know it seems like splitting hairs, but it's important to be as precise as possible when determining the replacement balance you need.
Comparison of <a href=15-001 & 15-002' />
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