Paul from SWISCO responded:
June 25, 2014
You are correct, I think it's best to use S190-440 for both windows. In regards to replacing both sides with a new balance system, we find that after a period of time the other springs start to break or the sash starts to move unevenly. We suggest replacing both sides so that you don't have to go through this process again in just a short period of time. You can put both new springs in one sash and move the old springs to the other window, or perhaps just keep them on hand as an emergency backup.
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