Recommendations for Installing spiral balances

Whenever we deal with old wood windows like this, our spiral balance of choice is the Series 500. We also use the 17-012 bracket (sold separately). The balance has a 9/16" diameter tube and its various spring strength options are usually rated for heavier sashes, though I highly recommend getting an exact weight before you pick any of them. You don't want to guess that.

As for length, I can't really say for sure if a 40" balance will work. We don't really base length on total sash size; instead, what you want to do is measure the height of the visible glass and then add 3" for the bottom sash and 1" for the top sash. For example, if the height of the visible glass for both sashes is 20", then you want a 23" long balance for the bottom and 21" for the top. Does that make sense?

Let me know what you get with that formula and I'll see what sizes are available. I will also need that precise sash weight just to be safe.

Thanks for this information! Your assessment is spot on, I agree on all points. Now, these two sizes were not available in our catalog to begin with, but we just added them for this morning. See our S500-43 and S500-41. I recommend the Red Tip color option in both cases, based on your sash weight.

Please note however that we currently only have 2 of the 43" balances in stock at this time. If you order any more than that, there will be a lead time of several weeks.

Otherwise, let me know if you had an other questions!