Selecting the proper spiral balance for non-tilt window

Question

I just received and installed the S500-25 balance springs I ordered a week ago, all went well and windows work fine!

Need to replace springs on 3 more windows of different size and cannot remove sash to weigh it. The previous window glass area is 31" x 27", aluminum frame, with impact rated, single pane glass and weighed 27#. These are 43" x 26" glass area, aluminum frame, impact rated, single pane glass as well. Tube is 29" x 5/8". Need to select the proper rating unit.

Also need to see if you can provide top sash guide as pictured below.

Tom · Accepted Answer

I'm afraid knowing the size of the window alone isn't enough to calculate the weight. There are just too many variables in place. My advice to you is to disconnect the balances from the sash, place a scale on the window sill, and gently lower the sash on top of it. It won't be 100% accurate but it should do fine for your needs.

As for this guide, I'm afraid I don't recognize it. Would it be possible to see what it looks like while installed? That may give me a better idea as to what its function is and whether anything we sell will work.