32"x40" double hung parts

Thanks for posting, Doug. Looks like you have old Certainteed windows. With that in mind, I recommend the following parts: the 15-192 pivot shoe, the Series 170 and Series 171 coil springs, the 15-156 cover, 15-157 drum, and finally the 26-175 pivot bar. The video below will show you how all these parts work together.

In my experience, there isn't a reliable way to determine spring strength from window size alone. There are a lot of variables that would still effect the weight of the sash, like what kind of glass is uses and how many panes are in there, the material used in its construction, etc. The best method is to get the number printed on the old springs. If that's not possible, then I need to know the exact weight of the sash instead. You can determine that by placing it on a scale.