Metal industries DH vinyl new construction window 1994

You will definitely need stronger springs. In your case, you need to bump it up to two springs per side.

As for the exact weight, you want to use one 7 pound spring per side and one 8 pound spring per side; that would be our S190-740 and S190-840, respectively. Altogether that adds up to 30 pounds of support, which should be perfectly fine for your sash.

You will also need a new double spring clip and an extra bushing per side. That would be our 15-181 and 15-182.

I feel confident that these changes will work for you, but let me know if you had any questions or reservations.

I'm afraid that won't be possible. 30 pounds is a pretty significant increase in sash weight and the Series 190 doesn't have any strength option stronger than 9 pounds. That means that if you only use one spring per side, the most you can hope for is 18 pounds of total support, which is not even close to sufficient. In my estimation, you have no choice but to increase the number of springs used per side.

This is one of the consequences of changing the glass, unfortunately. To be perfectly honest, most situations like this leave the homeowner without any options at all; I very often see someone install insulated glass that makes the sash way heavier than any balance can support and they end up with an irreparably heavy window. It's a very common oversight on projects like this.

Each product code I suggested so far is a separate part. None of them are sold together, unfortunately, but they're fairly simple to assemble once you have them all in hand. The spring just screws to the shoe and the clip just screws to the window track. 

Note that you will have to drill an additional hole for the double spring clip but that's about the only handywork involved. You can take the old screw into a local hardware store to have them match up the appropriate size.