Re: Too weak for Double-Hung Windows?
On my original windows on my home a little silicone spray made a big difference.
One problem with insulated glass is that it's very, very heavy. Spring counterbalances aren't as good as the old rope and pulley systm in terms of frictio nand drag. plus all the effort ot make the wndow totally air tight, ends up creating a lot of drag as well.
I know our repalcement windows on our last house were fairly heavy and hard to open, while the 86 y/o windows that are in good condition that we now have can practically be opened with one finger. You have to be carefuly that they don't take off on you.
The biggest concern would be if the frames are warped. Marvins are good quality so that shouldn't be an issue like a cheaper vinyl window. But of the house has settled or the hwindow header was inadequate, the sashes could bind if the window is no longer square.
I agree with contacting Marvin. They may have some suggestiong.
1925 Two-Story Stucco Beaux Arts Neoclassical