renz
Member
I've used both the Marvin Tilt-Paks and the Pella replacement units, and I highly recommend the Pellas. The Marvin setup uses track/balances separate from the sash halves, so the squareness of your opening is a factor. Pella is a complete 'box' that is designed to be adjusted to fit unsquare openings. Remove the existing window stops and sash halves, install and caulk the 'box' into the opening, and reinstall the stops. Very slick. Just be sure to have the Pella rep measure for you -- they deduct a certain amount from the opening size to ensure a correct fit.
