Vinyl windows inserts are replacement windows designed to fit into a home's pre-existing window frames. The advantage of this is that you don't have to remove the entire frame structure of the window to replace your windows. These windows are now made in various materials, including wood and fiberglass. Consumer Reports found that the Andersen 400 Series windows performed well.
Replacing windows with window inserts can improve energy efficiency and have a significant impact on how soundproof a home is, allowing for more privacy and peace and quiet. Measure various parts of the existing window frames before you order window inserts. If the current frame has the wrong measurements, it may not be a good candidate for a window insert.
To check if a frame is square, measure both diagonals. A perfectly square frame has no difference in the two measurements. Using a level, check both sides of the frame to ensure they're straight, since the replacement inserts need to fit against a straight surface. Once measurements are taken, order a replacement window that's about 1/4 inch smaller in both directions than the frame. If a window frame isn't square or has twist, contact the seller to ensure the window insert fits a frame with those measurements.