We are thinking of making our home more energy efficient. We thought that replacing our single pane windows with aluminum frame with the double pane windows with vinyl framing. After receiving several bids of Milgard and Simonton window installers, we were shocked at the cost. I discovered your website and like the idea of window inserts. Will the inserts fit in the original aluminum frames, or will the frames need to be replaced. Our home was built in 1974.