Ironically I'm installing double hung, 6 over 6 vinyl replacement windows, made by Harvey Industries in woburn, ma. I purchased them through Portland Glass. These come with a life time warranty, 20 yr. to the next owner in case I sell the house. I'm 51 yrs. old and the windows will out live me. These are one of the best replacement windows made and they are suspect if not installed properly. I happen to be installing them. If the company, store, or salesperson has an independent contractor that is paid by the window, install them, chances are you will have integrity issues if they are installed with haste. Like all that is FOR SALE, you get what you pay for. Windows must be installed plumb, level, and, square, properly insulated, ( no expanding foam ). The trim on the exterior must cover the majority of the vinyl in order to protect them from the sun, the vinyl is weakest at the edges. If they were not measured properly and the window is too small this needs to be adressed. If the window is too big, the opening needs to be enlarged, a vinyl window that just fits in the opening is a bad thing, unless the house is made of vinyl there needs to be aprox. 1/4'' all around for proper installation. houses move and breath and different materials act differently. I will gladly post some pic's, wife has the honey do list going, I was lucky to sneak this in.