This needs to be the number on the window you are having an issue with. The original serial number can be found in several areas on our windows. If it's a window that tilts in to clean the outside, you can find the sash label by tilting in the bottom sash and finding the white label with black bar code on the side. We would need the first number to the left above the barcode. Example; 123567-02. Newer orders will have a W in front of the number. Serial numbers can also be found on the screen label. .If you need assistance finding the number, please call 1-877-9WINDOW.