Every Peter Kohler window and door has a unique serial number.

Windows: The serial number is located on the operating part of the window. It is a 6 digit code followed by a 3 digit code. Depending on the style of windows, the serial number will be located in a various locations.  For casements or awnings, open the window to 90 degrees and the serial number is is located on the inside of the frame (lock side) and can be seen when the window is open.  For slider windows, the serial number is located on the bottom of the frame or on the side of the sash (operating part) of the window. To locate the serial number, unlock the sash (operating part) and lift it at least 3” (75 mm). The serial number may be located on the frame and can only be seen when the sash is lifted. If it is not on the bottom of the frame, it will be located on the side of the sash. To access the side of the sash, make sure the sash is open 3” (75 mm) and then depress both tilt latches (located on the top of the sash) and tilt in the sash. The serial number will be on the side of the sash.

Doors: Open the door to access the long narrow inside of the door (stile). KOHLER is stamped on the wood part of the stile and the serial number is located on the hinge side of the frame, which can be seen once the door is opened.