I have just fitted the large Aluminium unit into a UPVC half glazed door. Had a few issues, one being that did not realize it had a guillotine cover to lock it, this made it awkward to fit in anything other than a flush door. In order to fit it to my door had to use some frame packing to over come the depth difference above where my door bottom panel is recessed. Perhaps web site could make this clear. I have to say I am not a fan of the nylon through bolts with aluminium friction nuts. I hope they do not fail over time. On the plus side it seems to be fairly draft proof once fitted which was a deciding factor in replacing the last flap made by a different firm.