I've had some double glazing fitted and something just didnt look right about the top vents. The square lead looked very small. I've now compared them to next door and all the other houses in all surrounding roads and the windows are approx 20-22". 22" is the original spec on the last few wooden frames around. The ones fitted in my house are 18". I explained to the guy that I wanted the house to look original, so Im not sure why he had them manufactured to this size. Basically my house looks odd from all the rest now. Its a 1930's semi. Do I have the right to withold the balance?