I am fitting a cooker hood with 125mm ducting over a 1.5m length to an outside brick wall. I hired a core drill (at great expense for one hole I felt) that cuts a standard hole of 127mm. The problem is that the 125mm alu ducting will not go through the hole because, although it's said to be 125mm the actual outside dia of the coil is about 135mm. Is there a 'tradesman's secret' way of getting the duct coil through the hole, or, is it possible that I could adapt and fit a smaller coil, i.e. 100mm or would this interfere with the function of the hood?
Any advice would be appreciated.