I have had my backboiler replaced, a hole is left where the gas fire and boiler was taken out in the chimney breast. I am looking at bricking this over but leaving a vent or hole for continued ventilation as the chimney's remain uncovered. I would like to build a cupboard door over this, will this be enough ventilation? important point is that I have a hole in the floor already which I can only think was further ventilation for the old boiler.
