no good having air bricks/grills around the house anyway as they have to have at least 5mm spaces and no insect screens/mesh or any closable device.
Clear as mud as the man said,nightmare usually trying to work out existing vents.Either get 100cm2 core vent or get a new heating system which will save you money..........552 is 65% efficient as against new combi,s which must be above 90%
tam
July 2008