I'm going to put an air vent into each room of a flat which currently gets some black mould during the cold snap in winter. There is only one air vent at present and the flat has central heating, double glazing, a shower, a cooker and the tenant's laundry on the radiators, which all adds up to condensation and black mould in the winter. My logic says that the ideal position for the vents is at the top of the walls (hot air rises, or rather cold air displaces it) but the most suitable place would be behind the radiators as the tenants wont be able to block up the vents as easily there. Is there any reason why I shouldn't do this? Thanks.