Kathy, is it mold or mildew on the walls? Chances are that you can't tell without having it tested. The chances are too that if it really is mold and it is heavy on the walls that the spores are already in the air and in your heat ducts. I agree with bc but if your father's problems are breathing or allergy related, having it tested before you do anything else. Your county health people will know how to sample and where to have the samples sent at low cost.