If the basement cannot be ventilated with the furnace fan running and their is no possible way of ventilating it,chances are good it has air quality issues. I would point this out to them and let them know that cleaning the carpet and leaving it in such an environment could cause even more indoor air quality problems than they already have. I would suggest to them that you can clean it and then install a dehumidifier and air movers with an ozone or such a machine for at least 48 hrs.DennyH said:Would you clean a basement with no windows wich means no air flow longer time to dry.He had a flood down there cause there is a big water stain.Possible mold.Should i clean!!! Or will i be responsible for any mold growth..