I told DH I would not buy another house with out a window in every bathroom with a tub or shower. The house we have now just has the vent fans. If they aren't running for 4 hours after a bath/shower there will be mold growing in the shower and even behind the walls. If you have steam in an enclosed room it will not go away, but seep into the walls, floors and grout. I noticed black specs in the bath that my niece used while staying here and after all said and done we had to replace the bath walls. There was mold behind the walls growing out the molding edges to the outside. She did not keep the vent fan running enough time to remove all the humidity from the shower and kept the bath door shut when she left the room. The contractor and insurance adjuster said vent fans have to be run several hours to remove the humidity, no just while taking a bath or shower.