Thank you for your question on the models L250 and L250L. The L250 is a ceiling mount ventilation fan. The L250L is an in-line ventilation fan. This means the L250 would be mounted right in your ceiling. The L250L would be mounted somewhere else in the home with duct work running to the room you needed it too. You would need to supply a grille or inlet for the room it is being used in. I hope this helps but if you have further questions, please contact Technical Support at 800-637-1453.