I mounted mine under the deck in aft end of port sail locker. Ran 3.5 inch vent behind galley and under seat of dinette with outlet under dinette seating next to head. I took 2.5 inch off of this to the head and then onto forward cabin. Instructions said to run largest vent to furthest end and to T smaller lines off of it. I choose to run the largest vent into the main cabin where I wanted most of the heat. We get lots of heat in the main cabin and head and a lesser amount into the forward cabin. The heated head in early mornings of spring and fall is a real plus.