I'm in the process of selecting an air conditioner to self install on my Hunter 310. I've concluded that the 12,000BTU is the right size even though the factory offered the 10,000BTU as an option. The question now is Mermaid(boatUS) or Marine Air Cabinmate(West Marine). They both have their pros and cons. The Mermaid is available with electric heat which can be used while out of water, but... it does not offer variable speed fan. They say that it may freeze the coils if speed is lowered. The Marine Air(also named Domestic Environmental) has the variable speed fan but only offers the Reverse Cycle heat which works only if boat is in the water and the water temp is above 40 degrees F. Also, how do you pick the right size pump? I know it based on the water head but do you measure from the intake to overboard discharge or just to the unit. Two different techs gave me opposing answers. The pump and the unit will be below the water line, so is head important when below the water line? Does the duct have to be insulated since it runs in interior space? The Hunter drawing shows the unit in the cabinet under the sink with three duct coming out of the unit(one 5" and two 3")but have trouble finding a distribution box with this configuration and hate to start with two and split it again later. One 3" is for the forward berth, one for the quarter berth, and the 5" for the main cabin. I spend a whole day on my knees pulling wires from the electrical box on one side of the boat to the other side so I'm not ready to give up on this project. Any opinions or advice will be appreciated. S/V Calaloo