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Add an Air Conditioner to Your Boat - page 2

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Photos by Capt. Vincent Daniello

The boat’s existing air conditioner originally supplied power directly to a 250-gallon-per-hour seawater pump. We replaced that pump with one double the capacity (see L, photo at the bottom of this page), and routed seawater to the new air conditioner with continuous uphill pitch, and then downhill to the overboard discharge. We also installed a pump-relay box (F), which powers the pump when either air conditioner requires it.

Along with the 10-gauge three-conductor wire we pulled from the electrical panel to supply the air conditioner, we ran another 14-gauge three-conductor wire, which we connected (G) at the pump-relay box to power the pump. The three-conductor wire that led from the existing air conditioner electrical box (H) to the seawater pump was moved to the appropriate terminals (I) on the pump-relay box. To tell the pump when to run, we connected 16-gauge two-conductor wires from the pump power-output terminals in each air conditioner’s electrical box (J2) to each of two pump trigger inputs in the pump-relay box (J, K).

How to install an air conditioner on your boat - photo 2

“In some installations, a second through-hull, strainer, and pump just to supply the new air conditioner might be easier,” Meister says. “Then you wouldn’t need a pump-relay box, extra pump-power wire, and a pump circuit breaker on the electrical panel.”

To supply cold air, we ran a 7-inch (inside diameter) insulated air duct up behind the seating, through a bulkhead, through a locker in the cabin, and up into the air-conditioned space, avoiding sharp bends that hinder airflow. Any restrictions significantly decrease cooling and can cause icing and excessive noise.

Meister supplied a plastic vent box and grill, which we mounted in a King Starboard box angled about five degrees to help cold air flow aft. “The secret to cooling a room is to get that air rolling along the overhead,” Meister says. 

“Both the duct and return air path have to accommodate the total air flow,” Meister warns. “You can only push out as much air as you let in.” Skimping on return air is as bad as restricting the duct.

To provide our required 160 square inches of return-air path, we cut two 16-inch by 2½-inch slits under each toe kick on the port and starboard bench seats, and then made six 4-inch holes inside each seat back to let air flow down to the air conditioner below. This also created air-conditioned stowage beneath those two seats. 

Adding the air conditioner took two of us every bit of three days. Was it worth it? I’ll let you know on the next hot day with no breeze.

How to install an air conditioner on your boat - photo 3


For safety, neither the air-conditioner intake nor the return air path can draw from the engine room, engine room bilge, or any space where exhaust gas might leak or collect.