How to Install a Boat Heater

Extend your watersports season with a little onboard heat.

LAKE PITT IN BRITISH COLUMBIA is one of the few freshwater tidal lakes in the world and is fed by glaciers, so it never gets above 72 degrees. And in Canada we have a short waterski season with cool mornings and evenings, so I decided to install a Heater Craft 300 air heater on my 2009 Malibu vRide, to maximize my time on the water. The project took approximately six hours and the total cost was $505.6 copy

The system takes your engine’s warm coolant and converts it to hot air, so you need to run two lengths of 5/8-inch heater hose from the engine compartment through the stringers and exit them at the bulkhead behind the helm. Two hoses are required: one is the supply and one the return. To make the job easier, I used a fish tape, which is a semi-rigid, vinyl-coated metal spring on a spool that looks like a plumbing snake. I did one pull from beside the transmission to the floor access between the helm and observer’s seat, and another from that point to under the helm. Once the fish tape is through, tape the heater hose to the end and pull the tape out while feeding in the hose.4 copy

Locate an enclosed area large enough for the heater. On my boat, such a space was behind my subwoofer, so I removed the subwoofer panel to gain access to the bulkhead. For more working space, I also removed the driver’s seat. Mount the heater box on the bulkhead with the screws provided. I mounted mine with the heater core ports pointing down and with a slight slope down at the ports, which will allow the best drainage during the winterization process. Connect the two 5/8-inch heater lines to the heater box. Water will flow in either direction through the core, so don’t worry about which line connects to which port.

Connect the supply line to the engine at the intake manifold. Locate and remove the half-inch brass NPT plug on the top of the manifold, which is near the thermostat housing. I opted to install a ball valve at this location, so I can shut off the heater circuit if a problem occurs. All the fittings are half-inch NPT and are available from your local hardware store. Use pipe joint compound on all the fittings, to ensure there aren’t any leaks. I opted to use Heater Craft’s low RPM Y-pipe for the return line, to improve water flow through the heater core at idle, thereby improving heater operation. I installed the Y-pipe after the transmission and before the raw-water pump. Ensure that the 5/8-inch fitting is pointing toward the water source, which creates a Venturi effect to draw water through the heater core.

Heater Craft supplies a three-speed motor with the kit, and I wanted a factory look, so I ordered a three-position OEM switch (ON-OFF-ON) and cover. The switch replaced an unused accessory switch on the dash. The three-position switch allows only two fan speeds, so I went with the high and medium speeds. Remove the circuit breaker panel under the throttle control. Fortunately, in my case, there were two existing 15-amp heater circuit breakers that had nothing connected to them. Connect a hot wire from the circuit breaker to the switch’s hot terminal and then run ground wire from the fan motor to the ground bus located under the dash. Now run the high-speed fan wire to one side of the switch and the medium-speed fan wire to the other side of the switch. Last, you’ll need to ensure the switch’s ground terminal is connected if you want the switch to light up correctly when you turn the fan on.5c copy

Now you need to run the heater ducts. I installed a three-vent unit. Two vents were hot tube pull-out style hoses and the third was a fixed vent. I put one of the hot tubes in the walkthrough to the bow, another hot tube in the starboard cupholder pocket and the fixed vent in the subwoofer panel.

Use a four-inch hole saw to cut a hole for the walkthrough hot tube. For a cleaner cut, I recommend starting from one side, and when the pilot bit comes out the other side, stop and finish the hole from the other direction. Mount the hot tube with the included screws. Repeat this step for the fixed vent in the subwoofer panel — except this hole is only three inches in diameter.

I decided to put the last hot tube in the starboard gunwale cupholder pocket, which required that I fabricate a little bulkhead to mount the hot tube, so I made a template out of cardboard and then transferred the template onto 3/4-inch plywood. Cut a four-inch hole to mount the hot tube into the plywood bulkhead. I covered the plywood bulkhead with some plastic heat-shrink covering I had in the garage. Run the three-inch ducting from the heater box to the vent locations, attach them with supplied ties from the kit and you’re done.

The first time I used it, I was really surprised at the volume of air that comes out of each vent — and you can’t believe how good it feels to instantly get warm after a chilly run.

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