How to Install Marine Hot Water Heaters

How to Install Marine Hot Water Heaters

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If you have a shower on your boat, you'll want to have hot water aboard as well. Water heaters on boats don't use pipes; instead they use hoses. This means that you won't have to understand any of the pipe connection techniques that a plumber spends years learning; you set the water heater in place, connect the hoses, connect the wires then turn on the water heater. When the hot water is ready, you can sigh with relief.

Items you will need

  • 1-1/2 inch hoses (2)

  • 1/2-inch hoses (2)

  • Teflon pipe thread tape

  • Pipe wrench

Step 1

Put the water heater as low as possible in your boat. Marine water heaters come in a variety of sizes, including short, squatty heaters that can be placed in an engine room that has a very low overhead (ceiling). Water is heavy, and a hot water tank will change the trim (balance) of your boat.

Step 2

Screw one end of a 1-1/2 inch hose onto the water heater's inlet port and connect the other end of the hose to the below-deck extension of the potable water inlet connection on your deck. Use Teflon thread tape on both connections. This is the "fill" hose. Make certain that the potable water inlet has a valve and O-ring seal so that sea water washing over your deck won't backfill into your water heater.

Step 3

Wrap the threaded end of the water heater vent port with Teflon thread tape and screw one end of a 1/2-inch hose onto the port. Tighten the connection with a pipe wrench. Wrap the threaded portion of the water system vent (which extends up on your deck) with Teflon tape and connect the vent hose to it. Tighten all connections with a pipe wrench. If the deck vent is no higher than your inlet port, where you fill the tank, you'll know when your water tank is full because it will overflow.

Step 4

Wrap the threaded end of the hose to your boat's "house" water system (the water system that serves the galley, the kitchen and bathroom) in Teflon thread tape and thread the water heater's outlet connection onto it. Tighten the connection with a pipe wrench.

Step 5

Attach the power wire to the appropriate breaker in your boat's breaker box. If a ground wire is provided with the heater, attach it to the appropriate ground at or near the breaker box.


  • This task involves electrical work aboard a boat. Observe all appropriate cautionary measures, including working on an insulated mat.


  • If possible, add an extension to your potable water vent: add a length of PVC pipe to the vent with a PVC coupling and on top of the extension add two 90 degree elbows to form a U-shape. This will keep water from blowing out of the tank when it's full and keep sea water from entering the tank when the boat heels (leans over).
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