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Marine Water Heaters Reviews and Buying Guide

Marine Water Heaters Reviews and Buying Guide

Marine water heaters are used onboard boats to produce hot water for various uses such as washing up and showering. Due to the nature of where they will be installed, they should usually be designed to be small in size and lightweight so they can be fitted onto vessels. They should also be tolerant of saltwater conditions as well as humid and wet environments.

If you are looking for a solution to provide hot water for your boat, this article will provide more information on the best options available and what features to look for in a marine hot water heater.

We have also taken a closer look and reviewed two products that we think are worth considering.

When Are Marine Hot Water Heaters Used?

As you know, boats are used for a variety of activities such as short day trips, leisurely cruising or water sports. Some people are lucky enough to live aboard their boats. Having a good supply of hot water is useful in any number of situations including washing up after meals or warming up after a swim.

If your boat trips are longer-term and your vessel has berth sleeping facilities, you will most probably have showers too which will require warm water. For example, having a yacht hot water heater will be ideal for post-race showers as well as longer sailing trips.

Some vessels are often more than recreational for some, as they are used as floating homes on canals and marinas. Living aboard your boat long term means that your requirement for hot water is a necessity rather a luxury. Therefore, a reliable supply is required.

These scenarios call for a boat hot water heater to be fitted aboard your vessel.

Types of Heaters and Their Features

Most marine heaters for vessels have a corrosion-resistant casing, for example, stainless steel or aluminum, to protect from salty water and air.

The tanks can come in different sizes depending on the scale of your boat, what you need it for, and how many people use it on board.

If you are sharing the boat with a few people, showering and washing up needs will be more a lot larger too, which is something to consider. Typically, you will find tanks that hold 6 gallons. However, this can go up to 20 gallons.

A boat water heater is typically powered by a heat exchanger which utilizes wasted heat energy from the boat engine. In addition, depending on the model, electricity or propane gas is used as a backup or alternative method for when the engine is not running.


Electric marine water heaters are perfect if you want to get access to your hot water supply while the boat engine is off. Without heat exchange taking place in the engine and your appliance, you can find yourself short of warm water.

Models powered by electricity have a magnesium anode heating element and use the immersion heater that is usually located in the lower part of the tank.

These can be cheaper to run, especially if you use solar panels onboard your boat to generate electricity.

Propane Gas

Some heaters also come as propane gas models. These are more common on smaller vessels and are not quite as popular as the other types. They rely on engine performance, and as they are closed combustion, can be mounted anywhere in the boat.

Marine Hot Water Heater Reviews – Top 2 Products on the Market

We’ve selected two products we think are two of the best marine hot water heaters worth considering if you choose to purchase one for your boat.

Prices pulled from the Amazon Product Advertising API on:

Whale Marine Water Heater – Premium


Whale F600 Water Heater, 6-Gallon Capacity, 120V, Front Heat Exchanger, 13 Inches W x 19 Inches D x 13 Inches H


This model Whale water heater uses an efficient double-walled heat exchanger system utilizing the boat’s engine. It uses the hot water from the engine’s closed cooling system to heat the water in the tank while the boat is running.

If you are using hot water while stationary or when the engine hasn’t been run in a while, it can also run off electricity using a heating element. Either connect the boat to mains when it’s moored or connect up to the generator.

The unit is made of durable materials and you can choose the cover material.

Material options for this include:

  • Galvanized steel which offers good value corrosion resistance but does weigh in on the heavier side.
  • Stainless steel which offers effective corrosion resistance and looks a bit more modern. These are a bit lighter than galvanized steel.
  • White epoxy-coated aluminum which typically blends in well with existing boat features.

All of these casing options create a durable and robust model that ensures a good life span. For you and your boat, it’s good value for money.

It has an electrical input of 120v and can hold 6 gallons of water. This is the usual benchmark capacity for these sorts of marine water heaters.

For safety, it is ‘ignition protected’. This means that when it is being run in the engine room, it is safe and contained. Any sparks can pose a fire risk when there are engine fumes are around. It’s there important to have appropriate safety measures in place.

If the water in your areas is hard with higher dissolved salt concentrations or high currents, corrosion can be an issue for a boat’s hot water tank. To prevent this, the Whale unit comes with an anode made from magnesium that will prevent this from happening so fast.

These anode rods will corrode themselves rather than the tank, so will need replacing every 6 months or so. This is similar to how the rods act in the water heating appliances installed in your home – it’s a protective measure to keep the tank clean.

The rods are easy to install. Simply remove the drain valve and existing anode, then screw the new replacement part in. Once complete, put the drain valve back into place.

What We Like

  • Quick to heat water
  • Easy to install
  • Good value for money
  • It can run off electric or heat power

Minor Drawbacks

  • Whale water heater capacity is only 6 gallons
  • If you are going to be using water that is harder or has higher dissolved salts, the anode magnesium rods will need to be replaced every 6 months to prevent corrosion.

Kuuma Marine Water Heater – 11 Gallon


Kuuma 11G 120V Front Exchanger SS water heater - Force 10 Marine Products


Well known boat manufacturers such as Beneteau, Boston Whaler, and Sea Ray install a Kuuma marine water heater as standard on their vessels which proves that they have a good reputation and are reliable.

This model is corrosion resistant as standard, as the casing and the tank are made using marine-grade aluminum.

It too works using a front heat exchange with the engine closed cooling system. As it is also dual power, it can run on either engine heat or electricity. This means it too is designed to use shore power when plugged in at the dock, and engine heat when it is available. You can expect it to retain the heat because of the good insulation on the unit.

For safety, it is ‘ignition protected’ for when it is being run in the engine compartment. This means it is safe and contained, and will not create sparks which could cause a fire risk with the engine fumes around. Additionally, the units include a high-temperature limiter with automatic reset.

It has a large capacity of 11 gallons. This means it is suitable for boats with a larger hot water requirement. Kuuma also offers smaller 5 or 6 gallon models, as well as much larger models at 20 and 26 gallons.

A Kuuma is typically easy to install and comes with hose barbs and ports for domestic water.

What We Like

  • 11 gallons capacity which is above average for marine use
  • Effective when using both modes
  • Easy to install

Minor Drawbacks

  • Use of a magnesium anode is highly recommended to extend the life of the tank


Final Thoughts

Marine water heaters can be game changers for life onboard your boat. Whether it’s to do the washing up or take that much needed warm shower after a dip in the ocean, it can bring a lot more comfort to your vessel.

Installing a water heater for your boat is not as difficult as it may sound. Models are compact models designed to be easy to mount and come with installation guides to help you. Obviously, if you’re in doubt, contact a professional to help you with this.

The main points to be considered before you purchase one, are what capacity of water do you need and how often will the boat be running? The number of people on board and time the boat spends with engines off will have an impact on your requirements.

These two marine hot water heater brands offer the added benefit of being able to be run on both electric and the boat engine. Also to note is the fact that the Whale water heater can be fitted to an RV to provide water heating solutions on the road.

Prices pulled from the Amazon Product Advertising API on:
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