Marine Water Heaters: Things to Look For and An Overview of the Popular Brands

Marine water heaters are indispensable components of boats, yachts, and other marine vessels, ensuring a steady supply of hot water for various onboard needs. From providing warm showers and enabling efficient dishwashing to supporting essential systems like heating and equipment sanitization, hot water plays a vital role in maintaining comfort, hygiene, and functionality while at sea.

In this exploration, we will look into the different types of marine water heaters, factors to consider when choosing one, and the best brands to choose from.

Marine Water Heaters: Things to Look For and An Overview of the Popular Brands
Atwood marine water heater (photo: amazon)

Marine Water Heaters: Selecting Tips


Marine water heaters are designed to withstand the demanding conditions of life on the water, including vibration, saltwater corrosion, limited space, and power availability.

They provide instant and ample hot water using different energy sources, including electricity, propane gas, or harnessing wasted heat energy from the vessel’s engine. This versatility allows users to choose the most suitable and efficient option for their specific needs.

Designed with compactness and lightweight in mind, marine water heaters are strategically installed in the engine room or other confined spaces to optimize space utilization onboard. Despite their small form factor, these heaters are constructed using high-quality materials capable of withstanding harsh and highly humid environments. They are engineered to endure exposure to both fresh and salt-aggressive water conditions, ensuring long-lasting performance and durability.

Available Types

These heaters come in different types, each offering distinct advantages and considerations.

Tank-type water heaters store a predetermined volume of hot water, ready for use whenever needed. They are reliable and provide a steady supply of hot water, making them suitable for vessels with higher hot water demands.

Tankless water heaters, on the other hand, heat water on demand as it flows through the unit. They offer continuous hot water without the need for storage, making them efficient in terms of space and energy consumption.

Heat exchanger water heaters utilize the vessel’s engine coolant system or an external heat source to heat the water, offering an alternative energy-efficient option.

As technology advances, marine water heaters are experiencing innovative developments. Eco-friendly and energy-efficient technologies are being integrated into these systems, enhancing their performance while minimizing environmental impact. Integration with smart systems and remote monitoring capabilities are also becoming more prevalent, enabling users to have better control and efficiency in managing their water heating needs.

Most manufacturers design water heaters for boats and yachts with corrosion-resistant casings, typically made of materials such as stainless steel or aluminum. Similarly, the storage tanks of these marine water heaters are constructed using stainless steel or other metals with protective coatings.

The available tank sizes for most marine water heaters typically range from 6 gallons, which is the most common size, up to 20 gallons.

Fuel-Type Options

When choosing a marine water heater, one crucial factor to consider is the fuel type it utilizes. The available fuel options for marine water heaters include electricity, propane gas, and diesel. Each fuel type has its own characteristics, advantages, and considerations to keep in mind.

When selecting the fuel type for your marine water heater, consider the availability and cost of the fuel, the specific needs and limitations of your vessel, and the overall efficiency and performance of the chosen fuel type in meeting your hot water requirements.

Electric-Powered Marine Water Heaters

  • Electric marine water heaters are popular due to their ease of use and widespread availability of electrical power on most vessels.
  • They are typically more straightforward to install and require minimal maintenance compared to other fuel types.
  • Electric heaters are often energy efficient and can provide a consistent supply of hot water.
  • However, reliance on electricity may be a limitation in remote or off-grid boating scenarios, as it requires a reliable power source.
  • Most heating elements work on 110 V when hooked to the shore power.

The electric unit utilizes immersion heaters that are usually positioned in the lowest part of the tank, where the water is the coldest and where the unit can get the maximum from the heating element. Special attention is also given to the water inlets and outlets for a minimal mixing of cold water into the hot.

Propane-Powered Marine Water Heaters

  • Propane gas is a commonly used fuel for marine water heaters, offering convenience and versatility.
  • Propane heaters are independent of electrical power, making them suitable for boats that may not have a consistent electrical supply.
  • They can heat water quickly and provide hot water on demand.
  • Propane gas cylinders are readily available, making refueling relatively easy, although storage of propane cylinders must be done with caution.

Diesel-Powered Marine Water Heaters

  • Diesel-powered marine water heaters are often favored in larger vessels where diesel fuel is readily available for other onboard systems.
  • They can efficiently heat large volumes of water and are well-suited for boats with existing diesel fuel tanks.
  • Diesel heaters may have higher installation and maintenance requirements compared to electric or propane options.
  • It is important to ensure proper ventilation and exhaust systems when using diesel fuel for heating.

Things to Consider When Buying a Marine Water Heater

When choosing a marine water heater, here are some key features to consider:

  • Capacity: Determine the appropriate size based on the hot water needs of your boat or yacht. Consider the number of people on board and the typical usage requirements.
  • Fuel-type options: Evaluate the available fuel options such as electricity, propane gas, or waste heat from the engine. Choose a fuel type that aligns with your vessel’s setup and availability.
  • Material and corrosion resistance: Look for water heaters made of high-quality materials like stainless steel or corrosion-resistant aluminum. These materials ensure durability and longevity, especially in the corrosive marine environment.
  • Energy efficiency: Consider water heaters that are energy-efficient to minimize power consumption and maximize the utilization of available resources. Look for features like insulation, efficient heat exchangers, and adjustable temperature settings.
  • Safety features: Ensure the water heater has safety features such as thermostats, pressure relief valves, and overheat protection mechanisms. These features help prevent accidents, maintain optimal performance, and protect the unit from damage.
  • Warranty: Check the warranty coverage provided by the manufacturer. A longer warranty period demonstrates the manufacturer’s confidence in their product and provides peace of mind for potential issues.
  • Ease of installation and maintenance: Look for water heaters that are easy to install and maintain. Consider factors such as access for installation, availability of spare parts, and ease of flushing the tank or replacing heating elements when needed.
  • Compliance with regulations: Verify that the water heater meets relevant safety and compliance regulations for marine vessels. This ensures the unit adheres to industry standards and provides a safe operating environment.
  • Recovery rate: Consider the water heater’s recovery rate, which indicates how quickly it can heat a new batch of water after use. A higher recovery rate ensures a steady and continuous supply of hot water, especially during periods of high demand.
  • User-friendly controls: Look for water heaters with user-friendly controls and displays that make it easy to set and adjust temperature settings.

Top Marine Water Heater Manufacturers

  • Atwood
  • Torrid
  • Superstor
  • Isotemp


Atwood marine water heaters are known for their reliability and efficiency as electric heating units. They are equipped with high-quality 1.4 kW and 1.5 kW Incoloy heating elements, designed to quickly provide hot water and withstand accidental operation when the tank is empty. This feature is particularly important as it prevents damage that could occur to copper heating elements in such situations.

Designed to be lightweight, Atwood water heaters feature casings made of high-corrosion-resistant aluminum, allowing them to withstand the corrosive marine environment. It’s worth noting that only two models, the EHM6 SST with a 6-gallon tank size and the EHM11 SST with a 10.5-gallon tank size, have casings built from stainless steel, providing added durability.

Specialized aluminum alloys are used for the tanks, offering an extended tank life while reducing the overall weight. This weight reduction is crucial for boat construction, where minimizing weight is a key consideration.

The heat exchangers in Atwood marine water heaters employ a superior double tube construction, effectively preventing any possibility of engine coolant contaminating the freshwater system. This design feature ensures the integrity of the freshwater system, enhancing safety and efficiency.


Torrid marine water heaters are available in two series: the Standard and Explorer series.

The Standard series is available in both horizontal and vertical configurations, offering tank sizes ranging from 6 to 30 gallons and power options from 1500 W to 4000 W maximum.

The Explorer series is also available as horizontal and vertical, but heating water up to 50 gallons. All models have two high efficiency heat exchangers allowing water to be heated by the coolant from the engine, hydronic heating system or generator. Additionally, all vertical models incorporate two heating elements for enhanced performance.

With a 5-year warranty against tank failure, Torrid marine water heaters are designed to resist corrosion. They feature protective elements such as a heavy-duty glass lining, stainless steel outer jacket, and an oversized magnesium anode rod. A safety thermostat cut-off adds further durability, making Torrid boat heaters ideal for high-temperature environments.

Furthermore, the high-density fiberglass insulation in Torrid water heaters helps to retain hot water in the tank for extended periods, maximizing hot water usage efficiency.


Superstor marine water heaters are highly efficient units that feature a high-efficiency extended surface heat exchanger with a finned tube, a stainless steel corrosion-resistant storage tank, and 1.5 kW heating elements. These components ensure extended performance life and make the water heaters suitable for dock-side power use.

To prevent energy waste and reduce heat loss, the Superstor water heaters are equipped with 2-inch, CFC-free, water-blown foam insulation. This insulation is not only effective but also environmentally safe.

The Superstor marine water heaters offer different capacity options, including 6, 12, and 20 gallons, allowing users to choose the size that best fits their needs. The recovery rate ranges from 22 to 39 gallons per hour, with a delivery temperature of 155°F. Additionally, all models come with a 5-year warranty, providing peace of mind to the users.


Isotemp marine water heaters are available in three different groups, categorized based on their shape and diameter. The Basic models have a tank size ranging from 6.3 to 19.7 gallons, while the Slim models have a capacity of 4, 5, and 6 gallons. Both the Basic and Slim models have a cylindrical shape and can be installed horizontally or vertically, delivering excellent performance and fast hot water delivery in either position.

For installations in narrow and limited spaces where the Basic and Slim models may not be suitable, the Isotemp manufacturer offers the Slim Square model. This model features a 4.2-gallon tank size and provides easy installation in three different positions, accommodating space constraints.

Isotemp hot marine water heaters are constructed using high-quality materials, including stainless steel for the casing, tank, tubes, and all elements that come into direct contact with water. This ensures durability and resistance to corrosion.

The Isotemp water heaters utilize heat from the engine coolant system, as well as a standard 750 W or 1.2 kW immersion heating element, to provide hot water. Some models, such as the Isotemp Basic models 6403 D and 6753 D, feature a dual heat exchanger for enhanced performance.

All Isotemp water heater models come with a 5-year limited warranty, offering peace of mind and ensuring the reliability of the product.

How to Ensure Enhanced Performance and a Longer Lifespan

To ensure a longer lifespan and easier maintenance of the water heaters, it is recommended to adhere to the following guidelines:

  1. Install the unit in accordance with local codes and regulations.
  2. Incorporate a shut-off valve and drain valve in the installation to facilitate maintenance and repairs.
  3. Position the heater near the floor for convenient draining and flushing operations.
  4. Take measures to protect the unit from freezing temperatures, as this can cause damage.
  5. Use unions for plumbing connections when installing the heater for easy disconnection if needed.
  6. Properly vent air from the heater to ensure optimal operation.
  7. Prior to turning on the power, ensure that the tank is filled with water to prevent damage.
  8. Regularly flush the water from the tank every other month to eliminate sediment buildup.


Marine water heaters are crucial for ensuring a comfortable and convenient experience on boats and yachts. They provide a reliable source of hot water, allowing users to enjoy showers, clean dishes, and perform other necessary tasks while on board.

With a wide range of options available from manufacturers, boaters can choose water heaters that meet their specific needs, including fuel type options, safety features, and compliance with regulations.

When selecting a marine water heater, it’s important to consider factors such as capacity, recovery rate, and installation requirements. Following proper installation and maintenance procedures recommended by the manufacturer will help maximize the lifespan and efficiency of the water heater, ensuring it functions optimally throughout its service life.

By investing in a high-quality marine water heater, users can enjoy uninterrupted hot water on their boating adventures. These heaters are designed to withstand the demanding conditions of the marine environment, providing reliable performance and convenience.

So, whether it’s taking a refreshing shower after a day of water activities or preparing a hot meal in the galley, a marine water heater is an essential component for enhancing the overall experience on board.


Are Marine Water Heaters Suitable for Use With Saltwater?

Yes, marine water heaters are designed to withstand the corrosive nature of saltwater. They are typically constructed with corrosion-resistant materials such as stainless steel or aluminum to ensure durability and longevity in saltwater environments.

Can I Use My Marine Water Heater While Underway or Only When Docked?

Marine water heaters can be used both when the vessel is docked and when underway. However, it’s important to ensure that the water heater is securely installed and that all safety precautions are followed to prevent any accidents or damage while the boat is in motion.

What Is the Typical Lifespan of a Marine Water Heater?

The lifespan of a marine water heater can vary depending on factors such as usage, maintenance, and the quality of the unit. On average, a well-maintained marine water heater can last anywhere from 5 to 10 years or more. Regular maintenance, including flushing the tank and inspecting the heating elements, can help prolong its lifespan.

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