Marine Water Heaters: An Overview of the Popular Brands

Atwood marine water heaterAtwood marine water heater
(photo: amazon)

Marine water heaters are the electrical or propane-powered heating appliances used in the boating industry for space and hot water heating and where the shower, washing-up, and personal hygiene are the main applications. Check out the buying tips and most popular brands and models used in North America.

These boat heaters provide an instant and sufficient amount of hot water using electricity, propane gas, or the engine's wasted heat energy, resulting in great benefits for the users.

Marine hot water heaters are designed small and lightweight, installed mainly in the engine room and restricted areas. As they are made of high-quality materials, they can work in a harsh and very humid environment - subjected to fresh and salt-aggressive water conditions.

Marine water heaters: Types and features

Most of the manufacturers design water heaters for boats and yachts with a corrosion-resistant casing like stainless steel or aluminum and stainless steel or metal storage tanks (with protection). The most available tank sizes for most marine water heaters are in the range of 6 gallons, as the most common size, up to 20-gallon.

Electric-powered marine water heaters

The electric unit utilizes the 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.

Most heating elements work on 110 V when hooked to the shore power.

Propane-powered marine water heaters

Propane hot water heaters are specially constructed for the marine environment, with no electricity needed that only depend on the engine's performance. With the closed combustion, they are reliable units that can be mounted almost anywhere inside the boat.

The difference between the superior and lower quality marine hot water heaters is the part selection, where the Incoloy sheathed heating elements are found in high-quality models; while others are built from copper (subjected to failure if not fully immersed in water when energized), heavy-duty heat exchanger, usage time/recovery rate, insulation...

The thermostat has to be factory calibrated, and Coast Guard approved (UL) for spark-ignition protection.

Top marine water heater manufacturers

  • Atwood
  • Torrid
  • Superstor
  • Isotemp
  • Webasto


Atwood marine water heaters are reliable and efficient electric heating units, equipped with high-quality 1.4 kW and 1.5 kW Incoloy heating elements. The heating elements are designed to provide hot water quickly and withstand accidental operation when the tank is empty, which is usually fatal for copper heating elements.

Designed as a lightweight heater, Atwood has a casing made of high-corrosion-resistant aluminum so that it can work in the corrosive marine environment. Only two models, EHM6 SST with the 6-gallon tank size and EHM11 SST with the 10.5-gallon tank size, have casings built from stainless steel.

Specialized aluminum alloys are also used for tanks, providing an extended tank life while reducing the total weight, which is essential for boat construction.

Superior heat exchangers use double tube construction, which prevents any possibility of engine coolant contaminating the freshwater system that is running through.


The Torrid marine water heater provides a 5-year warranty against tank failure, backed up by 2 protective elements against corrosion; heavy-duty glass lining and oversized magnesium anode rod. With these two protective elements and safety thermostat cut-off, Torrid boat heaters are constructed to last longer and easily work in a high-temperature environment.

High-density fiberglass insulation keeps the hot water longer in the tank and increases hot water usage.

Super efficient heat exchanger, made of high-quality copper with a silicon bronze casting and 1.5 kW stainless steel sheathed heating element will provide great 15 gallons per hour recovery with 40 F rise.


Superstor marine water heaters are high-efficiency units consisted of the high efficiency extended surface heat exchanger with the finned tube, stainless steel corrosion-resistant storage tank, and 1.5 kW heating elements for longer performance life and dock-side power use.

The 2-inch, CFC-free, water-blown foam insulation is environmentally safe and used to protect the unit from energy waste and reduce heat loss.

You can choose models with 6, 12, and 20-gallon capacity and recovery rate from 22 to 39 GPH with the delivery of 155 F. All models come with a 5-year warranty.


Isotemp hot marine water heaters can be found in three different groups, based on the shape and diameter; Basic with 6.3 to 19.7-gallon tank size and Slim with 4,5 and 6-gallon capacity, both cylindrical in shape. Either installed horizontally or vertically, great performance and fast hot water delivery are achieved in both positions.

The Slim Square with 4.2-gallon tank size is another model from the Isotemp manufacturer that provides easy installation in three different positions, in narrow and limited space where the Basic and Slim models are not viable solutions.

High-quality material like stainless steel is used not only for the casing but also for the tank, tubes, and all elements in direct contact with water.

It uses heat from the engine coolant system and a standard 750 W or 1.2 kW immersion heating element.

Isotemp Basic models 6403 D and 6753 D models have a dual heat exchanger for even better performance.

All models come with a 5-year limited warranty.


Webasto water heaters for boats and yachts offer four types of marine heaters for space and water heating.

For longer heater life and easier service...

  • Install a unit per local codes.
  • Install a shut-off valve and drain valve.
  • Locate the heater near a floor for easy draining and flushing.
  • Protect the unit from freezing temperatures.
  • To connect heater use unions for plumbing.
  • Always vent air from the heater.
  • The tank must be full of water before the power is turned on.
  • Flush water from the tank every other month to get rid of the sediments.
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