Hot Water on a Narrowboat & Widebeam: Gas, Diesel, Calorifiers & Electric Explained
Hot Water on a Narrowboat & Widebeam: Gas, Diesel, Calorifiers & Electric Explained
Hot water is something most of us take for granted at home. Turn on a tap or start the shower and hot water is simply there.
On a narrowboat or widebeam, there are several different ways of achieving the same thing.
A modern boat can use diesel heating, LPG gas, engine heat, an electric immersion heater or a combination of several systems. Choosing the right setup depends on how you intend to use your boat, whether you will have regular shore power, how often you cruise and whether you're planning to live aboard full-time.
In this guide, Central Boating explains the main narrowboat and widebeam hot-water options, how they work and the advantages of each.
How Does Hot Water Work on a Narrowboat?
There isn't one standard hot-water system used on every narrowboat.
Many modern boats use a calorifier, which stores hot water in an insulated cylinder. The water inside can potentially be heated using several different sources, including:
The propulsion engine
A diesel-fired heater
A 230V immersion heater
Another option is an LPG gas water heater or boiler, which can provide hot water without relying on stored hot water in quite the same way.
The best solution depends heavily on how the boat will be used.
A continuous cruiser has different requirements from somebody spending most of their time connected to shore power in a marina.
What Is a Calorifier on a Narrowboat?
A calorifier is essentially the boat's hot-water cylinder.
Cold water is pumped from the freshwater tank into the calorifier, where it is heated and stored until required at the taps or shower.
The cylinder is insulated to reduce heat loss, allowing the water to remain hot after the original heat source has stopped operating.
Calorifiers are available in different capacities and configurations. Some have a single heating coil, while others have twin coils that allow different heating circuits to transfer heat into the stored water.
Many can also be fitted with a 230V immersion heater.
This makes a calorifier particularly versatile because you're not necessarily dependent on one source of heat.
Heating Hot Water From the Boat's Engine
One of the most useful ways to heat water on a narrowboat is by making use of heat already being produced by the engine.
When the engine is running, hot engine coolant can be circulated through a coil inside the calorifier.
The engine coolant and domestic water remain separate, but heat is transferred through the coil into the stored water.
For owners who cruise regularly, this is extremely useful.
You can spend several hours cruising and arrive at your destination with hot water available for showers and washing up without having needed a separate heat source solely for the water.
Diesel Hot Water and Heating
Diesel-fired heating is extremely common on modern narrowboats and widebeams.
Hydronic diesel heaters, including systems manufactured by companies such as Webasto, heat coolant which is then circulated around the boat.
Depending on the installation, the same system can supply:
Radiators + calorifier + domestic heating circuit
This means one diesel heater can provide both central heating and hot water.
It's particularly useful for liveaboards and continuous cruisers because the system doesn't depend on a shore-power connection.
During winter, the diesel heater may already be operating to heat the boat, with the calorifier being heated as part of the system.
During warmer months, the system can be operated when hot water is required without needing to run the propulsion engine.
What Is a Webasto Heater?
Webasto is one of the well-known manufacturers of diesel-fired heating equipment used on boats.
Rather than directly heating the air inside the boat, a hydronic system heats coolant.
That hot coolant can then circulate through radiators and the calorifier.
The principle is therefore similar to a wet central-heating system in a house, although the equipment and installation are designed around the requirements of the vessel.
Correct sizing and installation are important. Bigger isn't automatically better, and the heater needs to be matched appropriately to the heating circuit and expected use.
Electric Immersion Heaters
Another way to heat a calorifier is with a 230V immersion heater.
An immersion is an electrical heating element fitted directly into the calorifier.
When the boat is connected to shore power, this can be one of the easiest ways to produce hot water.
Rather than running the engine or burning diesel simply to heat the calorifier, electricity from the shore connection can power the immersion.
This makes particular sense for boats that spend significant periods in a marina.
Can You Run an Immersion Heater From Batteries?
Potentially, but this needs careful consideration.
Heating water requires a significant amount of energy.
If an immersion heater is being supplied through an inverter, that energy ultimately has to come from the domestic battery bank.
A modern lithium system with a suitably sized inverter and sufficient charging capacity may be capable of supporting substantial 230V loads, but that doesn't automatically make electrical water heating the most efficient use of the stored energy.
For owners wanting to run substantial domestic equipment from batteries, the complete electrical system needs to be designed around those loads.
You can read more about this in our Narrowboat & Widebeam Electrical Systems Guide.
Gas Hot Water on a Narrowboat
LPG is another established way of producing hot water aboard a narrowboat.
Some boats use instantaneous gas water heaters, while others may use suitable LPG boiler systems.
An instantaneous gas water heater heats water as it is required rather than relying entirely on a tank of previously heated water.
Open the hot tap and the appliance heats the water passing through it.
For some owners, this is very convenient because you're not limited to the quantity of hot water stored in a calorifier in the same way.
It can also be useful when cruising away from shore power because producing hot water isn't dependent on a large electrical system.
Gas Boilers on Narrowboats and Widebeams
Some boats use LPG boilers capable of providing domestic hot water and, depending on the system, central heating.
This can provide an experience closer to a conventional domestic heating system.
However, installing a gas boiler on a boat isn't simply a matter of taking any household boiler and fitting it aboard.
The appliance must be suitable for the intended application and the installation needs to account for the marine environment, including combustion air, flue arrangements, ventilation, gas storage and pipework.
LPG installations also need to comply with the relevant safety requirements, including applicable Boat Safety Scheme requirements.
Gas work should be carried out by somebody appropriately qualified and competent for the particular LPG and marine installation involved.
Instantaneous Gas Water Heater vs Calorifier
These systems work in fundamentally different ways.
An instantaneous gas heater produces hot water when you need it.
A calorifier heats and stores a quantity of water for later use.
An instantaneous heater can therefore provide convenient hot water without first waiting for an entire cylinder to heat.
A calorifier, however, has the major advantage of being able to make use of several different energy sources.
For example, you could heat the same calorifier from the engine while cruising, from a diesel heater while moored and from an immersion heater when connected to shore power.
Neither approach is automatically better.
It depends on the boat and its owner.
What About a Gas-Free Narrowboat?
Gas-free narrowboats and widebeams are increasingly possible thanks to modern lithium batteries, solar systems and high-powered inverter/chargers.
A gas-free specification could include:
Induction hob + electric oven + lithium batteries + inverter/charger + solar + diesel heating + calorifier
This removes the need to carry LPG for cooking and hot water.
However, removing gas doesn't remove the energy requirement.
Instead, more of the boat's domestic demand moves onto the electrical system.
Induction cooking, electric ovens and other high-powered appliances can place considerable demand on the batteries and inverter.
A gas-free boat therefore needs a properly designed electrical and charging system rather than simply replacing individual gas appliances with electric alternatives.
Gas vs Diesel Hot Water: Which Is Better?
There isn't a universal winner.
Gas hot water can provide convenient on-demand heating and can work without placing a substantial load on the battery bank.
Diesel heating works particularly well when integrated with a calorifier and radiator system. It also uses fuel already carried for the propulsion engine.
A diesel/calorifier system can provide another significant advantage: multiple methods of heating the same water.
You could use:
Engine heat while cruising
Diesel heating while moored off-grid
An immersion heater while connected to shore power
For many liveaboards, that's an extremely flexible combination.
However, someone who prefers instantaneous hot water or already intends to have LPG aboard may find a suitable gas system attractive.
What Size Calorifier Does a Narrowboat Need?
There's no single correct size.
The amount of hot water required depends on factors including:
Number of people aboard
Shower usage
Available installation space
Whether the boat is recreational or residential
How frequently the water can be reheated
The type of heating system installed
A couple using a narrowboat for weekends will have very different requirements from a family living permanently aboard a large widebeam.
A bigger calorifier provides more stored hot water, but it also occupies more space, carries more water weight and requires more energy to heat.
The calorifier should therefore be sized around the vessel and expected usage.
How Long Does Hot Water Stay Hot?
A properly insulated calorifier can retain heat for a considerable period, although the exact time varies between installations.
As hot water is used, cold water enters the calorifier to replace it. This gradually reduces the temperature of the stored water.
How much usable hot water you have therefore depends on the calorifier capacity, starting temperature, incoming water temperature and how quickly the water is being used.
This is particularly important when several people want showers one after another.
Can You Have Hot Water Without Running the Engine?
Yes.
You absolutely don't need to run the propulsion engine every time you want a shower.
With a suitable system, you could use a diesel heater while moored, an immersion heater when connected to shore power or an appropriate LPG water heater.
Engine heating is simply another useful source of otherwise available heat.
This flexibility is one of the reasons we like to establish how an owner intends to use their boat before specifying the system.
What Is Best for a Continuous Cruiser?
For a continuous cruiser, independence from shore power is particularly important.
A diesel heater combined with a calorifier and engine heating can work extremely well.
While travelling, the engine can heat the water.
When staying in one location, the diesel heater can heat the calorifier without needing to run the propulsion engine solely for hot water.
An immersion heater can then provide another option whenever shore power is available.
Gas can also be a practical solution for continuous cruisers, particularly where LPG is already being carried for cooking.
What Is Best for a Marina-Based Narrowboat?
A marina-based boat has the advantage of regular access to shore power.
That can make an immersion heater particularly useful.
You can heat the calorifier electrically while connected to the marina supply and retain engine or diesel heating for when you're away cruising.
There's little point burning diesel unnecessarily to produce hot water if you're already connected to a suitable mains electricity supply.
Hot Water on a Liveaboard Widebeam
Widebeams used as permanent homes can have significantly greater domestic requirements than occasional-use boats.
There may be multiple occupants, a large shower, washing machine, dishwasher and greater overall water consumption.
Hot-water capacity should therefore be considered alongside:
Freshwater tank capacity
Heating system
Electrical system
Bathroom design
Number of occupants
Available storage space
A residential widebeam shouldn't simply be treated as a wider narrowboat. The systems should be designed around the expected domestic demand.
Water Pumps, Accumulators and Water Pressure
Heating the water is only one part of the installation.
Most modern narrowboats and widebeams use a pressurised freshwater system.
A pump draws water from the freshwater tank and supplies the taps, shower and hot-water system.
An accumulator may also be incorporated to help smooth pressure changes and reduce unnecessary cycling of the water pump.
Water pressure, pump specification and the requirements of the hot-water equipment all need to be compatible.
This is particularly important when installing equipment that requires particular minimum or maximum operating pressures.
Expansion and Pressure Relief
Water expands when heated.
That needs to be accounted for when designing a pressurised hot-water system.
Depending on the installation, suitable expansion provision, pressure-relief valves and other safety devices may be required.
These components aren't optional extras to be considered after the main installation has been completed.
The calorifier, water pump, pressure settings, valves and expansion arrangements should be designed as a complete system.
What Is the Best Narrowboat Hot Water System?
The best system is the one that suits how you intend to use your boat.
For many modern liveaboards, a very flexible arrangement is:
Calorifier + diesel heater + engine heating + 230V immersion heater
That gives you three different ways to heat the same stored water.
Cruising?
Let the engine heat it.
Moored away from shore power?
Use the diesel heater.
Connected to a marina?
Use the immersion heater.
Alternatively, an appropriately designed LPG system can provide convenient gas-fired hot water and may suit owners who already plan to carry gas aboard.
There isn't one specification that's right for everybody.
Choosing Your Hot Water System When Building a Boat
Hot water shouldn't be considered in isolation.
Before specifying a new narrowboat or widebeam, we'd want to know:
How many people will live aboard?
Will you continuously cruise?
Will you spend most of your time in a marina?
Will you regularly have shore power?
Do you want LPG aboard?
Are you planning an all-electric galley?
Do you want diesel central heating?
How many showers are likely to be taken each day?
How much freshwater will the boat carry?
Once those questions are answered, it becomes much easier to design the right system.
Central Boating's Approach
At Central Boating, we believe the systems inside a boat should be designed around how the owner will actually use it.
Hot water, heating, plumbing and electrics are all connected.
There's little value in specifying a huge electrical system that doesn't suit the owner's lifestyle, just as there's little value installing an oversized calorifier that occupies valuable storage space without being required.
Depending on the build specification, our narrowboats and widebeams can incorporate calorifiers, diesel-fired heating, engine heating, immersion heaters, pressurised freshwater systems and other equipment selected around the requirements of the vessel.
The aim isn't simply to install more equipment.
It's to build a system that makes sense.
Planning a New Narrowboat or Widebeam?
If you're planning a new narrowboat or widebeam, it's worth discussing your hot water, heating, electrical and plumbing requirements together at the beginning of the design process.
Whether you want a traditional LPG installation, diesel heating, a modern gas-free liveaboard or a combination of engine, diesel and electric hot-water heating, the right solution starts with understanding how you intend to use the boat.
Speak to Central Boating about designing a narrowboat or widebeam around the way you want to live.
