Diesel central heating, or forced air combustion, was originally developed for cab or engine pre-heating in the automotive industry, this category of heating is now a common form of modern narrow boat heating. With the growth of the marine leisure market these heating systems have become highly sophisticated in functionality whilst being compact and simple to operate. Sometimes known by brand names of Webasto or Eberspacher

Forced air combustion systems are common on narrowboats after originally developed for the automotive industry
Diesel central heating can be used on a narrowboat
A thermosat can be used to regulate the temperature on narrow boat

Narrowboat Diesel Central Heating Systems… Introduction

Air and Water…

Specialist marine configured systems are available for both wet (hydronic) and dry (blown air) installations and come in a range of outputs to suit craft from small cabin cruisers to the largest wide beam boats. Both types of system can be fueled by either LPG or fuel oil. The majority of installations found on narrowboats on the inland waterways will be fueled by diesel. A forced air combustion system is commonly known as diesel central heating or referred to as the brand names, Webasto or Eberspacher.

For example, a basic installation could be a warm air blower servicing a single duct for keeping a cabin warm. At the opposite end of the scale, a sophisticated install could include heating water for domestic use through a calorifier, supplying a number of radiators and fan assisted heat exchanges controlled via a multi event timer and even integrating with a marine air conditioning system.

Electronic Control…

The use of electronic control units not only allows for simple diagnostics in the event of a fault but also enables remote heating control via smartphone applications for top of the range models.

For many narrowboat owners these systems provide the closest marine alternative, in terms of ease of use, to a familiar domestic heating system.

Pressure, Combustion, Heat Exchange, Circulation, Exhaust…

Whether the burner is diesel or gas fired the basic operating principle is the same. For hydronic or wet systems, a signal from the control unit warms up a glow plug whilst simultaneously activating a fuel pump. The motor starts up which drives an impeller. This impeller draws air in through a dedicated intake, fuel is added and the resultant mixture is pressurised and forced into the combustion chamber. The glow plug ignites the mixture which combusts. The resulting hot air combustion gases are driven through a heat exchanger which transfers the heat into the systems circulatory liquid. This liquid is pumped through the calorifier, pipe work and radiators and the expended gases are expelled through an exhaust which vents externally.

In the case of warm air blowers the principle difference is that air is usually drawn in from the cabin, passed through the heat exchanger and then pumped back into the cabin, creating a circulatory system.

Forced Air Combustion… Diesel Fuel Management

A lot has been written regarding the recent changes to red diesel we use on the inland waterways and on narrowboats. Discussions range from how tax is levied to a rise in diesel bug to increased moisture content related to the introduction of bio-diesels. Ours is not to speculated on the whys or wherefores here, only to try and be objective and in simple terms relay what the manufacturers recommend for their systems.

Reduce Service Costs…

Faults are not usually singly caused by fuel problems (aside from running out) and often arise from a combination of issues. However, careful management of our fuel and an awareness of potential fuel related issues can go a long way to extending the life of burner components and a reduction in servicing costs.

As narrow boat users, most of us cannot specify the quality of fuel we put in our tanks so have to be content with what we are given. Manufacturers of these heating systems will rightly say that the burners run best on high quality fuel and it has to be said there is no incentive for marine fuel suppliers to vend anything but good product. What we can do as users is manage how we look after our fuel and with this in mind there are a number of things we can do.

Summer and Winter Diesel…

According to the UK Petroleum industry Associations information, the UK is in a zone that specifies fuel should operate down to at least minus 15‘c. Diesel fuel contains wax, a property of which determines the fuels resistance to premature combustion. When the temperature is low enough the wax starts to crystallize & solidify, in turn blocking filters & fuel lines. To help combat this the blending of delivered fuel changes between 16th November to 15th March. Now, most of us most of the time would never be affected by this and probably couldn’t care less, but the implications for live-aboard (or even weekend narrow boaters) during the winter months are obvious. If you have summer grade diesel in your tank during the winter months you could be laying yourself open to problems. Good fuel management and rotation is the answer. First and foremost, check with your supplier as to how they manage their fuel and work with them to ensure you always have as good a quality fuel in your tank as you can.

Water from Condensation & FAME…

This storage consideration leads on to another interesting subject which we can go some way to managing. As the level in your tank falls so condensation can form on the inner walls. Diesel is lighter than water so a layer of water can build up in the bottom of the fuel tank and in in-line filters. It is for this reason there is usually a water trap in the line from the tank to the engine. The bio-diesel content of the fuel blends we buy often contains high levels of water. It’s at the meeting of the fuel and water particles that the “diesel bug”, a soup of microbes & yeasts, can breed. Again, fuel rotation can help but it is a good idea to keep the tank topped up during winter to reduce condensation build up. Many marinas and marine fuel suppliers are actively offering FAME free diesel. FAME refers to fatty acid methyl ester, or bio diesel, which is hygroscopic or in other words absorbs water. No FAME means no water absorption means less chance of diesel bug. Check with your fuel supplier and ask the question.

Check Your Filters…

Your heating unit will come with some form of filtration. Check the manufacturers recommendations before adding marine water traps or non-approved filters as the fuel delivery is usually finely calibrated and the addition of non-standard items in the fuel feed can upset this calibration. If you do decide to fit some form of filtration, please ensure the unit is to marine specification as the types of in-line filters used in road vehicle heaters will not be acceptable to your BSS examiner and could be potentially dangerous.

Narrowboat Diesel Central Heating… Installation Guide

Talk to the Experts…

Always refer to the manufacturers installation guide with specific reference to the Boat Safety Scheme. It is possible to install these units if you have good plumbing and electrical  skills but if you are unsure, ask your chandlery, system supplier, local BSS examiner or narrowboat builder for advice and assistance.

Heat in and Heat Out…

First of all, work out the correct Kw rating for your narrow boat. The “bigger the heater the better the output” is not always the best route to take.

Too Many Kilowatts…

We need to balance heat loss from the narrowboat with the heat output of the radiators. When we understand the heat loss side of the equation we can quickly realise that if the heater is only ticking over whilst keeping the radiators adequately warm, then the burner will not burn out any carbon produced in the tick-over cycle. This can lead to increased maintenance costs and potentially short burner life.

Therefore specifying a heater which can output significantly more heat than is necessary will be detrimental to the heater operation and will be of no benefit to the user.

Too Many Radiators…

On the other hand, too many radiators in the system can also be detrimental as the heater will be overworking to warm up the radiators. It may not be able to cope with the rated Kw output of the radiators and as a consequence the radiators will loose heat quicker than they gain it. The result is a cold narrow boat, or cold areas on the boat, and high fuel consumption and resulting bills.

Talk to your narrowboat / widebeam builder or canal boat design consultant and work out the best rated system for your needs.

Separate Supply Tank…

If you are lucky enough to be designing your narrowboat in conjunction with your canal boat builder, it may be worth considering the installation of a separate diesel tank specifically for the supply to the heater. This way you have greater control over what to put in it and can manage the propulsion diesel and heater diesel separately. Many owners benefit from using kerosene or domestic heating oil for the heater as quality tends to be more consistent.


The heater/burner units are usually installed in the engine bay, close to the calorifier if fitted. It is important to ensure there is adequate ventilation and fresh combustion air supply as if the air supply is hotter than the manufacturer specifies then the fuel air ratio will change and excessive carbon may be produced. Also, if the heater becomes too hot then internal electrical components can prematurely fail.


When installing pipework, pay particular attention to what the manufacturer recommends. Pipework material selection depends generally on operating conditions and what you as the customer requires. With reference to information in the Plumbing chapter, we need to be mindful of the different types of pipework available and how they work in the marine environment.

Briefly, plastic pipes are easy to install and have good insulating properties but you must make sure they are rated to deal with temperatures above 100’c and allow for any longitudinal expansion. Copper pipes are also easy to install but have a smaller curve radius. They can be used as a heat source if left un-insulated and you can purchase finned convector pipe radiators.

The biggest potential disadvantage is the systems susceptibility to galvanic corrosion if heat exchangers or calorifier coils are of a different metal such as stainless steel. Rubber hoses can also be used but are prone to sagging, producing airlocks, and temperature resistance needs checking. Unlike your domestic system, you may find main flow and return pipes should be 20mm to 22mm depending on the manufacturer.

Planning for Accessibility…

Think carefully when planning the installation. The last thing you need is to have to fully remove beds, dinettes or even kitchen units to be able to access a leaky joint. With this in mind, pipework should be installed to be as accessible as possible. If you are fitting out your own canal boat, a comprehensive narrowboat design will ensure these situations are elminated.

We can’t say it enough but please do check with the manufacturers guide to installation.

Narrowboat Diesel Central Heating… Keeping It Running!

Computerised Diagnostics…

Servicing of these units is usually a specialist task. Service agents will have the correct ECU interfaces to diagnose error codes and it is inadvisable for the home DIYer to go digging around in the internals of the heater. Depending upon the make of heater you specify, it is possible to clean and change any internal filters fairly easily at recommended intervals.

Change the Coolant…

Coolant fluid has a shelf life of around 2 years so a change of this should be planned for alongside the replacement or cleaning of any fuel filtration installations. One manufacturer recommends a 2000 hours service so build the cost of this into your narrow boat budget.

Maintain Your Batteries…

It is important to maintain a good state of charge in the narrow boat batteries. Some heaters have a low battery voltage shut-down mode. If the state of charge means a supply of less than 10.5 volts for 20 seconds or so then the heater will fail to start.

This is put into perspective when you remember there is a glow plug in the heater which will draw around 8 amps during the starting phase. In fact, some of the older heaters will draw far more and this leads us on to another maintenance/service consideration, and that is cable maintenance.

Cable Connections…

You will have already ensured that the cable size is correct for the current draw and length from the battery to the appliance. Check all terminal connections for security and if they are badly corroded, clean or replace. Check along the length of the cable for chaffing or wear to the insulation and rectify if any damage is seen.

Wet Joints…

Where you have a calorifier and/or radiators fitted as part of the heating system, it’s good practise to go round them every so often checking for leaks at pipe joins. As we mentioned earlier, pipework expands and contracts during the heating & cooling process so joints and junctions, including hose clips, can become loose in time. Most pipework is neatly hidden beneath plinths at floor level but trust us, it’s well worth an hour or two with a screwdriver removing them every now and then for peace of mind.

Fail to Plan and Plan to Fail…

Why not consider doing the majority of checks and any maintenance during the summer months as it’s an unwritten law that the heating will fail when you need it most!

Diesel Central Heating

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