Living With Our Rapido 963f Le Randonneur Motor Home.

Tuesday, 4 October 2011

Deciding on a diesel boat heater

During the summer I was forced to consider replacing the central heating boiler on Kelly Louise because the Alde gas fired unit had sprung a leak, and, due to my own circumstances with this particular installation, there were all sorts of problems associated with rectifying the situation. Once I had decided to go for a brand new installation I conducted much research into the pros and cons of individual systems that are currently available, both in fuel type and brand. After deciding to replace with a diesel fired unit, I then researched the various brands and the (many) reported problems that had been associated with this type of heating in general. My final decision to buy was made, based on many factors which included cost, accessibility to a company who could complete the whole job that I required, and the reviews relating to the individual brands. Although this is my own personal opinion, I concluded that the Hurricane heater was probably the best option to fit, but due to cost, and the proximity of a supplier who could complete my own particular job, I chose to fit a Webasto Thermo Top C unit, which, so far, has worked very well. Here are some of the reasons I found along the way, why there have been reported problems associated with diesel boat heaters........
The problems relating to diesel heaters can be split into three categories.

The design of the installation.
Most people, when buying expensive pieces of kit such as this, would try and buy the best and biggest unit they could afford, thinking that they will be nice and cosy next time there is a major drop in temperature. With this type of heater, this is not the case. A large heater fitted to a small system will not work to its designed efficiency level, and will "tick over" most of the time, causing a build up of carbon. So, the first point of design is to calculate the correct output of a heater that will match the radiators and the calorifier that are or going to be fitted to the boat.
Once a suitable location for the heater has been decided upon, usually the engine bay, it should be noted that these heaters are not designed to intake their air supply any hotter than 25 deg C, so fitting an air intake from the outside (not a living space) should be considered.
Consideration should be given to the fuel tank that will be used to supply the heater. With the current tax legislation on fuel, it would be prudent to install a separate tank, which would future proof it against any further derogatory taxation.

*However, if the existing tank is used, a separate, smaller bore standpipe (better still the manufacturers own kit), should be fitted into the tank to supply the heater, with a similar small gauge supply pipe that doesn't pass through an engine type filter. A large diameter fuel stand pipe, (i.e. 12-15mm) or fuel system can cause two problems. 

1). It will alter the finely calibrated fuelling being delivered to the heater due to the fuel metering pump having to fight against the weight of fuel in the pipes. This in turn will cause a poor burn and a premature build up of carbon.
2). In some cases the weight of fuel hanging in the standpipe can overcome the one-way ball valve in the fuel metering pump and over a period of time the fuel will start to siphon back to the tank. This will cause the heater to take one or two attempts to start.

The consequence of supplying fuel to a heater through a large engine type filter is damage to the fuel pump's plunger due to excessively long priming times, and in some cases it can take upwards of 50 start attempts to sufficiently prime the engine fuel filter. During this time the pump is running without sufficient lubrication, which can affect its calibration. In both these cases the heater may appear to be working fine, but may fail over a twelve month period due to carbon build up caused by incorrect fuelling.

If the fuel metering pump's plunger has been severely damaged by running dry, then it may fail totally. It is thus imperative to install the correct fuel system and fuel tank stand pipe for your chosen heater*.

If a standard flow and return system of radiators is used, then one of the radiators, possibly a bathroom towel rail heater, should be incapable of being turned off. This will provide a bypass if all the other radiators are turned off.

Correct operation.
Many problems relate to "short cycling" of the heater, constantly forcing it to turn on and off, which causes the build up of carbon. For example, if the hot water is run off while the heater is on, this will force it to fire up again to bring the system back to temperature. Turning the heater on and off over too short a time can also cause this problem, and these heaters are generally not suitable to be placed on frost protection, only coming on around freezing point, unless it can be designed so that the radiators are allowed to heat up to their full temperature, so that the heater can run longer rather than on tick over. I believe the Webasto that I have does have electronic protection which stops the user from forcing short cycle use.

Type and quality of fuel.
The standard for red diesel, used on canal boats, until recently, was BS 2869. The standard for road diesel is higher at EN590, and this is still not widely available on waterways. Most heaters are however designed to run on EN590 diesel, but manufacturers generally agree that there should be no problem using the waterways diesel, as long as it is fresh. Diesel fuel starts to degrade if left in the tank longer than 6 months, so if possible, the diesel should all be used and replenished regularly. If fuel additives are used, they should be checked for suitability to use with your chosen heater. This is another good reason to use a separate small tank just for the heater.

The above are just common sense solutions to the potential causes of problems.

*I am indebted to Peter Collard, Technical Engineering Manager, Eberspacher (UK) Ltd. for providing further detailed information after reviewing my original article, regarding possible fuelling problems caused by incorrect installation, which I have now included as above*.

The Webasto UK marine website can be found here: Webasto Marine
The Eberspacher UK website is here: Eberspacher
The Hurricane Marine website is here: Hurricane diesel heaters

Other makes of diesel heaters that are not mentioned here are also available.

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