Choosing the best boat heater depends on a number of factors, explains Rupert Holmes, and you should also have a marine-compliant carbon monoxide detector

Diesel fuelled heating systems

Having a warm boat can significantly lengthen the sailing season, but the best boat heater for you depends on budget, the size of your boat, and whether or not you wish to install it yourself. In many cases fitting a commercially produced heating system can now be less expensive than it has been for decades. Part of the reason for this are the Autoterm diesel fuelled heating systems that sell for a fraction of the price of more established brands. And there are even cheaper unbranded heaters available online, though these rarely have type approval that’s valid in the UK or the EU, which makes installing one a risk that may not be covered by insurance. At the top end of the market the very best units have become even more efficient and quiet.

Solid fuel heaters

In my view, however, the first step in fitting heating is to consider whether a basic solid fuel unit might be all that’s required. I have a very simple charcoal heater on Ammos, my 30ft Discovery 3000 in Greece. It’s certainly not as convenient as a more sophisticated warm air type system, but took only two hours to fit, needs next to no maintenance and a €5 bag of lumpwood charcoal lasts the best part of a week in the depths of winter. On the downside it takes around half an hour to warm up, so a cold morning necessitates lighting the heater, then going back to bed to read the news. And enough fuel for extended periods is bulky and difficult to stow. The UK-built type I have is no longer produced, but the Newport Dickinson range offers good alternatives at reasonable prices.

A simple charcoal heater is quick to fit and can transform life on board

Multifuel stoves can also be good in larger boats, but the advantage of a charcoal heater is the compact flue – with a diameter of around 11∕2in (4cm) this is easier to fit and far more compact than the 4in (10cm) flue needed for burning wood.

Paraffin heaters

Paraffin heaters and drip-fed diesel stoves are less common these days, but are more convenient than solid fuel stoves as the fuel has a much higher energy density, making it easier to stow. It has to be remembered that every appliance that burns fuel is potentially lethal. By opting for a properly installed, type-approved product you minimise the chances of death through carbon monoxide poisoning.

Carbon monoxide alarm

carbon monoxide alarm

Any heater that burns fuel, whether diesel, gas, timber or charcoal, has the potential to emit carbon monoxide, a clear and odourless gas that can kill. It’s therefore important to fit carbon monoxide alarms. Domestic models are not recommended – look for units that conform to the EN 50291-2:2010 safety standard and are specified as suitable for marine use (the standard also covers caravans and motorhomes). My preference is an alarm that also has a digital read-out, as levels can be monitored before the alarm is triggered.

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Warm air central heating

A key advantage of warm air central heating type systems is they’re quick to warm up and can also be fitted with a timer, or remote control, for automated operation. The price gap for these systems compared to solid fuel has reduced, but disadvantages include the time needed for installation and their consumption of electricity. If doing the installation yourself, plan exactly where every element of the system needs to be located, then allow a full weekend with a helper for fitting. Newer models are much more efficient in their use of electricity, especially the latest units from Eberspächer, than those of two or three decades ago and are also quieter in operation. We also have more forms of generating power than 30 years ago and my experience on the south coast of the UK consistently says a 100W solar panel will usually cover the electrical requirements of a 4kW unit for two or three days a week, even in the depths of winter.

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Reliability has also been a long-running worry for many, but this shouldn’t be a concern for carefully installed systems maintained according to manufacturers’ schedules. It’s worth noting that many problems are associated with a build-up of carbon at the business end of the unit. As this is accelerated when the device is running at low power it’s often worth resisting the temptation to fit an over-sized device – a smaller one that’s run hard may be a better long-term option.

Reliability problems can also stem from wiring. A couple of years after installation the heater on Zest, my partner’s 36ft-footer, became difficult to start up. When trouble-shooting we measured the voltage at the unit – despite the 4m wiring run being within specification, there was a 1.5V drop over the length of the wires. Replacing this with oversized wiring two sizes larger solved the issue at a stroke.

Spending time on board out of season means condensation can be as big a problem as keeping warm. If only the saloon is heated, warm, moist air that escapes into cold cabins, heads compartments and lockers will create large amounts of condensation in these areas.

Ensuring heat can reach as many parts of the interior of the boat as possible is therefore important and confers a clear advantage to systems that duct heat to every area on board. Beyond that, either good ventilation or a dehumidifier is important to keep condensation at bay.