Best boat heaters – diesel, solid fuel or warm air central heating?

Charter holidays were about lazing around in the sunshine, I’d always thought, but when my PBO colleague Laura Hodgetts invited me on a spring charter holiday to the Polish lakes it was a very different experience. Our Antila 33.3 was a fairly simple yacht with no electronics, but it did have something I considered extremely luxurious… heating!

After fun-packed days exploring historic towns, pine forests and World War II bunkers, we’d cosy up at anchor with a bowl of freshly cooked pierogi (dumplings) and sauerkraut, and play cards with our charter hosts, Patrycja and Wojtek. Aching from the exhilaration of pulling ropes and grinding winches, it was wonderful to retire to a warm saloon, later to be lulled to sleep by the quiet whir of the blown-air diesel heating.

It’s possible to install your own diesel heating system

I soon realised you don’t have to own a boat with all the mod cons to benefit from heating, and if you’re in northern climes it can make all the difference between laying up for winter, or enjoying off-season sails and making the most of quiet, secluded anchorages.

How to choose the best boat heaters?

Daniel Hawkes of Keto, a dealer for Webasto, explains that any size yacht can be fitted with a diesel air heater.

“We’ve done a Cornish Shrimper, Merry Fischer 695 and Beneteau Antares,” he says. “Since Covid, we’ve seen a new wave of boaters that are definitely younger, and they don’t want to slum it the way previous generations did. Their perception of what they want is what they’re used to and they’re not going to compromise. If they want to do that, they can go camping in a field.”

The good news is that heating systems come in all shapes and sizes to suit your budget and fuel type. A simple setup would be a solid-fuel stove that burns wood or coal, or an LPG (gas) heater, fuelled by propane or butane.

Webasto’s reverse-cycle air conditioner also acts as a heater. Credit: Webasto

More sophisticated systems include electric heaters – which unless you have a substantial battery bank tend to require a generator or run off shorepower – and diesel heating, either as ‘forced air’ or ‘Hydronic’, the latter being a system that involves a boiler and can heat water too.

There are also air conditioning units known as ‘reverse-cycle’, which can generate both cool air and warm air, but only if the sea temperature is sufficiently warm. Most cruising boats are fitted with separate systems, with air conditioning running on electrics, and heating on diesel.

The output of heaters is either rated in kW or BTU/hr (British Thermal Units), with 1kW being equivalent to 3,412 BTUs.

In addition to heat output, you might want to factor in consumption, emissions and the amount of space your heating system will take up. If you’re simply after a solution for keeping frost and damp at bay over winter, a low-wattage plug-and-leave tube heater such as the Dimplex ECOT1FT will do the job, especially if combined with a dehumidifier. But for this article, let’s assume you’re after a heater to keep the crew toasty while onboard.

Best boat heaters: Solid fuel

A solid fuel stove provides a powerful, reliable heat that needs no electricity and is completely separate from your engine or battery bank. PBO contributor Rupert Holmes runs a charcoal heater on Ammos, his 30ft Discovery 3000.

A solid fuel stove is simple to run and maintain. Credit: Max Liberson

“It’s certainly not as convenient as a more sophisticated warm air type system,” he admits, “but it 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 winter.”

While Rupert’s UK heater is no longer produced, he recommends as an alternative the Newport Solid Fuel Heater from Dickinson Marine. This small, stainless steel unit is intended for casual use, burning 1in to 2in-thick wood, a handful of charcoal briquettes or coal, and has an ash tray and damper control. You can also burn presto logs, which are made of compressed, recycled wood waste such as sawdust.

“Multifuel stoves can also be good in larger boats, but the advantage of a charcoal heater is the compact flue,” advises Rupert. “With a diameter of around 1½in (4cm), this is easier to fit and far more compact than the 4in (10cm) flue needed for burning wood.”

Best boat heaters: LPG

Many boats, from weekend cruisers to liveaboard narrowboats, already have an LPG system running for the galley stove, making the addition of an LPG heater a convenient extension of a ready fuel supply. Unlike diesel heaters with their distinctive pump and fan noise, many LPG models run quietly. They’re also more convenient than solid fuel stoves as the fuel has a much higher energy density, making it easier to stow.

An LPG heater is a straightforward solution if you’re already using gas for your galley

Every appliance that burns fuel is potentially lethal, but LPG is heavier than air which means any leak will collect in the bilge. A properly installed system is perfectly safe, but a poorly fitted one could be disastrous. Your boat should have a gas-safe locker, drainage vents and a carbon monoxide detector.

The Newport P900 Propane Fireplace is designed with a unique vent system allowing the combustion process to be isolated from the boat’s interior, and has a built-in blower for even heat distribution.

The Propex HS2000E Heater, meanwhile, is a blown-air system powered by propane/butane gas, but with a 230V mains electric option.

On the portable side, Compass24 sells mobile and petroleum heaters, but warns that a gas heater produces water as a combustion product, so moisture is an issue to consider.

Due to the risk of carbon monoxide, they shouldn’t be used as a night-time heat source, and are described as ‘not optimal’ for long-term heating solutions.

Best boat heaters: Electric

An electric heater is quick to warm up a small boat, but the downside is it requires 230V shorepower, and has a high consumption compared to other types of heaters.

Compass24 sells a range of fan heaters, with the Ceramic Heater being wifi controlled. The Ecomat 2000 Classic has an overheating protection and safety switch in case it topples.

Dimplex oil-free 2kW Column Radiator is energy efficient and heats up fast. Credit: Dimplex

PBO’s sister magazine Yachting Monthly produced a buyers’ guide to portable heaters, rating the Dimplex Essentials 2kW Oil Filled Radiator as giving the best all-round heating performance, and the Dimplex 2kW Oscillating Ceramic Heater best for instant room-filling heat.

Note that Dimplex now sells oil-free portable heaters, such as the 2kW ECR Column Radiator, which it claims has up to 30% faster warm-up compared to oil-filled and uses 10% less energy.

Best boat heaters: Combined air-con/diesel air heating

A combined diesel air conditioner and heating system uses what’s known as a reverse-cycle air conditioner.

In cooling mode, the sea is the unit’s raw water source, and there’s an overboard discharge for the excess heated water. In heating mode, the direction is reversed; the evaporator becomes the condenser and vice versa. Heat is extracted from the sea water and directed back into the cabins.

Note that these reverse-cycle systems stop working effectively when seawater drops to around 4°C to 6°C.

Combined heating and cooling systems are best suited to larger vessels as the larger, noisier parts can be kept in the engine room, and you can add a diesel water heater into the circuit for when the outside water temperature is too cold or the generators are switched off.

On the other hand, diesel or fuel-fired air and water heaters can operate in much colder – including sub-zero – air temperatures.

Best boat heaters: Diesel air heating

Air heating, also known as ‘forced’ or ‘blown-air,’ draws a small amount of diesel from the boat’s main tank (or a separate tank, if on a petrol boat) and blows warmed air into cabins via ducting. Typically fitted on boats from 22ft up to 70ft, it provides rapid heat, with minimal start-up time, with setup costs starting from under £2,000.

Systems range between 2kW and 8kW, and the right one for your boat doesn’t necessarily come down to size, though this is the main indicator. Other factors include the type of boat, the amount of glazing, the number of cabins, the boat’s thermal insulation properties, and your intended cruising area. Your dealer, or installer, will be able to survey your boat and make the calculations.

Webasto’s Airtop 2000STC diesel heater. Credit: Webasto

On our early season Polish charter, the 2kW Webasto diesel heater warmed the 33ft boat nicely, using about 2lt of fuel a night. However, as a rule of thumb you’re looking at 2kW for sub-30ft boats; 4kW for 30-40ft boats; 5-6kW for 40-50ft boats and 8kW+ for boats over 50ft. Bear in mind the whirring fan and tick of the fuel pump means they’re not a completely silent option, and although primarily running off diesel, will use a modest 1-3A to run the fan, which will need to be factored into any off-grid power equations.

You can self-install a diesel-heating unit, or pay to have it installed, on any vessel, be that a yacht, powerboat or canal boat. Installers such as Webasto and Krueger will also service and repair units. Some models of diesel air heater, such as Webasto Air Top 2000S will also act as a dehumidifier on ‘fresh air’ mode.

Diesel air and water heating

A combined air and water heater has an internal burner which heats hot water and pumps it around the boat through pipes. Heat is dispersed into the cabins through radiators, towel rails or through air vents via an electric fan.

While these take longer to generate heat than blown-air units they can also be used to heat water for washing-up and showers, without having to run the engine.

Stay safe

Sadly, there are cases every year of carbon monoxide poisoning from boat heaters, whether cheap Chinese heaters or exhausts bought online, blocked flues or, for example, a kerosene heater running in an unventilated space. Fuels such as gas, coal, wood, oil, paraffin, etc. need sufficient air to burn safely.

Have fuel-burning appliances checked by a qualified technician. Marine surveyor Ben Sutcliffe-Davies recommends a CO detector be fitted in every cabin. Ensure your alarm is certified (BS EN 50291-2), test it routinely and never remove batteries except to replace them.

Heaters represent a cross-section of the market but other brands are available

Diesel heaters: expert Q&A

Sam Goodland is the sales manager of Krueger, a dealer for Eberspächer

Which units do you sell?

We sell mainly Eberspächer diesel heater units, and look after heating and air conditioning for a lot of trade companies that run commercial charter fleets. We also deal with individual boat owners, and in fact have seen an increase in people wanting to fit the unit themselves. We’ve noticed people seem to be getting more competent. Probably down to your articles!

Self-installation is fine as long as you follow the rulebook, and we can arrange a video call or check in person to ensure it’s fitted correctly. Eberspächer does a one-year warranty if you fit the heater yourself, and three years if you use an accredited dealer.

What’s the smallest size boat that can accommodate diesel heating?

You can have a heater on anything from 22ft upwards. Sometimes customers request them for open cockpits with covers, though of course you have to take into account the heat loss. Note, the unit itself is hidden in a locker, never exposed. A cockpit locker or lazarette is pre-ventilated so it can go in there. If it’s in an engine bay we’d duct the heater to a fresh air source, either in a locker or back inside the living area. The latter is more efficient as it’s recycling the existing air.

The compact Eberspächer diesel air blown heating unit. Credit: Ali Wood

Does it use the boat diesel tank?

The diesel comes from the same tank as the engine. A standard system will have a standpipe that feeds from the bottom minus 10-15mm so it doesn’t suck up the gunge. If you have diesel bug, the heater will be the first thing to show because it’s got a tiny little fuel pump which is a lot more sensitive than your big engine one. So if you have any issues with fuel, the heater will come up with a fuel code and let you know it’s either blocked or the fuel quality isn’t good enough.
How much diesel you use depends on the size of the heater. On a 2kW heater, you’re using 0.5lt/hr on maximum, 0.12lt/hr once it drops to the lower setting, so over 8 hours overnight on a 32ft sailing boat, around 1.2-1.5lt.

What if you’ve a petrol boat?

MCA Coding prohibits a petrol heater on a petrol boat because it’s too combustible. Petrol boats can have diesel heaters, and these will be fitted with a separate diesel tank. The electronic ignition heater can’t be in the same locker as an existing petrol tank near petrol fumes.

Eberspächer’s Hydronic diesel heating system heats water

How does the air and water combi system work?

Eberspächer’s Hydronic system works like your boiler at home. You have a base boiler that feeds a coolant circuit going around the boat, and you’ve got your calorifier just like a hot water tank at home. To generate heat you can use a radiator, towel rail or a fan matrix. The latter is effectively a radiator with a fan on the back and it spreads the hot air really nicely rather than like with a radiator where it heats the one corner. If you want hot water as well as heating this is a good system, but it’s more complex and therefore more costly. Hydronic water heating systems are easier to fit on larger boats because of the smaller diameter of the coolant pipes.

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