The best diesel heaters for boats have seen some great improvements over the past few years. They're the most common form of heating onboard motorboats and sail boats. Duncan Kent talks through the options and what to avoid.
Best diesel heaters for boats – This article was first published 7 July 2021 – it was revised and updated 15 December 2023
I live on my boat all year round, come rain, hale, snow and heat wave. The climate I live in lends itself to having some reliable heating fitted. It can be very tempting to try one of the very low priced copies of the real deal heaters from Webasto or Eberspacher.
A good number of the low-cost, often cloned diesel forced air heaters available online do not conform to UK or EU laws and regulations.
Most budget diesel forced air heaters were originally designed for trucks or motorhomes, which have different requirements and are not subjected to such a vigorous environment as that found in a sea-going yacht.
I bought a second hand Taylors Paraffin heater for one of my boats, after paying for it to be professionally serviced and important bits replaced, it was still slightly less expensive than new, but not by much.
I chose the Taylors heater because it requires no electricity at all. But it’s a faff compared to pressing an igniter button and having hot air pumped around the place which is what you get with a blown air heater. The downside is that they need some electricity to keep working and they’re noisy, especially for the neighbours who have to put up with the exhaust noise.
There’s a few second hand heaters on the market. Make sure if you do buy something second hand, that you get it professioanlly serviced and also when running any kind of combustible burner inside your boat ensure you have a good quality carbon monoxide detector fitted to your boat.
Buyer beware. We recommend trusted heater manufacturers with certified warranties and customer service backup. Buying a diesel heater intended for use in road vehicles rather than boats, or a diesel heater that does not meet UK safety standards, could pose a risk to life.
If you want heating you can trust then here’s our guide to the best diesel heaters for boats
We’ve divided this guide into two sections, with the best boat heaters for boats up to 38 foot and the best diesel heaters for boats over 40 foot.
The best Diesel heaters for boats up to 38 foot
Eberspacher Espar Airtronic S2 D2 L 12V 2.2kW (7500BTU) with EasyStart PRO 7 Day Timer
One of the most popular manufactures of best diesel heaters for boats , Eberspacher, has recently upgraded its Airtronic heaters, giving them a power boost mode for fast initial heating plus continuously variable temperature settings.
They also now have a fresh air mode to improve air circulation through the boat on warm days.
Years of continual development has made these heaters more economical, quieter and more importantly, reliable.
The wide range of controls on offer includes various panels with switches and LCDs, or there’s the latest, EasyStart Call, which allows you to operate your heater using the proprietary smartphone app.
The app turns your phone screen into a simulated control panel and transmits your selected settings to a GSM module installed in the heater.
Models include the Airtronic D2 and S2 D2L (<32ft LOA), D4+ and M2 D4L (26-39ft), D5 (36-49ft) and the D8LC (49-62ft).
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Webasto Air Top 2000 STC 12v Marine diesel boat heater kit
Webasto’s steplessly modulated heating systems are renowned for their high build quality, performance and reliability.
The range features numerous safety devices and procedures, including flame detection and exhaust heat sensing, to ensure safe operation.
The smaller and less sophisticated model is its Airtop 2000STC, a 2kW heater that offers up to two outlets, thermostatic controls, external temperature sensor, air intake silencer and low-noise fuel pump.
The new MultiControl digital timer/temp controller offers instant access to functions plus a quick start button and is sealed against water ingress.
Webasto are known as one of the leading manufacturers of best diesel heaters for boats and appear much the same as Eberspacher heaters… but they are different and have small differences.
For larger yachts there’s the high-output, multi-mode Airtop Evo 3900 (<40ft) or 50 (<50ft).
Both are powerful, yet quiet and economical and can be controlled using a MultiControl, a TeleStart wireless remote pad or via a mobile phone app using its ThermoCall system.
The temperature is regulated using intelligent blower control whereby the heater output and fan controls are separately sensed to reduce power and fuel consumption.
The Evo series has also been upgraded with ECO mode for reduced electrical power consumption, Boost mode for maximum output and Ventilation mode to provide fresh air to the cabins on a hot day.
Wallas 22GB Coastal Kit
Wallas recently updated its 2.2kW (22GB) and 3.2kW (30GB) Nautic models by changing their blower motors to brushless types.
The result is more power and output capacity, allowing the boat to heat up quickly, efficiently and quietly.
Its new laminar flow burner offers low emissions of CO2 and NOx, and is designed to work with blended bio-diesel.
Renewable materials are used in its construction, although it retains high-grade aluminium components where necessary.
The new control panel offers smooth PI-controlled thermostat adjustment and two-step air boost protection against accidental operation.
Like most systems now, Planar heaters can be controlled via your phone
New kid on the block, Russian-built Planar heaters appear to be a genuine compromise between cost and quality, although there seems to be little difference in the latter to the higher-priced brands.
Planar’s UK distributor is currently small, yet it holds a full range of spare parts (unlike many of the cheaper Chinese models) and the reviews on its service have so far been excellent.
Its Autoterm Air marine range comprises a 2kW and 4kW heater; however, larger units can be made specifically to suit.
The standard kit comes with a basic rotary control panel offering stop/start, capacity and air temp control and LED indication of heater status.
The next level has an additional seven-day timer, ventilation mode and an LCD for temperature indication.
Finally, there’s a GSM modem option with smartphone app for remote operation via the mobile phone network.
This offers all the features of the more advanced LCD control panel, only on your smartphone.
Visit www.planarheaters.co.uk
Refleks Stove Heater Refleks 11032-66M heater
The Refleks stoves are popular with more traditional year round cruisers. Seen in working boats, fishing boats and a wide array of sail boats and traditional motor cruisers, the Refleks diesel heaters are king of the cold. They’re sturdy drip fed units that radiate heat rather than blow it around.
The larger Refleks stove heater models have additional internal pipework that allows further radiator heat or hot water heating. This small unit is the most basic and most budget friendly though and considered practically bomb proof.
The advantage of the drip fed heaters is that you don’t get the loud exhaust noise associated with blown air diesel heaters.
Total heat output: 1.6 kW (1400 kcal/h)
Fuel consumption: min. 0.12 l/h
Fuel consumption: max. 0.30 l/h
This one is for area volume sizes of approx. 14 – 23 Cu. Mtrs.
Buy now from Hartlepool Marine Supplies
for more info on Refleks heaters go to the manufacturer site
Blakes Lavac Taylors Diesel Heater Britannia 079D Stainless Steel
Fuelled by red or clear diesel, fed from from its own gravity tank – Header tank version – or pumped direct from the boat’s supply – main fuel tank version.
It is a superbly simple heater for boats. Fitted to a bulkhead the heater radiates heat rather than pumps hot air around ducting.
As a gravity fed unit this is virtually silent running.
An excellent choice for anyone wanting to live aboard or use their boat year round. This model suits a smaller boat up to 38 foot.
Features:
Made of high-quality materials well bolted together
Up to 2.1 kilowatt output
Front opening door gives access for maintenance or adjustment
Supplied with a 1.5 gallon tank, a safety on/off fuel control valve, in-line fuel filter, pipe work and fittings for installation
Externally vented and bulkhead mounted
Through-deck fitting flue sections also supplied
Available in a brass or a Stainless Steel finish.
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A digital timer offers instant access to functions
Webasto Air Top Evo 3900 Marine Heater
Webasto’s steplessly modulated heating systems are renowned for their high build quality, performance and reliability.
The range features numerous safety devices and procedures, including flame detection and exhaust heat sensing, to ensure safe operation.
The new MultiControl digital timer/temp controller offers instant access to functions plus a quick start button and is sealed against water ingress.
ECO mode for reduced electric consumption, power mode PLUS for +10% more heat output (from 3,500 W to 3,900 W) and ventilation mode to supply fresh, cold air to the interior on hot days.
It is supplied with a universal marine kit which includes copper fuel piping and appropriate connections, fittings for installation and rotary controller. Ducting or Outlets are sold separately as an added extra.
Fuel Consumption Control Range: 0,17 – 0,42 l/h -Nominal power consumption control range: 15-36W –
Weight: 5.9kg -L x W x H: 425 x 148 x 148 mm
Webasto Air Top EVO 40 4kW 12v Marine Heater Kit with MultiControl HD 7-Day Timer
The Webasto Air Top EVO 40 is compact, quiet, and economical heater requiring from 0.18 to 0.43 litres of diesel per hour.
Suitable and trusted for many types of marine installations and certified for installation in passenger areas and in proximity to dangerous substances.
This Webasto Air Top EVO 40 heater comes with a complete installation kit to install into your boat. This components option can also be viewed perhaps as a starter kit, supplied with basic electronic temperature control. This kit does not include ducting or air outlets – please see our range of additional ducting outlets and digital controllers to enable a truly bespoke and cost-effective Marine solution.
Marine 12volt 4.0kw kit Contents:
• Webasto Air Top EVO40 self regulating 12 volt air heater with
• MultiControl HD 7-Day Timer with On-board diagnostics
• All electrical harnesses and connections
• 1.8m Stainless steel exhaust silencer supplied with lagging insulation (measured lengths of 24mm stainless steel exhaust pipe are available if required)
• Copper Fuel pipe system, complete with fuel metering pump
• 1 x Fuel Stand Pipe
• All necessary clips and screws for this installation included
• Comprehensive installation manual
• Stainless steel Heater mount bracket
• Stainless steel exhaust hull skin fitting
• Webasto Air Top EVO40 24 months warranty
Eberspacher Airtronic M2 D4 L 4KW 12v Diesel 2 Outlet Marine inc Easy Start PRO
One of the best known makes of marine heaters, Eberspacher, has recently upgraded its Airtronic heaters, giving them a power boost mode for fast initial heating plus continuously variable temperature settings.
They also now have a fresh air mode to improve air circulation through the boat on warm days.
Years of continual development has made these heaters more economical, quieter and more importantly, reliable.
The wide range of controls on offer includes various panels with switches and LCDs, or there’s the latest, EasyStart Call, which allows you to operate your heater using the proprietary smartphone app.
The app turns your phone screen into a simulated control panel and transmits your selected settings to a GSM module installed in the heater.
Models include the Airtronic D2 and S2 D2L (<32ft LOA), D4+ and M2 D4L (26-39ft), D5 (36-49ft) and the D8LC (49-62ft).
Buy it now from heater parts direct
Eberspacher Hydronic S3 HS3 Universal 5kW 17000BTU Vehicle Water Heating Kit including Easy Start PRO 12v
Diesel fired water heater with 5 kW heating power, for cabin interior saloon heating and engine pre-heating.
The Hydronic can heat domestic hot water if coupled with a plate heat exchanger, hydroplate or calorifier.
The kit includes
Eberspacher Espar Hydronic S3 D5E CS
Water pump and fuel pump
Easy Start Pro Controller with 7-day timing and altitude switching
Heater wiring harness and electrical accessories
Mounting bracket and fixing bolts
Features:
Stepless modulated heating from 1.3kW up to 5kW depending on requirement.
dimensions: 215 x 91 x 144 mm.
Silent running fuel pump
The Hydronic S3 Economy has a service life of 3000 hours. That’s just over 8 hours a day for 365 days of the year!
Buy upgrade kit from Butler Tecknik
Buy complete kit from Butler Tecknik
Note: We may earn a commission when you buy through links on our site, at no extra cost to you. This doesn’t affect our editorial independence.
Common issues are incorrectly designed exhausts, corrosive steel clips, screws and brackets, plastic fuel lines and filters, and non-watertight casings.
Some really cheap models lack thermal sensors, overheat alarms and shutdown modes, thereby presenting a very real risk of an onboard fire should the heat outlet accidentally be covered by a carelessly placed sail bag or drooping sleeping bag.
There’s also the possibility of carbon monoxide entering the boat if a fender is left dangling over the exhaust while the heater is running, or if the silencer is of poor quality with crimped, rather than welded seams.
All these are very typical scenarios found on a cruising yacht and highlight the need for the appropriate, built-in safety devices listed in the regulations.
Recent advances in diesel forced air heaters
As with most marine equipment, heating systems have been subject to gradual improvement over the past decade, both in regard to technical features and from a safety point of view.
Many are also now more economical on fuel and efficient on output, and the introduction of brushless fan motors has resulted in them using less electrical power and running much more quietly.
New glow ‘pins’ rather than the older style glow ‘plugs’ have greatly improved fuel burn efficiency too and gone a long way towards eliminating ‘coking up’.
Many recent diesel heater models now have a boost function just to pre-warm the boat and an eco-setting in which it just ticks over enough to retain the temperature within a narrow range.
There has also been a good deal of improvement in the controls.
In the past they’ve been simple electro-mechanical devices with either a rheostat or multi-way switch to select the temperature range.
Then along came more accurate controls with LCD displays and built-in seven-day timers.
Now, there are wireless remotes on offer and you can even control heaters by mobile app or online, so that you can switch the heater on when you’re a few miles away and climb aboard a toasty boat whatever the weather.
How much will a diesel forced air heater cost me?
It’s important to work out what you need for your installation before attempting to compare prices.
Most kits come with enough bits for a single outlet and the minimal amount of ducting. So, if you want two outlets, you’ll need to measure carefully and price it in, along with a grill and a T-piece connector (£60).
Many owners now fit silencers to the fresh air intake as well, to quieten the ‘roar’ heard with older models, plus anti- vibration rubber mounts to lessen the sound of the fuel pump are also available.
Continues below…
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The cost can increase if you want a fancy controller, too.
They usually come with just an analogue rotary-type knob with an LED or two to indicate operation status.
While this might suit some, others may want a remote panel with an LCD to show what’s going on (£150- £200), or even control via their phone.
Don’t be fooled by the ‘free’ app though, it’ll only work if the heater is connected to the GSM network, and that involves buying a modem and a SIM card (£200-£300, plus around £7.50/ month for the SIM).
If you get an advanced control box it’s worth fitting a temperature sensor. Finally, check how long the standard control cable is, as an extension can sometimes mean it’s cheaper and easier to opt for a wireless remote (£150).
Marine heater safety
Many of these heaters are designed for vehicles and don’t always list a specific marine kit.
Check the kit contains enough lagging to double-lag the exhaust and make sure the exhaust outlet is stainless or bronze and angled up to allow for a swan-neck in the pipe to eliminate back-feed of water.
It is also worth double checking the kit is marine specific.
Automotive heaters are designed to be fitted externally, so do not require the same standard of air-tightness on the joins around the exhaust and on the welds around the silencer.
Similarly, metal fittings may be galvanised rather than stainless steel, and vulnerable to rust, and fuel lines not of the same specification.
The critical safety issue is that of carbon monoxide.
A properly installed heating system will run without issue, but as we’ve seen too often, an exhaust leak or other fault can be fatal.
All boats should have a CO alarm anyway, but check yours is in date and working.
FIREANGEL FA3820-EUX10 BATTERY STANDALONE CARBON MONOXIDE ALARM
Buy carbon monoxoide detector from Screw Fix