An Analysis Of Boat Heating Systems

We have long heard the praises of the Danish Refleks diesel drip heater sung by the many expedition sailboat owners that have them, but since we simply don’t have a good place for one, or its chimney, on Morgan’s Cloud, we had never had the chance to use one before the month we spent on Polaris in Greenland. During that month, the Refleks heater burned 24/7 with total reliability and perfect combustion, with no smell of diesel or smoke, despite some strong and gusty winds.

The Refleks has many advantages over the Eberspacher (Espar) bus-type diesel hot air furnace that we have long used on Morgan’s Cloud including:

  1. The Refleks is a fundamentally simple piece of gear. About the only major spare you need is a regulator. Contrast that with the Eberspacher and Webasto heaters, which are complex computer-controlled furnaces with scores of parts, the failure of any one of which can bring the whole system down. On Morgan’s Cloud we have pretty much a whole spare heater in parts. Having said that, I have to admit that in the 12 years and the approximately 6000 hours it has run since we fitted it, the Eberspacher has never let us down—but read on to learn about the cost of this reliability.
  2. Ideally, the Eberspacher and Webasto heaters should be completely stripped and cleaned, as well as having the glow plug and some other small parts replaced, every one to two years. Although I have taught myself to do this from the service manual, it is not a process for the mechanically faint of heart. In fact, I dread it enough that when we are near a dealer I trust, I delegate it to them. Worse, the fan units in the Eberspacher only last some 2000 hours and are a real pain to replace. The result is that we tend to replace this part on a preventative basis before the end of its life, further adding to the cost of operation. The Refleks requires more frequent cleaning but this is a simple process that uses no expensive parts. Michael (owner of Polaris) informs us that the cleaning requirement is monthly for the Refleks when running continuously and more often when used intermittently since the lighting process dirties it more than continuous operation.
  3. By far the biggest advantage is that the Refleks uses absolutely no electricity in contrast to the furnaces, which are hogs. Our Eberspacher can eat through 70-100 amp-hours in a 24 hour period when it is really cold.
  4. The Refleks is not only a source of heat; we used it to melt snow for water, dry clothes, and cook on. Turned up it will boil a kettle in just a few minutes and turned down it will nicely simmer a pot of porridge.

Having said all that, diesel furnaces are not without some advantages:

  1. There is nothing like the instant heat at the flick of a switch, particularly at sea, that our Eberspacher gives us, in contrast to the partial disassembly and messing about with fire lighters that getting the Refleks going demands.
  2. The furnaces have forced draft exhausts, rather than chimneys, that can be routed in fairly complex ways and that are not subject to the drawing problems that natural draft heaters like the Refleks can suffer from. Polaris had a large diameter and tall chimney installed for the winter, but this would be impractical if sailing and Michael tells me that they have had the heater blow out in gusty gales with the smaller chimney installed. Also, even the small Refleks chimney is very vulnerable to a stray sheet, unlike the furnace exhausts which can be placed well away from such hazards. This vulnerability of the chimney means that I have met several sailboats in the Arctic over the years that cap off their chimneys at sea, thereby depriving themselves of heat at the very time it may be most needed to thaw out a chilled watch-stander.
  3. The forced air furnaces distribute heat nice and evenly throughout the boat, which the Refleks does not. However, while the Refleks on Polaris is not so fitted, they can be ordered with heat exchanger coils that will feed registers in other parts of the boat. This often requires the addition of a small circulating pump, although, if one is really canny with the installation, convection in the water lines will do the job, doing away with even this small electricity user.
  4. The Refleks draws its combustion air from the cabin, which requires sucking in quite a bit of cold air through the ventilators to replace it. This is both good and bad; good because it clears stale moist air from the boat, bad because it is less efficient than the partial or even total recirculation that a furnace can be set up to do. On Morgan’s Cloud we can adjust various vents to vary the amount of outside air brought in by the Eberspacher: more in humid conditions, less when it is cold and dry.

In summary, both systems have their pros and cons. I think that if we were fitting out an expedition boat from scratch we would have a Refleks with a heat exchanger and registers, and an undersized Eberspacher hot air system; the first for long periods in port or at the anchor and the second to knock the chill off at sea and on brisk mornings. As both Polaris and Morgan’s Cloud have, I would also install a heat exchanger hot air blower off the engine cooling system, since this delivers what is essentially free heat whenever the engine is running. This is a lot of mechanical stuff for one function, it is true, but being cold in the high latitudes is at best a trip spoiler and at worst dangerous.

Read our post on a comparison of fuel efficiency between the Refleks and bus heaters.

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Meet the Author


John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

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21 comments … add one
  • Jackson Hole Skier Dec 5, 2009, 7:39 am

    Any heating system (or any system for that matter) on an expedition sailboat bound for the high latitudes should include redundancy.

  • Mike R Mar 6, 2012, 1:00 am

    Hi John ,

    We have had a Refleks M62 on our 48 foot fiberglass sailboat for two years now in Maryland. This winter has not been much of a test but the winter before was with regards to the heaters ability to keep our vessel comfortable. We have no insulation right now just 1/4 in skins on either side of a 3/4 inch balsa core ( this is just the area above the waterline). We have the ability to keep the vessel at 60 degrees with and outside air temperature of 18 degrees. With this gradiant we have the heater on a setting of 10 which is the highest it will go. Temperature at the plate of the heater is 500F with diesel. Believe it or not but wien can get jet fuel for less since most airports dispose of it during daily testing. Just a heads up. Jet A will burn 150 F hotter at any given setting on the Refleks.

    We intend to insulate our boat with 1 inch of Armaflex in the next year or two and shoud see a substantial savings in fuel. We are also planning on upgrading to the M62 with the heating coil for raditors as well.

    Fuel consumption at current is 9 gallons per seven days at 18 F outside with 60F inside temp. Water temp was 35F. We see 7 gallons per week with the Jet A under the same conditions. This should improve with the insulation and radiators.

    Customer service is great as well. I have asked tones of questions over the past few years and I always get a response within a day. They were also supportive of us using bio fuels. So hi marks there.

    Hi marks also for Hamiton Marine in Maine and Daryn. He is the best at offerig advice for installing the stoves and the store, Hamilton Marine is the only company that imports the stoves into the States that I know of.

    Hope this is some real world info for folks. We love the stove. Run it 24/7 and have no regrets about installing it.


  • John Mar 6, 2012, 9:12 am

    Hi Mike,

    Great information, thank you so much. Jet A, who knew?

    Let us know how the Armaflex works out.

  • Giancarlo Mar 6, 2012, 4:45 pm

    we ll start tomorrow morning the insulation of our boat with Armaflex-Armasound,if you are interested i might report in this post in the future

    • John Mar 7, 2012, 8:35 pm

      Hi Giancarlo.

      That would be great to have a report on how the Armaflex works out, thank you.

  • Jeff H Nov 1, 2012, 11:44 pm

    Hi John,

    Has anyone used a heat exchanger hot air blower off the generator cooling system, since this would deliver what is essentially free heat whenever the generator is running as opposed the main engine(s)?

    I have an all electric boat, so the generator sees action while at anchor.

    Great site!

    Best Regards,
    Jeff Harrison

  • Paul Mills Nov 2, 2012, 4:54 am

    Hi Jeff,

    I have seen this on a bigger boat where they ran their generater for several hours, twice every day. It was so good they were planning on adding the spare coil in their calorifier intio the system as well. From memory, I think they had aso plumbed it into their main engine (they never needed both on at the same time).

    It is possible to use a vehicle matrix and blower – a friend Charlie put a transit one in his Ovni 385 and it worked well.

    See for some examples.

    Best wishes


  • Andy Marsh Nov 2, 2013, 9:53 am

    We have a Refleks 61 msv stove with a separate air intake, it has a coil fitted that heats our 60 lt hot water tank, 2 radiators, wet locker and towel rail, On a test we ran the heater with a full 40 lt tank and it burnt for 240 hours on diesel, we have burnt kerosene and it did burn a lot hotter, the outside temperature was 10 c and we had a temperature inside of
    22 c in the cabin with the heater, in our sleeping cabin it was 15 c. Our Yacht is a 14.6 m steel blue water cutter and has 2″ of closed sell foam insulation throughout down to the water line, I am in the process of fitting a heater matrix form a land rover into our hot water system, as we have a duetz air cooled main engine and a yanmar air cooled generator, i am hoping to heat our hot water with this system When the engines are running, i did encounter one problem with the regulator on the refleks when we could not get full heat, i found that the inlet valve had waxed up over many years, once i cleaned this the fire rain at full power again. for many years i worked as a trawler man and have had refleks heaters on-board, i was very happy to find one fitted to our yacht Norna Biron.

  • Gert Jan 21, 2014, 8:48 pm

    Refleks heaters or the swedish Glembring heaters are both verygood, the most important thing is to use good clean fuel into the systems.. beaware of diffrence between summer or winter diesel we called here in Sweden. some sailboats maybe not use for long periods and had filled their tanks wit summer fuelthen its hard to to get it run good as the fuel parrfines in the pipes below 10 c….. best thing to run on only kerosone last hours before system is turned of for long time (summer)

  • Gert Jan 21, 2014, 8:56 pm

    Well I have some diffrekt heaters in my old fising boat and my newest one is an finnish manufacured diesel stove tht runs automaticually and on 12V DC supply,, is called SAFIRE 3200A (3,2Kw) is just swith on/off after 3 minits its lite it up by it self (no matches or lighters) and he heat is adjusted electroncally an very smooth.. is made orignally for cottages without 220V/110V AC… but work good in bigger boats,, and its vry secure.. the DC comsumption fro 12 v battery is lov run several days on 50Ah battery…. Ok,,,, but I stil use My refleks m60 drip burner (pot burner in europe) and Glembring IG92 stove.. always have lot of diffrekt heaters onbord some fit in diffrent situations, give me an mail if any technical questions regarding refleks or glembring…

    • John Jan 22, 2014, 1:02 pm

      Hi Gert,

      Great first hand reports and a very good point about winter fuel, thanks very much.

  • Trevor Robertson Mar 20, 2014, 2:59 pm

    There seem to be three drip feed diesel heaters commonly available: Reflex (Denmark), Dickinson (Canada) and Sigma (Canada). They all work similarly and, I think, use the same carburettor. Iron Bark has a Dickinson andI have had a little experience with the other two. They are all fine heaters, but I think the Sima is the best of them.

    · The Reflex does not have a booster fan so can be hard to light in windy conditions. The fan is only needed for a few minutes until the chimney heats up, but is very useful while that happens.
    · The Dickinson has too much metal and not enough holes in the shielding which reflects heat back into the firebox and sends it up the chimney, wasting fuel.
    · The Sigma has corrected both these faults.

    I have used the Dickinson for two winters frozen in NW Greenland and intermittently during another winter in Antarctica. It was used intermittently in Antarctica because I could not carry enough fuel on the 5000 mile Southern Ocean approach voyage to keep it going full time. The heater is now 17 years old and still going strong.

    In Greenland I usually turned the heater off while I was asleep or off hiking, so it ran about 14 hours perday for the 8 months or so of winter and an average of 4 hours per day for the remaining 4 months of the year. Total fuel usage was 850 litres per year, and the cabin temperature was typically between 8 and 14 deg C. After the heater had been off over night the cabin temperature was usually a little above or just below freezing, but after lighting the heater running and with the stove on for morning coffee, the temperature soon got back to at least 8 deg C. Iron Bark is a 35ft steel vessel insulated with 32mm (1-1/4”) foam to the waterline. I bulk-headed the ends of the vessel off and let them freeze and built a snow-block cover over her in winter to save fuel. The fuel was standard winter grade, low wax diesel.

    I decoked the burner kettle once per month but could probably have left twice that time. I believe the use of an atmospheric damper significantly reduces the amount of coking, as does running the heater on a higher setting. When I find one, I will add a damper. The carburettor needs cleaning if the heater has been unused for more than a few weeks as the diesel in the float chamber can evaporate and gum up the float and needle valve. Iron Bark’s heater is gravity fed from a 10-litre tank with a filter in the line. The tank needs filling every other day.

    The flue is 76mm (3”) stainless steel with a quick disconnect dairy fitting in deck that allows me to remove the chimney and blank off the hole in a few moments. Dairy fittings are 316 stainless steel (food quality) and quite cheap where available. The fitting is designed to let a farmer flush his pipes out easily after every milking. The chimney has an extension, again on a quick disconnect dairy fitting, that allows me to extend its height above deck to approx 1 metre when the snow is deep.

    It may make sense to also have a solid fuel stove for areas where firewood is available. Iron Bark’s is a homemade affair, based on a piece of 200mm (8”) rectangular hollow section (RHS) steel. I have seen others fabricated from gas cylinders, large diameter pipe and so on; all seem to work satisfactorily. Iron Bark has another of the ubiquitous dairy farmer’s fittings in the flue. This allows me to change heaters in about 1 hour. I have used this heater successfully in New Zealand, Labrador and Patagonia but unless you have a much bigger boat than me or are willing to carry a deck cargo of firewood, you will need stop to cut wood every 3 or 4 days. Cutting firewood is pleasant exercise but the boat does end up with a lot of bark and wood chips underfoot. If I could have only one heater, it would be diesel fired.


    • John Mar 21, 2014, 9:17 am

      Hi Trevor,

      Welcome to AAC and thanks very much for the very useful comment and all the tips. I was not aware of the Sigma option at all, never mind the differences between it and the Reflex.

      Just finished reading your article about wintering over in Greenland in “Voyages” and enjoyed it very much.

  • Colin Wright Sep 21, 2014, 4:17 pm

    Hey guys, we have a center cockpit peterson 44. Lived aboard 10 years now. We had an espar d5 but it broke down every year costing almoUst 800$ per year to repair on top of the fuel cost. We couldn’t run it on anchor because of the power draw. After the third year of failure, when we needed it most we went for a refleks, but one modified in the uk by a company called lockgate. WOW! what a difference. The lockgate has a high volume back boiler which runs 4 radiators on emerald and a hot water tank. The boat is bone dry, homely and the whole system uses 1/4 amp per hour when running. We burn 50 litres every 8 days, running 24hrs a day. We alsospent

  • Mark Tilley Nov 20, 2014, 4:43 pm

    Hi John,

    Here’s another brand that’s worth noting – the Hurricane, made by International Thermal Research in B.C. (

    Our unit (the Combi II 42K BTU, or about 12kW) provides cabin heat to three separate thermostat controlled radiators, the hot water hose runs just under our our salon floors and keeps them warm and it also heats DHW so we were able to basically swap out our old electric DHW tank for this unit, which is just a bit bigger.

    One of the selling points is that the burner nozzle is low pressure, unlike other systems, making it less problematic and more tolerant of various grades of fuel.

    We’ve been living on board our 43′ sailboat boat in Toronto year round for 5 years now and are quite pleased with it.

    • John Nov 21, 2014, 8:36 am

      Hi Mark,

      Thanks for the real world information, always the best kind.

  • Marc Dacey Nov 20, 2014, 9:10 pm

    Well, Mark Tilley, this is fortuitous. I’m going to be buying a second heater this year (I have a Mermaid Marine Air heat pump, but it’s only good to water temps of 5C) and I’m in Toronto with a steel 41 footer at National YC. The only contenders I’ve looked at are Webasto, Wallas and Espar. If you wish to chat about the proper way to live aboard in winter around here, I would be very eager to listen and the first pint’s on me. Please feel free to drop me a note on my blog, the address of which I believe is connected to my member name here. Thanks.

  • Jim R Mar 9, 2016, 9:47 pm

    Do the Refleks systems fitted with coils circulate plain water or some kind of other solution through the radiators?

    • John Mar 10, 2016, 8:30 am

      Hi Jim,

      I believe I’m right in thinking that they circulate an anti-freeze solution, otherwise damage would be done if the boat was allowed to freeze. Anyone know for sure?

      • Jim R Mar 14, 2016, 12:31 am

        I read several manuals and believe this is true as well. Do you also use your heating system to warm the engine before starting when cold? Several sources mentioned that as another benefit of the hydronic system to use a heat exchanger in both directions. I am wondering if that would be a good thing to add or overkill.

        • John Mar 14, 2016, 8:44 am

          Hi Jim,

          No we don’t. We don’t have a hydronic Espar, ours is forced air. I’m aware of this option, but to my way of thinking it would represent more complication than it’s worth unless one planned to be operating in very cold places a lot of the time.

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