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.

Refleks Advantages

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:


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.

Easy Maintenance

Ideally, the Espar (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.

No Electricity

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.

Cooking Too

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.

Espar Advantages

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

Instant Heat

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.

No Blowback

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.

Heat While Sailing

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, and the blow back problem, means that I have met several sailboats in the Arctic with Refleks heaters 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.

Better Distribution

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.

Air Exchange Flexibility

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.

Like what you just read? Get lots more:

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.

55 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 Post Oct 5, 2019, 12:14 pm

        Hi John.
        I realize that this comment is somewhat off topic, however. . . Having previously read the articles and comments on the Force 10 stoves, I wonder how the Dickinson units compare. I would not have known of their existence but for this article. My preference would be to support a Canadian company. It certainly appears to be a well made product.
        Any insights?

        Colin Post
        Still in the quest for a good cruising boat!

        • John Oct 6, 2019, 8:22 am

          Hi Colin,

          I don’t have any experience with Dickinson stoves, but Colin wrote about them:

          By the way, when you have a question like this, don’t forget the search box at the top right of every page on this site. That’s how I found the article above.

  • 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.

    • Stein Varjord Nov 30, 2016, 6:40 am

      Hi Jim

      Rereading this informative thread i noticed this question. Fluid heat distribution systems can use pure water, but all the makers strongly recommend using antifreeze in the water, like in the engine cooling system. It prevents freezing, reduces corrosion and gives a higher boiling point.

  • Dick Stevenson May 19, 2016, 5:18 am

    Hi John,
    I thought this might be of interest to those thinking about heaters, particularly the small space I was able to get the Refleks into.
    Dick Stevenson, s/v Alchemy

    Refleks: Early days field report: s/v Alchemy May, 2016
    We have been in cooler/cold climates and do not like our season curtailed by ornery weather and cold. That said, neither do we in any way enjoy being uncomfortable: we like being warm and able to dry out. Being warm may not be mission critical, but for us, being able to get warm when relaxing and not underway is live-aboard-cruising critical. Our Eberspracher/Espar forced air diesel furnace amply met those criteria, but at the expense of a good deal of electrical energy usage, regular infusions of money/time/effort for servicing and occasional, though relatively rare, breakdowns which were beyond my capacities. This may be a personal irritant, but we also find it quite noisy.
    After much research, I had been eying Refleks stove heater/furnaces for years, but had been unable to figure out an installation on our 40-foot boat (Valiant) of modest interior proportions relative to many modern 40 footers. I considered other stove-heaters. Most important, those with experience seemed to choose Refleks and always seemed happy. Also, among other more minor caveats, there were occasional reports from users of other stove-heaters of worries/problems leaving the stove going when unattended which seemed to not be a worry with the Refleks.
    I finally had a plan and when near a Refleks dealer in the Netherlands that I had visited a few seasons earlier (Watersportcentrum de Rietpol in Spaarndam). There I received Ursul’s (extremely knowledgeable and experienced with Refleks) good housekeeping seal of approval on my idea. It helped immensely to have Ursul and the full line of Refleks stoves and accessories ready at hand and I spent an afternoon going repeatedly from store to boat and back with bits and pieces till it all “dry” fit. This was incredibly more effective to the design-on-a-napkin/order-by-mail method I had anticipated doing and the process enabled me to “fine tune” the design and installation in ways that would have been difficult otherwise.
    After all the above work, installation was straightforward and the directions were more than adequate. Mine was particularly easy as I can gravity feed from my fuel tanks and thereby finessed a day tank and fuel pump. I do not know whether this will be important in the future, but I installed my stove on a removable pedestal (3 inches or so) that will allow me to drop the stove and remove the chimney piping and stove with a good deal of ease as well as installing an additional fuel shut off valve.
    We lit ours first try and have had little trouble in perhaps 30+ starts/uses. We have yet to use it in greater than steady 20 knot winds with higher gusts. It uses approximately 1 liter (quart) of fuel in 8 hours of use in its lowest heat output setting. We warm the boat on a higher setting (usually) and turn it down when the boat is warm. On our 40 foot insulated boat (modest interior volume) the lowest setting keeps the boat warm and dry in 5-10 C, 40-50F without a problem. Warmer outside temps have us cracking the hatches to keep from overheating. A fan directed over the chimney makes a large difference in getting the boat heated quickly. We also bought an Ecofan that sits on our stove’s top plate and circulates air. It works solely by heat and makes no noise. It is brilliant! Warmth in the boat becomes surprisingly evenly distributed over time.
    The whole set up is a large jump in our happiness with heating systems as well as with redundancy. As I write this, we sit at anchor in Falmouth on a cloudy damp 50-55 degree F (hatches cracked open) day with the boat comfortable on a liter of fuel and no noise, no smell, no fuss, no amp use.
    Installation is shoe-horned into a space at the end of a 2-leafed table. The table is an island where, before the stove installation, there was just barely room for a small to medium sized person to squeeze through the space between table and bulkhead. The stove now lives in that cozy contained space. All dimensional set-offs were right at the minimal end to Refleks’ directions (or pushing the envelope a bit) and I was concerned about the woodwork around becoming overheated. I was also concerned about exposed metal surfaces of the stove being able to burn people.
    Even at ¾ full heat*, which we use in the mornings to get the chill off more quickly, the woodwork becomes warm, but never so hot as to need to pull one’s hand away. (The Ecofan is always in use and, when getting going, we have a Hella fan moving air around the upper parts of the chimney distributing heat that might otherwise go out of the boat. These fans clearly make the heat less concentrated.) Even in such a closed space, nothing was over heated or been a worry. I was prepared to use shielding on areas of anticipated over-heat, but that has not been necessary to execute.
    Protecting people was a priority. I used Refleks’ chimney shielding for the accessible parts of the chimney. Even at ¾ heat, the shield is never hot enough to burn, and one can let a hand rest on it. The body of the stove also seems to remain unable to harm at higher heat levels. There are places where a bad burn could occur, but at this stage, my estimation is that you would have to work to do so: very similar to the dangers of one’s cooking stove. The “cozy” installation placement, while perhaps not optimal for heat distribution sandwiched in as it is, does serve to keep the stove out of the way and far less likely to be “bumped” into.
    We were concerned about smell. In what I suspect is well over 100 hours of run time, we have rarely noticed any smell at all. We are aware this may change in high wind situations, but are quite pleased so far. There has also been no interior dirt/ash/soot in the slightest.
    Reports indicate that use of the stove/heater is limited to sustained heel angles less than 10 degrees. That said, they are used on many fishing boats that get bounced around a lot, but generally are not at sustained heel angles. For heat when heeled over sailing, the Eberspracher/Espar is hard to beat when it is 0 dark 30 and wet and cold outside.
    The Refleks is also not “quick heat”. On a cold morning we close off the saloon and in 30 minutes the edge is off the cold and in an hour or more we are opening up the whole boat to spread the warmth. The Espar is much faster at warming the boat.
    The above deck chimney is something that can catch lines and find ways of getting into trouble. Ours is tall (better draft) and we remove it when not in use and underway.
    Some rare reports of sooty backdrafts usually attributed to an initial learning curve, but we have not experienced any yet.
    Possibility of spilt fuel, especially on my gravity fed installation.
    Jury is still out on what wind level will cause difficulty lighting or issues when lit such as blowing the fire out or blowing fumes back into the boat. My researches have not revealed reports like this, but they seem possible.
    Minimal. Push a supplied cleaning rod through every few weeks and clean the burner trough of debris from the starter method one uses. Cleaning a filter as needed. Using a soot cleaning tablet every 2 weeks when the unit is used 24/7.
    SUGGESTIONS: (please confirm with others)
    We have a “cooking plate” top with a side chimney. Reports seem to suggest this design puts out more heat. Also, it is particularly easy to light as the plate is removable and so enables easier placement of the initial lighting medium. The top plate is also a brilliant place for the heat operated fan, the Ecofan. I suspect on some bored cold rainy day we will actually attempt to make a pot of soup on the top plate.
    A wire “poker” can be an aid to positioning the burning starting medium to the area where the fuel is weeping in and this aids starting.
    A Hella fan, or any of its type, circulating air over the top parts of the chimney as it exits the boat adds to overall heat output.
    *We have a “cooking plate” model and plate temperatures at low heat are in the 280-320 degrees F (150 C) whereas at ¾ heat the plate rises to 540 F (280 C). Surrounding furniture have seen a high of 120 F (50 C) when at high heat output, but is usually in the 80-90 F (30 C) degree range.

    • John May 19, 2016, 8:54 am

      Hi Dick,

      Great report, thank you so much. Really useful and balanced.

      Get’s me thinking. If Dick can get a Reflex into a Valiant 40…

    • Petter :-) May 24, 2016, 7:05 am

      Hello Dick,
      For others reading your review and experience, I can attest to the versatility and ruggedness of the lovely Releks heaters. I also have one with a hot plate and love this heater.

      Here is something I think works well when it comes to diesel supply to the heater; it is gravity fed from a plastic 12l tank located in a cupboard above the stove. The diesel return line from the engine goes via this tank. When the tank is filled up, there is an overflow line that takes the diesel back to the main tank. This setup servers two purposes; ability to fill the tank without and additional pumping system and ensuring that the diesel that lands in the stove is clean. It has been through two filters before passing into the main engine diesel pump.


      • John May 24, 2016, 8:45 am

        Hi Petter,

        Now that’s cunning idea.

        • petter May 24, 2016, 12:20 pm

          If there is a way to post a picture, I may do so to show connections to the tank and the setup – and as a confession the idea is not mine. Apparently this is common on seagoing ships.

  • Stein Varjord May 19, 2016, 8:45 am

    Hi Rick. Nice report.

    I’ve also used Refleks a bit. There are other heaters with similar working principles, but Refleks has the most experience and maybe biggest choice of models. You can get bigger ones with a lot more output and you can install water spirals to distribute the heat in all of the boat. Can also be installed later on most models. Then you also need a small electric circulation pump, but it’s consumption is a fraction of a normal Eberspacher etc. About 70% of the heat goes into the water circuit. You can use it for radiators, fans or even floor heating. Very nice system.

    There is one danger with this type of heater, which seems to be the same on several other brands: It has a regulator outside of the burner. This is the unit that doesn’t like too much constant heel. It’s also the most vulnerable part. It’s smart to educate yourselves on the details around servicing it. It’s quite a simple completely mechanical unit, so no trouble, but smart to prepare…

    The danger with it is that it has a tiny overflow of fuel that is supposed to be returned to the tank. Since this overflow happens quite low down, it can’t be gravity transfer. Most have a small bottle to collect it and pour it into the tank now and then. Since this is quite rare, its easy to forget. The danger is if the bottle is full. Then the overflow can’t go on and in some cases that leads to the fuel level in the burn chamber gradually rising. That increases heat, of course. It can gradually become red hot and then even let out open fire. This takes time, so no shocks, but still serious. A friend of mine had his boat burn out this way. He kept the burner on all winter without being there mostly, so not the smartest, but have a look at the issue…

    • Dick Stevenson May 20, 2016, 3:43 am

      Hi Stein,
      Thanks for the heads up. I have heard about this issue and am able to monitor any drips and/or overflow easily. So far I have not had a drop, but we have only used it at anchor or tied up and some motoring in calm weather. Good suggestion: I will become better acquainted with the regulator: better done ahead of time than when cold and in a hurry.
      My best, Dick Stevenson, s/v Alchemy

  • Bill Attwood May 19, 2016, 2:37 pm

    I have installed a Refleks 60M on Kinsa – a 36 foot boat. It required removing the bottom arm of the “L” settee berth and putting a half bulkhead in to prevent feet rolling off into the oven when the berth is being used at sea. I have an insulated panel of stainless steel backed with insulating “wool” behind the stove pipe, but at the moment no form of insulation for the half bulkhead. This gets quite hot, so I shall install another insulating panle there i.d.c. The oven sits in a stainless bath, bolted through to the sole bearers, and overflow from the regulator will collect there. Since the sides of the bath are 75 mm high, any overflow will soon be noticed and dealt with. We shan´t be letting the oven run when we are not on board.
    I very much like Dick´s idea of the plinth, allowing the oven to be dropped, as removing the oven and flue pipe would difficult, but retrofitting this is too much of a hassle.
    The only problem we have had is that the regulator became clogged with very fine hairs and stopped working. No idea how exactly this happened, but probably as a result of some job I was doing on board. The regulator is very easy to disassemble and clean, but I believe that new stoves have a different type of regulator which is only factory serviceable. We install a 50 cm extension flue above deck when at anchor which works well, and have the yacht type flue cap. An insulated above-deck flue is recommended for cold temperatures. When sailing we use the watertight cap.
    We are able to boil a kettle on the hot-plate, and use it for slow cooking – stews and such. I believe the hot water coil can be used without the electrical pump, although the pump is recommended. The Ecofan sounds a great idea, and I will investigate this – thanks Dick.

  • Dick Stevenson May 20, 2016, 4:12 am

    Hi Bill,
    Every installation of a stove to a small sailboat has seemed to me a creative exercise on the owner’s part, certainly some more elegant than others, but all have needed to be creative. Space is best planned for during the boat’s initial design, even if the space is a bookshelf or the like at first leaving the owner to decide later whether to put in a stove.
    I wonder whether the hairs you reported clogging the strainer could have been from fuel hose/piping which, before you bought it, was stored in such a way that insects/spiders etc made a home inside. I always appreciate it and feel better when I buy fuel hose (or any hose/piping for that matter) that is capped or taped on the end and cringe when unprotected hose/pipe is dragged out of a dirty damp storage facility.
    Along those lines, I connect the ends of my on board water fill hose together when stored making an endless loop where nothing can get in to make a home in its inviting dark damp interior. Connecting the ends also helps the coiled hose stay together and not spring apart in irritating ways.
    I agree, the insulated flue seems to make a difference, when casually compared to friends with flues without insulation.
    My best, Dick Stevenson, s/v Alchemy

  • Bill Attwood May 24, 2016, 3:31 pm

    Hi Dick.
    I guess the hairs might have accumulated in storage, but a very good tip to check all pipes and hoses when buying. I’ ll also Tape the ends of my spare Bits of copper piping.
    PS are you enjoying Falmouth (Kinsa’s home Port). Do try the Jacob’s mussels which you can buy from the wet fish Shop in the main street. Eat with samphire Grass – you’ll think You’ve died and gone to Heaven.

    • Dick Stevenson May 25, 2016, 3:53 pm

      Hi Bill, Thanks for the suggestions: just the kind of thing we love, but picked up the easterlies and are now in Kinsale. Dick

      • Marc Dacey May 25, 2016, 4:06 pm

        There’s a nice harbour and good eating in Kinsale. My family’s from Clonakilty, judged “the prettiest town in Ireland” just to the west, but it’s rather shallow, or so I understand.

  • Taras Nov 28, 2016, 9:46 am

    Hi guys!
    I’m re-insulating my aluminum boat with Armaflex 25mm currently. It has a self-sticking side.
    Do I need to prepare the aluminum somehow before sticking the new insulation on it?

    • John Nov 28, 2016, 9:56 am

      Hi Taras,

      I would guess yes, but the way to settle these kinds of questions is to talk directly to the manufacturer. Crowd sourcing this kind of information is not generally a good idea as there are many people on forums who will just guess, like I just did, and that can cause you untold grief.

      • Taras Nov 28, 2016, 10:33 am

        I would love to hear something from manufacturer, but it’s not always possible, and not always the person on the other end is knowledgable enough.

        PS: I wrote few emails to Armaflex, without getting any reply, also tried calling them.

        • John Nov 28, 2016, 5:33 pm

          Hi Taras,

          Bummer and does not say good things about Armaflex. Given that they are not helping. My guess is:

          • Wire brush off any corrosion.
          • Wash with soap and water
          • Wash with alcohol to degrease.

          You could use something more aggressive like MEK, but given you will be using a lot in confined space, I would use alcohol.

          • Marc Dacey Nov 29, 2016, 1:42 pm

            Given that there are many products capable of producing good results (including the cheap and cheerful air-gapped closed-cell insulation held with battens), companies that don’t support their products generally make a quick exit from the “preferred supplier” list. I have encountered distributors here in Canada for boat products where it’s a (very) part-time pursuit by what is likely a retired individual. Nonetheless, the support is there. If they can’t pick up the phone at the factory, buh-bye.

          • Taras Nov 30, 2016, 8:08 am

            Well from my research – Armaflex seems the best fro insulating aluminum and preventing mold, but quite expensive (specially here in Europe)

            I don’t have any corrosion on aluminum, just some spots of glue that was holding old insulation – hard pieces of 30 year old weird insulation.

            I was thinking because Aluminum oxidizes to prevent corrosion, the glue might not stick well to it?

  • Denis Foster Jan 19, 2019, 3:42 pm


    Reading this interesting chapter and discussions. May I ask a question :

    We have twin Webasto heaters on our Hallberg Rassy 46 since we are in the Med we don’t use them often. Just a few times a year in the winter.
    Is it better to run the Webasto from time to time even if we don’t need the heat or is better to let them unused for long periods or do they need to be “summerized”. I have understood that turning them off is done by their specific control knobs and leaving the electricity on untill a complete shutdown.

    Thank s for your advice.


    S/Y Hibernia II

    • John Jan 20, 2019, 11:42 am

      Hi Denis,

      You definitely want to run the heaters once a month for at least 15 minutes to flush all the fuel through the system and dry out any dampness. I have this directly from a technician who knows everything there is to know about this type of heater. Also see Dick’s comment below. If you run them regularly, no need to summerize.

  • Dick Stevenson Jan 19, 2019, 5:34 pm

    Hi Denis,
    We have and Eberspracher which I believe is similar
    When in the Med, we pushed the season a fair amount and so used the heater a fair amount. We did not “summer-ize it, but did run it hard at least once a month to get fresh fuel in it and to give the unit some exercise. There was all sorts of advice and formulas for ensuring that these type units kept operating, but we found most of them black magic.
    In the Med, techs were hard to come by, so when we were near someone who was competent, we had it serviced: once a year if we could. This cost a bit, but improved reliability enormously, and, most important, when we wanted heat, it was really nice to have.
    My best, Dick Stevenson, s/v Alchemy
    Ps. Marin in Marmaris, Turkey, always did good work if you are that way.

  • Denis Foster Jan 20, 2019, 6:32 pm

    Thank s Dick and John for sharing your knowledge

  • Andrew Craig-Bennett Jan 6, 2020, 9:32 pm

    My experience is mainly with solid fuel stoves but I’d welcome thoughts on an installation point before I get into fitting a Refleks into ‘Kukri’.

    I think that, for use under way, it’s best if the flue comes out on deck in the ‘slot’ between mainsail and foresail, ie about abeam of the mainmast, because this is a low pressure area. It’s important not to have the flue anywhere near the downwash of air off the mainsail when under way. You definitely want the cabin to be at higher pressure than the top of the flue if you want the stove to ‘draw’ as it should. Also, a boat with a rigid dodger or a doghouse must keep the companionway closed with the wind forward of the beam because the wind passing over the dodger creates a lower pressure area in the cockpit.

    Does this match your experience?

  • Dick Stevenson Jan 7, 2020, 9:33 am

    Hi Andrew,
    I know of Refleks stoves/heaters being located in multiple locations below decks and have never heard concern in this area. Most boats have few choices.
    Mine is in the salon forward almost amidships with the chimney offset on the port side (in the “slot” you mentioned but because that was the only choice). Friends have theirs quite near the companionway steps and another on the starboard side quite far forward with their chimneys almost straight overhead.
    Once fired up and drawing, I have found chimney draw to be unaffected by whether the boat has the companionway cracked open or not.
    My chimney is in front of the mast. Our use of the Refleks while sailing is almost exclusively down wind because of heeling considerations with some light air reaching. Rolling beyond suggested limits seems not to matter as long as the boat rolls back to vertical with regularity.
    Steady conditions are best: any gusts or slatting sails in the foretriangle might push wind down the chimney and even blow the fire out. You do not want any “downwash” or any rapidly changing flow, mainsail or headsail.
    Motoring with the Refleks going has been just fine.
    Your concern about pressure differentials is probably warranted, but I have not heard others talking about issues in this area. I have paid attention to what is best when firing up a cold stove in heavier winds (gale) or when wind is across a wharf or marina, but have yet to come up with a “formula” and have always been successful, sometimes with a couple of tries.
    My best, Dick Stevenson, s/v Alchemy

    • Andrew Craig-Bennett Jan 7, 2020, 6:39 pm

      Thanks Dick,

      That’s most helpful. For the 29 years that I owned my last boat I had Shipmate solid fuel stoves and they were excellent, but I don’t want to set out on a longer voyage with what Conor O’Brien called “a deck cargo of coal”, so a liquid fuel stove is indicated!

  • Rosemary Adamick Feb 11, 2020, 9:08 pm

    I am curious if anyone had a comment to make regarding hydronic heaters?

    • John Feb 12, 2020, 10:51 am

      Hi Rosemary,

      There’s a lot to like about the Espar hydronic heaters: less current draw, no need to run big ducting, each cabin can have its own thermostat, will heat the shower water, and more efficient since they don’t lose heat in the ducting. On the downside, they are generally more expensive and more complex. On balance, if I were doing it again on a boat over about 50 feet I would go hydronic. 40-50 feet, it’s a toss up. Smaller boats, forced air.

  • Dick Stevenson Feb 13, 2020, 8:13 am

    Hi Rosemary,
    Agree with John’s comments.
    I would add that (I believe) Refleks and others have hydronic systems. One of Espar’s appeals in their forced hot air systems is that it is usable underway when sailing (heeling). Not sure whether that is the case for a hydronic system and doubt it is the case for a drip-diesel system.
    In a hydronic system, I would also consider being able to direct the heat from running the engine, either directly or in some sort of heat exchanger, into the circulation system of the radiators. This is particularly nice on long cold days of motoring and even the heat generated in the 20+ minutes or so of coming into an anchorage and settling in will take the edge off a cool night.
    Random thoughts, My best, Dick Stevenson, s/v Alchemy

    • John Feb 13, 2020, 10:43 am

      Hi Dick,

      I’m pretty sure the Espar hydronic will run when healed.

    • Stein Varjord Feb 13, 2020, 10:53 am

      Hi Dick,
      I also agree with John’s comments and yours. Just wanted to add some potentially useful info. Espar is the US market name for the german company Eberspächer, which is the same company as Webasto. The products are mostly the same. They both sell forced air and “hydronic” systems. So do several other companies. Several Chinese ripoffs do exist at a fraction of the price. Some report that they work fine, while others have less pleasant experiences.

      Neither forced air nor water distribution systems are affected by boat heel or draft, since they are both fan driven. The burn chamber and draft are not gravity sensitive, even though the heater unit should be mounted in the right orientation. Both types of system are meant for intermittent use. They have some points needing regular service and some parts with limited life time. If the boat is a liveaboard in cold climates, these types of heaters may run the whole winter without service, but that should be seen as mildly surprising. The service procedures can definitely be DIY, but you need the right parts and tools. Some parts are a bit expensive. Youtube and such can help with the procedure.

      As for alternatives, the Danish Refleks ( has been mentioned. I have this. The advantage is that they use zero electricity and are meant for continuous use. They still need cleaning of the burn chamber about once a month, which is an easy procedure. The only somewhat complicated part is the regulator. It might be smart to carry a backup. Refleks heaters can indeed have a heat spiral that will distribute about 70% of the output to radiators. That means they will need a circulation pump to run, which makes it use electricity, but still far less than any of the previously mentioned systems. I have this too. The weakness is that these are not happy with large angles of heel for extended periods of time, (we have a cat) and that they can turn off in especially strong winds by air pushed down the flue. There are several other brands with a good reputation and a similar system as Refleks. Canadian Dickinson ( and Swedish Glembring ( come to mind.

      Another alternative worth considering is a full on central heating system. These are small version of home central heaters. They are essentially the same as “Hydronic” water heaters, but scaled for continuous use. They are more expensive to buy, but require far less frequent servicing, far cheaper parts and are mostly far more reliable. Several good brands, like: Maritime Booster (, Kabola (, Post ( All these three are Dutch brands operating worldwide. There are more companies too, but I don’t remember the names.

      As mentioned, We have a Refleks with connected radiators, which works very well. However, I’m considering changing to a proper central heater, not sure when or which one yet. There are several reasons:
      – All diesel kept outside of the living spaces. Our engines are in the sterns. The central heater fits there. The Refleks can sometimes give a slight bit of smell when not in use, and any potential diesel leak would be in our salon.
      – More control of where the heat goes. Sometimes we don’t want all of the boat to be heated.
      – Fewer chores. Cleaning the Refleks once a month in the winter isn’t really a problem, but once a year is better!
      – Simpler user interface. The Refleks is very easy to use, but it’s hands on, and you need to learn it. I’m not the only user. A proper central heater is run via a simple panel and mostly automatic.

      This is an endless topic, of course, so I guess I’ll remember more when this has been posted. Sorry for being so wordy.

  • Dick Stevenson Feb 13, 2020, 5:14 pm

    Hi Stein,
    All good information and appreciated. I did not know that Espar and Webasto were related.
    We have both a Refleks and and an Eberspracher on Alchemy, neither hrdronic, and I agree with all your points. I do not believe I have ever run into a boat with a central home type heating system but will look at the sites you mention.
    My best, Dick

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