Just as at home, the heart of any boat heading for colder climes will be a heater of some sort. There’s nothing quite as satisfying on a cold, wet night as settling down in the warmth of a good boat in some wild, windswept anchorage without fifteen layers of thermal wear to keep you warm!
But there are many different ways to approach the question of how you provide the heat to keep the boat cozy and dry. Having tried most of them along the way, here are some thoughts that might help you choose what’s right for you and your boat.
Properly installed with an adequate air supply and an efficient and leak-proof flue, virtually any form of commonly-available fuel can be used. Combined with a fully-insulated hull and deck, all will provide the kind of dry heat that is so effective at providing warmth and keeping condensation at bay.
But in order to get the best out of them it’s necessary to consider a few common problems in the first place, such as siting the stove on an existing boat, where the joinery may dictate what type of stove you can install. And just to reinforce a common theme throughout this saga: Time, care and thought devoted to achieving a correct installation will be critical to ensure that any heater will operate safely and effectively.
Even the best heater will underperform if an optimal installation cannot be achieved. A classic example of this is where the saloon seating will not allow a bulkhead-mounted stove to be installed down at floor level, in which case your upper body and head will be toasty and your legs and feet freezing—hot air rises, after all.
Assuming you have the space to make a good installation, let’s start by considering the types of fuel available, and how they can be used:
Thank you for the article!
What would you choose from Refleks, diesel airtronic or hydronic heater for 36-38ft sailboat to be used as full-time cruising boat in North Europe?
two very different beasts – and I’ve covered my thoughts as to which to choose and where in Part II, so it might be best to wait for that as it it covers the options in more detail than I can achieve in a comment.
I might add though, that some people choose both….
I installed a Refleks model such as you pictured but without the radiator coolant option. It is more than adequate for my 40 foot boat. Fans can distribute heat till the boat heats up and then the worry is that the boat will get too warm even at low heat. We have 1 year living with it and probably 80+ days of lighting it.
The top hob allows for much easier lighting than friends have with a different model without the access that top plate removal allows.
The top plate allows a fan to sit on the plate operated solely by heat, a very fun and functional option.
I situated my stove on plinths sized to allow the stove to drop and be removed as the piping needs a couple of cm to come free.
I put a petcock just before the regulator to allow for easy and clean removal with the possibility of no or little diesel spillage.
The flue I have is not an “H” design, but is tall and has worked well in winds of 25+ knots gusting higher. The longer length is insulated which, friends tell me, is a real plus to good draw.
We installed it in quite a cozy little nook with our fingers crossed about surrounding woodwork and have found it unnecessary to heat shield further.
It is a marvelous piece of kit!
I bought it in the Netherlands where there is a wonderful woman with much Refleks experience and product enough so we dry fitted it at her dock (more info if wished). This made the whole design much easier.
Maintenance has been a doddle.
Short time, I will write more later,
Dick Stevenson, s/v Alchemy
lots of useful points, thank you. And you’re right, attention to detail really pays in achieving an optimal installation, especially if you build in ease of servicing.
In really windy conditions the H flue is the icing on the cake, although insulating the pipe helps too.
We’ve had a Refleks system on two different boats and had continual, significant blowback problems on both in strong wind situations. In some cases, the blowback would extinguish the flame. Elongated, insulated flues, a ‘Charlie Noble’, a separate outside air intake, cleaning and a new regulator didn’t help. Occasionally though, they worked wonderfully. It wasn’t obvious why that was. We had a 20 litre day tank (make sure you get one with a fuel level sight glass) that required manually filling every third day when using it 24/7, so, fuel use wasn’t insignificant. Our new (to us) boat has a Sigmar SIG170 diesel heater, so, maybe it will be third time lucky. We already know we have to change its insallation as the regulator hasn’t been installed fore/aft as it should be.
Hi Colin We have a Taylors Mod 089 diesel heater on board, which we really love. The heat it produces sucks out all moist on board so we never experience wet and cold linen in the bunks, and dry bread and biscuits still cracks even after weeks on board. We keep it burning day and night when at anchor (living and sailing at high latitudes). Having a small hatch leading into the cockpit kept open at all time when the heater is burning gives good circulation of the air in the cabin and prevents building of CO2. After washing clothes we often hang them in the cabin during the night to find them dry next morning. The down side on our boat is the “hazel” every day with the chimney above deck, which has to be taken down before sailing since it comes in conflict with the boom, and then put up again when at anchor. But we can very well live with that because of all the pleasure the heater gives inside. I have to mention one episode on the down side, which can be an advice to others; As many diesel stoves, ours also have tubes for heating fluid in radiator systems, which we arranged. The secondary heater for this system was a Weabsto ST90, but the Taylors were thought to be the number one heater in the system. We had to mount a separate circulation pump in order to get the heated fluid circulated in the radiators, since it wasn´t possible to have the radiators mounted in a line where the second radiator was slightly higher than the first one and so on, to get a natural circulation of the hot fluid in the system. This functioned very well until one day, or more precise, night. Shutting down lights and radio, and so on for the night we accidentally turned off the circulation pump. 30 minutes later, just after the light was out in the sleeping cabin and sweet dreams was on its way, a loud booom woke us up. The whole boat was filled with steam. What happened was that from the minute the circulation pump stopped the fluid inside the pipes of the Taylor heater became so hot it started to boil. Pressure increased inside the radiator system and finally a rubber hose (armed to withstand 12 bar) gave in an exploded. After that the Taylors was disconnected from the system since we, as mentioned, have it burning all day and night when at anchor, and don´t want having a fear that it once again will have an unintentional shutdown. (The power consumption from a constant running circulation pump is also an issue to bear in mind). The Webasto was promoted the number one heater on the radiator system, with the addition of a heat exchanger connected to one of the engines, so that when they are running we heat the radiator system if a sirculation pump is engaged. A system, which actually functions very… Read more »
As a mechanical engineer with many years experience designing and installing all sorts of heating systems in houses, for the sake of the other readers who maybe thinking of installing heating on a boat, I should point out that ANY heating circuit that is not vented, ie open to the atmosphere, as with the closed radiator circuit on your boat, MUST have a pressure relief valve installed. This is a device that, if a predetermined pressure is reached in the circuit (usually in a radiator circuit 3 bar), the safety valve opens and vents the hot coolant or steam safely outside or on a boat possibly into the bilges. Your braided hose let go at 12 bar (approx 173 psi!!!???) but imagine if every piece of pipework in the circuit was soldered copper? You would have been sitting on a much bigger bomb!
good ventilation is essential for safety and comfort, and on our boat we have four good sized dorades and also crack the hatches a little. Managing the flue is a nuisance, but you soon get used to it, I’ve always found.
Your’e quote right about the need to always ensure that the circulation pump is on – otherwise the problem you had is an all too common result. Again, it’s a question of ritual. With the Refleks the first thing to do is switch on the pump, and it’s also the last – I usually leave the pump running for around 15 minutes once the heater has been shut down.
But living aboard lends itself to such activities – adjusting solar panels etc through the day, and once you’re used to being off-grid it just becomes another daily chore.
The best book I have ever read on the subject of heating boats was this one, which emphasizes the need for proper air circulation. A review is here:
I would also hope you would deal with the differing potentials of various fuels in terms of “wet” and “dry” heat (propane is pretty “wet” compared to diesel) and the issue of exhaust gases and particularly carbon monoxide aboard either a “too tight” boat or one in which the exhaust system is occluded or improperly installed.
I’ve covered ‘wet’ heat in Part II, and ways around it. In fact (thank heavens) there are very few hear systems left that cause that problem these days as nearly all vent externally.
Good ventilation at all times and care taken with installation of exhaust systems is of paramount importance, but requires (at least) a whole article (if not a book!). There are so many variables with different forms of construction and heater systems.
I’ve installed quite a few different types of heater over the years and never faced the same challenges twice. Most systems come with detailed instructions with safety absolutely to the fore, so I’d argue that the best option is to follow their instructions to the letter and then review those instructions with regard to your boat and its layout.
Hi Colin and all,
For a quite detailed field report on a Refleks, including installation, maintenance, use, etc. and a comparison to Eberspracher type furnaces, please go to my comment at the AAC site: https://www.morganscloud.com/2009/12/01/an-analysis-of-boat-heating-systems/.
Dick Stevenson, s/v Alchemy
I have a Taylors 079 heater, gravity fed, which works very well. I usually use kerosene, (paraffin) as my prefered fuel. The only problem I have ever had with it, was when the flame was blown out by strong winds while moored . This was caused by the positioning of the flue (near the mast), and the wind direction. At anchor, the boat is free to swing, and this never happens. My boat is steel, 11m long and well insulated. The heater is in the saloon, and warms the whole boat. I am set up for double glazing on the hatches and cabin ports, which also helps conserve heat. Five large Dorade vents with adjustable inlets take care of ventilation.
we’ve all had that problem at one time or another, and there are a number of ways to reduce that eventuality. First, flue length is important, especially if the stove is not mounted as low as possible in the boat. Additional lengths added above deck may be necessary to achieve a good ‘draw’ which will reduce the possibility of blowback putting the stove out. Insulating the flue above deck is relatively easy and can also help. Finally, as per the article, the H shaped ‘Charlie Noble’ flue cap works wonders, even in really strong winds. If you opt for all of the above you’ll have an excellent and windproof installation, in my view.
My heater is mounted just above the saloon sole, so my flue length is over 2 m. I have the standard Taylors “Charlie Noble” , which rotates, and exhausts downwind, as it has small wind vane. I will make up a H shaped one to try. At the moment, I am in the tropics, so no need of a heater, but it was sure nice to have in cold regions.
the flue length sounds OK and I’ve seen those flue caps – never tried one, but I hope it works well. The H shaped flues seem to really come into their own in very windy conditions. Ah, the tropics – seems like a distant memory at the moment, and with Newfoundland on the menu for us this summer I guess our heater will come in handy..,,
Great article. I have a Sigma 180 diesel furnace onboard, that works well, but I did have to get an adapter (readily provided by Dickinson, in B.C.) as the low-sulfur fuel wasn’t burning cleanly. However, this issue being resolved, it heats wonderfully. But the next step is properly insulating the deckhead and hull.
that’s an interesting one, as the only experience I’ve had with poor burning diesel has been the other way around, with our old dyed ‘red’ diesel clogging up Webasto/Espar burners. As this was basically agricultural fuel oil, maybe that’s no surprise. But I suppose there are so many supposed forms of diesel these days?
Re: diesel and kerosene heaters
I’d like to add a caution with respect to the statement ” most heaters will run happily on either fuel, although you may need to adjust the regulator”
Speaking from experience, if you run a Dickenson heater using kerosene with the diesel orifice fitted, the stove will eventually overheat and become totally out of control. Totally out of control means the stove pipe glowing cherry red and paint blistering off the bulkhead.
The reason is that the lower viscosity fuel will gradually fill the bowl at the bottom of the stove until it overflows, no matter which setting you have the regulator on. This is a bad situation. After Dickinson sent me the correct orifice everything worked fine. I don’t know if Dickenson supplies both orifices with a new stove, as I bought this one second hand.
thanks for that – I have no experience with the Dickinson stoves, but have run both fuels in other stoves, and once the regulator has been adjusted for kerosene they worked fine. But it sounds like the Dickinson uses a fixed jet, whereas most others I’ve tried have an adjustable flow regulator that can be turned down to cope with the thinner kerosene.
Thanks for the good summary of stoves. In this article, you have touched on the 2 technologies that I have the most experience with. Here are a few additional thoughts to what you have written.
Solid fuel stoves are great for weekending type use but require dedication to be used for a lot more than that. I have found that making your own firewood that is short and chunky works quite well, especially if you sort by type of wood. On our last boat we had a Newport Dickinson and tried all sorts of fuels before finally deciding on either chunky logs or coffee logs. I do worry about sparks flying around so a spark arresting screen should be used unless the flue is really long. You do need to be very careful as the exhaust gases from these can do damage to sails and awnings, I would not be willing to have a charlie noble mounted near a sail. Finally, I have used these in a decent seaway and have no worries about that other than the burn risk which can be reasonably mitigated. All of the old ships used to have wood galley stoves.
I have also used a Refleks a bunch and really like it. Once you learn to light it (my preference is toilet paper thrown in the bottom), they are great and the only problem I have ever had was a plugged regulator which I cleared up in not too long. As stated above, a pressure relief is required in case you have problems with the circulation pump. I have used these stoves with some motion and never had a problem but I know some people keep them running in pretty extreme conditions (I remember seeing something about Skip Novak’s boats running them full time but I can’t verify if this is true).
For any technology that isn’t forced air, I think it makes sense to consider some form of small fan like a computer fan to keep air circulating. On a cold night shortly after installing the stove on our last boat, I keep stoking the stove to try to heat things up and then finally stood up and realized that the air at head height must have been 100F, it just needed to be mixed.
I am looking forward to hearing your thoughts on diesel forced air heaters. If we decide to put heat on our current boat, I think that this is the most logical solution and it will come down to how well we think it will work and if we can stomach the cost which has so far convinced us to simply layer up more.
many good points that I certainly agree with.
Solid fuel stoves can be messy and finding good quality/suitable fuel can be an issue, but I have to say I found my old ‘Pansy’ stove effective, not too dirty and charcoal was a cleanish fuel. With wood stoves (and I’ve used these on old working boats) some sort of spark arrester is a good idea. Lots of the old working boats sued call stoves (over here at least) not just for heat but cooking, so it can be done!
The Refleks is great once you have the hang of it, but I’m not convinced of the wisdom of using them underway, especially from cold, when the fuel would tend to gather on one side of the burner pot. A blown air heater might be better in that regard.
And a fan is always useful for mixing the air – cheap, quiet ones are now widely available and they use very few amps, so why not?
I really enjoyed the article and look forward to the future articles. I’m wondering if there will also be an article on insulation and the possibility of retrofitting insulation to an existing boat?
I looked at the Dickinson Antarctic. It’s not as good looking as the Refleks but it does have a window to view the flame which I think would add a aesthetic value to the ambience in the cabin. Also, from looking at the specks on the Dickinson I was given the impression that the heater could be run underway up to 15 degrees of heel.
An article on insulation might well be of interest – thanks for the suggestion.
Having a window to view the flame is nice, aesthetically, and can be a useful safety feature. Boreal have just told me that they have agreed a new version of the current stove which has this feature as well as an improved internal coil for the radiators, which is a good move in my view.
Way back in the day we had solid fuel stoves on boats, an aptly named Tiny Tot that burned charcoal and, later, a larger Lunenburg Foundry stove fired with wood or soft, smoky Cape Breton coal. I recall powering along in dead calm with a plume of smoke blowing straight back, choking the helmsman. Clay flowerpots set upside down over the stove burners were sometimes used as well, the clay absorbing the moisture from the open flame, or so we were told.
Now we have a Dickenson Alaska diesel fired heater with Charlie Noble head that not only warms and dries out the cabin but casts a lovely flickering light, the perfect companion to red wine and warm sentiments.
On more technical points, our stove is fed directly from the main fuel tanks with a small electric pump supplied by Dickenson. In early years we were troubled by backdrafts when anchored in strong winds until I concluded that the dodger over the main companionway was acting as a very large extractor vent, creating low pressure in the cabin that the forward facing cowls could not counteract. I arranged a fresh air feed from the lazarette area to the bottom of the heater which seems to have mostly cured that problem but think that a little computer fan in the fresh air supply line would be a good idea.
Contrary to your advice, we often run the heater at sea including 21 days straight in April between Ireland and Nova Scotia. The stove and carburetor are orientated fore and aft so heel does not have a big effect on fuel level in the pot. Admittedly, backdrafts are occasionally an issue, more often when the stack is on the windward side. I would have expected it to be the other way around, when the stack is under the boom to leeward, but have been told that it is high pressure air spilling off the sail on the windward side that overwhelms the stack. I cannot imagine being at sea in cold waters without a source of dry heat and am willing to absorb (literally and figuratively) the occasional challenges of balky equipment to achieve that end.
In a week or so I will be departing the Caribbean, heading for Nova Scotia on a friend’s gaff rigged cutter that is equipped with a solid fuel heater stove. Back to the future …
it’s an amazing fact that sometimes the simplest devices are in need of careful installation. One of the challenges of writing this article was being too specific as very boat is different and what works beautifully on one won’t do so on the another. I’m an inveterate tinkerer and love to get things working just right, and have resorted to many tactics to do so with a range of stoves.
Great point on ensuring adequate air feed to overcome differing pressure areas – good food for thought.
I would like to see how the hatches in the first and second images are insulated. Un-insulated glazing and frames sweat and loose considerable heat, the bigger the windows the bigger the problem. There are probably more answers than hatch designs. What I know is that it was the drip, drip, drip of the hatch over my bed that motivated me to design a set of storm windows for my boat.
That hull is probably R-15, but that hatch is R-1. More to the point, windows are accessible, while adding hull insulation is impractical or at least difficult on most boats.
How? Replace screens with 1/8″ acrylic. That alone will cut the heat loss 50% and will eliminate dripping. Add insulated covers, inside or out (not curtains).
if I’m correct in my assumptions the first image is the companionway of our boat and it’s basically uninsulated. We do have a blanket that can be suspended there if needs be. The second image is of a fixed port light in a Boreal (in build) and a wooden surround will be installed there.
Stopping condensation around aluminium hatches is a challenge, but a cheap and effective fix is to install a layer or two of bubble wrap up against the acrylic lens. Or, a more sophisticated fix (used by Boreal) is to install a second, removable acrylic lens a few inches below the hatch – this sounds more like your fix.
It’s never possible to cure this entirely, I’ve found, but any of the above will go a long way towards ameliorating the problem. In addition, on our own boat we had curtains made that are larger that the internal dimensions of the hatch so that any drips fall on there – not us in bed!
Yes, hatches are always a problem. When we wintered over (twice) in Arctic Norway, we removed the trim around each hatch, stuck up some thin transparent plastic, and reinstalled the trim. Worked very well.
A few years ago we installed a Oceanair on one hatch and that works surprisingly well as double glazing, but only with the shade closed, which makes things dark.
As for ports, you can see our solution here:https://www.morganscloud.com/2010/02/01/bezels-for-boat-ports/
While I’ve not “wintered over” far north, I’ve done a lot of winter cruising and a little winter live-aboard in Maryland, spending over a hundred nights below 20F. My heater starts loosing ground around 20F, unless I can supplement with electric, so I’ve had to focus on the details. Catamarans are bad because there is so much area. Fortunately, my builder use a thick core and an insulated liner. The hull side and roof are actually pretty darn good. Below the water line is solid glass, but on a cat that is also below the floor, so carpet does the trick. The only really bad spot in the head floor!
I too have used a blanket over the door. One time it snowed and buried the door, and melt/refreeze bonded the blanket to the door and hull like fiber glass and epoxy–no was was the door opening. So I crawled out the slider and dug out 3 feet of snow, and then added slightly warm water. But generally, a blanket helps with drafts, though it is always in the way.
I’ve attached 1/2-inch foam yoga mat to the inside of the door using 3M Dual Lock and “buttons” that I wrote up in Practical Sailor. The foam eliminated the need for the blanket most of the time and was much easier to live with. This method can also be used to attach foam covers to hatches, though the stiffer foam tiles work better for that. Don’t Velcro direct to the lens–you can actually pull the lens out (done it in testing).
If the hatches take screens, that’s a no brainer. Easy, neat, and durable. Should be a hatch vendor option IMHO.
It’s amazing how well bubble wrap sticks. Just wet and stick. It makes no sense, but it works pretty well. It seems to work best on acrylic and not so well on anything else, at least for me. Quite practical for a one-time trip, such as snow birds run into.
I love the look of the wooden enclosures. I’m sure they’re warm.
Nice article. I never fail to be amazed by how poorly most boats are designed for even cool weather. I guess I shouldn’t be, since the waters really empty out. I just got back from a 4-day tour of several Chesapeake towns that will be standing room only, anchor 3 miles away in the summer. I was alone. The high temperatures were 70-80F with a 8-12 knot breeze–how easy can it be? But few boats are in the water yet.
We sailed on an old ’70s sloop down lake in October for several seasons, because the wind is great in October and the days can be warm and the passing fronts mean you’ll get a nice breeze back every four days or so. But the nights were cold and the rudimentary electric heaters weren’t really good enough. We found condensation from breath worse than the cold, alas, and the solution was cracking the hatch…which attracted shore birds and sparrows on deck, for some reason. That’s when I started to get interested in heating the boat.
I have installed insulation from the waterline to the deckhead on Kinsa (Rustler 36). Not a quick or easy job. In visible areas and most lockers 20 mm closed cell foam held in place with ceiling, itself screwed to wooden bearers bonded to the hull. In under bunk lockers and hanging locker the same foam glued direct to hull, with outer covering of “plastic leather”. In spite of using the recommended glue, this hasn’t worked well. The areas which are not insulated are: hatches – easy to install as needed, as they are mounted in teak frames, giving significant depth and a good surface for fixing; windows – not so easy but a lash-up with bubble wrap or similar possible: coachroof sides – the worst problem as they are solid grp, with no core; deckhead – cored so better than coachroof. Has anyone any suggestions for the coachroof sides? Highly visible, so bubble wrap not a solution!
ps having the nightmare job of removing the remaining glue after stripping the old headlining behind me, I am wary of glueing stuff in place if it might later gave to be removed.
congratulations for taking on one of the more awful jobs! Stripping everything out and removing old glue and mould is no fun. As to gluing the insulation in pIace I don’t think there is a perfect answer, but I’ve seen reasonable results after through cleaning with acetone using large blobs of sealant and then strips of this neoprene glued on the outside along the gaps between sheets.
Hi Colin and all others interested in this topic,
Insulation is a key factor. When I built my boat, I sprayed about 10mm of foam directly onto the inside of the hull and deck. After trimming, I ended up with about 60 mm of insulation . I installed press studs to attatch mosquito screens to the hatches, and curtains to the doghouse ports. These studs also attatch the 4mm clear acrylic panels which I use for double glazing. The seal is not 100% air tight, even with neoprene strips, but I have no condensation issues. They also let in a most of the available light, which is nice. I only have four hull ports, four dog house ports and three hatches, so stowage of of the clear acrylic panels when not in use, is easy. This has worked well for me.
Can you give a bit more detail about the spraying of insulation. Exactly what product you used, the method of spraying, how you finished the surface etc.
Thanks in advance
It was over 20 years ago, so I cannot remember the exact name of the product, but it is a polyurethane closed cell foam, that I had sprayed on to the interior of the hull and deck. I do how ever remember that it took a hell of a lot of trimming, which I did mostly using a very sharp, flexible fish fillet knife. I had the naval architect, Dudley Dix, supervise the building of my hull. He was in Cape Town at that time, but now lives in NZ. You could try contacting him, as he has much more knowledge than I do. As an aside, the foam does burn, and gives off horrible smoke which I am sure is poisonous. I set it alight when cutting the deck with an oxy acetylene torchto fit new hatches, and when welding the new frames in. It only burnt locally, and was easily extinguished with a wet cloth, but I would hate to have a major fire.
at the time you’re talking about sprayed on PU foam as a very popular option for steel at the build stage, although I think it’s less popular now.
It did form a gap free mass, and if done with care by a skilled operator worked well. But the problem of repairing damage, the possibility of moisture becoming trapped behind voids and the potentially deadly fumes in the event of a fire were not negligible.
Most builders are going over to ‘building’ tips of solid insulation which requires more skill and labour, but can be removed in the event of damage. In the old days, some steel builders even used rockwool, which worked surprisingly well.
Sailing through Tasmanian winters at around 43degreesS I am an enthusiastic user of a Hampshire Heater (the oblong prototype before they became HH). A few comments: The lower on the bulkhead the better, but they do put out a good amount of heat through the bottom of the unit. Another advantage for mounting is the small diameter of the flue, about 2 inches. I use BBQ briquettes which are cleaner both before and after than coal but leave more residue. To light the unit I use small kerosene fire lighters, the ‘Redhead’ available individually wrapped in foil are great when lighting the fire under way.
One major dislike is the smoke blowing sternward while in the cockpit. I have come across flue extensions adjustable and projecting a couple of metres out off the beam – that helps but doesn’t solve the problem as the boat swings at anchor.
One has to be a bit surreptitious in this part of the Nanny World as regulations here prohibit the dumping of ash at sea (I have watched myself emptying a handful of ash while in the hills the forestry department conducts deliberate management burns!).
Thanks for an engrossing article.
Good Article. We’ve installed a Kimberly wood stove (by unforgettable fire). We’ve only gotten to installing about 1/2 the insulation in our rebuild at this point, but once that’s completed we expect it to be cozy inside, even on cold days.
We are installing Thermobreak closed cell foam insulation with adhesive backing which is then held in place with the ply lining. By installing 3 layers of 25mm it makes cutting and installation far easier. At 75mm thickness this has an R value of 2.34 which compares to Rockwool at 1.42. The diesel boiler is a Canadian Hurricane 2 from International Thermal Research, with a forced air exhaust that allows it to be used underway by venting aft through a 5 inch mushroom at deck level, with double wall pipes for insulation.