Ode to hydronic boat heating, and Sure Marine Service

Ben Ellison

Ben Ellison

Panbo editor, publisher & chief bottlewasher from 4/2005 until 8/2018, and now pleased to have Ben Stein as a very able publisher, webmaster, and editing colleague. Please don't regard him as an "expert"; he's getting quite old and thinks that "fadiddling fumble-putz" is a more accurate description.

27 Responses

  1. Ben Ellison Ben Ellison says:

    Funny or sad? The snow in New Bern — which stayed on the ground longer than it has in a very long time — mostly melted away today. I took almost as much time writing this entry as I did installing Gizmo’s new heating system, relatively speaking.

  2. Evan says:

    Ben – can you comment on the sensors that you’re using for the outside weather data and the refrigerator interior temperature? Thanks!

  3. Xavier Itzmann says:

    Congrats on the Hydronic!
    We installed a Eberspächer D4 diesel air heater in July 2015 and we love it except for the noise the intake air pump makes (we have silencers on the warm air outlet ducts to the cabins).
    Later that winter that we met Goldcrest of Lymington in Barcelona and it was quite an eye opener to see how silent their boat was while keeping quite toasty aboard… clearly if one likes one’s quiet, there is no option other than Hydronic heating.

  4. Ben Ellison Ben Ellison says:

    Hi Evan, The outside temperature is coming from the LCJ Capteurs CV7-V wind sensor at Gizmo’s masthead, as discussed here:
    (With the barometric pressure added by the LCJ Windy Plug in the fly bridge cabinet).
    The refrigerator temp is coming from a Maretron sensor via their TMP100 (same as the engine block and inside temps). I’m about to add another TMP-100 to get dripless shaft bearing, raw water pump, transmission and battery temps into the N2K network, and will write up. I’m not sure you can put enough temp sensors on a boat, especially if you can custom alert and alarm them as Maretron allows.
    I’m also about to install a Yacht Devices humidity sensor that will hopefully add Hum Outside and Dew Point to that Maretron weather page at top, and perhaps even help predict fog:

  5. Evan says:

    Ben – thanks for the info on the sensors. I also have a TMP100 which I use for engine EGT and engine room temperature. Still plenty of channels left and I’d like to add the fridge and ice maker internal temps. But still puzzling over how to route the sensor to the interior of these devices. How did you run the wires into your fridge?

  6. PeterH says:

    Ben –
    Great piece as always. This answered a lot of questions for me. Do you have a sense if the total current draw for this type of hydronic system is more or less than the current draw for the Webasto Forced Air heaters? (I know there’s various sizes that could affect current draw). By a lot? Or a little?
    – Peter

  7. Ben Ellison Ben Ellison says:

    Thank you, Peter. I did fudge the specific power needs of Gizmo’s hydronic system in the entry, but it is a complicated subject.
    For instance, the Sure Marine Webasto TSL17 page shows Start-up consumption of 8.8 amps for 30 seconds and “Full” consumption of 3.8 — which I can sort of see on the boat’s Victron BMV. But there’s a lot going on with the little boiler given its ceramic igniter, combustion fan, and ability to adjust heat output. I can hear various cycle changes if I turn off the radio and pay attention, and that exhaust tube (exterior) temp I’m measuring rarely stays constant.
    Plus there’s the circulation pump, the Surewire box, and the intermittent heater fans (though my Real 6400 reportedly only uses .71 Amp in high mode). I’ll try to do some careful overnight amp counting along with outside and inside temp monitoring when I’m back on the boat, but my gut feeling is that the heater consumption was like the refrigeration consumption during my ICW trip (and note that reefer would have worked less if the boat was colder 😉
    Back to Peter’s question, Sure Marine shows the Webasto Air Top 55 — similar to the TSL17 with 18,750 Btu — with Start-up consumption of 10 amps and Full on consumption of 7.4. That’s more than the TSL but circulation pump and additional fans aren’t needed, and as noted actual heater consumption over time is hard to quantify. (Though I think that Simarine Pico monitoring could do the job, and maybe I should try it.)

  8. Stephen Hill says:

    Congratulations on the hydronic heater installation. You’d just finished up most of the initial installation when I met up with you in Camden last June (on a very hot day). Glad to hear it is doing the job as you’d hoped.
    Best wishes
    Stephen Hill
    Tug’n (Nordic Tug 37)

  9. David Short says:

    I just want to second the nomination of Sure Marine as a great supplier. Replaced my rusted Trident propane solenoid with a SS one from Sure, plus a better pressure regulator & custom hose. Great help from Todd Glenn.

  10. Ben Ellison Ben Ellison says:

    Thanks, Stephen, I remember. I think you noticed that I didn’t have the right switch to work with the engine heat exchanger, and maybe I can blame the hot day for forgetting that part.
    Here’s a little YouTube fun, some guy bench testing the Webasto Thermo Top C, the glass jar of diesel fuel a nice touch: https://youtu.be/EErcbFNjQ_8
    But the Top C does fire up the same as my TSL17 (though it comes with a circulation pump attached and may have different wiring on top). Its manual has more detail on amperage consumption in different modes:

  11. PeterH says:

    Hi Ben:
    Thanks for that additional info. I appreciate that the different parts of the system have different energy requirements. If you’d be willing to post your thoughts on current draw of the whole system down the road, I’d be super interested!
    – Peter

  12. Bruce says:

    Excellent article, Ben. A note for those on sailboats who are planning on sailing in high-latitudes and being on the hook for extended periods of time (and without a generator or a huge battery bank): take careful note of the power consumption of hydronic units. Our Webasto DBW2010 uses far too much power to run for days without a good charging source.

  13. jan-kees says:

    Ben. why did you selected Webasto, we have Kabola, and that runs quiet and also allows hotwater radiators etc.

  14. jan-kees says:

    Ben. why did you selected Webasto, we have Kabola, and that runs quiet and also allows hotwater radiators etc.

  15. Ben Ellison Ben Ellison says:

    Jan-Kees, a big part of my decision was a system that could fit on my particular boat. Transom mounting the air intake and exhaust outlet were nearly impossible and access to the cabin side cramped.
    At any rate, I don’t have comparative experience or opinions regarding other boiler brands, but it is comforting that the little Webasto I got has purportedly been used in over a million trucks.
    Also, while I didn’t know it beforehand — and Kabola may have similar — there’s a sophisticated diagnostic app available for the Webasto if it has problems:
    PS I don’t think there is any reason that a Webasto radiant system can’t also run radiators, but again I didn’t have the right spots.

  16. Kees says:

    A Webasto or Eberspächer hydronic is smaller, doesn’t use as much electricity, and can run of a 12V battery directly. However, it is also rated for only 3000 hours of operation and it doesn’t generate as much heat. If you live on-board in a cold climate and intend to run the boiler for long periods you’ll need to replace the blower motor on the Webasto or Eberspächer every year or so (3000/24 = 125 days.)
    Ben’s TSL17 is 17000 BTU which converts to 5 KW. The size of the unit is about 4 L (232x105x165 mm).
    My Kabola KB40 (the smallest Ecoline Combi) is 13 KW, but uses 182 W of AC current and is 515x655x450 mm = 151 L big and weighs 80 kg. It can make as much steaming hot water as you want for showers and doing the dishes, and it is *totally* soot free. Because it uses a much hotter flame it is also higher efficiency so uses less fuel.
    So it is just a completely different proposition in almost every way.
    So I think, that for the size of boat and intended use, Ben chose wisely.

  17. Kees says:

    For the USA read Espar for Eberspächer (identical).
    For Kabola the nearest equivalent is Olympia, as used by Matt Garand in Ben’s reference above — see http://www.suremarineservice.com/olympia-boiler.aspx
    For some reason the Olympia claims a much lower fuel consumption compared to the Kabola, which I don’t really understand — they both use basically ‘household’ equipment so should be somewhat comparable.

  18. Chris Ellingsen says:

    My friend has an Espar air heater on his boat, and it works very well. Seems to be lot simpler installation as long as you have the room to pass a 4″ duct throughout the boat.
    As for the polaris replacement, I imagine that in addition to the new boiler shown, you also need another heat exchanger for the DHW, or a conventional gas water heater.

  19. Ben Ellison Ben Ellison says:

    Thanks for all that solid information, Kees! I did not actually know about the 3,000 hour fan life on my Webasto TSL17, but that will likely be far into the future given the way I intend to use the (as you surmised).
    Chris, I’ve never had a separate domestic water heater. During the decades I had the Polaris boilers, the radiant heat system was “open” — meaning the water flowing under the floors was the same as what came out the hot taps. That didn’t cause any problems at all, but is no longer allowed because some open systems did have issues with water contamination.
    So the HTP is a true combi that heats domestic and heating water separately, and now my radiant loops are closed.

  20. Bob Austin says:

    Thanks for the great write up and explanation of a hydronic unit.
    In 1993, we were outfitting our Cal 46 for Alaska cruising, and had ordered the “new” Force 10 hydronic system. About 3 months before we were ready to sail from S. Calif., we were informed that Force 10 was not going to sell any (more?) of their diesel heaters, which we had ordered. (We were told there was a fire box problem) A quick check of products available revealed the Proheat truck heaters might work–and we ordered one. The X 45 is now sold by SureMarine as a boat heater, with some modifications, but basically the same unit. Ours even came in the diamond plate box. The 45,000 BTU unit was perfect for the Cal 46. We were able to get 3 of the “radiator boxes” with computer fans, and thermostats, which Force 10 had already built and shipped to us. One in the foreword stateroom, one aft stateroom and one in the main saloon gave excellent heat distribution. In the hanging lockers we used a single loop of bare copper pipes, as we did several loops of bare copper tubing in each of the two heads (under the towel racks).
    It was a very simple system all in one box–fuel pump, (1/4″ lines), atomizer pump, forced draft blower, and coolant circulating pump. There were the air intake and exhaust which were concentric, as in the Webasto, and 3/4″ circulation output/input lines. There was a copper expansion tank included, with coolant fill cap. One switch for the on/off of the main ProHeat unit, and each radiator unit had its own thermostat for the 12 volt fan. There was a thermocouple in the main unit which kept the coolant between 150 and 180 degrees when the unit was running.
    We did not include the water heater loop, since we ran either the generator or main engine daily; either of which heated water. When the engine was running we had a red dot radiator and fan under the companionway steps, which heated the main saloon and the center cockpit, which was fully enclosed with canvas.
    The only issue was that the unit exhaust was fairly noisy. (More outside than inside). Our current draw averaged about 5 amps, and about 8 amps on start up.

  21. Jeffrey Orling says:

    Heat is wonderful… not doubtaboutit… I have Espar Airtronic 4 installed on a 36′ sailboat. 3 outlets keeps the boat toasty. Once design temps have been reached you can'[t even hear the heater… and barely as it’s warming up the cabin. It’s no louder than ambient wind and waves and passing boat sounds. Heat is dry and using diesel is convenient… no other fuel to deal with. Install was quite easy and running the trunk line was not a problem. I try to avoid pipes which can and do leak.

  22. B. Engle says:

    Ditto from me on the always outstanding Sure Marine. Their showroom is amazing, their inventory is extensive, and their seasoned advice has saved me plenty. Big sale or small, they have always gone above and beyond. And they’re so price competitive that I don’t shop out-of-state anymore. I just go to Sure Marine and they set me up. Can’t sing their praises enough.

  23. Åge Bergerud says:

    Live in Norway. Bought a Benetti SailDivision 79 RPH. My wife and I live on board.having some problems with the existing AirCondition/ heating system.
    We need to heat up living room, dining room, kitchen, hall, bridge, 5 cabins and the engine room.
    We have a closed circuit, with glycol, running through all the rooms. This system is working perfect. This means, we want to use this system in combination with a new heater.

  24. Harry says:


    I’m preparing to add heat to our Saga 43, anticipating a year of summer time sailing in the Canadian Maritimes (as far north as Newfoundland). Looking at “extreme lows” of upper 40’s. Sure has been exceptional on the phone already — but they recommend that I consider the 2010, which at 35,000 BTU seems overkill.

    So, your little TL17 has serviced Gizmo well in temps into the 30’s, right? Are you still happy with the performance and durability?

    I sort of think I’ve been steered toward (and willingly followed!) a system that is perhaps far more complex than my use-case suggests. After reading your post, I’m seriously considering dialing back the design.

    • Ben Ellison Ben Ellison says:

      Hi Harry. Yes, I’m very happy with the performance and durability of my hydronic heating system. I think it’s clocked well over 2,000 hours without any issues and I just used it quite a bit on a 10-day cruise, mostly for hot water showers and dishwashing but also to take the edge off chilly mornings.

      With the boat in the water all last winter in Maine, I used the heater in some really cold conditions, but it was for work projects where I arrived already warm and well dressed, not for living aboard. I also let it run for extended periods to keep the unwinterized engine room above freezing in sub zero air temps with the harbor water near freezing.

      I do understand why Sure Marine is recommending a larger boiler, but suspect you’d be pretty happy with the TL17 for summer in Maritimes. Note though that my main fan heater is at forward cabin floor level facing forward, which is ideal for heating the relatively small galley, head, and sleeping area, plus I have a propane cooking stove that can add significant heat for short periods. That warm air does rise into the main cabin with all its glass, but 17,000 btus has a modest effect up there with temps in 30’s or less.

      I’ll add that Gizmo is going to spend this coming winter in a large drafty building in Rockland and I was pleased to learn that the yard will probably be OK with me running the boiler when I’m aboard for projects. They want to see and smell it in operation first, but I don’t think there will be a problem as it runs quite clean. In fact, I never see smoke and I’ve never had to clean the cabin side in the area of the exhaust output.

  25. Harry says:


    Thanks so much for the replies. The propane one looks pretty nice (and I hadn’t noticed it before), but getting an air duct from the back of the boat (a sailboat) to the front is a big challenge. Also, I only carry two 10 lb propane tanks. My old Cozy Cabin propane heater would burn about a pound a night (the boat is actually CNG, so the propane heater was cobbled together to use 1lb camp bottles — not ideal, I know) and so I could imagine not getting more than a week out of the house propane system. Still, have to think about that solution.

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