The Offshore Voyaging Reference Site

Boat Heating—Part II

When I used to teach sailing many years ago, the season generally began in March—a month that could be bitterly cold in Britain’s wonderful climate. So it wasn’t surprising that when supper was cooking the crew were cheered up a little by the additional warmth.

The only propane-powered heater option at that time was the truly nasty catalytic heater that also vented the products of combustion directly into the cabin. As burning one gallon of propane produces around 0.8 gallons of water, these sources of heat inevitably turned the cabin into a dripping crypt streaming rivers of condensation, with the added threat of death from carbon monoxide poisoning. So you ended up opening the hatches to stay alive and, in doing so, let the cold right back in—ahh, the good old days!

Happily they don’t make those things anymore and new, safer propane heaters are on the market:


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Dick Stevenson

Hi Colin,
Another very nice review.
A couple of thoughts:
For the Eberspracher (as well as others like it I would guess), your suggestion of closing off outlets might generate enough back pressure to give the unit trouble. I would check with the manufacturer. My 40 foot boat has 3 outlets and the installation had louvers which cut down the free flow of air even when fully open. In one episode of trouble shooting, the company had me working out the area actually unobstructed for air to flow freely into the cabin and suggested it was too little. Since then, I have removed the louvers on the 2 main outlets and usually leave the third open. Heat is so fast that we notice little difference.
I have both Eberspracher (which came with the boat almost 20 years ago now and a Refleks, which we have lived with now for 1+ years. I like having both, but would choose Refleks hands down if restricted to one heater. Your evaluations of the pros & cons was right on.
Friends who have a “bus” type automotive heater all love it for its simplicity after installation and feel the amount of heat output is impressive. They are also quite inexpensive overall. For a power boat, this type of heat seems like a no-brainer and those sailboats who like redundancy (and basically free heat while underway under power) might consider this as well.
My best, Dick Stevenson, s/v Alchemy

Colin Speedie

Hi Dick
Hmm, that’s an odd one, as I’ve never encountered that before with any Webasto or Eberspacher installation. And certainly (for example) when we are planning for bed we’ll close down the aft vents so that more heat is diverted to the fore cabin to warm it up – always works fine. Same with the heads in the morning. We always leave the main saloon vent open, so we’ll have a minimum of two open at any one time, but as I say, that’s a new one on me.
And I like the ‘waste heat’ idea, too, although someone did warn me not to overdo the number of those heaters as it can cool the engine too efficiently, especially if linked to an existing calorifier etc.
Best wishes
Colin

Dick Stevenson

Hi Colin,
I suspect that all forced hot air heaters are concerned about back pressure, but, from your experience, some sound more flexible than others. I was never sure that back-pressure played any part in the troubles I experienced, but I was clear that the installation was not up to Eberspracher’s specs.
To quote from my installation manual, “Each model of heater has a maximum back pressure rating that can not be exceeded” (underlining in the manual). They go on to say that this is related to keeping the furnace cool enough and preventing overheating. They then elaborate with more details and admonitions, but the above is the gist of it. The instruction manual continues with a multi-page “Ducting system back pressure guide and work sheet” where it has you work out how many right angle corners etc. are in your ducting as well as other contributions to back pressure which leads to a “rating” for your particular installation.
The above is from “Supplemental” instructions for the D5L and are for a unit at least 10 years old.
That said, this morning we are at anchor in Wreck Bay, West Kyle in the Clyde area of Scotland, it was (for recent weather) a balmy 8C/46F this morning and 14C in the cabin. The Reflex alone had the cabin at 16.5 in an hour or so and the whole boat comfortable in a couple of hours. If the cabin had been much colder I might have opted for an hour of the Eberspracher working at full output (what it likes best) and also the Refleks on low which we are likely to leave going all day.
My best, Dick Stevenson, s/v Alchemy

Dick Stevenson

Hi All,
The underlining referred to in the above comment did not make it through the copy and paste and into the comments. In the manual “can not be exceeded” was underlined for emphasis. Dick

Colin Speedie

Hi Dick

yes, that makes sense. I have seen problems with collapsed ducting due to heavy kit being stowed on it that choked a heater. And I totally agree, these heaters like to be run hot otherwise trouble will soon ensue. Thanks!
Best wishes
Colin

Grenville Byford

Dear Colin,

THE CAR HEATER TYPE….. I think you are selling this bit of kit rather short. Evidently, it cannot be the only form of heat as (like a car) the heater only works when the main engine is running. On the other hand is relatively cheap to buy and install, and the heat it produces is essentially free while the engine is running anyway. In any area, the high Arctic for example, where motoring is a regular feature of life, this is a huge bonus. I have one installed at the bottom of the companion way on the Revenge (37ft, Steel Construction). It keeps the main cabin too warm if anything….. If anyone is interested, I can look up the brand I have installed.

Best regards,

Grenville

Colin Speedie

Hi Grenvile
no, I like them and recommend them. But I’m aware that they have a limited use for general heating – when at anchor for long periods, for example. And (see my comment to Dick above) it’s as well to make sure that they do not work too well!
But, in moderation, yes – why not?
Best wishes
Colin

Chris

Hi Colin,
Well researched and balanced article, you writing never disappoint us!
We have a Webasto water/ air heater on our boat and so far it has worked well ( touch wood!), when in warmer climate we use it to heat up the water balloon at anchor, so it is used on a semi regular basis, which in theory should help keeping it functional for when we really need it ( I hope).

When we ordered our Garcia exploration 45 we did not specify the refleks type stove because there was no obvious place to fit it, unlike on the Boreal. I hope we will not come to regret this decision as we are in the process of heading south towards Patagonia and even in Southern Brazil’a Rio Grande where we are weathering a cold front right now it starts to get coolish at night. I will order a spare combustion chamber as per your recommandation.

As a side note, on paper at least, our genset consumes about as much fuel as the heather. So worse come to worse we can run electrical heater off the genset.

Finally on the topic of car type heater, while it is a good idea I am always a bit concerned to hang off some non critical gear on one of the most critical system : the engine cooling system. Do you think this could work by using the hot water from the water balloon instead of the engine coolant circuit and would it require a circulation pump?
Many thanks
Best regards
Chris de Veyrac

Colin Speedie

Hi Chris
The water/air heaters, I am told, are more reliable than the air heaters although I’m not sure exactly why! If it’s working well, then all being well it should continue to do so.
Yes, it’s always a good idea to carry a spare burner assembly, which, when swapped out, leaves you the time to clean up the old one at your leisure.
I have no experience of running car heaters off a calorifier, but imagine that you might need to (a) fit a small circulating pump (no big deal – that’s what Boreal have in the Refleks/radiator system) and it might be better to have valves that would isolate the engine when it’s not in use. But – it might all get a little complicated!
Webasto do supply their water heaters to work radiators I believe, so maybe they could advise and/or supply a proprietary kit.
Thanks of the kind words, too.
Best wishes
Colin

John Harries

Hi Colin and Chris,

Our car/bus heater is plumed in series with the water heater heat exchanger coil (calorifier) and it works fine without a pump.

Some worry that such a system will rob too much heat from the engine, but I don’t think this is really a problem since, as I understand it, the thermostat on the engine will stay shut until the engine reaches operating temperature preventing much water from circulating to the heater and calorifier.

And yes, I think it’s a very good idea to have valves to isolate the engine in case a leak develops, which we do, although we have never used them.

Colin Speedie

Hi John and Chris
I was assuming that Chris was intending to heat the water in the calorifier via the Webasto, not from the engine, e.g. when at anchor. If that’s the case, then surely a circulation pump would be an advantage if not a necessity?
And the comments I’ve heard from engineers about the risks of overcooling have been more to do with not allowing the engine to reach full operating temperature after the thermostat has opened – but – this is a grey area I’m sure and (as always) there must be ways to ensure this is not a risk.
Best wishes
Colin

John Harries

Hi Colin,

Oops I misunderstood. As you say, in that case a pump will nearly always be required.

On the worry of about too much heat being robbed by a bus type heater, I guess I’m still sceptical because my thinking is that if that were the case the thermostat would never open. Or to put it another way, once it’s open the engine is at temperature and all is good anyway.

That said, I have to admit that I’m a long way from totally sure about this.

Eric Klem

Hi Colin,

Your posts on this subject have me thinking about heat again but hopefully I will be able to resist the temptation. Here in New England, we tend to only sail in relatively warm weather and I gather that people in Britain and other places regularly push the season quite a bit more. We launch in a week and will be the first boat in the water where we are if that says anything about fair weather sailing.

I started thinking about how long we could run a propane heater on the 22 lbs of propane we carry. Using Dickinson’s numbers for high heat, we could run for 86 hours and get a total of 470,000 BTU. If we used their small diesel stove, it would use 3.9 gallons for the same amount of heat and could deliver it a lot more quickly if desired. While the fuel weighs about 5 lbs more (I suspect net it will be less due to storage requirements), you can carry a heck of a lot more diesel due to density and it is so much easier to refill. Given this, I guess that I could see using propane if it were for occasional overnights at the ends of a season but I can’t see using it for a whole lot more than that.

Thanks for the series.

Eric

Colin Speedie

Hi Eric
absolutely correct, I think, and I drew the same conclusion into my recommendations. You carry an awful lot of diesel, it’s cheap and fairly straightforward to hook up a supply to a heater.
But for your local, intermittent use, propane, which burns very cleanly and so doesn’t need such regular servicing might well be a better bet than diesel.
Best wishes
Colin

Dick Stevenson

Hi Eric,
I sailed Long Island Sound for decades and some of the best sailing is April/May and Oct/Nov so enjoy being on the water early. This is, perhaps, the only time you will have your favorite anchorages to yourself.
A friend with a propane heater on board felt like he went through way more propane than he wished to keep his 40 foot boat warm on trips up and down the ICW in the US. This was in part as he needed to find propane in many locations without a car. This was in the US where propane refills are relatively easy to find. In many parts of the world, this becomes even more problematic. Also, does the heater run on butane or a propane/butane mix. Some stoves/burners seem to care and sometimes that is all you can get and/or you do not know what you are getting.
As a reference, on my moderately well insulated boat, I use about a liter/quart of diesel running my Refleks on its lowest setting for 8-10 hours. The lowest setting, after initial warming, is sufficient heat for my 40 footer on an average day of 8-10C/45-50F. Any warmer and we crack open the hatches a bit more.
BTW, I wrote a field report on installation, use, maintenance on my Refleks for these pages a year or so ago.
Let us know what you find about the amount of propane needed for boat heating as I believe you are correct in evaluating propane as best for weekend or occasional usage. The figures you quoted sounded unrealistic to me.
My best, Dick Stevenson, s/v Alchemy

Colin Speedie

Hi Dick
you raise a very pertinent point about heaters that burn butane or propane or are happy with both. From my experience I’ve seldom seen butane outside northern Europe, but certainly there you often have the choice. But as you suggest, not all stoves are happy with both and you should stick with the fuel that the heater was designed for. Not only that the regulators are set at different pressures and the bottles are different.
And actually, butane isn’t the best bet for really cold climes anyway, as the regulators tend to ‘freeze’ when the ambient temperature drops towards 0C, which necessitates warming it up. I’ve been told that German RV’ers use electrically warmed butane regulators, but that all seems to be entering an over-complicated world to me – at least for boats.
Thanks for a very helpful comment.
Best wishes
Colin

Eric Klem

Hi Dick and Colin,

Thanks for the thoughts. Dick, your fuel burn rate experience mirrors my own with a Refleks and is low enough that it is dwarfed by engine fuel consumption if you motor regularly.

Eric