Really small heater for 18ft boat

chrisbitz said:
There's another very big difference from your boat to your bathroom - insulated surfaces. The walls on my boat are very cold, so as soon as warm air touches a cold surface, it condenses.

I presume your bathroom walls weren't thin and cold and exposed to outside air, so my guess is that's why your walls weren't wet.

I wouldn't mind betting that the humidity in your bathroom increased massively though?
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No the humidity didn't increase at all - in fact it was very 'dry air'. To be honest after the two hours were up, and when I re-entered the room, I too was expecting it to be more like a sauna! I should also like to re-emphasise that my experience of using this type of heating onboard is that despite the 'chemistry' (of which there is no dispute ) I actually experience little or no condensation at all. This also appears to be the experience of many other contributors to this thread. I ran the bathroom experiment in an attempt to determine why.

There could of course be something in what you say as my cabin interior is largely of wooden construction with little or no exposed GRP. It could also be that the condensation is collecting somewhere else, such as the bilge perhaps? My thoughts at the moment are that the poster above is probably right, and the secret lies in ventilation . With adequate through flow of air, the cabin itself in effect acts as a heat exchanger. Air is drawn in via the mushroom vents, is warmed by the heater and then rises before leaving through the slightly opened hatch. This also explains why the CO alarm isn't going crazy, as the warmed air also carries away any remaining and potentially harmful combustion gas (CO being slightly lighter than air).

As the heat by generated by the ceramic plates is a radiant heat, and not dependent on the warmed air effect to do its stuff, this more than counters the effect of cold air being drawn in from outside the cabin , which also prevents oxygen depletion, an obvious cause for concern. I would however still emphasise that my heater does have an ODS (oxygen depletion sensor) which should cut off the gas if this were to occur, however in several years of use it has yet to come into effect. The presence of an ODS being the main reason why the manufacturers are permitted to market the heaters as indoor safe.

To answer the OP, in order to heat the cabin of an 18ft boat it is my experience that you don't have to fork out hundreds of quid. A cartridge powered radiant heater will easily do the job, and as long as you take sensible precautions, adequate ventilation and a CO alarm, will keep you both warm - and dry!
 
chrisbitz said:
There's another very big difference from your boat to your bathroom - insulated surfaces. The walls on my boat are very cold, so as soon as warm air touches a cold surface, it condenses.

I presume your bathroom walls weren't thin and cold and exposed to outside air, so my guess is that's why your walls weren't wet.

I wouldn't mind betting that the humidity in your bathroom increased massively though?
Click to expand...

Many years ago, we were looking at the method of heating used in our church. At that time, "giraffe" style bottled gas heaters were being used to heat the church on Sunday - no heating at other times, and it actually wan't that effective anyway - the space was too big. Anyway, I managed to borrow a recording Hygrometer from work, because one thing we were concerned about was the possibility of condensation and damp damaging the building. The graph it produced was fascinating! During the week, when the church was unheated, the humidity reading was along the bottom of the graph. On Sunday, when the heaters went on, the humidity shot up to 100%! We switched over to an infra red "radiant heat" system sharpish after that - and have had much less trouble with efflorescence and other damp related problems with the plaster and stonework (Churches are especially susceptible to this, given the materials and antiquity of the structure).

I'd say that if you can avoid putting water into the air you're heating, it is a good thing. Remember that it isn't the condensation you can see dripping on your head that is the worry - it is the condensation in inaccessible spaces where it gathers in the end-grain of the wooden fittings and bulk-heads that is the real concern.
 
Through the ups and downs of speculation, grave concern, flat optimistic ignorance like my own, and some genuine professionals' opinions, I'm finding this heating-engineering thread much more interesting and thought-provoking than anyone could have told me I would. :)

But I'm firmly on the side of finding solutions for tiny cabins, which effectively leap-frog the irritation & damage of condensation and avoid the frightening potential dangers of asphixiation and fire. Seems to me that everything that's needed, exists now...but needs downsizing.

True, some elaboration of kit and fitment is required if there's never to be more than inconsequential risk of exhaust entering the cabin...but how much more content will you be with ducted dry hot air or a small piping hot radiator in your cabin, started with a flameless click?

How much longer would your sailing season be? And how much would such comfort add to your estimate of a boat's worth?

Seems to me there are issues of convenience, efficiency, self-contained compactness and affordability...but mostly, the trouble is that until somebody does it, the majority don't believe it's even possible...so we continue burning toxic gas & naked flames in the saloon. :mad:

Being no heating engineer, I'm wondering if anyone reading this can give answers, without using default manufacturers' names...we already know there are pretty expensive 'compact' flued heaters out there...their cost eliminates them from the OP's realm of enquiry.

So: what volume of hot water is needed, to feed a small (30cm x 50cm?) radiator at a consistent 70ºc? How big a boiler? And how much propane would be needed to keep the boiler up to temperature? How much insulation would be needed round the boiler?

Could the whole thing (minus ducting) fit within the size of a 20 litre jerrycan? Could it sit, boiling away in a vented cockpit locker, and be disconnected from ducts on Sunday night to go home? The longer I think of it, the more possible it sounds...so what have I missed? :confused:
 
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Geysers

dancrane said:
...Could the whole thing (minus ducting) fit within the size of a 20 litre jerrycan? Could it sit, boiling away in a vented cockpit locker..
Click to expand...

Sam Youles fitted a simple caravan type of gas water heater to Norseman. Instead of a faucet, he rigged it to a thermostatically controlled 12v pump and a series of radiators.

Were your lockers deep enough it would be trivial to rig such a system. It was not that efficient as a lot of heat went up the chimney, but it worked.
 
Humidity

Surely the humidity that we expect to find is actually relative humidity. This is a measure of the amount of water vapour in the air compared to the max amount of water the air can carry as a percentage. But of course air can hold more water vapour at a higher temperature. So if the cabin has been warmed the air seems dry.
What happens when the cabin cools down that I imagine will be when the moisture appears on walls etc.
olewill
 
No idea if these mini fan-heaters are any good...but as they only use 100w at 220volts...that's....less than 0.5 amp, isn't it? Presumably it'll run through a cigar-lighter 12/240 volt converter? Ah...I begin to see the flaw...it's more like 8 amps, from a 12v battery, isn't it? :(

http://bit.ly/124goAx

May just be worth splashing out £8 on, if your 18-footer has a hefty battery. Certainly compact!
 
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dancrane said:
No idea if these mini fan-heaters are any good...but as they only use 100w at 220volts...that's....less than 0.5 amp, isn't it? Presumably it'll run through a cigar-lighter 12/240 volt converter? Ah...I begin to see the flaw...it's more like 8 amps, from a 12v battery, isn't it? :(

http://bit.ly/124goAx

May just be worth splashing out £8 on, if your 18-footer has a hefty battery. Certainly compact!
Click to expand...

Running electric heating form a 12v system is obviously very limited in power. A 100w minim fan heater is not going to give much heat. However if you reckon that you could spare 10 or 20 amps from the electrics. ie when engine is running and charging then 100 or 200 watts might just help a bit. One option might be to get an old hand held hair dryer. These often have a 12v motor to drive the fan. You would need to replace the element with something suitable for 12v at 10 amps or more. A mesh of stainless steel locking wire might be used to replace the element wire. You will have to experiment with length and gauge of wire. I might suggest you start with lightest locking wire and check the resistance (current on 12v) of around 2 metres or more. The wire will need to run red on test and will be cooler with fan running over it. You will need an amp meter of course to check current consumption. Of course you could use an inverter just make sure the heat from the inverter goes into the cabin and is not lost.
Just a thought olewill
 
I've been doing some calcualtions on the cost of heating on a boat. It seems (have to check them again) to show that buying the system (new) is the most important factor in the total cost of using it over a 5 year period.

Whatever way you look at it, central heating using diesel is always the most expensive, followed by propane central heating.

Even if you use the system all winter, diesel is still the most expensive. Changing to red diesel, if possible, would then save money but is still third expensive, after diesel and propane.

On a small boat central heating is not that useful, a stove makes more sense.
If a stove can be used, a wood burner would be the cheapest, by a big margin. And since I am working on a small pellet stove, that would be easier to use and maybe even cheaper to run than a wood burner.

Here is my overview (in euro)
kostenverwarmingaaanboord.jpeg
 
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Or the other way around? :) Good insulation of the boat, some hot bodies inside.
At 0'C and storm wind steel boat with half bunks occupied is comfy inside, but with 2 inches of foam all round. Never had anything more for heating than a kerosene lamp. Fiberglass is not so much better then steel, but rarely insulated. :confused:
And that's from one who wears skiing jacket in UK, while everyone around just a Tshirt...
 
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Ah, maybe I have added some confusion, maybe stove is not the right word. Could a stove be for cooking? But I think I read about stoves and heaters as being the same thing.

Maybe I should call it a furnace?

Anyway, a wood gas stove gasifies the wood to burn the gas and charcoal remains.
My stove ehr, heater/furnace burns everything and uses a flue to get rid of the exhaust.
 
Eberspächer are bringing out a bioethanol heater at this year's London show. That would be ideal for you and many like you. When we has an 18footer, a very long time ago, we had a catalytic mounted on the back of the louvred cabin door and it kept us very snug and warm even when boating well into November and starting in April.
 
I doubt I'll be under any shelter more airtight than a boom-tent this year, so I'm beginning to feel more kindly towards the Origo Heat Pal. Looks big for a dinghy - about the size of a bucket, isn't it? But doesn't that reflect a mighty output, for 4-season dinghy cruising? :confused: :)
 
It is big DC :eek: but packs up to half the size in the picture (similar to the second picture!) The Origo one burner stove maybe the answer, but the big cover on the Heatpal makes it safer.

IMG_2971.jpg


It doesn't kick out that much heat but enough to take the chill off on really cold days, I have used mine throughout the winter whilst staying on the boat and it's just right with a bit of through ventilation - I would buy another :)

IMG_2970.jpg
 
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I did a test of a Trangia camping stove as a heater (here) only cos I have it on board but now also have a Vapalux M320 paraffin pressure lamp that I've just tested, here are the results:

Initial cabin temperature 10.6c, humidity >95%
15 mins in temp 13.9c, humidity >95%
30 mins in temp 15.3c, humidity 93%
1 hour in temp 17.2c, humidity 85%

Interesting, very small amount of condensation on the windows but the humidity reading is going down as the temperature rises. The Vapalux wins hands down over the Trangia (as a heater) as it will keep going for a claimed 11 hours on a full tank of paraffin (1L). That means it's only burning 100ml/hour, a very small amount. Lighting is no problem, after fitting a new mantle & pump leather, following the instructions I've lit it 3 times with no problems (flare ups). I ran it for 2 hours last night & it got too hot in the cabin so opened the hatch some more & put it on the top companionway step. Spares I got from Base Camp (very friendly), lamp bought for £55 inc. P&P off ebay & looks hardly used. These lamps can also be used to cook on if you make something like this...:)

Pics:

P1070007.JPG


P1070006.JPG
 
Yes I would like a Vapalux one day. Interesting what you say about the Trangia as the Origo Heat pal is VERY expensive (£140) for what it is (a burner in a heat shield) I wondered if you could buy a Trangia burner or even an Origo one and stick it in a biscuit tin or just have it open.

I have a Trangia burner which is spare as I have it linked up to a little gas bottle (much easier/quicker to use!) so I might try that - should have done it in the first place and saved a load of money :rolleyes: I have probably just bought the equivalent of another Trangia by buying the Heatpal - idiot and could have used the money to buy a Vapalux or oil lamp....groan!
 
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V1701 said:
Initial cabin temperature 10.6c, humidity >95%
15 mins in temp 13.9c, humidity >95%
30 mins in temp 15.3c, humidity 93%
1 hour in temp 17.2c, humidity 85%
Click to expand...

I think you will find that the humidity was rising, only the relative humidity was falling as warm air has the capacity to hold more water.

The trouble is that if you don't let all that warm wet air out it deposits more moisture as it cools down. Good ventilation is key.
 
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