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Old 20-09-2014, 15:38   #1
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Diesel stove with water filled radiators

Hi all,

We have a new boat (new for us, anyway) which has a diesel drip heater/ stove with a water filled coil in it connected to a number of radiators filled with water/ anti freeze. An electrical water pump is fitted to aid the water circulate. Has anyone seen this kind of system anywhere and any opinions on its pros and cons? How necessary is the pump? Couldn't find anything on the forums about this.

My main concern is the expansion tank: For some reason it's not a closed system, but the actual tank has a hose coming out on top (close to the lid where you fill water in) which leads to an open plastic container/ bottle which is lower than the expansion tank. This has several implications which I don't really understand, and maybe someone here has experience or more imagination than I do?

- Sometimes, especially when the loops to some of the radiators are closed, water gets pushed through the expansion tank into the plastic container, just to be sucked out again a few seconds after. I'm talking about roughly a liter of water going back and forth within seconds. What the hell?

- Today we tried to have the heater on without opening any of the radiators, and without switching the pump on. The result was an owerflowing plastic container and we had anti freeze in the bilge and a lot of air in all radiators. There was probably also air in the hose close to the stove, as the hose there started to smoke (and we switched the stove off right away).

Shouldn't it only expand when air is in the system?

Is the open plastic container normal/ a good idea? Or should we remove it and close the hose and make the system properly closed? Then there would be no obvious vent for potential high pressure situations except wherever the system is weakest.

Any help, especially experience with such a system is highly appreciated. The polar night is approaching and we will freeze or be frustrated fighting with this on a daily basis otherwise!

Cheers,
Phil
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Old 20-09-2014, 16:47   #2
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Re: Diesel stove with water filled radiators

I don't know about the first issue (the litre of water in and out).
The second issue is simple. You boiled the water in the stove and it expanded vastly, spilling everywhere. You must run your pump if you have the stove on. If not you will boil the water out then melt your coil in the stove.

Your system is designed for low pressure, and an open sytem. If you close the system you will burst pipes all over the place. With an open system the pressure never builds and so there will be no leaks, well not ruptures from pressure anyway.
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Old 20-09-2014, 17:27   #3
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Re: Diesel stove with water filled radiators

Agreed, keep the pump on when the stove is firing as the system is now.

If you wanted to make it a closed system, you would need a temperature and pressure relief. I would actually add two relief valve. A standard water heater T&P relief valve, mainly for the temperature relief which is about 190 degrees or there about. The pressure side would be too high, unless your using a British version. Then a second pressure relief set at oh 10 psig, both draining to the bilge.

APOLLO Safety Relief Valve,3/4 In,15 psi,Bronze - Relief Valves - 3EEY2|13211B15 - Grainger Industrial Supply

I expect that originally they had a standard T&P relief installed where the open cup is. This as an expansion tank does nothing in a open system. The problem is the standard T&P pressure setting (in the US anyway) is up at 125 psig. which isWAY too high for the heating loop on the boat. With a standard T&P relief, things would get more then exciting with that system under no flow conditions.

Why I call for a second relief at 15 psig. which will pop off before life gets interesting.

Really if you plan on using the stove a lot in warm weather, drain all the water out of the loops. That will prevent you from having to deal with a BLEVE, (boiling liquid expanding vapor explosion). That loop without circulation will make steam rather quickly. as you have already found out.
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Old 21-09-2014, 00:50   #4
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Re: Diesel stove with water filled radiators

Hei,

Thanks for your replies. I came to similar conclusions during my sleep and will keep the pump running from now, and probably some of the radiator loops open to remove heat.

Your thoughts about the closed vs. open system make a lot of sense, and I think I will stick with it as it is and see how it goes.

We will likely never be in warm areas and need heat well distributed to fight condensation, so removing the water is not an option unless life continues to be as interesting as it was yesterday night!

Cheers,
Phil
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Old 21-09-2014, 11:10   #5
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Re: Diesel stove with water filled radiators

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Originally Posted by phipseml View Post
Hei,

Thanks for your replies. I came to similar conclusions during my sleep and will keep the pump running from now, and probably some of the radiator loops open to remove heat.

Your thoughts about the closed vs. open system make a lot of sense, and I think I will stick with it as it is and see how it goes.

We will likely never be in warm areas and need heat well distributed to fight condensation, so removing the water is not an option unless life continues to be as interesting as it was yesterday night!

Cheers,
Phil
Good decision if it ain't broke don't it. It sounds like a hell of a good idea for a cold climate.
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Old 23-09-2014, 11:54   #6
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Re: Diesel stove with water filled radiators

Autumn, and a young man's fancy turns to heating his boat. . .
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Old 23-09-2014, 12:19   #7
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Re: Diesel stove with water filled radiators

Your system is common in older commercial fishing boats. Usually to either transfer heat to area far from the stove or to heat a hot water tank. With the pump off you will make steam. Water expands 16x when it becomes steam and is unrestricted. If the system were closed without circulation you could have an explosion. You need to balance your heating needs with your fuel flow. Probably one or more radiators would have to be left on. I have something like it , but with a pellet stove.
An open system is easier than a closed system. At close to zero pressure, leaks are less of a problem. You loose water to evaporation, but don't need an expansion tank or pressure relief valve. But a relief valve would be a good idea near where the water comes out of the stove.
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Old 24-09-2014, 01:10   #8
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Re: Diesel stove with water filled radiators

Hei there,

Yes, heating the boat in various places is very good! We got the system pretty much working by now, with the pump on all the time and some radiators open. We start to get a feeling for it.

If we keep the first two radiators in the loop on, there is almost no heat coming to the other ones, so we kept them off to transport heat to more important and remote areas. This ir probably because the pump isn't strong enough? I'll experiment with a bit more water in the expansion tank (highest point in the system, just downstream of the pump close to the cold water intake at the stove) to slightly increase the pressure in the system and see if that helps to increase flow in the tubes and circulation of hot water to the other radiators.

We do hear the water boiling or close to boiling in the stove, though, no matter what we do. The explosion like loss of water into the expansion tank has not happened anymore though, and I suppose that's alright, although a bit noisy. Adds to the atmosphere, I guess...

Cheers,
Phil
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Old 24-09-2014, 11:45   #9
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Re: Diesel stove with water filled radiators

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Originally Posted by phipseml View Post
Hei there,

Yes, heating the boat in various places is very good! We got the system pretty much working by now, with the pump on all the time and some radiators open. We start to get a feeling for it.

If we keep the first two radiators in the loop on, there is almost no heat coming to the other ones, so we kept them off to transport heat to more important and remote areas. This ir probably because the pump isn't strong enough? I'll experiment with a bit more water in the expansion tank (highest point in the system, just downstream of the pump close to the cold water intake at the stove) to slightly increase the pressure in the system and see if that helps to increase flow in the tubes and circulation of hot water to the other radiators.

We do hear the water boiling or close to boiling in the stove, though, no matter what we do. The explosion like loss of water into the expansion tank has not happened anymore though, and I suppose that's alright, although a bit noisy. Adds to the atmosphere, I guess...

Cheers,
Phil
Is it possible the remotest radiators have air entrapment. Sounds about like the heating system I grew up with. The radiators had air bleeds at their top ends.
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Old 25-10-2014, 07:23   #10
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Re: Diesel stove with water filled radiators

Hi everybody,

Just to let you know that we got the system running almost without problems. The trick was to air it properly and repeatedly, and to find the balance between heat production and removing heat from the radiators. Now we can have most of the radiators open simultaneously, although sometimes air collects in one or two and stops circulation and brings the water to the boil. How is this air coming in there??

Anyway, this system (while it works) is worth a lot. It's warm everywhere, even in the bilge and in cupboards and under seats and other hidden areas where the hot water hoses go. Really good against cold and condensation. I would also think it's cheaper than electricity in the long run.

Cheers,
Phil
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