Small solid fuel stove with a back boiler?

[jetzi]

Since our solid fuel stove is located way at the fore of our 65' NB, the aftmost room doesn't get enough heat in winter. I'm considering installing a second, small solid fuel stove in there before it gets too cold. Since we have our cauliflower hot water tank in that room, I'd like to get one with a back boiler so that I can have an alternative way of heating water (redundancy = win on a boat). I've heard good things about Boatman stoves, and it looks from their website that they can take a backboiler, but they aren't responding to email at the moment.

 

Currently we have a twin coil calorifier, one fed by the engine and the other on a circuit with an Eberspaecher diesel hydronic heater and two radiators. Water only circulates in the radiators with the Ebersplutter on. Ideally I'd like to put the radiators on their own circuit with their own pump, so that I can use the engine heat or the back boiler to heat the boat without needing to have the Ebersplutter on.

 

Finally, to save space I would like to mount the secondary solid fuel stove on top of the box above the calorifier tank. It would also be quite nice to have it at eye level. However I am concerned about the considerable weight that would be mounted quite high and also whether there might be boat safety issues with this plan, so I might have to take up floor space if this is the case.

 

1. Can anyone recommend a small solid fuel stove that can take a back boiler?

2. Is it possible to add a back boiler to the Eberspaecher circuit so that I share its coil in the calorifier?

 

3. Is it possible to separate the radiator circuit out using a separate water pump? (There would be three different things on the Eberspaecher circuit - Eber, back boiler, and rads.)

 

4. Can you think of any issues with mounting the stove where I'd like to? Here's a diagram so you can better picture what I mean - the calorifier is on the bottom left with the stove mounted on the box above.

 

[Edders]

On point 4, I think the flue would be too short.

 

[Chewbacka]

If you use a 'normal' boat chimney then the flue 'height' will be short giving a poor draw on your stove, so you may need an extra long chimney to give you adequate height.

As the stove is close to the roof, radiant heat onto the roof will also need considering, maybe requiring an overhead fire proof insulating board.

If the boat should bash head on into something (including you being hit head on by another boat, rare but not unheard off) you need to consider how to stop the stove falling forward. 

 

All manageable, but best considered in the design stage.

 

Added - forgot to mention - beautiful diagram

Edited June 13, 2019 by Chewbacka

[Onewheeler]

The Boatman bloke usually responds to emails eventually, but never speedily! They're good stoves and he's a nice bloke. Try ringing or persist.

[Jen-in-Wellies]

20 minutes ago, Onewheeler said:

The Boatman bloke usually responds to emails eventually, but never speedily! They're good stoves and he's a nice bloke. Try ringing or persist.

I get the impression that Boatman Stoves is basically a bloke in a shed making stoves. If he is answering emails and phone calls, then he can't make stoves at the same time. He will get back eventually and his stoves are very good.

+1 on the comments about stove flue draw, potential heat damage and collision movement risk with the stove above the cauliflower. It will also mean that a circulation pump is required to move water from the back boiler down to the cauliflower. This will need to run all the time while the fire is lit, or you'll get vapour locks and boiling in the back boiler. The pump will use a lot of power from your batteries when you are not on shore line.

 

I'd suggest having the stove at floor level and raise the calorifier up if you possibly can. This will allow you to use gravity circulation through the calorifier and a pump shouldn't be needed. I'd have enough radiators in the loop as well after the cauliflower so that the heat from the back boiler will be dumped when the cauliflower is up to full temperature. Again you risk boiling in the back boiler if you don't. Careful planning of the radiator sites, types, pipe runs and using large bore pipes will let gravity circulation do its thing. I have this set up on my boat and it works well.

You'll already have a circ pump with the Ebersplutter, but removing the need for it when on solid fuel will save a lot of power and make the inside of the boat quieter. Not really answering all your questions, but some more things to think about.

 

Jen

Edited June 13, 2019 by Jen-in-Wellies

[Onewheeler]

Having collected our stove, i can confirm that he is basically a bloke in a large shed on an industrial estate, the sort where people still make stuff.

[Taslim]

My fist thought was uprate the existing stove & radiator system to include the cold parts of the boat. Two stoves seems one to mamy unless your boat is a pretend Trad with Cabin.

[MtB]

4 hours ago, ivan&alice said:

 

4. Can you think of any issues with mounting the stove where I'd like to? Here's a diagram so you can better picture what I mean - the calorifier is on the bottom left with the stove mounted on the box above.

 

Well as no-one else has pointed it out, heat rises so a stove near the floor heats a space better than a stove fitted half up to the ceiling like in your diagram! 

 

Granted radiant heat will from the stove will radiate downwards but convection heat will make the room very hot at head height yet remain cool at the floor. Stratification, this is called. Disrupting stratification is the main function of an Ecofan, a function many here struggle to grasp - mainly those who don't own one... 

 

 

 

 

Edited June 13, 2019 by Mike the Boilerman

[Rob-M]

We have The Hobbit stove which is a small stove and has an optional back boiler. We don't have the back boiler so I don't know how it performs.

[system 4-50]

Shortly to become available, one preloved Puffin stove with separate, never-installed (never got around tuit) brand new back boiler fitting for it.  I'm changing to a Webasto.

[jetzi]

22 hours ago, Edders said:

the flue would be too short

 

22 hours ago, Chewbacka said:

the flue 'height' will be short giving a poor draw on your stove, so you may need an extra long chimney to give you adequate height.

 

22 hours ago, Jen-in-Wellies said:

+1 on the comments about stove flue draw

Raising the stove on top of the cauliflower would take 850mm off the length of the flue. Is there a way to calculate how long your flue/chimney should be to ensure adequate draw? Seems that a long chimney would be an easy fix for this, but it wasn't something I'd considered so thanks for pointing it out.

 

22 hours ago, Chewbacka said:

radiant heat onto the roof will also need considering, maybe requiring an overhead fire proof insulating board.

If the boat should bash head on into something (including you being hit head on by another boat, rare but not unheard off) you need to consider how to stop the stove falling forward. 

Thanks, I planned to tile the whole corner with something that could handle the heat. If I do raise the stove I'll be sure to do the ceiling as well. And I'll bolt it down to stop it from falling. All good points to consider.

 

22 hours ago, Jen-in-Wellies said:

It will also mean that a circulation pump is required to move water from the back boiler down to the cauliflower. This will need to run all the time while the fire is lit, or you'll get vapour locks and boiling in the back boiler. The pump will use a lot of power from your batteries when you are not on shore line.

 

I'd suggest having the stove at floor level and raise the calorifier up if you possibly can. This will allow you to use gravity circulation through the calorifier and a pump shouldn't be needed. I'd have enough radiators in the loop as well after the cauliflower so that the heat from the back boiler will be dumped when the cauliflower is up to full temperature. Again you risk boiling in the back boiler if you don't. Careful planning of the radiator sites, types, pipe runs and using large bore pipes will let gravity circulation do its thing. I have this set up on my boat and it works well.

You'll already have a circ pump with the Ebersplutter, but removing the need for it when on solid fuel will save a lot of power and make the inside of the boat quieter. Not really answering all your questions, but some more things to think about.

 

Raising the calorifier is a possible but difficult task and being that I won't be able to mount the stove under it will take up more space. However the prospect of being able to do this without pumps is HUGE. We don't use the Eber and the rads at the moment (in fact they are disconnected following a minor leak) as we could only really use the Eber with the engine running due to its large power draw and our woefully inadequate electrical system. Of course with the engine running, we don't need the Eber to heat the water. I don't think it's possible to run the Eber circ pump independently of the heating, which is a shame because I'd like to be able to use the engine heat to heat the boat.

 

I'm a little hazy on how the gravity system works. My assumption is the water is heated low down (hence needing to put the stove on the floor), hot water rises into the calorifier tank, sucking cooler water (but still hot) through the system to replace it, whereupon the heat source re-heats it? I'm a little lacking in confidence that this will work, at least unless I get some professional help to design it. Or is it just a case of having the heat source as low as possible, the tank as high as possible, and using large bore pipes?

 

I'd be willing to give up the floor space for a pumpless system. The calorifier tank is a heavy thing though - 380 in diameter and 700 high (almost 80 litres I think) - will I be sacrificing stability to have this raised?

 

22 hours ago, Taslim said:

My fist thought was uprate the existing stove & radiator system to include the cold parts of the boat. Two stoves seems one to mamy unless your boat is a pretend Trad with Cabin.

Our single stove is right at the bow door, and there are 2 seperate rooms the heat has to make it through to heat the third, aftmost room. That stove has no boiler so heat transfer is by convection only. To even heat the bathroom in winter the fire has to be unbearably hot in the saloon. The Eberspaecher/radiator combo works but not nearly as well as solid fuel. Two small fires would just distribute the heat so much better. Unless I could attach a back boiler to my current stove and run hot pipes the 50-60 odd foot to the calorifier way aft. (We have a Morsø Squirrel).

 

21 hours ago, Mike the Boilerman said:

Well as no-one else has pointed it out, heat rises so a stove near the floor heats a space better than a stove fitted half up to the ceiling like in your diagram! 

 

Granted radiant heat will from the stove will radiate downwards but convection heat will make the room very hot at head height yet remain cool at the floor. Stratification, this is called. Disrupting stratification is the main function of an Ecofan, a function many here struggle to grasp - mainly those who don't own one... 

This is a good point, but I was hoping that the radiators would help distribute the heat downwards as well - if you look at the diagram, I planned a radiator under the desk/bed to warm the tootsies.

 

19 hours ago, system 4-50 said:

Shortly to become available, one preloved Puffin stove with separate, never-installed (never got around tuit) brand new back boiler fitting for it.  I'm changing to a Webasto. 

Might be interested if you are looking to sell! PM me a price, model number and location? (It will take me at least a few weeks though to be ready for it)

 

 

 

Does anyone have any thoughts about sharing the second calorifier coil between rads, eber and back boiler? Are there any reasons I couldn't / shouldn't / wouldn't / mightn't / mustn't do this? Does it make a difference if I am trying to make this whole circuit gravity fed?

[MtB]

4 minutes ago, ivan&alice said:

Or is it just a case of having the heat source as low as possible, the tank as high as possible, and using large bore pipes?

 

This is broadly it. Water expands when heated so hot water has a lower density than cold water, so gravity makes cold water tend towards the lower part of a system and the lighter weight hot water tends to 'float' on top of it. If you put a heat source at the bottom and a heat load at the top, the hot water rises to the top where it gets cooled, and the cool water falling to the bottom gets heated, resulting in water circulation with no pump! The forces involved are microscopic though, so big pipes and waterways are needed to minimise the hydraulic resistance and get any useful amount of flow. The tiny connections and waterways inside an eber would reduce gravity circulation to virtually nothing.

 

 

[Rickent]

If you get a boatman stove , be prepared to fight to remove the ash as it does not have a seperate ash door and thus is a right pain.

Search boatman stove review by MTB and it will tell you everything you need to know. 

[Alan de Enfield]

I'm sure you have seen this diagram before, but note that you need a fireproof hearth with dimensions larger then the stove, and it should be 'fire / heat proof'.

Often, concrete slabs are used, add these to the weight of the stove, the weight of the backboiler and the weight of the water all sitting on top of your 'cauliflower cupboard' and it would need some substantial framing.

 

 

Boat Stoves Fitting Guidance.pdf

[MtB]

1 hour ago, Alan de Enfield said:

I'm sure you have seen this diagram before, but note that you need a fireproof hearth with dimensions larger then the stove, and it should be 'fire / heat proof'.

Often, concrete slabs are used, add these to the weight of the stove, the weight of the backboiler and the weight of the water all sitting on top of your 'cauliflower cupboard' and it would need some substantial framing.

 

 

Boat Stoves Fitting Guidance.pdf 893.64 kB · 2 downloads

 

Ivan, most of the 'requirements' in that link are twaddle. Impossible to comply with (in a narrowboat) and widely ignored. While it is 'best practice', don't tie yourself in knots trying to comply with it, nobody else does. 

 

 

[Jen-in-Wellies]

5 hours ago, ivan&alice said:

Raising the calorifier is a possible but difficult task and being that I won't be able to mount the stove under it will take up more space. However the prospect of being able to do this without pumps is HUGE. We don't use the Eber and the rads at the moment (in fact they are disconnected following a minor leak) as we could only really use the Eber with the engine running due to its large power draw and our woefully inadequate electrical system. Of course with the engine running, we don't need the Eber to heat the water. I don't think it's possible to run the Eber circ pump independently of the heating, which is a shame because I'd like to be able to use the engine heat to heat the boat.

 

I'm a little hazy on how the gravity system works. My assumption is the water is heated low down (hence needing to put the stove on the floor), hot water rises into the calorifier tank, sucking cooler water (but still hot) through the system to replace it, whereupon the heat source re-heats it? I'm a little lacking in confidence that this will work, at least unless I get some professional help to design it. Or is it just a case of having the heat source as low as possible, the tank as high as possible, and using large bore pipes?

 

I'd be willing to give up the floor space for a pumpless system. The calorifier tank is a heavy thing though - 380 in diameter and 700 high (almost 80 litres I think) - will I be sacrificing stability to have this raised?

Mike the Boilerman has answered this too. Big bore pipes, as much as possible in 28mm, though you can get away with some 22mm sections, including the coil inside the calorifier. Have the pipes rising from the stove to the calorifier top coil inlet, out the lower connection to the coil, then level,  to each radiator, then returning to the stove at the level of the stove backboiler lower intake. As few bends as possible and those with swept bends, rather than elbows, if you can manage it. No drops and rises in the pipes.

 

I don't know of any calculations, though I'm sure it can be done with a chart of water density against temperature, flow rates in pipes and elbows and the wattage of each radiator. I just did mine as above and it worked first time. Seems like magic!

 

Looks like your calorifier is currently on the starboard side. 80l of water inside weighs 80kg, plus maybe 10kg extra for the copper and insulation, so a considerable weight. Moving it up will change the centre of gravity of the boat, but you will be having maybe 60kg of stove near the floor, so little worse than what you were proposing. Moving it from starboard to port will upset the trim a lot, but adding a stove will also change the boats trim, so you need to take that in to account fitting a stove anyway, or risk having the boat leaning over.

 

The amount it needs to move up depends on the position of the calorifier coil, compared with the stove back boiler outlets, so if the coil is relatively low down in the cauliflower, then it needs to be raised more. However, a lower coil will heat a larger proportion of your 80l. Just as a comparison, the height difference between the top outlet of my stove back boiler and the inlet to the calorifier coil is around 22".  The lower outlet from the calorifier coil comes out just under gunwale height and goes to finrads in the bathroom and bedroom. Just an example from a system that is known to work. I don't know how close to the edge my system is, but the stove needs to be almost out before circulation stops, from what I can tell by pipe temperature.

 

On flue height, for most stoves, the house installation instructions give recommended flue heights hugely in excess of anything available on a boat. People fit them in boats anyway, but it could be a bit marginal. If you add extra height with an external chimney you will lose that cruising a canal with low bridges and tunnels as the chimney will need to be removed, or the canal infrastructure will remove it for you! If the stove is lit while cruising it will lose a lot of its draw.

 

Jen

Edited June 14, 2019 by Jen-in-Wellies

[Rob-M]

7 hours ago, Rickent said:

If you get a boatman stove , be prepared to fight to remove the ash as it does not have a seperate ash door and thus is a right pain.

Search boatman stove review by MTB and it will tell you everything you need to know. 

That was why I went for a hobbit as it has a separate ash door to easily remove the ash pan.

[jetzi]

On 14/06/2019 at 10:27, Mike the Boilerman said:

This is broadly it. Water expands when heated so hot water has a lower density than cold water, so gravity makes cold water tend towards the lower part of a system and the lighter weight hot water tends to 'float' on top of it. If you put a heat source at the bottom and a heat load at the top, the hot water rises to the top where it gets cooled, and the cool water falling to the bottom gets heated, resulting in water circulation with no pump! The forces involved are microscopic though, so big pipes and waterways are needed to minimise the hydraulic resistance and get any useful amount of flow. The tiny connections and waterways inside an eber would reduce gravity circulation to virtually nothing. 

OK sounds good. What if I was to lower the Eber to below the level of the calorifier too? I guess there is a reason for an integrated pump.

 

This kind of suggests that I won't be able to connect the rads and back boiler in series on the Eber circuit. Would I be able to put these in parallel though? Unless I go and get a 3 coil calorifier (do those exist?) I don't see how I can make the plumbing work out for a gravity system.

 

On 14/06/2019 at 10:32, Rickent said:

If you get a boatman stove , be prepared to fight to remove the ash as it does not have a seperate ash door and thus is a right pain.

Search boatman stove review by MTB and it will tell you everything you need to know. 

Yeah, an ash door is a must have. Thanks for pointing this out.

 

19 hours ago, Jen-in-Wellies said:

Big bore pipes, as much as possible in 28mm, though you can get away with some 22mm sections, including the coil inside the calorifier. Have the pipes rising from the stove to the calorifier top coil inlet, out the lower connection to the coil, then level,   to each radiator , then returning to the stove at the level of the stove backboiler lower intake. As few bends as possible and those with swept bends, rather than elbows, if you can manage it. No drops and rises in the pipes. 

The radiators themselves have rising pipes, though. How does the gravity system handle that? Is there enough pressure to send the water up and through the rads? I am going to want at least 3 rads, with the furthest (bedroom) one being about 10m from the calorifier. Ideally I'd put one in the saloon too which is about 15m away. But this feels like a less likely possibility for a gravity system.

 

19 hours ago, Jen-in-Wellies said:

The amount it needs to move up depends on the position of the calorifier coil, compared with the stove back boiler outlets, so if the coil is relatively low down in the cauliflower, then it needs to be raised more. However, a lower coil will heat a larger proportion of your 80l. Just as a comparison, the height difference between the top outlet of my stove back boiler and the inlet to the calorifier coil is around 22".

I suppose for a gravity system that the higher the calorifier, the better, so if I am going to move it I would move it right up to below the roof, I think. Then again, the lower the heavy things are, the better for the boat. So perhaps there is a happy medium.

19 hours ago, Jen-in-Wellies said:

On flue height, for most stoves, the house installation instructions give recommended flue heights hugely in excess of anything available on a boat. People fit them in boats anyway, but it could be a bit marginal. If you add extra height with an external chimney you will lose that cruising a canal with low bridges and tunnels as the chimney will need to be removed, or the canal infrastructure will remove it for you!

On the Stort last month we had to take our current chimney all the way off anyway. And being that the future stove would be right next to the cruiser deck I could probably take the chimney down without even taking my hand off the tiller. So I'm really not concerned about that little bit of extra effort. It would be pretty nice to have the chimney on a spring so that it would just get bumped down by bridges as and when required!

 

[Jen-in-Wellies]

46 minutes ago, ivan&alice said:

The radiators themselves have rising pipes, though. How does the gravity system handle that? Is there enough pressure to send the water up and through the rads? I am going to want at least 3 rads, with the furthest (bedroom) one being about 10m from the calorifier. Ideally I'd put one in the saloon too which is about 15m away. But this feels like a less likely possibility for a gravity system. 

Dunno. I've no experience with this on conventional rads. I used finrads. Someone else may be along shortly.

47 minutes ago, ivan&alice said:

I suppose for a gravity system that the higher the calorifier, the better, so if I am going to move it I would move it right up to below the roof, I think. Then again, the lower the heavy things are, the better for the boat. So perhaps there is a happy medium.

Happy medium I reckon.

 

[TheBiscuits]

51 minutes ago, ivan&alice said:

The radiators themselves have rising pipes, though. How does the gravity system handle that? 

They shouldn't.   One big pipe comes off the backboiler goes up and runs along the boat at gunwhale height.  

 

The rads are dropped down from this run and then join into the one big return pipe that runs along the floor back to the stove

[Jen-in-Wellies]

1 hour ago, ivan&alice said:

OK sounds good. What if I was to lower the Eber to below the level of the calorifier too? I guess there is a reason for an integrated pump.

 

This kind of suggests that I won't be able to connect the rads and back boiler in series on the Eber circuit. Would I be able to put these in parallel though? Unless I go and get a 3 coil calorifier (do those exist?) I don't see how I can make the plumbing work out for a gravity syste

No idea if this would work or not, but perhaps a valve in the return pipe to the stove back boiler. Using a design of valve that offers minimum resistance to flow when fully open. Ebersplutter T'd in to the hot and cold side of the calorifier/radiator circuit. With the stove out, close the valve, then the ebersplutter will circulate round the circuit with the pump. Ebersplutter and pump turned off, gate valve open, fire lit. Gravity circulation works round the cauliflower/radiator circuit, but won't go round the ebersplutter/pump, due to the relative heights (below back boiler) and resistance to flow of the stopped pump. You would have to be careful to ensure you open the valve when lighting the fire, but no more problem than having to remeber to turn a pump on, which a lot of boaters seem to be able to cope with fine. Some folks I know leave a cardboard sign with "PUMP!" written on it inside the stove when it is out to remind them. Substitute "PUMP!" with "VALVE!". If you accidentally left the valve open when running the Ebersplutter, then I suppose the water might take the route through the back boiler in preference.

Would this work?

Jen

[Jen-in-Wellies]

Drawn out in ASCIcad^(tm)

 

    ________________________________To calorifier and radiators
    |                            |
Ebersplutter    Back Boiler
    |                           X valve
    |______________|________________From calorifer and radiators

 

 

Edited June 15, 2019 by Jen-in-Wellies

[tree monkey]

Have a look at this chap, custom made and a decent price and bloke

http://www.thefireweaver.com/

 

[jetzi]

 

So this is what it would look like with the calorifier and the stove switched around (for a backboiler and gravity fed central heating).

 

It's a pretty tight nook for the stove and it would require elbows to route the flue outside, out of the way of the calorifier tank. There is about 150mm of clearance to each side and the back (obviously the sides here would have to be very heat-proof).

 

Certainly neat and takes up very little room, but I'm not sure if this is a feasible solution?

 

 

Sorry for not thanking you for your AsciiCAD diagram @Jen-in-Wellies, that looks great and means that I would be able to use a single calorifier coil for both the backboiler and the Eber, and it means that the stuff in the Eber won't slow down the gravity feed from the back boiler when I'm using the stove. Looks great! I'm going to enquire about having a steel platform for the calorifier welded on top of the gunwale. Moving the calorifier does feel like a rather herculean task but you have me so enamoured with the gravity feed idea that I have to at least consider it.

[Alan de Enfield]

10 minutes ago, ivan&alice said:

 

So this is what it would look like with the calorifier and the stove switched around (for a backboiler and gravity fed central heating).

 

 

My first thought would be you appear to be boxing in the stove on 3 sides and the top, you will not get much in the way of heat circulation and the bottom of the cauliflower will get pretty hot.

 

I removed a dressing table (in our little 30 footer) and put a small (3Kw) stove in its place, but did leave the 'top' open to allow for heat circulation, but, basically it didn't do much circulating it just 'stopped in its cupboard'. Only got any circulation when I fitted a 6" fan (230v) at ceiling level blowing downwards and forward (along the boat)

Then it worked well.

Got the temperature up to 54*C at head height before we gave up the test (or collapsed) and opened the windows and doors and shut down the fire.

 

For 'size' those are 6" tiles

 

Edited June 29, 2019 by Alan de Enfield