Back boiler heating?

[Psycloud]

We have a Villager Chelsea Duo which I believe can take a back boiler. I am wondering if this could then be used to heat the 4 radiators that run the length of the boat?

 

Currently they are connected to a non-functioning Eberspacher at the other end of the boat but presumably I could change the plumbing so that the pipes extend to the back boiler and disconnected from the Eberspacher?

 

So if I run the pipes under the front step and put in a pump somewhere would this work or are back boilers not suitable for this kind of installation?

 

Thanks

 

David

Edited January 4, 2013 by Psycloud

[MtB]

Yes you could!

 

You would need a cold feed and expansion tank too, which is usually the tricky bit. Along with a reliable electricity supply for the pump, as should the pump stop while the stove is alight, the water in the back boiler will boil. Paradoxically, the last thing you want a boiler to do is boil.

 

MtB

[Psycloud]

Yes you could!

 

You would need a cold feed and expansion tank too, which is usually the tricky bit. Along with a reliable electricity supply for the pump, as should the pump stop while the stove is alight, the water in the back boiler will boil. Paradoxically, the last thing you want a boiler to do is boil.

 

MtB

 

Hmmm - well the cold tank is just behind the boiler but of course the feed runs all the way to the back where the Eber was so is there any reason why the pump can't be at the opposite end to the stove? A bit like this:

 

 

<Stern--Header+pump-----Rad----Rad----Rad----Rad----Stove--Bow>

 

What sort of pump would be the right sort of thing for this please?

 

Thanks

 

David

Edited January 4, 2013 by Psycloud

[MtB]

Hmmm - well the cold tank is just behind the boiler but of course the feed runs all the way to the back where the Eber was so is there any reason why the pump can't be at the opposite end to the stove? A bit like this:

 

 

<Stern--Header+pump-----Rad----Rad----Rad----Rad----Stove--Bow>

 

What sort of pump would be the right sort of thing for this please?

 

Thanks

 

David

 

Ah you have an expansion tank already. Cool!

 

That config would be fine. Dunno about the pump, I know NUFFERN about boat heating.....

 

 

MtB

[nicknorman]

As mike implies, back boilers can be very dangerous if things go wrong. The scenario is the circulation stops for some reason (pump failed etc) so the water in the boiler heats up and boils. The steam pushes all the water out of the boiler and that allows the boiler metal to heat up well above 100degC. Maybe even glowing red hot! Then a big blob of water decides to glug past the steam into the boiler, hits the very hot metal and explosively turns to steam. The explosive expansion can blow the boiler apart with corresponding injury and damage from the shrapnel. That is perhaps an extreme case, but it has happened.

 

Therefore I would say best to design the system with at least a bit if natural convective circulation, even if it has to be supplemented by a pump to get all the rads hot. The pump should be reliable with a design that does not impede flow if it stops. Bolin make such pumps but they are expensive.

Edited January 5, 2013 by nicknorman

[GUMPY]

Bolin make such pumps but they are expensive.

 

Not any more they stopped making them last year

[nicknorman]

Not any more they stopped making them last year

Oh dear! I guess they were too expensive.

 

Solar heating system suppliers are a good source of such pumps but you have to make sure they can cope with high water temperatures.

[Caprifool]

The 12volt solar pumps are made for high temps and are cheap enough to keep a couple of spares.

[PaulJ]

Hmmm - well the cold tank is just behind the boiler but of course the feed runs all the way to the back where the Eber was so is there any reason why the pump can't be at the opposite end to the stove? A bit like this:

 

 

<Stern--Header+pump-----Rad----Rad----Rad----Rad----Stove--Bow>

 

What sort of pump would be the right sort of thing for this please?

 

Thanks

 

David

 

I have tried this before- on a Squirrel boiler ,22mm flow and return pipes with a 12v ciculation pump (think may have been a Johnson). I am guessing it did circulate the water- but only through the last couple of rads. It definately did not circulate anything through the boiler which did just that.Boiled.

Moved the same pump back to near the boiler,(on the return pipe) wired it through a pipe stat(on feed pipe right next to boiler) and system worked perfectly with no dramas and afaik still is..

[Paul C]

We've just removed a stove with a back boiler and replaced it with one without a back boiler. Partly for the reasons given in the thread - that there exists this requirement to keep water circulating all the time. For some people, this isn't an issue, but for us its a massive one. We don't liveaboard, but do use the boat regularly and plan to have the heating on when we do visit (unless its a nice warm day like today was). So, the scenario is, we'd arrive at the boat maybe 11:30am, get the stove going, and then leave at 2:30pm and there is still a bit of wood in the stove so we leave it to burn out and cool down of its own. If we had a back boiler, we'd need to leave a circulation pump running. We might not return to the boat for 3-4 days.

 

I guess there could be a temperature-controlled way of making the pump turn on or off, or a way to plumb it so enough flowrate arose without a pump at all (ie gravity fed).

 

The only other thing to consider with your plans is that doing the modification might require:

 

- The fireplace to be rebuilt (tiling, heatproof boards, etc)

- Every panel along the length of the boat to be removed, to gain access to the pipework (ie if the height between top-bottom pipe needed to be changed for gravity feed, or a slight slope created on it. etc)

- If the pipes are under the floor.......big job.

[PaulJ]

We've just removed a stove with a back boiler and replaced it with one without a back boiler. Partly for the reasons given in the thread - that there exists this requirement to keep water circulating all the time. For some people, this isn't an issue, but for us its a massive one. We don't liveaboard, but do use the boat regularly and plan to have the heating on when we do visit (unless its a nice warm day like today was). So, the scenario is, we'd arrive at the boat maybe 11:30am, get the stove going, and then leave at 2:30pm and there is still a bit of wood in the stove so we leave it to burn out and cool down of its own. If we had a back boiler, we'd need to leave a circulation pump running. We might not return to the boat for 3-4 days.

 

I guess there could be a temperature-controlled way of making the pump turn on or off, or a way to plumb it so enough flowrate arose without a pump at all (ie gravity fed).

 

The only other thing to consider with your plans is that doing the modification might require:

 

- The fireplace to be rebuilt (tiling, heatproof boards, etc)

- Every panel along the length of the boat to be removed, to gain access to the pipework (ie if the height between top-bottom pipe needed to be changed for gravity feed, or a slight slope created on it. etc)

- If the pipes are under the floor.......big job.

Running the pump through the pipe stat does that. I set mine at about 30 degrees ish. Light the stove and when the boiler water gets up to the set temp it switches on pump. When boiler goes out (or you go out)pump will always continue to run until the water temp is below this. This could be a while after the stove itself has gone out. As a bonus,when the stove is only ticking over the pump will cut in and out and save battery power. Most importantly,for someone like myself with 3 second memory, I never have to remember to switch pump on -or off.

[Psycloud]

I have just read a review which said "whatever you do don't get a back boiler on this model or you will get no heat in the room" - does the back boiler reduce the heat from the stove significantly then?

[nicknorman]

I have just read a review which said "whatever you do don't get a back boiler on this model or you will get no heat in the room" - does the back boiler reduce the heat from the stove significantly then?

The stove still produces the same amount of heat overall, but a good bit of it goes to the back boiler. Therefore the boat receives the same amount of heat overall, but it will be better distributed. With most boat stoves, they have to be run pretty slowly to avoid overheating the space around the stove, in particular any woodwork in the vicinity. With a BB you can probably run the stove faster without overheating the local area, thus increasing the overall heat into the boat in practice. If the stove is in a large cabin (or room in a house) that is partitioned off from the rest of the boat/house and doesn't have any radiators, I can see that the reduction in the local heat might be too much, but I would have thought that for most boats, adding a BB would not excessively reduce the available heat for a modest sized cabin. You could always add a rad at the far end of the cabin, which could be turned on or off as required, if you were concerned about the max available heat in the cabin.

 

Usually a BB has a kw rating which, when compared to the stoves rating, will give you a good idea how much heat as a proportion is lost to the BB.

 

ETA checked the Villager website. The stove is 5kw. With a BB then you get 1.6kw to the room and 3.4 kw to the BB (at max output). So yes, it does cut down the heat to the room by a lot! Might still be OK with a rad in the same room / cabin as the stove.

 

The other thing to consider is how much space inside the stove is taken up by the BB. clearly the max space for fuel is reduced and this might affect how long the stove will run between refuels.

Edited January 9, 2013 by nicknorman

[canals are us?]

Generally the back boiler is only as thick as the fire brick/bricks it replaces. The back boiler on most models forms the baffle plate.

 

I can't wait to plumb my new woodwarm back boiler stove in when it arrives. Having 3 rads on gravity circulation on my 50ft narrowboat

Had to wait 5 weeks for the company to make it.

 

Had 3 villager stoves in the past, A medium size in 1990, only did small, medium and large then, AHI and berkley integral and always found that the stoves boiler gave more kw output than the manufacturer claimed and also gave out good room heat as well. Last place needed no radiator in the room about 7m x 6m, Villager Berkley integral boiler.

 

James

Edited January 9, 2013 by canals are us?

[nicknorman]

Generally the back boiler is only as thick as the fire brick/bricks it replaces. The back boiler on most models forms the baffle plate.

 

 

Oh yes that will mostly be true for multi fuel stoves (which OP's is) - I was thinking about wood burners which generally don't have firebricks.

[Bee]

As nicknorman says, a system with a bit of natural convection is desirable, if you can get a full convection system then so much the better, the advantages are simplicity and cheapness - no pumps or electrics. The tricky part is getting a nice uphill and downhill slope on the pipes, the natural trim of the boat, bows higher than the stern, is exactly opposite to what you need and pipe runs can look a bit odd, however I had a 62 foot boat with a convection system and it worked fine but I was struggling for every 1/2 inch of slope, if I had to put heating in a narrowboat again though I would make a huge effort to do the same again, a boat without heating is pretty mich uninhabitable and to sit and shiver because of a battery or pump problem is no fun.

[Psycloud]

Hmmm - that is quite some loss although I wonder how much of that ever made it into the room anyway or just went up the chimney.

 

There is a large rad about 5ft (pipe run) from the stove so as has been said the heat in the boat may be more evenly distributed.

 

Overall, given the length of the boat (and that the heat never gets past the lounge area) and the fact the rads are already there along the length, would this be a good investment? It's brass monkeys in the sleeping areas.

 

[nicknorman]

Hmmm - that is quite some loss although I wonder how much of that ever made it into the room anyway or just went up the chimney.

 

The 5kw should be nett heat into the room. What goes up the chimney is extra, though these sorts of stoves are pretty efficient, approaching 80%.

 

Overall, given the length of the boat (and that the heat never gets past the lounge area) and the fact the rads are already there along the length, would this be a good investment?

 

If we lived aboard I would have a BB but as ours is a holiday boat, we don't. Of course you could always get an Ecofan instead...(ducks for incoming).

Edited January 9, 2013 by nicknorman

[Serenity Malc]

As nicknorman says, a system with a bit of natural convection is desirable, if you can get a full convection system then so much the better, the advantages are simplicity and cheapness - no pumps or electrics. The tricky part is getting a nice uphill and downhill slope on the pipes, the natural trim of the boat, bows higher than the stern, is exactly opposite to what you need and pipe runs can look a bit odd, however I had a 62 foot boat with a convection system and it worked fine but I was struggling for every 1/2 inch of slope, if I had to put heating in a narrowboat again though I would make a huge effort to do the same again, a boat without heating is pretty mich uninhabitable and to sit and shiver because of a battery or pump problem is no fun.

 

 

Yello,

 

I'm planning a gravity fed bedroom radiator from my lounge Becton 7 with back boiler. It's a reverse layout boat with the expansion tank and water tank in the bow ( bedroom ). I assume the cold feed can be run parallel to the floor as it's gravity fed from the high level expansion tank and runs down to the stove with the natural rake of the boat ...... BUT my question is what level is required for the hot outlet from the stove to the radiator ? It obviously needs to feed water against the rake of the boat. I was thinking of using a long radiator no more than about a foot or so tall to minimise the 'uphill' gradient.

 

Are there some maths to be done here ? I was thinking of a figure of maximum height gain per metre for a given pipe diameter. I'm guessing a water tube level would be the best tool to use to measure these heights ? It's approximately 7 metres from the hot stove outlet to the radiator inlet.

 

Thanks Malc.

Edited January 10, 2013 by Serenity Malc

[Bee]

Hi

If I read it right the stove is towards the stern and the rad at the fore end, this should be fine, the principal is that hot water rises therefore the top pipe must rise to the end of the run and then fall to the bottom pipe on the boiler, so long as that is followed it should work,the heat will drive the whole lot round. Be careful if you are on dry dock as the boat will sit flat. Take the expansion pipe and tank from the highest point in the circuit, I am suddenly nervous of my facts here so if anyone has any doubts I am happy to be put right!

[MoominPapa]

We don't liveaboard, but do use the boat regularly and plan to have the heating on when we do visit (unless its a nice warm day like today was). So, the scenario is, we'd arrive at the boat maybe 11:30am, get the stove going, and then leave at 2:30pm and there is still a bit of wood in the stove so we leave it to burn out and cool down of its own. If we had a back boiler, we'd need to leave a circulation pump running. We might not return to the boat for 3-4 days.

hout a pump at all (ie gravity fed).

We're in a similar situation, but don't find it a problem. As long as the air inlet on the stove is shut down 20 minutes or so before leaving, heat generation is minimal and isolating the batteries (and therefore switching off the pump) as we leave has never had bad consequences. Our system allows some gravity flow even when the pump isn't running, so that probably helps.

 

MP.

[Serenity Malc]

Yello,

 

 

Thanks Bee .... the expansion tank is already fixed at high level in the bow ( bedroom). The Becton is in the stern lounge. The expansion tank is already plumbed in to the main water pump supply and has a ball cock fitted. The stove outlet is approx 22mm. I'm thinking to plumb the hot feed to the rad in again 22mm copper to also act as a radiator as it passes through the bathroom. I'm sure that I'll need a reducer at the rad and pressure release valve somewhere with a vent to the bilge or somewhere suitable.

 

My main query is how much height raise I could possibly get away with to properly retain circulation using 22mm copper pipe along 7 metres length ? Also could the cold feed to the bottom of the stove be plumbed in a smaller diameter pipe ?

 

Cheers Malc.

Edited January 10, 2013 by Serenity Malc

[nicknorman]

Yello,

 

 

Thanks Bee .... the expansion tank is already fixed at high level in the bow ( bedroom). The Becton is in the stern lounge. The expansion tank is already plumbed in to the main water pump supply and has a ball cock fitted. The stove outlet is approx 22mm. I'm thinking to plumb the hot feed to the rad in again 22mm copper to also act as a radiator as it passes through the bathroom. I'm sure that I'll need a reducer at the rad and pressure release valve somewhere with a vent to the bilge or somewhere suitable.

 

My main query is how much height raise I could possibly get away with to properly retain circulation using 22mm copper pipe along 7 metres length ? Also could the cold feed to the bottom of the stove be plumbed in a smaller diameter pipe ?

 

Cheers Malc.

 

If the system already has a header tank it won't need a pressure relief valve - excess pressure will be vented via the header tank. You should however have a header tank overflow into the bilge or outside.

 

I think gravity circulation systems design is not an exact science but its worth bearing in mind that every little restriction can add up to become significant. Therefore avoid pipe section changes in the main loop, do not install more couplings / fittings than necessary, install curved angle fittings, not sharp right angle ones etc. make sure any shutoff valves are full bore etc

[Supertramp]

Hmmm - well the cold tank is just behind the boiler but of course the feed runs all the way to the back where the Eber was so is there any reason why the pump can't be at the opposite end to the stove? A bit like this:

 

 

<Stern--Header+pump-----Rad----Rad----Rad----Rad----Stove--Bow>

 

What sort of pump would be the right sort of thing for this please?

 

Thanks

 

David

 

My back boiler is pumped to 3 rads. I have a 240v standard domestic heating circulation pump on a pipe stat set at 30c, its really quiet and cheap to run,(mostly on shoreline or inverter). - however, there is also a 12v pump in circuit (Jabesco i think) attached to a 2nd pipe stat set to 60c. Both pipe stats are on the top exit pipe from the boiler. This gives me a fall-back in case of mains failure to the primary pump, and a backup should the stove get too hot.

Both pumps are free flowing if not on, so don't restrict the flow.

[Psycloud]

My back boiler is pumped to 3 rads. I have a 240v standard domestic heating circulation pump on a pipe stat set at 30c, its really quiet and cheap to run,(mostly on shoreline or inverter). - however, there is also a 12v pump in circuit (Jabesco i think) attached to a 2nd pipe stat set to 60c. Both pipe stats are on the top exit pipe from the boiler. This gives me a fall-back in case of mains failure to the primary pump, and a backup should the stove get too hot.

Both pumps are free flowing if not on, so don't restrict the flow.

 

Thank you - I will keep this setup in mind