back boiler question

[capnthommo]

hi. I have just been considering whether to get a solid fuel stove with a back boiler as I think retro fitting the boiler might be a little troublesome if it later turns out that I could do with one. The idea is to have it there if I should decide that I need to use it to heat the calorifier via the second coil or maybe just run a couple of radiators. But I am concerned that running a back boiler with nowhere for the hot water to circulate, or with no water in the boiler at all would cause problems. Can anybody let me know if I am correct - that the back boiler needs water in it and that it needs to circulate even if it is doing no actual 'work'.

Basically, is it ok to use a sf stove with an empty back boiler and if not how do I get round it without going to a lot of plumbing trouble because I may not actually need it. The added cost of the boiler seems slight compared to what I imagine is the considerable hassle of retro fitting.

cheers

nigel

[Keeping Up]

I can't speak for all back boilers, but the majority of them won't put up with being run dry

[barge sara]

Same suggestion as the 'empty calorifier' post.

Check with the stove manufacturer?

[capnthommo]

I can't speak for all back boilers, but the majority of them won't put up with being run dry

 

cheers for that. it's pretty much as i expected then. so if i ran it with water in and just a short(ish) loop of pipe to allow it to cycle but without anything else on it would that work, generally speaking that is?

cheers for the quick response BTW

nigel

[barge sara]

so if i ran it with water in and just a short(ish) loop of pipe to allow it to cycle but without anything else on it would that work, generally speaking that is?

 

A shortish loop with no radiators or calorifier to sink the heat will probaly result in the water boiling and a cabin full of steam.

Might give you a condesation problem!

[ditchcrawler]

cheers for that. it's pretty much as i expected then. so if i ran it with water in and just a short(ish) loop of pipe to allow it to cycle but without anything else on it would that work, generally speaking that is?

cheers for the quick response BTW

nigel

It would boil and could be quite dangerous.

I think you will find that you can run some boilers vented and DRY as they are steel but check with the manufacturer first.

[Berty]

Got a vague memory of someone telling me it would be alright to fill the boiler with clean sand, and run it that way. Then you have no worries about it overheating and exploding.

 

If you do want to run a short loop just to give it something to do, I'd want to put a pressure relief valve and expansion tank in there too (assuming a sealed system).

 

Cheers,

Berty

[capnthommo]

okay thanks everybody. my paramount concerns are safety, and not damaging the boiler. if i go for this option then i may put in a temporary rad about 20 feet away to satisfy those priorities and then add or change out for the calorifier later. i just need to work out if the system can be made to thermo syphon as i dont really want to be running a pump, with the attendant extra engine time to power it. swings and roundabouts. time for a little more planning, i think.

i just think in winter it would be useful to have extra hot water from the 24/7 stove but if it turns out to be too complex...

[simon-l]

It would boil and could be quite dangerous.

I think you will find that you can run some boilers vented and DRY as they are steel but check with the manufacturer first.

 

Everything I have read when I was considering a back boiler (which doubtless isn't everything in the world ) is that you

 

must not run them dry,

must run a circulation pump and safety devices such as pressure release valves,

must make sure you have enough heatsinks (Calorifiers AND, for later when the water is hot, radiators) to dump all the heat into

 

if not the water may boil, the pressure may go up and the safety devices (assuming you fitted any) will release the pressure and steam messily and potentially dangerously into your boat.

 

I decided to stick with my old Palemo until I had a big enough wadge of notes to do it properly as it was all adding up at a fearsome rate

[capnthommo]

Everything I have read when I was considering a back boiler (which doubtless isn't everything in the world ) is that you

 

must not run them dry,

must run a circulation pump and safety devices such as pressure release valves,

must make sure you have enough heatsinks (Calorifiers AND, for later when the water is hot, radiators) to dump all the heat into

 

if not the water may boil, the pressure may go up and the safety devices (assuming you fitted any) will release the pressure and steam messily and potentially dangerously into your boat.

 

I decided to stick with my old Palemo until I had a big enough wadge of notes to do it properly as it was all adding up at a fearsome rate

 

yes. that's clinched it. too many concerns expressed and this one is the final straw. there are too many variables at the moment. i think it's no back boiler and see how it goes for a couple of years and then if it's necessary get a pro in to sort it. i can tackle most things but this looks like being one of those i leave to the experts and choke up the cash instead. and i don't want to get involved in too much of a marathon if it turns out i didn't really need it anyway. thanks again to everyone who replied, i think i shall put this one in the 'one day' box for the foreseeable.

cheers and have a nice Christmas everybody, particularly if you have to work over the break.

nigel

[alan_fincher]

Our boat has a Villager Heron with an installed back boiler that there is no evidence has ever been used for anything.

 

When I had the stove out of the boat, I examined the boiler part fairly thoroughly, and, although I can't be certain unless I tried to use it, it certainly didn't seem to have suffered any damage at all from the fact that the stove is regularly fired up, and that it is just an empty box.

 

It's just a basic mild steel one, but my guess is that on this stove, and similar models, (e.g. Puffin) you would get away with it.

[johnjo]

Check with manufactuer, but never just put a small loop and fill with water .

 

If you need to put water in then you'll need something to take the heat out of the water, like rads, chlorifier or towel rail, otherwise it'll just boil and vent steam if you're lucky or explode if you're not.

 

Filling with sand is OK but I'm not sure if there is a specific type of sand that is required.

[Tony Brooks]

Our boat has a Villager Heron with an installed back boiler that there is no evidence has ever been used for anything.

 

When I had the stove out of the boat, I examined the boiler part fairly thoroughly, and, although I can't be certain unless I tried to use it, it certainly didn't seem to have suffered any damage at all from the fact that the stove is regularly fired up, and that it is just an empty box.

 

It's just a basic mild steel one, but my guess is that on this stove, and similar models, (e.g. Puffin) you would get away with it.

 

 

I can confirm that our friends ran a Brunel with a dry back boiler with the connections open and it did not seem to cause any problems BUT:-

 

I suspect that if you piled solid fuel up against it and ran the stove hard regularly the heat from the fuel would scale and burn through a dry boiler in the same way that it will burn through the stove without fire bricks at the sides. The same logic suggests that piling it up with wood would not cause any damage as would keeping solid fuel well below the bottom of the boiler.

[bag 'o' bones]

yes. that's clinched it. too many concerns expressed and this one is the final straw. there are too many variables at the moment. i think it's no back boiler and see how it goes for a couple of years and then if it's necessary get a pro in to sort it. i can tackle most things but this looks like being one of those i leave to the experts and choke up the cash instead. and i don't want to get involved in too much of a marathon if it turns out i didn't really need it anyway. thanks again to everyone who replied, i think i shall put this one in the 'one day' box for the foreseeable.

cheers and have a nice Christmas everybody, particularly if you have to work over the break.

nigel

 

Fitting back boilers is easy! Knock out the pipe blanks, insert the boiler with a few blobs of fire cement and connect up.

 

Just for the record it was a Aarrow 'Becton Bunny' multifuel.

[nb Innisfree]

If you run BB dry you must run it vented, if it is closed it will explode, putting sand in won't stop it exploding if it is unvented.

 

When installed you must put a heat sink in that is big enough to absorb boiler output and will work on gravity circulation alone, do not rely on circulation pumps for this.

[Keeping Up]

When installed you must ... work on gravity circulation alone, do not rely on circulation pumps for this.

That's very nice in theory, and is obviously preferable, but probably the majority of back-boiler systems DO have to rely on a circulation pump.

[blackrose]

Hi Nigel.

 

When this question came up some time ago I replied that it was the equivalent of running a kettle dry. It seemed like common sense to me, but then some forum members said I was wrong and that it could be run dry.

 

As others have said, probably best to contact the stove manufacturers.

[Yoda]

I would suggest that the metal at the back of the fire is thinner with a back boiler. So some damage might be caused with a big fire and dry boiler.

 

On the other hand its been a while since I played with one so.....

[nb Innisfree]

That's very nice in theory, and is obviously preferable, but probably the majority of back-boiler systems DO have to rely on a circulation pump.

 

Yes I agree lots of boilers prob can only work on pump alone but it is very bad practice, sorry but it's not preferable but essential not to rely on pumps as a safety measure. If stove runs away then without failsafe heat sink(s) you can easily end up with a very dangerous situation. It's just basic good safety practices.

[DHutch]

That's very nice in theory, and is obviously preferable, but probably the majority of back-boiler systems DO have to rely on a circulation pump.

I would always aim to have atlease one that worked without a pump.

- All of emilyannes rads (two up front, one and the cal at the rear) work off convention alone and although the rear loop is a little sluggish at providing much heat the front loop has been very reliable and gets the radiators hotter than you can touch.

 

For safty conserns however, all systems should have a prv which should boiling occur due to lack of circulation should vent safely.

 

 

Daniel

[Smelly]

Hot having enough rads may result in the coolant boiling. Been there, done that, expansion tank doing a reasonable impression of Vesuvius... Not nice!

 

I've known two boilers on other folk's boats split when run dry.

 

If you fill it with sand with a mind to plumbing it in later won't it be as much hassle getting the sand out as it would just fitting the boiler when you're doing the plumbing? You'll still need to take the fire out, and probably the boiler to get the sand out; so de-mounting the boiler will be as much, if not more bother than simply putting it in as and when.

 

A suggestion if the fire comes with the boiler fitted would be to take it out, fill the blanks with bolted through plates then re-fit later when you're ready to fit the rads.

 

Finally, not all fires will like the cut outs being punched out; the castings may crack. Cutting them with on of these might be easier and less worry (hitting the back of 600 quid's worth of kit is un-nerving) but make sure you use a fast enough drill, my cordless was rubbish with them.

[Doorman]

yes. that's clinched it. too many concerns expressed and this one is the final straw. there are too many variables at the moment. i think it's no back boiler and see how it goes for a couple of years and then if it's necessary get a pro in to sort it. i can tackle most things but this looks like being one of those i leave to the experts and choke up the cash instead. and i don't want to get involved in too much of a marathon if it turns out i didn't really need it anyway. thanks again to everyone who replied, i think i shall put this one in the 'one day' box for the foreseeable.

cheers and have a nice Christmas everybody, particularly if you have to work over the break.

nigel

 

Don't be put off by 'too many concerns'!

 

We've had a Morso Squirrel fitted to our boat with a back boiler. The central heating is normally powered by a diesel boiler,

but, can also be heated via the back boiler (separately, not in tandem!). The system works fine and heats the furthest

rad in the bedroom to a comfortable temperature.

 

When specifying the system, I liaised with the boatbuilder regarding the safety of using this type of duel fuel heating method.

Fortunately, he was in complete agreement with using a pressure relief valve together with a vent valve at the uppermost

point of the back boiler. I've seen first hand, the effects of neglecting to include these basic but imperative components into

the circuit. A back boiler that exploded while running at a full head of steam during commissioning of the heating system.

Luckily, no one was hurt! That circuit had no vent, nor, relief valve built in. How the customer was supposed to vent the boiler

of air beats me.

 

We've used a Jabsco brass bodied circulation pump that has a variable flow rate for the back boiler. This is important, as you don't wish to be sending

the heating water through the back boiler at high volume, whereby it will not collect enough heat from the fire. In order that the two systems

can't be used simultaneously, the electrical control side has a circuit that includes an interlock. This is simply two relays with

normally closed/normally open contacts. When one boiler is activated, it's relaly dictates that the other boiler/pump cannot be activated

in error, and vise versa.

 

All this may seem too much hassle, but, believe me, it's worth doing from the outset. We save on diesel when using wood to heat the fire and the

whole boat, including the calorifier. It's worth the effort!

 

Seek out professional help if you're unsure about taking the job on. And when I say professional, check out his or her credentials, it was a so called

'professional' who blew the back boiler up on our friend's boat .

 

Good luck and all the best,

 

Mike

[smileypete]

I would expect that every stove manufacturer absolutely requires that their backboilers run unpressurised and vented.

 

Whatever their requirements for venting are, they must be absolutely kept to.

 

cheers,

Pete.

Edited December 26, 2009 by smileypete

[bag 'o' bones]

Seek out professional help ...................

 

A plumber?

[Doorman]

A plumber?

 

Don't be silly, I said a professional!

 

P.S. Apologies to all of you very capable plumbers out there, all three of you!

 

 

Anyone got a copper helmet to hire, or even a cast iron top of a cistern will do?