Back boiler heating?

[Kharikola]

Hi! I don't have a problem with my back boiler boiling! I have a 4k squirrel

Stove. I run 28 mm pipe in a circuit along the whole length of the boat

With four rads attached. I also have an expansion tank + a 12v pump

Which I rarely use. Sometimes the pipe circuit is enough and therefor

Close rads but no boiling back boiler,

Edited January 19, 2013 by Kharikola

[luctor et emergo]

Good luck to you all. I live in a 14 foot cabin, with just a boatmanstove, and i'm warm enough. Convection, pumping, etc, it matters not.. my coal stove keeps me warm

[Kharikola]

Keeping warm doesn't have to be complicated for a narrow beam! Forget diesel heaters! They are too expensive to run.

Edited January 19, 2013 by Kharikola

[Titan]

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.

 

What has become of the stove you have removed

[Paul C]

What has become of the stove you have removed

 

Its currently in the garden shed and will be placed for sale very soon!

[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.

 

I'm hoping to have the whole system 12v only - would a pump like this do the job?

http://www.elyboatchandlers.com/12v-central-heating-pumps/johnson-12v-magnetic-driven-centrifugal-circulation-pump?source=Froogle

 

I am also struggling to find a 12v pipe thermostat - is your 2nd stat 12v or 240v?

 

Thanks

[peterboat]

Hi a pipe stat is a switch as it gets hot a bi metal spring moves and makes a contact so any pipe stat within reason will do. Mine was bought from b & Q a good few years ago and is still powering my 12v jabsco

 

Peter

[blackrose]

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.

 

As far as the slope of the pipes on a convection/gravity (thermocycling) system is concerned, I think people often make the mistake of thinking the slope of the top run should rise all the way past the last rad. In fact, since the water will be cooling as soon as it leaves the backboiler, I think there should be a steep initial rise to the top run, then the top run should have a very shallow rise for a short length and then the top run should be level or even fall. Ideally the bottom run should fall all the way back to the backboiler, but as you say these slopes are often vey difficult to achieve unless short, long radiators are used.

 

But in the case of the OP, he will probably need to use a pump if the pipework is all on the floor.

[SamKingfisher]

The 6w pump on solarproject.co.uk is ideal. Sips leccy and long working life. Put full bore isolation valves each side of the pump and buy a spare (which you probably won't need but then can swap in with a butter knife and your hands in a few mins)

[smileypete]

A strap on cylinder stat can usually be used as a pipe stat, searching for cylinder thermostat too on Ebay may get more results.

 

A good backboiler heating system could have a mix of adequately sized gravity rad(s) nearer the stove, and more distant rads and calorifier on a pump. That way if the pump or electrics fail the stove can still be used. Also make the system 'self bleeding' so any air runs up towards the header tank vent or rad and not get trapped in pipes.

 

Could be well worth using the forum search to do a trawl of previous back boiler threads, then doing a diagram and asking lots of questions.

 

ETA Here's a great diagram from 'canals are us?' off another thread:

 

 

http://www.canalworld.net/forums/index.php?showtopic=51509&page=1

 

Though I'd rather have the circulation pump in the return pipe back towards the stove so it gets cooler water.

 

Another possible improvement is to have some way of safely shutting off the gravity flow so all the back boiler heat could be send to the calorifier and/or pumped rad, but it'd need some thought that one...

 

cheers, Pete.

~smpt~

Edited June 21, 2013 by smileypete

[Psycloud]

But in the case of the OP, he will probably need to use a pump if the pipework is all on the floor.

 

Yep - the in/out on the rads is at floor level and boxed in so I'm not too inclined to alter the radiators.

 

Hi a pipe stat is a switch as it gets hot a bi metal spring moves and makes a contact so any pipe stat within reason will do. Mine was bought from b & Q a good few years ago and is still powering my 12v jabsco

 

Peter

 

Thank you

 

The 6w pump on solarproject.co.uk is ideal. Sips leccy and long working life. Put full bore isolation valves each side of the pump and buy a spare (which you probably won't need but then can swap in with a butter knife and your hands in a few mins)

 

And thank you too

 

 

ETA Here's a great diagram from 'canals are us?' off another thread:

 

 

http://www.canalworld.net/forums/index.php?showtopic=51509&page=1

 

Though I'd rather have the circulation pump in the return pipe back towards the stove so it gets cooler water.

 

Another possible improvement is to have some way of safely shutting off the gravity flow so all the back boiler heat could be send to the calorifier and/or pumped rad, but it'd need some thought that one...

 

cheers, Pete.

~smpt~

 

I will try and draw something later but we will have to pump as everything is at floor level and the boat is 64ft. There is a tank (not fitted at the mo) laying under the stern deck that was previously part of an Eberspacher system. We only want to send water to the rads, the calorifier is not in use as we have a gas boiler for hot water.

[blackrose]

 

 

 

http://www.canalworld.net/forums/index.php?showtopic=51509&page=1

 

Though I'd rather have the circulation pump in the return pipe back towards the stove so it gets cooler water.

 

 

2 questions Pete: What's the benefit of having the header tank off the bottom run? My car header tank comes off highest point of the top run and so my system is self-bleeding. I've got it the top of the tank plumbed out through the side of the boat.

 

 

The tank & black pipe is now inside a cupbard. I've never noticed steam coming out the side of the boat so I think any heat loss is minimal. I think I put about 1 litre of water into the system every year.

 

The other question is does it make any difference whether the pump is pulling hot water from the backboiler or pushing cooled water back into it? In terms of pump longevity I'd have thought the latter was preferable.

Edited June 21, 2013 by blackrose

[smileypete]

I will try and draw something later but we will have to pump as everything is at floor level and the boat is 64ft. There is a tank (not fitted at the mo) laying under the stern deck that was previously part of an Eberspacher system. We only want to send water to the rads, the calorifier is not in use as we have a gas boiler for hot water.

 

If it's not going to be used to heat the calorifer, why not stick with things as they are than rather than fit a pumped-only system just to spread heat along the boat, which has to work in order for the stove to be used. Maybe try an ecofan or something similar.

 

 

2 questions Pete: What's the benefit of having the header tank off the bottom run? My car header tank comes off highest point of the top run and so my system is self-bleeding. I've got it the top of the tank plumbed out through the side of the boat.

 

 

The tank & black pipe is now inside a cupbard. I've never noticed steam coming out the side of the boat so I think any heat loss is minimal. I think I put about 1 litre of water into the system every year.

 

The other question is does it make any difference whether the pump is pulling hot water from the backboiler or pushing cooled water back into it? In terms of pump longevity I'd have thought the latter was preferable.

If there's a single pipe to the header tank, if the system boils the water being pushed out by steam then has to flow back towards the backboiler which may oppose the themosyphon and make things worse. With a separate feed and vent pipe as in the above diagram, the water can flow back down and along the bottom pipe instead, so it helps the thermosyphon rather than hinders it.

 

Agree about putting the pump in the return so it's pumping cooler water. With the smaller 12V pump and the pumped flow and return teed in near the back boiler it shouldn't be a problem where the pump is.

 

Another reason is that when it's first used the dissolved oxygen is likely to come out of the water as it's heated, with the pump between backboiler and rads a small 12V pump may then get airlocked. With the pump in the return the air will end up in the rads or backboiler coil instead. (With the backboiler coil it could be a good thing to include a 'dead leg' of pipe with air vent at the end, high up in the pipework to the calorifier coil to help catch this air)

 

cheers, Pete.

~smpt~

Edited June 21, 2013 by smileypete

[Shropshirecoal]

A well layed out thermosyphon system is the way to go, no worry about pumps and power failure. Your radiators must have the hot inlet at the top and cold return from the bottom, use as big a bore copper pipe as possible (28mm) and be sure to put a few drain valves and air bleed points at key positions. Avoid 90 degree bends, using a pair of 135's instead. Be sure to add inhibitor when filling as well as draining and flushing every couple of years, a system like this will give you little or no problems.

[blackrose]

If there's a single pipe to the header tank, if the system boils the water being pushed out by steam then has to flow back towards the backboiler which may oppose the themosyphon and make things worse. With a separate feed and vent pipe as in the above diagram, the water can flow back down and along the bottom pipe instead, so it helps the thermosyphon rather than hinders it.

 

 

I don't think it would be any worse then the thermosyphon having to push against water (potentially) in the vertical pipe going to the header tank on the diagram you pasted.

 

I prefer the main run to go right around the last rad and connect all 4 radiator ports to it. I think it facilitates thermocycling better than it having to go through the narrow channels of the rad as part of the thermocycling process. It think that would hinder thermocycling. If the system thermocycles around the main run it will go through the rads, but if it doesn't thermocycle it won't even reach the rads.

 

 

Anyway, as someone has already said, it's a bit of a black art so there are probably several ways to achieve a similar result, but all of this is off-topic as the OP is using a pumped system.

Edited June 21, 2013 by blackrose

[Psycloud]

OK here's a rough drawing of our layout:

 

So all pipes are boxed in at floor level - I do not want to alter this. I can't tell yet (as I've not taken any of the boxing in off) exactly how the rads are plumbed in to the 2 pipes.

 

I propose to put the pump at the front, near the step, with a stat on the outlet from the back boiler.

 

The broken Eberspacher will be removed from the system so presumably the pipework will be joined together at this point and the expansion/header tank incorporated - this is what I'm not too sure about. I want to keep the header below the stern decking.

 

Edited June 21, 2013 by Psycloud

[blackrose]

I've said this recently on the forum, but I'll say it again; if you must have a pumped system, install the pump between two full bore gate valves and always carry a spare on board so that when the pump fails you can easily whip one out and whop one in without having to drain and re-fill the entire system. Then you can just fix the broken pump at your leisure - or get another new one if it's beyond repair.

 

The other thing that might be possible is to fit some sort of themostatically controlled buzzer so that if the pump failed you'd be made aware?

 

Edit: they don't have to be gate valves of course. You can buy tap connectors with isolating valves which are also good for isolating any pump vibrations from the plumbing.

Edited June 21, 2013 by blackrose

[smileypete]

 

I don't think it would be any worse then the thermosyphon having to push against water (potentially) in the vertical pipe going to the header tank on the diagram you pasted.

Well, what way do you think is likely to be better and why? I always like to try to recommend the better way of doing things, to avoid problems like these for example:

 

http://www.canalworld.net/forums/index.php?showtopic=18205#entry290215

http://www.canalworld.net/forums/index.php?showtopic=46998#entry873746

 

 

 

I prefer the main run to go right around the last rad and connect all 4 radiator ports to it. I think it facilitates thermocycling better than it having to go through the narrow channels of the rad as part of the thermocycling process. It think that would hinder thermocycling. If the system thermocycles around the main run it will go through the rads, but if it doesn't thermocycle it won't even reach the rads.

Fair enough, but the vertical pipe at the end will only help as far as it's ability to lose heat, say 1 or 2% overall? If you tried lagging the vertical pipe at the end it would make no difference at all. Having all 4 ports connected on the rads can only help the thermosyphoning I'll agree.

 

OK here's a rough drawing of our layout:

 

So all pipes are boxed in at floor level - I do not want to alter this. I can't tell yet (as I've not taken any of the boxing in off) exactly how the rads are plumbed in to the 2 pipes.

 

I propose to put the pump at the front, near the step, with a stat on the outlet from the back boiler.

 

The broken Eberspacher will be removed from the system so presumably the pipework will be joined together at this point and the expansion/header tank incorporated - this is what I'm not too sure about. I want to keep the header below the stern decking.

 

Having seen the layout of the boat and looked up the spec of the stove and boiler I definitely wouldn't put a pumped-only system in. It's a fair amount of expense, hassle and risk just to divert some heat to the middle of the boat. Pity the stove isn't on the other side of the boat.

 

If you come across a cheap but decent 2nd hand diesel air heater like the airtop ones, that could go in the engine room and heat the back bedroom area quite nicely when needed, they're generally pretty reliable.

 

cheers, Pete.

~smpt~

[blackrose]

Well, what way do you think is likely to be better and why? I always like to try to recommend the better way of doing things, to avoid problems like these for example:

 

I didn't say it was better, just no worse.

Having seen the layout of the boat and looked up the spec of the stove and boiler I definitely wouldn't put a pumped-only system in. It's a fair amount of expense, hassle and risk just to divert some heat to the middle of the boat. Pity the stove isn't on the other side of the boat.

 

I tend to agree. To be honest looking at that layout I'm not even sure the last rad would heat the back bedroom all that much.

 

The gut feeling is to try to utilise the rads just because they're there, but it might be more trouble than it's worth. Perhaps it's worth thinking about a stove without a backboiler and a computer fan behind the stove somewhere, with perhaps a second fan along the corridor if possible.

Edited June 21, 2013 by blackrose

[smileypete]

 

I didn't say it was better, just no worse.

 

AAARRRGGHHH! Please, don't ask in the first place then. I'm sorry, maybe I shoulda just answered that it's standard best practice and pointed to google and UK plumbers forum.

 

Going back to the OPs problem, thinking about I'd rather move the stove across the boat and toward the middle near to where rad2 is, that way an Ecofan or something similar could be used to shoot some warm air down the corridor. Still could be worth putting a diesel/air heater in for cold mornings and coldest winter weather.

 

cheers, Pete.

~smpt~

Edited June 21, 2013 by smileypete

[canals are us?]

Don't forget the open vent header tank has to be at the highest point above the top of the rads.

 

Couldn't the first rad be gravity heated and then pumped? Top flow pipe from stove gently rising to the rad. 22mm copper would be acceptable.

The boiler stove end would need an auto air vent installed if the pipes dropped down to the floor to release air.

 

As a plumber I wouldn't be happy to rely on a fully pumped system on an uncontrollable heat source without at least one gravity rad to dissipate some heat from the boiler in the event of powercut /pump failiure.

I would change the rad at the end to a larger one to heat the space and possibly just have 3 rads. From memory the Chelsea solo boiler is 15,000btu so 5,000btu per rad which is 3 rads about 600x1000mm single convector.

You can wire in a pipe thermostat to automatically switch the pump on and off to save power and conserve the boilers life by reducing condensation.

 

James

Edited June 21, 2013 by canals are us?

[peterboat]

My old narrow boat had something similar to what you propose although my gas central heating still worked so I had two methods of heating water/space. I was very pleased with the outcome as on very cold days I came into a warm boat via the gas on a timer and then make the fire. As the stove heated up the gas used to shut itself off, in the morning I again woke up to warm boat because of the cas central heating perfik

 

Peter

[blackrose]

 

AAARRRGGHHH! Please, don't ask in the first place then. I'm sorry, maybe I shoulda just answered that it's standard best practice and pointed to google and UK plumbers forum.

 

Calm down dear...

 

I thought it was an open forum - so why shouldn't I ask? I can ask and still disagree. If you post a message, people have every right to ask questions about it without any obligation to agree. Nobody is forcing you to answer. If you don't like other people's opinions or ideas about what you've posted then AAARRRGGHHH! Please don't post in the first place!

 

It's not standard best practice - at least not according to the plumbers I know. As I said earlier, there are several ways to acheive the same result and one is not necessarily better than the other - the best installation on a particular boat depends a whole host of factors.

Don't forget the open vent header tank has to be at the highest point above the top of the rads.

 

Couldn't the first rad be gravity heated and then pumped? Top flow pipe from stove gently rising to the rad. 22mm copper would be acceptable.

The boiler stove end would need an auto air vent installed if the pipes dropped down to the floor to release air.

 

As a plumber I wouldn't be happy to rely on a fully pumped system on an uncontrollable heat source without at least one gravity rad to dissipate some heat from the boiler in the event of powercut /pump failiure.

I would change the rad at the end to a larger one to heat the space and possibly just have 3 rads. From memory the Chelsea solo boiler is 15,000btu so 5,000btu per rad which is 3 rads about 600x1000mm single convector.

You can wire in a pipe thermostat to automatically switch the pump on and off to save power and conserve the boilers life by reducing condensation.

 

James

 

My God! A plumber who dares to have some different ideas to Smiley Pete!

Edited June 21, 2013 by blackrose

[NorthwichTrader]

Somebody mentioned a thermostat that could ring a buzzer/alarm to warn of a pump failure!

For peace of mind, I guess it might be worth fitting something like that, even to a thermocycling set-up, just to save any worrying? If something could be set to alarm at a temperature that still gave you a chance to close the fire down?

Only thinking out loud, of course!

[Psycloud]

We already have the back boiler and the header so all we need to install is a bit of pipework, the pump and a stat so it won't be a massive expense. I would be up for fitting an alarm too if required.