Back Boiler

[DeanS]

Still to confirm what stove I've actually got.

A few friends are removing radiators from their boat, and giving me all the bits, so I'm thinking of fitting a back boiler on our coal stove. I'm also getting a heat exchanger from Biggles for heating from the engine.

To have BOTH systems connected, would I be able to do this:

 

1. Install 1 supply water pipe 75mm from the floor (just an example), all the way down the one side of the boat.

 

2. Install 1 return water pipe 30mm from the floor (just an example) all the way down one side of the boat.

 

3. Put T-pieces to drop the supply into each radiator (with a valve on each entry point).

 

4 Connect T-pieces to connect the return of each radiator to the main return pipe.

 

THEN.....

 

I guess it's all about connecting the supply nd returns....either to the back boiler, or to the engine heat exchanger. Do I.

 

1. Connect the supply from the top of the back boiler, with a T piece and a pipe going back to the heat exchange outlet. (with a hand valve to isolate the heat exchanger if using the back boiler).

 

2 Connect the return pipe to the bottom of the back boiler...and a T piece to connect it to the other side of the heat exchanger. (with a hand valve to isolate it if using the back boiler).

 

 

I think I also need to connect an open expansion pipe to the supply line side (filled with coolant/water).

 

 

Is there ever a time in this scenario I would want to isolate the back boiler at all?

I guess you only use the heat exchanger method if the coal fire is off.

 

 

What have I missed?

 

I dont use the boat engine for hot water, so dont need a big water calorifier.

 

 

THANKS!

[Rod a mod from Tod]

I would suggest any valve between any heat source and your safety device, in your case a feed and expansion vessel, would be a bad idea due to the fact if they are inadvertently left closed the water has no where to expand.

 

Steveo looking over Rods shoulder.

[fudd]

I would suggest any valve between any heat source and your safety device, in your case a feed and expansion vessel, would be a bad idea due to the fact if they are inadvertently left closed the water has no where to expand.

 

Steveo looking over Rods shoulder.

I haven't got an expansion vessel. Maybe I've missed something!

[DeanS]

I wouldnt put the expansion vessel on the engine side of the isolators..I would put it at the end of the radiator pipe run:)

 

Other than that.....is my plan solid?

[smileypete]

I'd have a sufficiently sized gravity fed 'heat dump' rad(s) near the stove, then put the more distant rads and the calorifier on a separate pumped circuit. That way you're not depending on a pump and elec to be able to run the stove.

 

Best do a diagram and take it from there, 'canals are us' did a great one on another thread:

 

http://www.canalworld.net/forums/index.php?showtopic=51509&p=962444

 

28mm copper pipe is usually used for the gravity bit, 22mm copper for the header tank top vent, and 15mm copper for the header tank bottom feed. The pumped bit can be in 15mm plastic except for about a metre nearest the back boiler.

 

Only things I'd change on the above diag is to use both the tappings at the top and bottom of each gravity rad to lessen flow resistance, and put the pump in the return to the back boiler where the returned water should be cooler.

 

What is essential is that the top gravity pipe must slope up towards the header tank top vent to make it self bleeding and prevent airlocks. And there must be NO valves whatsoever in this pipe. And last but by no means least the top of the rads must be above the level top of the backboiler, the further the better the thermosyphon is to keep the dreaded boiling noises at bay !

 

cheers, Pete.

~smpt~

Edited October 12, 2013 by smileypete

[Rod a mod from Tod]

Dean, I will ask Steveo to chip in again tommorow when he calls round. From what he said and from my limited knowledge from when i have worked with him if you have got isolating valves between your heat source be it stove or, heat exchanger from engine, if you have no room for expansion, or a blow off valve, you are bolloxed. BOOM!

 

We've been in the pub since the earlir reply so maybe more sense tomorrow.

 

Don't have nightmares.

[canals are us?]

This latest plumbing diagram is a much improved one.

 

 

Basically gravity to rads and pumped to calorifier. It can be any combination providing you have at least some gravity circulation.

From this post.

http://www.canalworld.net/forums/index.php?showtopic=60206&hl=%2Bthermocycling+%2Bquestions

 

Thanks Smileypete

James

Edited October 12, 2013 by canals are us?

[DeanS]

Would this installation work..see diagram below. When using the back boiler, valves A would be open, and valves B would be closed. When using the engine, then valves A would be closed, and B would be open. I would never use the engine for heating if the stove is on.

 

I understand the danger of heating a back boiler when it has no circuit to send the water around. All comments welcome, but this is what I'm attempting to do. Is there a better way. The Pump would be switched on when valves B are all open.

 

[Rod a mod from Tod]

Dean. Please don't take this the wrong way. But. Which part of DO NOT PUT VALVES BETWEEN A HEAT SOURCE AND A SAFETY OUTLET/DEVICE DO YOU NOT UNDERSTAND.

 

Perhaps your best optionis is to run your feed/expansion to the boiler/heat source side of your system rather than after your valves.

[DeanS]

Dean. Please don't take this the wrong way. But. Which part of DO NOT PUT VALVES BETWEEN A HEAT SOURCE AND A SAFETY OUTLET/DEVICE DO YOU NOT UNDERSTAND.

 

Perhaps your best optionis is to run your feed/expansion to the boiler/heat source side of your system rather than after your valves.

 

Ah. yes. Good point.

Would this be better.

Would I need a 2nd expansion tank on the heat exchanger loop as well?

 

[canals are us?]

I would class the heat exchanger as another heat source like the stove and they both must have a dedicated vent pipe for safety and no valves obstructing the vent pipe or cold feeds as otherwise I fear at present a potential bomb!

My belief also if you isolated the heat exchanger circuit you are effectively creating a sealed/pressurised system and if the engine was accidently run the water in the heat exchanger would have no means of expanding and once boiling would explode! The SFS is the same as no dedicated feed and vent as valves can block them.

 

I personally would be tempted to install separate rad circuits one gravity for solid fuel stove on one side of the boat.

Then another from the heat exchanger, this I would run in plastic and pump it with a 12volt or mains pump or option of both.

This would keep the plumbing system straightforward and safe

 

This is what I mean by separate cold feeds and vents, but please don't copy it as its only a demo drawing I did to show separate vents and I think it's far safer to install 2 separate heating systems as solid fuel heating can be lethal if not installed safely.

 

 

In the below image both heat sources have dedicated cold feeds and vents without valves obstructing and the solid fuel stove has a dedicated heat leak rad. The stove has a pump for rad circulation and the heat exchanger does too.

To use the stove you turn off the valve on the right and switch stove pump on. To run just the heat exchanger you turn the valve off near the stove and switch Exc pump on.

 

 

James

Edited October 12, 2013 by canals are us?

[DeanS]

How about this updated design.

Each loop A and B has a dedicated expansion tank.

Closing valves A and opening B allows heating the rads from engine.

Closing valves B and opening A allows heating the rads from back boiler.

 

[smileypete]

Would this installation work..see diagram below. When using the back boiler, valves A would be open, and valves B would be closed. When using the engine, then valves A would be closed, and B would be open. I would never use the engine for heating if the stove is on.

 

I understand the danger of heating a back boiler when it has no circuit to send the water around. All comments welcome, but this is what I'm attempting to do. Is there a better way. The Pump would be switched on when valves B are all open.

 

Will it work? Mayyyybe, but it looks wrong and dangerous on many levels.

 

Is their a better way? I'd just do something like the diagram in post # or #8, and tee in the engine circuit right by the back boiler.

 

OK it means the engine would heat the stove but if the stove is off just close up the vents and it'll function like a radiator

 

cheers, Pete.

~smpt~

[DeanS]

Surely my drawing is safe as it has 2 expansion tanks?

Forgetting to shut one set of valves wouldnt introduce danger, but would stop good circulation through the rads....which isnt a deal breaker, as it would soon become apparent, and shutting the one set of isolators, depending on the supply, could then be done. ...

 

I dont see an issue with my design...but happy to be corrected?

If it were possible to get direction changer valves, this might be better.

 

[DeanS]

The more I read about back boilers, the more worried I'm getting. I know nothing....but theres not a lot of clear advice out there:)

[smileypete]

Surely my drawing is safe as it has 2 expansion tanks?

Forgetting to shut one set of valves wouldnt introduce danger, but would stop good circulation through the rads....which isnt a deal breaker, as it would soon become apparent, and shutting the one set of isolators, depending on the supply, could then be done. ...

 

I dont see an issue with my design...but happy to be corrected?

If it were possible to get direction changer valves, this might be better.

 

Well the second drawing is much better, looks like we cross posted, but maybe you're looking for a complicated solution for a problem that probably doesn't exist in the first place.

 

Why not take the diagram in post #5 and change it as follows:

 

Add extra connections to the tappings on the gravity rads.

Add valves next to the bottom tappings on the gravity rads.

Tee in the heat exchanger circuit right next to the back boiler, ideally on the gravity side.

Move the pump shown from flow side to the return side.

 

What problem do you see with that which needs extra valves and header tanks?

 

cheers, Pete.

~smpt~

Edited October 13, 2013 by smileypete

[Rod a mod from Tod]

Hi Dean. Steveo's here and just had a quick look and says you would probably be ok with 1 expansion vessel branched to each side of your system.

 

Edit just to make sure. Branch in before diverters.

Edited October 13, 2013 by Rod a mod from Tod

[smileypete]

This latest plumbing diagram is a much improved one.

 

 

Basically gravity to rads and pumped to calorifier. It can be any combination providing you have at least some gravity circulation.

From this post.

 

Did you find that only half the tappings needed to be used on the gravity rads in practice?

 

I think that could work in some cases, but without knowing how good the thermosyphon is going to be it might be better to recommend using all of them, in case the thermosyphon is a bit weak due to a small height difference.

 

cheers, Pete.

~smpt~

Edited October 13, 2013 by smileypete

[canals are us?]

 

Did you find that only half the tappings needed to be used on the gravity rads in practice?

 

I think that could work in some cases, but without knowing how good the thermosyphon is going to be it might be better to recommend using all of them, in case the thermosyphon is a bit weak due to a small height difference.

 

cheers, Pete.

~smpt~

 

My rads are plumbed just using the 2 rad tappings like the first rad in the above picture and it has worked perfectly in my situation. It was blackrose who suggested using all four rad tappings like the last rad in my diagram. I used full bore lever valves on the flow into the rads.

http://www.canalworld.net/forums/index.php?showtopic=60206&page=2

Why not use all four I'd say as forum user fudd has done. I didn't as I wanted to be able to turn the rads off to heat the calorifier only and would of involved buying additional lever ball valves.

 

How about this revised diagram?

 

Exchanger on left SFS on right.

 

Simply linking the exchanger into the backboiler of the SFS and using a pump on the return to circulate water to the exchanger to the rads when using the exchanger only. When using the stove only the gravity system from the stove doesn't need a pump.

 

They then both have vent and cold feeds that are not restricted and no valves used.

The only disadvantage is when you used the heat exchanger to heat the rads the back boiler in the stove would act like a radiator.

Using the stove only the circulation is by gravity and being as the exchanger would probably be lower than the stove the exchanger would probably not act as a radiator. If you could get the exchanger flow pipe to constantly rise to the solid fuel's backboiler you may get the exchanger to heat under gravity circulation.

 

James

Edited October 13, 2013 by canals are us?

[Psycloud]

We were going to do this but at the last minute I decided to buy one of those recon Eberspachers. Got it installed on Friday and it's absolutely fantastic. For around £400 it was well worth doing verses the hassle of changing the current setup/pipework/pumps etc

[smileypete]

 

My rads are plumbed just using the 2 rad tappings like the first rad in the above picture and it has worked perfectly in my situation. It was blackrose who suggested using all four rad tappings like the last rad in my diagram. I used full bore lever valves on the flow into the rads.

http://www.canalworld.net/forums/index.php?showtopic=60206&page=2

Why not use all four I'd say as forum user fudd has done. I didn't as I wanted to be able to turn the rads off to heat the calorifier only and would of involved buying additional lever ball valves.

 

How about this revised diagram?

 

Exchanger on left SFS on right.

 

Simply linking the exchanger into the backboiler of the SFS and using a pump on the return to circulate water to the exchanger to the rads when using the exchanger only. When using the stove only the gravity system from the stove doesn't need a pump.

 

They then both have vent and cold feeds that are not restricted and no valves used.

The only disadvantage is when you used the heat exchanger to heat the rads the back boiler in the stove would act like a radiator.

Using the stove only the circulation is by gravity and being as the exchanger would probably be lower than the stove the exchanger would probably not act as a radiator. If you could get the exchanger flow pipe to constantly rise to the solid fuel's backboiler you may get the exchanger to heat under gravity circulation.

 

Looks good

 

I think what would happen is the backboiler would heat up, then the gravity rads would heat by gravity circulation. And as long as the heat exchanger flow and return run down to floor level and up again there shouldn't be any thermosyphoning through the HE when its pump is off.

 

Similar thing is done on larger systems when combining the output from 2 or more boilers, or both gravity and pumped heat sources, a 'header' is used, in this case the header is the backboiler itself.

 

OK there will be some heat loss though the stove when its out, but if the stove is ticking over its output could be topped up with heat from the running engine which isn't so easy with the setup using valves.

 

There's other ways of doing it but they could well be a solution looking for a problem. Is having the backboiler heated by the engine really a problem or not?

 

ETA: I s'pose you could have a 2 way 28mm ball valve on the back boiler inlet, with the gravity and pumped returns teed together on the non stove side and (most importantly) the header tank feed brought all the way from the header tank and teed in on the stove side. But if the engine is making plenty of heat why not have the backboiler heated and save the trouble?

 

cheers, Pete.

~smpt~

Edited October 13, 2013 by smileypete

[Pete & Helen]

Some interesting info on this thread but a couple of questions as I am thinking of converting my pumped CH to gravity.

1. Are the rads different for gravity systems? or is it any rad that you can connect the feed into the top and exit out the bottom.

2. What sort of rise do you need to get thermocycling

[smileypete]

1. No they're just standard rads, sized to meet the output of the backboiler. Standard rads have threaded tappings at the top as well for fitting an air bleed screw, but a threaded pipe fitting can be put in instead.

 

2. Depends, the more distance between backboiler top pipe and the top of the rad, the better! So best keep the back boiler down as low as possible and the rads as high as poss under the gunnel. Maybe 'canals are us' and others can say what they have roughly, but it's hard to know exactly without using a water level.

 

cheers, Pete.

~smpt~

Edited October 13, 2013 by smileypete

[fudd]

Some interesting info on this thread but a couple of questions as I am thinking of converting my pumped CH to gravity.

1. Are the rads different for gravity systems? or is it any rad that you can connect the feed into the top and exit out the bottom.

2. What sort of rise do you need to get thermocycling

Our rads are of the 4 tapped type. Try and get ones with 3/4" tappings. Then you can use 22mm fittings and it will help with flow.

We have 300mm rise over about 10 meters of pipe run. Our rads are 2 no 300 x 800 single convector and 1 no 450 x 600 twin convector at the end of the loop. We use all 4 tappings and the end radiator gets hot within half an hour.

[DeanS]

A quick question.

 

If your radiators are too hot......because you have a strong fire going. How do you turn the heat down, without turning the fire down?

 

or do you just have to open windows?