Another Heating Pump Thread.....

[jckm2000]

Following on from Julynian's topic on central heating pumps I'm wondering if I should go for a 12v pump and use the 22mm pipe I already own rather than buy a load of new, expencive 28mm pipe in the hope that my gravity system will in fact work.

 

Ideally I'd like the central heating to run free from electicity as we'll be without a shoreline in winter but the 12v pump on ebay that was mentioned would only draw .2 of an amp from my 24v system.

 

We'll have 6 x 90w solar panels and a 68amp DC diesel genny on board for back up (6 x 110amp bats).

 

Any thoughts?

 

C.

[Ex- Member]

Following on from Julynian's topic on central heating pumps I'm wondering if I should go for a 12v pump and use the 22mm pipe I already own rather than buy a load of new, expencive 28mm pipe in the hope that my gravity system will in fact work.

 

Ideally I'd like the central heating to run free from electicity as we'll be without a shoreline in winter but the 12v pump on ebay that was mentioned would only draw .2 of an amp from my 24v system.

 

We'll have 6 x 90w solar panels and a 68amp DC diesel genny on board for back up (6 x 110amp bats).

 

Any thoughts?

 

C.

 

Hi Timestamp

 

 

The pump is very low amperage and cheap, it's not going to drain your batteries in a hurry, just bought one today £24.00, to be honest I would use it and pressurise the system, gravity fed can be a pain on a boat if you don't get it right and problems difficult to sort out at later stages. That's me though try to use what I feel are less trouble free solutions. Also I think heat efficiency is better when under pressure, I'm sure I read that somewhere. What you'll save in pipework will probably about equal the cost 12v pump and accumulator + fittings.

 

By the way can I ask what Diesel generator you're using?

 

 

 

[jckm2000]

Hi Julynian,

Thanks for your reply. The genny I have, but not fitted yet, is a Hatz engined diesel powered German ex-military unit. I bought it from ebay.de, around £600 delivered.

It's not small but with the cover on it's reasonably quiet. I intend fitting it in the engine room.

 

Just like this: http://www.ebay.de/itm/1-9KW-DIESEL-HATZ-BUNDESWEHR-STROM-GENERATOR-NOTSTROM-STROMAGGREGAT-28V-SILENT-/170800775642?pt=DE_Haus_Garten_Heimwerker_Generatoren&hash=item27c48501da

 

 

I thought it was worth a punt.....

 

 

C.

[ditchcrawler]

Where is all this pressurised bit coming from? Most systems are fully vented.

[Ex- Member]

Hi Julynian,

Thanks for your reply. The genny I have, but not fitted yet, is a Hatz engined diesel powered German ex-military unit. I bought it from ebay.de, around £600 delivered.

It's not small but with the cover on it's reasonably quiet. I intend fitting it in the engine room.

 

Just like this: http://www.ebay.de/i...=item27c48501da

 

 

I thought it was worth a punt.....

 

 

C.

 

Wow very nice find, Searching the German ebay I didn't think of that, I'll be on there in a tick LOL Is this for charging 24 volt system ?

 

If you get a chance to measure it, that would be most helpful.

 

 

Thanks for the info.

 

 

[jckm2000]

Wow very nice find, Searching the German ebay I didn't think of that, I'll be on there in a tick LOL Is this for charging 24 volt system ?

 

If you get a chance to measure it, that would be most helpful.

 

 

Thanks for the info.

 

Dimensions are: 840L x 480H x 460W

It is indeed for charging a 24v system.....

Edited March 24, 2012 by jckm2000

[Tony Brooks]

Where is all this pressurised bit coming from? Most systems are fully vented.

 

I agree, although I have seen one totally sealed system using two expansion vessels on a Ebespatcher TYPE system. I have noticed that a certain member seems to get hold of the wrong end of the stick rather more frequently that one would hope and the be a bit forcefully in promoting his ideas.

 

To the OP.

 

Pipe as a gravity (convection) system and for your own safety stick with an open header tank. I would also have an open breather from the high point in the system which is often at the front of the boat. That way you are not relying on a thermostat or luck/your stoking skill on a stove to prevent an explosion.

 

If you fit a couple of valves linked with a length of pipe in the return run then you can fit the pump if it proves necessary. I do not see that reducing a short length to 22mm in the return run will make any significant difference to the gravity circulation. Just make sure the pump is of the centrifugal type and the you can blow through it before fitting it. If, by chance, you have flexible impeller pump then it will stop the flow unless it is running.

[Tony Brooks]

Hi Timestamp

 

 

The pump is very low amperage and cheap, it's not going to drain your batteries in a hurry, just bought one today £24.00, to be honest I would use it and pressurise the system, gravity fed can be a pain on a boat if you don't get it right and problems difficult to sort out at later stages. That's me though try to use what I feel are less trouble free solutions. Also I think heat efficiency is better when under pressure, I'm sure I read that somewhere. What you'll save in pipework will probably about equal the cost 12v pump and accumulator + fittings.

 

By the way can I ask what Diesel generator you're using?

 

 

All pressurising the system will do is to raise the boiling point of the water, In an industrial heat/process system you may well want to run the system at above 100C so it can be used to boil water in heat exchangers or produce superheated steam.

 

In my view this would be dangerous and pointless on a domestic system because:

 

The rads will have to be set at a much lower temperature to prevent burns.

It will put more pressure on the joints (which I would not want to do on plastic plumbing).

If a pipe split or a joint blew you could easily end up with superheated steam coming in your direction.

If a stove ran away to a boiler thermostat failed you would probably end up with an explosion venting superheated steam into the boat.

 

As higher operating temperature would increase the heat transfer into the boat EXCEPT this will not happen because of the maximum radiator temperature dictated by safety (is it about 60C?)

[Ex- Member]

All pressurising the system will do is to raise the boiling point of the water, In an industrial heat/process system you may well want to run the system at above 100C so it can be used to boil water in heat exchangers or produce superheated steam.

 

In my view this would be dangerous and pointless on a domestic system because:

 

The rads will have to be set at a much lower temperature to prevent burns.

It will put more pressure on the joints (which I would not want to do on plastic plumbing).

If a pipe split or a joint blew you could easily end up with superheated steam coming in your direction.

If a stove ran away to a boiler thermostat failed you would probably end up with an explosion venting superheated steam into the boat.

 

As higher operating temperature would increase the heat transfer into the boat EXCEPT this will not happen because of the maximum radiator temperature dictated by safety (is it about 60C?)

 

Hi Tony

 

Clearly I seem to have used the wrong terminology. My system is sealed then with accumulator and pump, the accumulator is pressurised around 1.5 bar, There is a vent above the stove which air is purged from. Not being a plumber or technical expert, but to me something under pressure is pressurised. Apologies to the original OP if it was misleading, although I think he knew what I meant.

 

 

That's me though try to use what I feel are less trouble free solutions.

 

Hardly forceful.

 

 

 

[Tony Brooks]

Hi Tony

 

Clearly I seem to have used the wrong terminology. My system is sealed then with accumulator and pump, the accumulator is pressurised around 1.5 bar, There is a vent above the stove which air is purged from. Not being a plumber or technical expert, but to me something under pressure is pressurised. Apologies to the original OP if it was misleading, although I think he knew what I meant.

 

 

 

Hardly forceful.

 

If the vent is open the any air pressure in the accumulator will have no effect on the water pressure because the diaphragm will be pushed into the bottom of the accumulator.

 

If the vent is closed then you have the danger of an explosion and superheated steam if a boiler stat fails or a stove runs away. You can go some way to mitigation this danger by fitting a pressure relief valve. However this relies on the valve opening in xx years time. I have seen number of such valves scaled up where they have weeped over the years and I would not trust one to protect me in any way.

 

I think that you are trying to expand domestic systems into boats. Those that use an "accumulator" are normally high pressure (mains pressure) systems with no tank in the roof (cost saving) with the "accumulator" being the expansion vessel for the central heating water when heated. They also tend to be combi-units which also use no storage cylinder and transfer of heat from the central heating part of the boiler to the hot water via a heat exchanger. I have questions as to their actual efficiency when you take the waste of water while you wait for it to heat up into account. I doubt the efficiency claims and suspect it is much more to do with no hot water cylinder and no loft tank making installation easier.

 

On a boat any "accumulator" is normally part of the domestic water system, NOT the central heating system. As I said I have seen such things on diesel boilers but if you really do have a solid fuel stove please think carefully and see what others say. I think you are risking very serious scalding if the thing explodes.

[Ex- Member]

If the vent is open the any air pressure in the accumulator will have no effect on the water pressure because the diaphragm will be pushed into the bottom of the accumulator.

 

If the vent is closed then you have the danger of an explosion and superheated steam if a boiler stat fails or a stove runs away. You can go some way to mitigation this danger by fitting a pressure relief valve. However this relies on the valve opening in xx years time. I have seen number of such valves scaled up where they have weeped over the years and I would not trust one to protect me in any way.

 

I think that you are trying to expand domestic systems into boats. Those that use an "accumulator" are normally high pressure (mains pressure) systems with no tank in the roof (cost saving) with the "accumulator" being the expansion vessel for the central heating water when heated. They also tend to be combi-units which also use no storage cylinder and transfer of heat from the central heating part of the boiler to the hot water via a heat exchanger. I have questions as to their actual efficiency when you take the waste of water while you wait for it to heat up into account. I doubt the efficiency claims and suspect it is much more to do with no hot water cylinder and no loft tank making installation easier.

 

On a boat any "accumulator" is normally part of the domestic water system, NOT the central heating system. As I said I have seen such things on diesel boilers but if you really do have a solid fuel stove please think carefully and see what others say. I think you are risking very serious scalding if the thing explodes.

 

Hi Tony

 

My system is diesel Bubble stove back boiler, I've never suggested it was solid fuel and the OP was following on from a thread I started about my central heating system.

 

The vent on top of the fire closes/seals when the system is completely full of fluid using a float mechanism. The accumulator tank is pressurised at 1.5 bar this has a pressure release valve should the system over pressurise. The boiler also has automatic shut off should water flow cease or slow and boiler get too hot. There's also a pressure gauge you I can easily view at any time. I also check the system every year before use, you can manually check if the pressure release valve works at any time by a simple twist of a knob. You can also test the vent on the fire by unscrewing the top cap and press down the float with a pin or matchstick like letting down tyres.

 

The system is plumbed to run through the calorifeir but I choose to isolate it as I too think it's a waste of heat, but it can be diverted there at the turn of a valve if necessary.

 

The system works well and heats 5 small to med rads and hot water if connected.

 

I really don't see a problem with this system if properly maintained like any other should be.

 

 

[smileypete]

Any thoughts?

Some sort of backup in case of pump failure might be handy.

 

Pumps can be noisy depending on how they're installed.

 

cheers,

Pete.

[Tony Brooks]

Hi Tony

 

My system is diesel Bubble stove back boiler, I've never suggested it was solid fuel and the OP was following on from a thread I started about my central heating system.

 

The vent on top of the fire closes/seals when the system is completely full of fluid using a float mechanism. The accumulator tank is pressurised at 1.5 bar this has a pressure release valve should the system over pressurise. The boiler also has automatic shut off should water flow cease or slow and boiler get too hot. There's also a pressure gauge you I can easily view at any time. I also check the system every year before use, you can manually check if the pressure release valve works at any time by a simple twist of a knob. You can also test the vent on the fire by unscrewing the top cap and press down the float with a pin or matchstick like letting down tyres.

 

The system is plumbed to run through the calorifeir but I choose to isolate it as I too think it's a waste of heat, but it can be diverted there at the turn of a valve if necessary.

 

The system works well and heats 5 small to med rads and hot water if connected.

 

I really don't see a problem with this system if properly maintained like any other should be.

 

 

If the system is vented by a "float mechanism" then at some time the vent must open. At that time the air pressure in the accumulator will have forced all the water out of it so the pressure in the boiler and system will be atmospheric. Every time yo twist the valve you will also vent pressure from the accumulator. Now, if you fill the system up via a filling loop from your domestic supply then things may work as you describe but on the face of it you have an automatic air vent above the stove and another way of filling it. In any case it would be hard to use antifreeze with a simple filling loop.

 

You know your boat but this does not sound right to me. The filling mechanism is missing from your description. My feeling is that things may not work as you think they do. However I think it is dangerous to propose pressurised central heating systems on a boat unless you are absolutely sure about the heat source.

 

Incidental, have you seen the reports about bubble type stoves ending up with flames coming out of the chimney - despite the cutouts.

[Ex- Member]

If the system is vented by a "float mechanism" then at some time the vent must open. At that time the air pressure in the accumulator will have forced all the water out of it so the pressure in the boiler and system will be atmospheric. Every time yo twist the valve you will also vent pressure from the accumulator. Now, if you fill the system up via a filling loop from your domestic supply then things may work as you describe but on the face of it you have an automatic air vent above the stove and another way of filling it. In any case it would be hard to use antifreeze with a simple filling loop.

 

You know your boat but this does not sound right to me. The filling mechanism is missing from your description. My feeling is that things may not work as you think they do. However I think it is dangerous to propose pressurised central heating systems on a boat unless you are absolutely sure about the heat source.

 

Incidental, have you seen the reports about bubble type stoves ending up with flames coming out of the chimney - despite the cutouts.

 

Hi Tony

 

The vent is a valve designed for this type application

Automatic Air Release Valve

 

 

http://www.seekpart....1104847537.html

 

This is situated at the highest point of the system and purges air from the system and automatically closes when all air is purged. Has a screw cap also with internal rubber washer to prevent any leaking should the valve fail.

 

 

I didn't mention a filling loop I assumed it's an integral part of the accumulator and pressure release valve, but of course there's a filling loop with valve at each end which I can up the pressure with if it drops below one bar.

 

However you can manually fill the system first of all with CH fluid by removing the Automatic Air Release Valve use a funnel and manually fill whilst running the pump. You can easily get 80 to 90% in the system before replacing the AARV and final filling and pressurising via the filling loop with tap water.

 

The systems fluid is around 80/90 % heating circulation fluid and 10/20% water. When you test the pressure valves you simply replace any lost pressure, you do have to unscrew the AARV though as you'll always put the air in the system that's in the filling loop, the input of water is minimal as you're just re-pressurising and not necessarily filling, the system has been plumbed in for over 3 years it's only ever lost 1 bar in pressure and that was when the heating wasn't used for 18 months.

 

I check the pressure and the Pressure release valve before using the system when winter approaches. System's never been a problem, when fitting though you do have to ensure every joint is properly connected and ensure you use pipe inserts. I rigged up a pressure tester using a cycle pump and checked each set of joints as the rads were connected.

 

 

 

Edited March 25, 2012 by Julynian

[Tony Brooks]

Hi Tony

 

The vent is a valve designed for this type application

Automatic Air Release Valve

 

 

http://www.seekpart....1104847537.html

 

This is situated at the highest point of the system and purges air from the system and automatically closes when all air is purged. Has a screw cap also with internal rubber washer to prevent any leaking should the valve fail.

 

 

I didn't mention a filling loop I assumed it's an integral part of the accumulator and pressure release valve, but of course there's a filling loop with valve at each end which I can up the pressure with if it drops below one bar.

 

However you can manually fill the system first of all with CH fluid by removing the Automatic Air Release Valve use a funnel and manually fill whilst running the pump. You can easily get 80 to 90% in the system before replacing the AARV and final filling and pressurising via the filling loop with tap water.

 

The systems fluid is around 80/90 % heating circulation fluid and 10/20% water. When you test the pressure valves you simply replace any lost pressure, you do have to unscrew the AARV though as you'll always put the air in the system that's in the filling loop, the input of water is minimal as you're just re-pressurising and not necessarily filling, the system has been plumbed in for over 3 years it's only ever lost 1 bar in pressure and that was when the heating wasn't used for 18 months.

 

I check the pressure and the Pressure release valve before using the system when winter approaches. System's never been a problem, when fitting though you do have to ensure every joint is properly connected and ensure you use pipe inserts. I rigged up a pressure tester using a cycle pump and checked each set of joints as the rads were connected.

 

 

So pretty much as I described in my first post except you only have one "accumulator" to both hold a supply to "top up" as required during operation and to accept the expansion.

 

In my view this is needlessly complicated and I can see nothing that will make it any more efficient than an open header-tank vented system. the one on my boat had a ball valve in the header tank (mini version of the one at home) and required no maintenance or checking apart from sticking my finger into the tank now and again for over 5 years and I knew that whatever happened it was intrinsically safe, requiring no additional safety valve.

 

Still if it work for you then fine, but I could not in all honesty advocate such a system to anyone else and I certainly can not agree it is any more efficient.

[jelunga]

All pressurising the system will do is to raise the boiling point of the water, In an industrial heat/process system you may well want to run the system at above 100C so it can be used to boil water in heat exchangers or produce superheated steam.

 

In my view this would be dangerous and pointless on a domestic system because:

 

The rads will have to be set at a much lower temperature to prevent burns.

It will put more pressure on the joints (which I would not want to do on plastic plumbing).

If a pipe split or a joint blew you could easily end up with superheated steam coming in your direction.

If a stove ran away to a boiler thermostat failed you would probably end up with an explosion venting superheated steam into the boat.

 

As higher operating temperature would increase the heat transfer into the boat EXCEPT this will not happen because of the maximum radiator temperature dictated by safety (is it about 60C?)

 

Tony,

I would just like to comment on your phrase "superheated steam",

Steam normally produced in a boiler used for driving a steam engine is normally wet steam. The water has bouled and steam is produced. It is at 100deg C, for the sake of argument.

Superheated steam is dry steam which has been heated up away from the original boiler to higher temperature. I speak from a seagoing marine engineer training and indeed a Claymills Victorian Steam Pumping Station background.

I do not think the stoves on boats are capable of producing "superheated steam".. However even pressurised wet steam can be bloody painfull and dangerous.

Am I just being a pedant?

[MoominPapa]

I do not think the stoves on boats are capable of producing "superheated steam".. However even pressurised wet steam can be bloody painfull and dangerous.

Am I just being a pedant?

Maybe you are being a pedant. Can I out-pedant you?

 

 

The thread is about (accidentally) pressurising the boiler, so it ends up containing saturated stream at some temperature higher the 100 degrees (because the pressure is higher than atmospheric) If the boiler then bursts and the pressure drops to 1 atmosphere, isn't the hotter than 100 degrees steam now superheated, ie at a temperature greater then its boiling point?

 

MP

[jelunga]

Maybe you are being a pedant. Can I out-pedant you?

 

 

The thread is about (accidentally) pressurising the boiler, so it ends up containing saturated stream at some temperature higher the 100 degrees (because the pressure is higher than atmospheric) If the boiler then bursts and the pressure drops to 1 atmosphere, isn't the hotter than 100 degrees steam now superheated, ie at a temperature greater then its boiling point?

 

MP

No because the steam will still be wet steam at 100 deg. C even when pressurised. Propulsion boilers for reciprocating engines typically generate steam around 150 psi. More or less depending on the need of the engine. This is still wet steam at 100 deg.

At explosive decompression time I doubt any pipework will have allowed the pressure to increase to anything like that high pressure. Even my pressure cooker only operates at 15psi at high pressure and 5 at low.

So no, I am quite convinced the steam is not technically "Superheated". If I had not downsiEd to move onto our boat I would still have my steam tables whichwould give helpful info.

 

But there again, it was a long time ago and my brain may be addled!

 

Just re read my last post. It is bollox. Of course as it gets pressurised the temp will increase. And therefore yes it will be hot. But I thought that to be called "superheated" steam had to be dry steam.

But at the end of the day it will still bloody hurt !

[Ex- Member]

So pretty much as I described in my first post except you only have one "accumulator" to both hold a supply to "top up" as required during operation and to accept the expansion.

 

 

In my view this is needlessly complicated and I can see nothing that will make it any more efficient than an open header-tank vented system. the one on my boat had a ball valve in the header tank (mini version of the one at home) and required no maintenance or checking apart from sticking my finger into the tank now and again for over 5 years and I knew that whatever happened it was intrinsically safe, requiring no additional safety valve.

 

Still if it work for you then fine, but I could not in all honesty advocate such a system to anyone else and I certainly can not agree it is any more efficient.

 

 

Well all I can say is the system works well, it's used in tens if not hundreds of thousand homes throughout this country and more so throughout the world. We're talking 1 to 1.5 bar hardly super heating and an unnecessary exaggeration to make your point about something you don't like or had experience of.

 

The system is intrinsically safe, or as safe as a gravity system. It also complies with BSS

 

Like any system it of course it needs maintenance, if you choose to do yours five yearly then that's you prerogative, ball valves can be problematic though and usually need adjustment over periods of time and regularly fail in my experience .

 

There are pros and cons to many differing systems. I was fully aware of the gravity system when deciding what to install, but chose pressurised system or sealed system as some prefer to call it as the better option for my requirements.

 

[Tony Brooks]

No because the steam will still be wet steam at 100 deg. C even when pressurised. Propulsion boilers for reciprocating engines typically generate steam around 150 psi. More or less depending on the need of the engine. This is still wet steam at 100 deg.

At explosive decompression time I doubt any pipework will have allowed the pressure to increase to anything like that high pressure. Even my pressure cooker only operates at 15psi at high pressure and 5 at low.

So no, I am quite convinced the steam is not technically "Superheated". If I had not downsiEd to move onto our boat I would still have my steam tables whichwould give helpful info.

 

But there again, it was a long time ago and my brain may be addled!

 

Just re read my last post. It is bollox. Of course as it gets pressurised the temp will increase. And therefore yes it will be hot. But I thought that to be called "superheated" steam had to be dry steam.

But at the end of the day it will still bloody hurt !

 

 

All I was trying to say is that the steam produced will be hotter than 100C and as such I would imaging it would be "dry" because it would be at a temperature high enough to ensure it tended not to contain condensation (until it cools a little).

 

I also wanted people to realise it would hurt more than "kettle" steam.

 

I would like to see some other views on the relative efficiencies and safety of sealed and open central heating systems.

[jelunga]

All I was trying to say is that the steam produced will be hotter than 100C and as such I would imaging it would be "dry" because it would be at a temperature high enough to ensure it tended not to contain condensation (until it cools a little).

 

I also wanted people to realise it would hurt more than "kettle" steam.

 

I would like to see some other views on the relative efficiencies and safety of sealed and open central heating systems.

Yes. Sorry Tony. I was reading it with an engineers hat on not as a sensible warning!

[Ex- Member]

All I was trying to say is that the steam produced will be hotter than 100C and as such I would imaging it would be "dry" because it would be at a temperature high enough to ensure it tended not to contain condensation (until it cools a little).

 

I also wanted people to realise it would hurt more than "kettle" steam.

 

I would like to see some other views on the relative efficiencies and safety of sealed and open central heating systems.

 

Hi Tony

 

 

The pressures involved won't boil the water, I think that's why the Pressure Release valves operate at 3 bar which seems a set level for these. Our rads get hot of course but no hotter than any of the rads in our land house.

 

If the system blew for any reason at 3 bar it would be about as explosive as bursting a small car tyre. This would most likely happen at a joint somewhere if the PRV failed. So would happen under floors or behind walls unless you prefer all your plumbing exposed and visible.

 

I also wanted people to realise it would hurt more than "kettle" steam.

 

That's a ridiculous assumption and assumes boiling water, although 90 degree steam from a kettle will hurt as well as 80/70 and 60 possibly. Why you feel the need to scare monger about a system that is widely used and clearly as safe as any other is a mystery. As I said different systems have different pros & cons depending on peoples different requirements.

 

 

[smileypete]

Hi Tony

 

My system is diesel Bubble stove back boiler, I've never suggested it was solid fuel and the OP was following on from a thread I started about my central heating system.

 

...

 

I really don't see a problem with this system if properly maintained like any other should be.

Why not get advice from the manufacturer? If they say the back boiler must run in an 'open' system, then do just that.

 

cheers,

Pete.

Edited March 26, 2012 by smileypete

[bargemast]

Well all I can say is the system works well, it's used in tens if not hundreds of thousand homes throughout this country and more so throughout the world. We're talking 1 to 1.5 bar hardly super heating and an unnecessary exaggeration to make your point about something you don't like or had experience of.

 

The system is intrinsically safe, or as safe as a gravity system. It also complies with BSS

 

Like any system it of course it needs maintenance, if you choose to do yours five yearly then that's you prerogative, ball valves can be problematic though and usually need adjustment over periods of time and regularly fail in my experience .

 

There are pros and cons to many differing systems. I was fully aware of the gravity system when deciding what to install, but chose pressurised system or sealed system as some prefer to call it as the better option for my requirements.

 

 

I have a pressurised system on my boat too, and have had the same on 2 of my barges in the past, all the systems I've seen on another (give a low number) 100 barges were exactly the same, and can say that I've never had any problems whatsoever.

 

I just looked up some information about KABOLA boilers that are sold in the UK too : My link the most interesting writing is at 4.1.6

 

Peter.

[Tony Brooks]

Hi Tony

 

 

The pressures involved won't boil the water, I think that's why the Pressure Release valves operate at 3 bar which seems a set level for these. Our rads get hot of course but no hotter than any of the rads in our land house.

 

If the system blew for any reason at 3 bar it would be about as explosive as bursting a small car tyre. This would most likely happen at a joint somewhere if the PRV failed. So would happen under floors or behind walls unless you prefer all your plumbing exposed and visible.

 

 

 

That's a ridiculous assumption and assumes boiling water, although 90 degree steam from a kettle will hurt as well as 80/70 and 60 possibly. Why you feel the need to scare monger about a system that is widely used and clearly as safe as any other is a mystery. As I said different systems have different pros & cons depending on peoples different requirements.

 

 

The boiling point of water at 3 bar pressure is about 270C so if your thermostat failed the safety valve would not open utile you had about 45psi of pressure and water in and close to the boiler at 270C. As soon as the pressure dropped with a pipe or joint failure that water would flash off into steam at 270C or very close to it. From memory the plastic pipe now so often used is not rated fro 270C @ 3 bar. I thought it was more like 180C.

 

I just would not want to risk the volume of steam and the temperature a failure such as that would produce within the confines of a boat.

 

I do not consider pointing out the risks of large volumes of high temperature steam scaremongering. In my view it is vital that others are given the information with which to make an informed decision about their boats. I note that you have yet to substantiate your claim about greater efficiency. I do consider advocating a system that is capable of producing these results without explaining the risks dubious.