'Sorry' it's vented multifuel heating systems again!

[master of none]

Sorry to rake over old ashes (pun intended) but I would like to get some clarification and further advice on multifuel/wood burning central heating systems.  I have a Rayburn mulitfuel cooker that will, as you know, also heat water and run a few rads. and this is my intention  The manufacturer clearly recommend that the water heating system should be a vented, open system, how can I safely adapt this to comply with French requirements demanding an unvented closed system?  I did read a little about the French equivalent of a header tank, minus ballvalve, can anyone expand on this (that pun wasn’t intended!).   It is my intention to store the hot water in an indirect/vented cylinder,  this also incorporates an electric heating element for when the multi fuel heating is not in use.  There will be at least one ‘open’ rad./towel rail to dissipate heat from the system. 

 Just to make matters a little more interesting (well I think so!), I am also intending to install a stove which I also already have, it is a Aarow Hamlet (6.5kw) multifuel stove which has the capability to heat water/rads. (with clip-in boiler (two outlets)) should we wish to.   This will be installed at the opposite end of an adjacent room.  Would there be any feasible method of combining these two heat sources for reasons of flexibility and/or extra capacity re: heating water/rads.?  Both manufacturers of course recommended that the hot water cylinder be position vertically above and as close as possible to the heat source?  Just thinking out load on this one really! But any ideas welcome. 

[jondeau]

Do the French insist on a sealed system?........A friends house near Matha has an old galvanised expansion tank in the barn close to the boiler.

The big problem with solid fuel appliances is that you can't just turn them off, even if you douse the fire the latent heat in the castings will still be liable to overheat them. With an expansion tank connected to the mains supply in the event of a leak from the system or a disharge caused by overheating, the mains will provide sufficient water to keep the appliance from running dry.

I have heard of solid fuel appliances being instaled with sealed systems........but you are taking a big risk.

 

I think that installing two solid fuel appliances in tandem could be very tricky as regards to overheating.......but I suppose it is possible as long as you monitor them very closely.

Some years ago in the UK I installed an oil fired boiler in conjunction with a solid fuel Aga.......one interesting phenomenon occured (both were connected to a twin coil cylinder) when the oil boiler was turned off, the hot water in the cylinder caused a reverse gravity feed which heated up the oil boiler.

 

[master of none]

Hello Jondeau, thanks for the reply.  The general consensus is that the French do not allow open vented systems, maybe the example you mentioned is a ‘well established’ system and predates current regulations. 

Obviously if I was to install an open vented system with a ballvalve the concerns you mentioned re: overheating in the event of a leak would be mitigated by the continuos flow via the header tank, depending on the nature of the leak and albeit with water damage implications, as I remember from my childhood when our backboiler burst during the night!

With regard to combining the two heat sources, I did wonder, apart from the overheating issues what the implications would be re: ‘fluid dynamics’ if, as it is likely, the heat sources were at opposite ends of the house inevitably there would be the potential for flow conflict but maybe this could be resolved using some kind of valve system.  This is probably the point where the experts start telling me to leave well alone as I’m out of my depth but I did say that I was only thinking out aload!  

[Jacqui Too]

This is the man to talk to: http://www.paul-gee.com/AGA.htm

Very helpful.

[jondeau]

In the UK sealed combi systems have more or less become the norm as well, however open vented systems are permitted and quite frankly are far superior in many ways. The rise in sealed combi systems in the UK is in my opinion far more to do with ease and speed of installation for the installer than any other reason, they're fine in small houses and flats but I would never install them in houses with multiple bathrooms.

It would be worth checking with the French Aga people if open vented systems are permitted, I really can't think of any reason why they would not be and if anyone would know for certain they would.

I don't think that combining two two heat sources (other than that they are both solid fuel) would be a great problem.....but it would need to be carefully worked out to avoid conflict.

It is quite difficult to be specific without seeing the proposed layouts...I'd be interested to hear how you get on and happy to advise on any problems you encounter.

[master of none]

Thanks for the continued responses.  I have undertaken further research and it would appear that I could combine two heat sources, using a cylinder with two independent coils but the Rayburn should be ‘dominant’ by zoning the other heat source.  This only applies to hot water and each source should still have its own header tank etc.

[Le Plombier]

The norm in France is the sealed system, devices are available to provide safety and prevent boiling

Open vented systems also exist but in my experience it is unlikely a French artisan would agree to install an open vented system

Whether a sealed or open vented system is installed they are both potentially dangerous if incorrectly installed

If a system is not installed properly overheating can result in the production of steam with, as the worst consequence, an explosion

Just installing an open vented system does not automatically make it safe

The sealed system depends upon a thermostatically controlled damper on the combustion air supply to the fire and a heat exchange tank where mains cold water can pass through to cool the system water, again thermostatically controlled. In my opinion this is safer and more controllable than relying on a gravity circuit and a radiator or similar to dissipate heat as on the old UK systems

In either event you should only proceed if you really know what you are doing

As with gas installations my standard advice for this type of installation is use a professional

Le Plombier

[jondeau]

[quote user="Le Plombier"]

a heat exchange tank where mains cold water can pass through to cool the system water, again thermostatically controlled. In my opinion this is safer and more controllable than relying on a gravity circuit and a radiator or similar to dissipate heat as on the old UK systems

In either event you should only proceed if you really know what you are doing

As with gas installations my standard advice for this type of installation is use a professional

Le Plombier

[/quote]

Hi Le plombier,

I have never seen one of those.......maybe it's a relatively new French thing.

However this would be not a lot of use with a solid fuel fuel system . If the system loses water due to overheating (safety valve discharge) or a leak on the sealed side of the system the amount of water in the system will be progressively reduced.......even with the boiler doused the latent heat can do terrible damage to the boiler, so fresh water needs to be introduced into it. The only way I have ever seen that done is through an expansion tank

Unless of course the heat exchanger tank thing can somehow introduce more water into the sealed system ?

 

PS: I'm not a professional any more.......but I did spend forty odd years in this field.

 

[Le Plombier]

Jondeau

Thats how it is done in france

I am a practising plumber here so I guess I should know

The safety controls are there to prevent the system overheating

Look on the Morvan boilers web site and you can see a diagrammatic layout of the system

I would not want to debate the detailed technicalities on an open forum as I personnaly believe this is not the type of installation an amateur should carry out because of the potential danger

Either way I am sure you will agree that whichever method is employed, unless you really know what you are doing it is potentially very dangerous to undertake this type of installation

Le Plombier 

[BIG MAC]

Sorry I don't know what the French term is but you can have a packaged 'Make up unit' here in the UK which will replenish a sealed system pretty much as described.

[Dave&Olive]

hi ok

          We have a Morvan boiler  running our C.H. and H.W. it is on a sealed system  . The air inlet is controlled by a thermostat. also if the water temp ( on the heating side ) goes over 100 C  it dumps the hot  tank via a boil valve . Donnot play with sealed systems if you are not sure.

          Dave

[IMG]http://i83.photobucket.com/albums/j311/daveolive/PDR_0002-2.jpg[/IMG]

[jondeau]

Ahh.....It dumps the hot cylinder.

Usefull.......but sadly not a remedy for a loss of water in the boiler system.

 

Big Mac.......nothing that I would use I'm afraid, non of the domestic ones I have seen are WRAS approved and the commercial stuff probably cost more than ones house would be worth.

[Dave&Olive]

hi ok

       The way this problem is solved is by fitting a pressure reducing valve in to the  top up link and to leave it turned on

pic 1

[IMG]http://i83.photobucket.com/albums/j311/daveolive/PDR_0076.jpg[/IMG]

and before you ask .. over pressure is by a ...

 pic 2

[IMG]http://i83.photobucket.com/albums/j311/daveolive/PDR_0074.jpg[/IMG]

and you are going to ask about what if air is trapped in the system then fit automatic bleed valves to the hot water and to both feed and return for the heating.

pic 3

 [IMG]http://i83.photobucket.com/albums/j311/daveolive/PDR_0073.jpg[/IMG]

  Dave

  

[jondeau]

I have to admit that did make me smile................a lot............I do hope the heat from the system does not ruin the diaphram in the pressure reducing valve. You could end up with a pretty large water bill.

 

Completely illegal in the UK of course.

 

Would it not be simpler to fit a conventional system ?

 

 

[powerdesal]

Dave,

I am seriously intrigued by the technical function of the blue 'dangly thing' in pic 3   [8-)]

[master of none]

Washing line???? or are these also illegal in France?

[Dave&Olive]

[quote user="jondeau"]I have to admit that did make me smile................a lot............I do hope the heat from the system does not ruin the diaphram in the pressure reducing valve. You could end up with a pretty large water bill. 

Completely illegal in the UK of course.

Would it not be simpler to fit a conventional system ?[/quote]

 hi ok

 glad it made you laugh ,some of the comments so far on this posting by ferry trained plumbers has made me laugh too

 illegal in the uk ..yes  but are we not in France ???  the reducing valve is too far from the boiler for the heat to affect the spring and disc type valve.

  and this is a conventional system ...

 and the washing line is his

[IMG]http://i83.photobucket.com/albums/j311/daveolive/PDR_0077.jpg[/IMG]

  Dave

[jondeau]

Dave........I love it.

 

Unfortunately you could be strung up by the danglys if a UK water company found you doing it.

 

Cheers. JD

 

My best to the cat...........

[Jo]

Oh! one lucky cat!!!![:D]