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 plumbing in a wood burner with back boiler 
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Joined: 18 Aug 2007, 01:40
Posts: 132
Location: les eyzies, Dordogne
Hi
We are looking at installing a wood burning stove with boiler (as well as solar) problem is we are using self levelling concrete as our floor slab and need to put the pipes for the radiators in this as we are not having a screed. I ahave several questions about this and if anyone can offer advice that would be great.

1. Can we use the flexible plastic pipes rather than copper if we feed the stove straight to the radiators or will the temperature be too high. can we use thermostats to control the temp of the water before it goes to the radiaturs., therefore if it gets too hot the water can be diverted to the boiler.

2. If we lay the pipes in the slab we will put them in insulation tuibes to allow for expansion. We want to use plastic so we don't have to have any joins under the slab.If i can't use plastic, can i buy copper tubing in one peice at a diameter suitable for a stove.I think we need 28mm.

3.If we lay the floor now and put the piping in do the woodburners in the uk and france have the same size fittings at the back.

Thanks so much in advance for any help.If anyone has any useful links to sites that show how to plumb in a woodburning stove with a back boiler that would be great.
Love ginette


26 Jun 2010, 11:59
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Joined: 04 May 2008, 04:46
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Location: Central Brittany
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Not sure about the plastic issue as I am not a plumber.
However I do know that if you are going to put in copper pipes under concrete then they must come with a plastic outer coating as there is some sort of reaction between the concrete and the copper.
You can buy plastic coated copper pipes from a plumbers merchant. What I did was to get a plumber to use his bending machine and put a right angle in the pipes (cold feed and hot take) for me (20 euros but it was worth it to know that I had no joints under the floor.).
To do this he had to strip away the plastic coat around the bend so I carefully reapplied the coating (once pipe was bent) and used copious amounts of tape to protect it from any ingress of cement. I then put the pipes into position and laid my floor slab with the up parts now just waiting for the stove. If I have got the diameter wrong then I will be able to use a reducer to get the right one to connect to the stove.
Good luck

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27 Jun 2010, 23:05
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Joined: 17 Jul 2003, 11:10
Posts: 8158
Location: Now Hereford previously 33 & 87
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I believe the first two meters from the boiler must be in copper in the UK – suspect the same is true in France but is essential any way.
You need one radiator which has no thermostat to which you can dump excess heat. Unlike gas or fueil a wood burner does stop producing heat immediately you damp it back.
You can buy coils of copper which will need plastic protection if laid in the slab. Plastic will also need to be in gaine
On some but not all French CH systems there are flow and return manifolds after the boiler with valves to shut off or reduce the flow to individual radiators or rooms. So the individual pipes are smaller than the 28 mm. Other systems progressively reduce the sized as radiators are tapped off the feed.
Pipe unions are not an issue you may need to go a real plumber’s merchant as opposed to a shed.


28 Jun 2010, 06:48
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Joined: 04 Feb 2004, 18:51
Posts: 535
Location: Hautefort 24
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Run copper pipe from the stove to manifolds then use Per or multicouche in the floor in conduit to allow pipes to move, protect them from the concrete and allow them to be replaced. You will need a header tank above the stove with an open vent and this is best done in copper.

To control the water temp to the radiators you can use a 3/4 way valve or 'ballon tampon', you shouldn't use thermostatic valves on the rads. .

All threaded fittings are available in France to fit the stove boiler tappings


28 Jun 2010, 11:28
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Joined: 18 Aug 2007, 01:40
Posts: 132
Location: les eyzies, Dordogne
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Hi all
Thanks so much for the reply it has been a stressy few days getting to grips with the plumbing over here but i think we are getting there.

We are going to use copper 28mm pipe for the first 4m then reducing to 16mm PER in gaine.The wood burning boiler will probably be the Hercules 30b, big enough to supply all the 10 radiators we need (we have worked the sizes out using an internet site to help us). We want to heat the radiators first before the hot water so we don't have to heat the whole tank everytime. The only problem is that Broseley, the stove makers, say that under no circumsatnces can we let the return water from the rads go back to the woodburner as the condensation it will cause will cause problems with sulphuric acid corrosion.

He suggested that we run all the water to the storage tank first and then it will be distributed from there.I read on a previous posting that someone (Rod or James123 i think) have similar systems that heat the rads first so i know it can be done but not sure how.

The guy at Broseley spoke about having a thermal store but not sure if we would need one if we were using solar aswell or whther we could just use a normal balon.I have also seen mentioned a balon de mellange (mixing tank) and not sure if this is a better option. So confused.

All we need to know really for now is whether we can run the radiators seperately and if so where does the return pipe end up.We want to lay the self levelling concrete asap and as there will be no screed we need to get the pipe layout right.

Any help would be great.
Thanks in advance

Love ginette


29 Jun 2010, 14:27
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Joined: 04 May 2008, 04:46
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Location: Central Brittany
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I am not a plumber however my first question is if you have heated the water in the back boiler and it has done its rounds, then where else can it go other than back to the boiler for a re-heating. Isn't that how it works. The way you describe reads like the chap from the stove company is suggesting that you only put hot water into the boiler. Doesn't sound right somehow. Or I have missed something.

I hope a plumber will put thins right if I am wrong but from what I have read, from the plumbers on here, is that 28mm is the recommended smallest to go to have a self cycling hot water/heating system ie no need for a pump.
I don't understand why you are reducing it to 16mm and therefor restricting your flow and introducing the need for a pump.
I ask because I don't know and will be in your situation soon

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29 Jun 2010, 23:58
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Joined: 18 Aug 2007, 01:40
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Location: les eyzies, Dordogne
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I thought the same thing regards the water going back to the boiler but the Broseley engineer said that if cold water (rad return) goes back to the boiler it will cause problems with condensation and sulphuric acid corrosion and the boiler will die after a few years. he said the water should always go to the boiler first, but this seems a bit daft as you have to heat the whole tank before you get the rads warm. i asked him why there were four inlet/outlet pipes on the back and he said they were for different ways of plumbing it in, but why would i need 4 holes if everything had to go to the tank first. :?

We are looking to use a pumped system but want to put a gravity back up in place in case we get a power cut and can still get rid of the heat if needed.
Good luck with your project.This is all a bit of a rush for us as we usually research things well in advance but because we have changed to self levelling concrete and therefore no screed, we need to lay some of the pipes before the slab goes down.
Good luck
Love ginette


30 Jun 2010, 00:20
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Joined: 18 Sep 2008, 16:40
Posts: 56
Location: Morbihan and Devon
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Hi, I've got a wood burner central heating system in England. The four inlet/oulets on the boiler are so that you can have one system to feed all the radiators, where you can turn them on or off as required, but one system which goes to , preferably, an upstairs radiator which is always on that acts as a heat sink. This is very necessary if your pumps stops for any reason (power cut etc). Also if you have a thermostatic switch on the outlets, it will stop the pump pushing cold water back to the boiler as the boiler gets up to temperature. The stove operates best where the inlet temperature is as near the outlet temperature as possible. My boiler is 25 years old and I have had no problem. Don't forget you must put inhibitor in the system to avoid corrosion. Steel boilers will rust very quickly and you end up with the radiators getting blocked up at the bottom. If you read the instructions with the stove I'm sure it will explain it all.

Hope it goes well

Martyn


30 Jun 2010, 07:18
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Joined: 26 Jun 2006, 20:22
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Location: cornwall and dordogne 24580 nr rouffignac perigord noir 24
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i think you want a thermalstore ,it has to located ubove the stove (gravity )you dont really want to go 28mm -16mm, the smaller pipe can only carryso much heat ,this is the reason bigger pipes are used ,the thermal store is a big cyl 200-700ltrs that has flow +return from fire going from it ,then htg ,ufhtg and hot water comes from there ,you can control it all with stats etc , youwill alsohave mains pressure hot water as the store is only gravity fed , im better at talking that typing , we are going to our place 23rd july , you are 20mins from us
rod


30 Jun 2010, 07:33
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Joined: 18 Aug 2007, 01:40
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Location: les eyzies, Dordogne
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Hi Rod

i think you are right Rod, the more we look into it, the more the thermalstore seems like the way to go. i know i will need to heat the tank everytime but at least the thermal store will allow us to heat the rads in the morning before we get the fire back up to hot. Putting a thermostat on the return pipe sounds essential to stop the corrosion issue.

Thanks Martyn for the info on inhibitor, this site is great for finding out info.
Rod when you are over Rod maybe we could meet you for a cup of tea do chat about diy.
Thanks again.
Love ginette


30 Jun 2010, 11:17
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Joined: 04 May 2008, 04:46
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Location: Central Brittany
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Rod I understand most of your post but one bit is still confusing me, How can I have mains pressure hot water if the thermal store is "gravity fed"?
I am obviously missing something and any pointers in the right direction would be gratefully received.

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30 Jun 2010, 18:38
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Joined: 05 Oct 2006, 17:47
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Location: 87
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I think what Rod is trying to convey is that by having the termastore above the heat source, natural convection (thermo syphon) will take place. This often referred to as gravity circulation.

The importance of relying on thermo syphon rather than using an electrical circulator (often referred to as a pump) is that in the event of an interuption to the supply of electricity (often referred to as an electricity cut) the heat from the appliance will continue to be absorbed by the Thermastore.

To offer less frictional resistance to the thermo syphon flow, the pipework needs to be at least 28mm for domestic appliances. The reason for 4 tappings on a heating appliance is allow the installer to put the cylinder or Thermastore on either side so that the pipework does not have to 'crossover'.
regards F14


30 Jun 2010, 20:11
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Joined: 26 Jun 2006, 20:22
Posts: 2878
Location: cornwall and dordogne 24580 nr rouffignac perigord noir 24
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Bentley wrote:
Rod I understand most of your post but one bit is still confusing me, How can I have mains pressure hot water if the thermal store is "gravity fed"?
I am obviously missing something and any pointers in the right direction would be gratefully received.

hi the thermal store is fed from a cold tank ,some are build in to the top of store , the hot water is made by a mains pressure coil running thru store , it comes out at 75c say if store is up to 80c so it has a blend valve that mixeswith cold to get it back to 55-60c,so its just the coil that is under mains pressure ,so safe on solid fuel or even with another heat source aswell


30 Jun 2010, 20:25
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Joined: 26 Jun 2006, 20:22
Posts: 2878
Location: cornwall and dordogne 24580 nr rouffignac perigord noir 24
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babychoccake wrote:
Hi Rod

i think you are right Rod, the more we look into it, the more the thermalstore seems like the way to go. i know i will need to heat the tank everytime but at least the thermal store will allow us to heat the rads in the morning before we get the fire back up to hot. Putting a thermostat on the return pipe sounds essential to stop the corrosion issue.

Thanks Martyn for the info on inhibitor, this site is great for finding out info.
Rod when you are over Rod maybe we could meet you for a cup of tea do chat about diy.
Thanks again.
Love ginette
hi you wont need a stat on the stove return just a stat that wont let htg run untill the store is up to 70c min , the bigger the store the better for flexability ,i do quite a few here in uk , im not sure if they are recognised in france , yes pm me you contact details
rod


30 Jun 2010, 20:39
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Joined: 29 Jun 2010, 10:45
Posts: 22
Location: Alles-sur-Dordogne
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I have completed a number of projects like yours and can answer your questions as follows : -

1.Its good advice from the Broseley guy and to go for a thermal store
2. You can control the temperature of the water to the radiators by using a mixing valve.
3. Plastic pipes are fine for the central heating flow and return , however you must start in copper.
4. Yes , you can use 22mm tube - the only difference between french and Uk 22mm is the wall difference ( to bend french 22mm you need to heat it up first).
5. If you are concerned about corrosion to your stove , look into fitting a Laddomat 21 which regulates the return temperature to the wood boiler stove. Or you can fit a pipe thermostat to the gravity flow or return pipe depending upon which stove you fit.

Michael


30 Jun 2010, 21:06
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