Wood burners... again

[Bannon]

For the past couple of years we've been using a 7kw wood burner in our little annexe and prior to moving over to the 'big house' once renovations are complete.

Wnat we want to do now is install another one - only larger,  plus we wondered if these can be used to run a couple of rads (not water, just rads) using some sort of heat exchange unit. If this is possible a) how is it done and b) what size wood burner in kw would we need?

Thanks Guys.

[LesFlamands]

Depends on the volume you want to heat. The woodburner has the same (roughly) total output if it heating the room or if it is fitted with a back-boiler. The purpose of the backboiler is to heat water for radiators which is a relatively efficient way of  distributing heat around a building.

With a villager stove, for example, the larger models offer an output of 15kW which is usually enough to heat 300 cubic metres (depends on insulation etc.). You have two choices of boiler, one of which is integral and rated at 15kW and therefore could suck all the power from the fire into heating water. In reality this only happens when heating the system from cold or if the system is overrun and has too many rads. for the capacity of the boiler. The second boiler option is a bolt in backboiler rated at 10kW which even in the worst case should leave you 5kW to heat the space in which the stove is sited. Obviously, wood is a somewhat inconsitent fuel and you would be wise to make allowances for this when designing the system.

[Thumper]

I've just finished doing this myself. We bought a woodburner (off eBay, but there you go) and had a backboiler professionally made and fitted. Total cost about £500. It's a relatively simple 10Kw burner with a single front-loader and able to take logs up to about 20". We could have spent anything up to £1000 or more, but this one looked OK for the job. Perhaps with hindsight I might have gone for something a little more sophisticated, but so far it has worked well enough. I've never done this before, so may have made some errors (and am happy to learn if anyone sees glaring mistakes and wants to point them out), but this is what I've since done:

The burner is fitted into a typical French farmhouse-type fireplace, and fills it reasonably well without looking dwarfed. First job was to fit a flue pipe from the burner to the top of the chimney. It won't be seen, and I'm not too worried about heat-loss, so I've gone for the cheaper single-skin aluminium stuff that's available from any bricolage and painted the first section matt-black with heat-resistant paint. Then I fitted a baffle plate into the chimney. I set in a series of angle-iron brackets around the whole rectangle of the chimney, as low down as I could without being visible, and then made my first "plate" out of plywood, faced for the time being with aluminium sheeting - I'll explain later. It's in two pieces, one each side of the flue-liner, with a pair of half-moon cuts that join around the flue. 

From the higher outlet (the hotter one!) of the backboiler I've sent 28mm copper pipework up the chimney to first floor level. I was only looking to run radiators through the first floor bedrooms, so none on the ground floor. It reduces at that point to 22mm, and stays that way from then on. I wanted it to work by gravity, so larger bore pipework was needed. The initial rise is about 3m vertical, and that seems to work well enough. After drilling a hole through the chimney breast in the first-floor bedroom, I've then run copper pipe throughout the top floor via four radiators. The pipework rises by a few degrees all the way, starting close to the floor, and ending up about 15 cms higher at the return point. From this outward (hot) pipe there's a T junction under each rad that leads up into the higher inlet valve of the radiator. Each radiator is also imperceptibly angled so that the hot water continues to rise and the cold sinks, depending on your point of view, to encourage the cycle.

At the end of the line the pipe doubles back on itself, and at this point I've sent off a spur that rises up to a small header tank. The outlet for this comes from the lower (return) pipe, so doesn't attract the hotter water, but maintains the fluid level in the system and allows for expansion. The return pipe runs parallel to the out-pipe, so falls all the way back to the boiler at the same angle. Under each radiator there's a similar arrangement of t-junction pipework to receive the cooling return water from each rad. There are valves on both inlet and outlet sides of every radiator. This return pipe goes back down the chimney (enlarged to 28mm again for the drop) almost parallel with the first one. However, I've included a branch and bypass system here that includes an electric pump. So far I've not actually needed to use it, but the theory is that I can speed up the flow if I ever need to, or "prime" the system when I first light the fire.

I installed this over Christmas and it took about five days. The first time I fired it up I realised my fundamental mistake . . . I'd connected up the pipes the wrong way round to the backboiler, so the return was going into the "out" and vice versa. Even so, the radiators were hot within 20 minutes and almost too hot to touch inside half an hour, and that was on a pure gravity-driven system . . . working the wrong way! I'm optimistic that it will work even better when I get it piped up the right way round. Meanwhile the woodburner does a great job of heating the downstairs all on its own. We soon learned, however, that you have to remember to keep stoking the woodburner towards the back of the chamber, so the main heat of the fire is next to the backboiler. If not the radiators cool quite quickly.

I've soldered most of the joints, but included some compression fittings here and there to make adding more radiators (or making changes/repairs) a little easier. I'm not a plumber, by the way, so you can do it yourself. I was pleased to discover no leaks when I filled it up the first time. I used plain water on that occasion, but once confident that there were no dribbles, replaced that with a corrosion inhibitor and antifreeze, for the times when it's cold and we're not there.

With all the pipework in place I've been able to cut and shut the plywood baffle plate in the chimney so I know I can take it out for access easily enough. I'll now use this as a template for a steel one.

I hope that helps.

[Deimos]

[quote user="Thumper"] and then made my first "plate" out of plywood, faced for the time being with aluminium sheeting - I'll explain later.[/quote]

I have a suspicion that there is a regulation about wood in close proximity to a flue tube (at least the “single non-insulated” flue pipes. Not sure what the distance is but there should be no wood within a certain distance of the flue pipe (couple of cm). Sounds like you are changing the plywood to steel which should get round this – so may be an idea to make this change a.s.a.p.

Ian

[Thumper]

Yes, it is being changed. The plywood version was only temporary while I was installing the stove, and now that I know it works and all the pipework for the radiators is in position, I'm using the wooden version as a template for a steel one. Wood's a lot easier to cut, and not so expensive if you make a mistake!

[Michael]

Thumper you made no mention of a safety valve on your 1920/50s design open vented system.What happens if the f/e tank freezes?{your boiler could be in orbit with a halo.}When you connected the pipe as the cold feed to the f/e tank did you put a tee in and continue up and over for the vent?If not i suggest its done,more correctly run a 15/mm cold feed & 22or20mm vent pipe.Not much confidence in the flue liner lasting long connecting direct to the boiler,think it will burn out rather quickly in the first metre.Good practise is to use a metre of  twin wall or vitro up to the register plate,gives a chance for the heat etc to dissipate.Good luck.Happy days.Michael.

[Thumper]

OK, so I'm an old-fashioned kind'a guy, but it was cheap, simple to install, has no moving parts, and virtually maintenance-free. You're right, I didn't mention the safety valve, but there is a pressure-relief valve fitted to the expansion tank. It's highly unlikely it's going to freeze with the concentration of anti-freeze and corrosion inhibitor I've used to fill the system - not unless it gets down to about 30 below. I'll take on board your suggestion about the twin-wall first metre - it would probably look better too.

[The Builder.]

Hello Thumper, I appreciate that you're an old fashioned kind'a guy and admire your invention but I think it's important just to point out to other readers thinking of copying in any way that your installation is completely unsafe.

Regulations are in force for the sole reason of keeping people alive and the DIY approach to heating installation will invalidate any insurance you may have and endanger yourself and others.

Please do not use this system until you have respected the normes.

[painterman]

Hi, although we haven't yet managed to complete on our french home yet (epic 8 month wait so far) we have been looking into wood burning stoves. We used to have a stove called a 'much wenlock' which was a multi-fuel stove- it was pretty good for us. We'd have another definately except that its a multi-fuel stove and the fire shops we've been looking into have had staff who have told us that we would be better off buying a stove that is just for wood, not wood and coal because of their design and efficiency testing which is done on beech and ash wood. We were told that to calculate how many Kw of heat we'd need for a room we'd need to do this calculation:

Kw = H x W x D and divide this by 14

So Kw = Height  x  Width x  Depth of room divided by 14 (so basically the volume of the room divided by 14) This can then be compared to the literature the shops/ technicians give you either over the phone or in person. Also if you needed to know how many BTU's this is the equivalent of then times your answer by 3400.

(eg: BTU's = (H x W x D divide by 14) and then multiply  by 3400 )

This should help you to work out what size in Kw or BTU's you need for your room sizes.

We've been looking into the Herald range of stoves from one of many suppliers we've been looking at, and we are still looking so can't and won't say if any are better than others because at this point we don't know and so you'd need to have a look on the internet too, but, when I rang the supplier they told me that when you choose to have a boiler option fitted for hot water and radiators that  the wrap around boiler option which is welded into the wood burning stove of their 12-16Kw model when they are made, gave out 45,000 BTU's, and that the 12-16Kw average equated to 3Kw room heat and 13Kw boiler for water (10 radiators) , but in comparison the clip in style boiler that you can buy and fit later only gave out 24,000 BTU's which is shared as 9Kw for room heating and 7Kw for the water. They told us ( at various shops) to be aware of the dimensions of the rooms that the fire would be sited in because too high a heat output might occur in a room if we were trying to heat alot of radiators making the room the fire was in too warm to be in comfortably but that if we tried to turn this fire down too low to make it comfortable in that room that the radiators in the other rooms may not get as warm as we would like (looking at the 10 radiator option). We are therefore thinking things through very slowly and taking the time to check it out as one stove can cost the best part of £900 plus all the other bits we're finding that have to be added on that don't come as standard. Also there is a minimum flue height of 4.5m but this is for British building regulations we are told. If anyone knows what the French miminum height for building regs for wood burning stove flues is then we'd like to know please too because it would help in the plans of our heating system..... when the house is eventually ours......

Hope this answers your question a bit/helps.

From Painterman and wife. 

 

[chenauds]

I originally had the same plan as Thumper and I brought over a large "Villager" with back burner which I ran for nearly 2 years as the sole form of heating without initially plumbing in to a CH system. I eventually decided that I would keep the woodburner as the main heat source for the largest room and back up with oil fired to give background heat for the rest of the house. I'm no plumber but having brought all the requisite piping, pump, thermostats and radiators from the UK I decided to go for it. I started lugging the rads. into place last May and slowly step by step started the installation of the 14/22mm 2 pipe system fed  remotely from the mains by a header tank. It was done this way so that the water, not being under mains pressure meant that I could use basic solder joints without having to braze. The system was up and running by September, I took my time in sourcing an efficient but inexpensive boiler/burner  of about 36KW output and managed to get the fuel tank gratis. On starting up I had only one soldered joint leak out of over 120 and two compression joint leaks in both of which cases, I had managed to leave out one of the olives? It has proved a resounding success.

On reflection, The good old "Villager" would have struggled to raise the entire house base level temperature to the level and with the controllability that the CH has done.

[virginia.c]

You seem to know what you are talking about as regards burners so I thought I'd hit you with an unrelated but sort of relevant question.  I am thinking of buying a property in the Dordogne which has been renovated and holiday let since 2001.  It has electric radiators in all rooms and the water is electric heated also.  Haven't got the brand name of the radiators yet but they look like trendy lozenges on the walls with fine mesh over.  The agent has the same ones in his office and tells us that the cost of electric heating (winter only hopefully) is comparable these days to buying oil or gas in France.  On principle not believing a word he says, is this utter rubbish?

There is somesort of of woodburner in the living room and an open chimney in the kitchen which we'd keep stoked up.  We can't afford to put a new boiler and rads in for some time.  We believe the house to be well insulated but there is no double glazing.

If you don't know the answers to my questions yourself - do you know anyone who might????

Desperately hoping for some feedback!

[Dick Smith]

He is probably telling you the truth. There is another thread on this topic open and running at the moment.

[Deimos]

Probably depends if you are on the gas supply or have a tank in the garden. People say a tank in the garden is comparable per kw to electricity (I have a tank in the garden but have not switched the boiler to electric for comparison - as so much depends on weather, etc.)

I think that on the gas supply gas is somewhat cheaper - but no personal experience.

Ian

[virginia.c]

How do I find this other "thread"?  I'm a relative novice to the Forum and am finding it tricky to navigate.  Doesn't help that I'm a luddite also!

 

many thanks

[Tresco]

Could it be this one?

http://www.completefrance.com/cs/forums/835650/ShowPost.aspx

Found by putting 'electric' into the little 'seach' box, top right of the screen. It's not a very good search function, but I hope the other thread helps you.

[Tresco]

Could it be this one?

http://www.completefrance.com/cs/forums/835650/ShowPost.aspx

Found by putting 'electric' into the little 'seach' box, top right of the screen. It's not a very good search function, but I hope the other thread helps you.

[Teamedup]

Due to problems with some pipework, we have lit our wood burner again after many many years of not using it. It is a Turbo Fonte and we bought it with the ability to heat radiators, the only one we found on the market at the time.

We have been discussing this foyer fermé of ours and truthfully we do not know of anyone else with a wood burning fire that heats as well as this does. I am in fact sick and fed up of people telling me how 'hot' their homes get with theirs, but strangely when I am chez eux, I need to keep a jumper or whatever on.

I have no idea if a quarter of a century on Turbo Fonte's wood burners are still as good, I would hope that they are. All I can say is  ours is wonderful, but don't go for one if you actually like being in a cold home, it would seem that lots of people do.

[powerdesal]

TD,

I would love to have more details of a turbofonte wood burning boiler, I googled their name but didn't really get much joy. Any chance?

Regards

ps. I hate cold homes, my body is not designed for it.  [:)]

[Tresco]

Here's the English version of their site.

http://www.turbofonte.com/english/presenteng.htm

[powerdesal]

Thats the one I found, doesn't tell you a great deal does it?

[Tresco]

No Steve, the site isn't the best I've seen.

I bet they'd send you a catalogue if you contact them though.

[ben]

Dear Thumper,

I read your account of installing a wood fired central heating system, from a year ago, and resolved to do the same myself. Can you please say a bit more about how your header tank works?  Your interlocutor said that you should fear a frozen tank, but you replied that this is not a worry since, you system is filled with plenty of antifreeze and inhibitor.  But isn't the header fed by mains water?  My plumbing experience is limtied to changing the radiator route on a combi fired system, so I probably need a short explanation of how the header works. Can you help out in a a few lines ?  Thanks ! 

PS - I plan to do upstairs and downstairs, about eight medium sized radiators (averaging between some small and some big), run from a 15 KW villager wood stove.  Any of your thoughts will be appreciated.

Yours, Ben Hooson

   

[Thumper]

Hi Ben. I'd almost forgotten about this thread! Every once in a while things come back to haunt you, I guess . . .

For those who besmirched my efforts all those months ago, the system is working fine. It's been inspected, and passed as safe, and I'm gearing myself up soon to extending it by another rad. As for the header tank - no, it's a completely sealed system, so no mains water. The antifreeze/inhibitor solution goes round all by itself, and the header tank merely holds enough fluid/air to compensate for expansion and contraction during heating and cooling. I've only had to top it up once. It works very like the header tank in a car cooling system, with a screw-on top that incorporates a pressure relief valve.

As I originally suspected, the electric pump is needed from time to time, especially to get the circulation going strongly in the first instance. Once it's up to temperature, it seems to circulate well enough unaided. If you're going to include downstairs radiators as well, then I'd imagine a pump would be essential. I know we were all told at school that "hot air rises", but my (perhaps limited) understanding of water is that it's the "weight" of the cooler water coming down through the system that forces the hotter water back up, and that a good height into the system encourages a faster circulation.

I hope that helps. Now I await a renewed tirade from those with plumbing degrees and shares in Elfin Safety.

[ben]

Thumper,

Thanks for your response. I get it. I suppose the pressure valve is set to blow at three bars or thereabouts...  but, initially, did you work out the suitabe liquid level in the header tank (determining cold pressure in the system) by trial and error, firing up the stove and seeing how high the pressure gauge went before it stabilized... ?  

Ben