simple heat exchanger ideas for wood stove flue pipe

[billi]

Hello

If i put flexible stainless pipe in my stove  flue (its 5 meters long ) in one loop so 10 meter pipe , get a temp sensor for the pipe coming out , a circulating pump and an expansion vessel and run a big radiator direct .

Is this a good or a bad idea ? Too dangerous perhaps ? Or should i run it as a open system ? I can place a pot of water on the stove-top and stick the two pipe ends in and then i assume i would not need an expansion vessel

Could i use copper with the stove flues or is the smoke too aggressive ?

Please advice and tell me that i am nuts

Billi

[Ted]

Reducing the temperature of the flue may cause problems with condensate and reducing the draw.

Can you wrap pipe around the outside of the flue rather than put it inside?

[dhaslam]

There is a boiler already available for  flues, might be a neater solution.   

www.charnwood.com/charnwood-flue-boiler.asp

[billi]

Thanks Ted  

attach it in the room around the outside flue is an option too , or try to keep the temp of the water higher then 55°

Dhaslam thanks  i know these and an option too had this one  in mind http://translate.google.com/translate?js=y&prev=_t&hl=en&ie=UTF-8&u=http%3A%2F%2Fwww.bab-gallon.de%2Fprodukte.php&sl=de&tl=en

i thought about experimenting first   before paying 400 euro for the heat exchanger only without the rest of the gear i need    ( My stove was only 120 euro new   but works good

Billi

[lightfoot]

Go for it Billi - extracting the heat post-burn/in the flue-way has it's advantages - being one of the principles of most high efficiency gasifying wood boilers.  I dare say you know all this already, but like Ted said - as with any wood boiler set-up - you would need to take measures to avoid extracting too much heat/excessively cooling the flue gases etc, and make sure the rest of the flue is well insulated and tall enough etc (some boilers rely on a fan).  I'm sure you could cobble something together - it may take a little experimenting to come up with the ideal set-up, but it's not rocket science.  A sealed system has it's advantages and doable with the right controls etc, but it may raise a few eyebrows - so I think a small pumped, open vented circuit (with a suitable F&E tank) might be the easiest/safest way to go for a home-brew project.


Good luck,

LF.


PS, I've just had a quick look at those German heat exchangers - they do look quite nifty and well thought out, but as you say, they're a little spendy!

[Ivan]

Billi,

I'd go for the stainless steel. Someone posted on the forum in the last week, that he found copper pipe failed within a short period, presumably due to gas corrosion. I've heard that copper wrapped around a flue pipe isn't very effective due to poor surface area of contact.

I'm not 100% certain, but my view is that you should either:

i) Let the gases come out of the top of the chimney at >250C
 
or

ii)Make sure the gases go into the chimney at <250C.


So the creosote forms either in the stove(ii), or not until it exits the chimney(i).

Woodboilers and pellet burners have very low exhaust temperatures for this purpose, and of course are much more efficient.

PS Not sure of the exact temperature. My guess is 250C, but it could be lower.

[billi]

thanks again all

i am just trying to find a solution for this winter , cause our new extension has no direct heater ( whole house has only a 5 kw woodburner  and no radiators ) and the new built extension  is not drying  out enough now in our climate ( my clay plaster needs fresh air , but us warmth  )

have to find a supplier for that flexible stainless   pipe here in Ireland then , or in Navitron ?

Why i always want to  reinvent the wheel  ?

Billi

[TwoHorsePower]

Billi - did you ever get your hands on flexible stainless to test the flue pipe heat exchanger?

I was thinking of doing likewise to my stove & ordering some DN12 stainless flexible from France (with half inch BSP females) if you want some - I'm in Northern Ireland

[billi]

THP

Dreaming Billi did not much  more, than dreaming this winter  about better heating
All i did was drilling a 12mm hole trough my flue pipe  and stickied  a metal  rod  through to find out how fast and hot the ends get = she nearly kicked me out 

But thanks for the offer  , i will think of it again

I think in my next live i open an online Hardware shop in Ireland 

Why france ?

Billi

[rogeriko]

In my experience here in Greece where we do not have any chimney regulations the heat created by the chimney is more than the fire. All those English woodstoves going directly into a double flue pipe and into the old sealed chimney are grossly inefficient. I think that a 5 kw fire will produce another 5 kw from the chimney if that heat is captured. Every house in Greece has a long single wall flue pipe curling around the rooms to capture this heat, my house has 8 meters indoors going up stairs and around 2 rooms before going outside and the heat gained is intense.

In my old house I put a large turbine fan to blow air down the existing chimney around the woodstove metal flue to capture this heat. The fan drew air from an upstairs bedroom and blew it back down into the living room and i measured air temperatures of over 80 degrees dont forget these chimneys glow red hot when there is a good fire roaring.

My current set up will heat 400 litres of water to 70 degrees in about 2 hours using pallet wood and heat captured from the chimney see photo

[TwoHorsePower]

Billi - I couldn't find a supplier of DN12 stainless here, hence France. Do you know someone who supplies this stuff in Ireland? I can only find DN16 suppliers locally. Thanks

[billi]

 i only checked germany  and  some ready made heatexchangers  that could fit in the flue pipe

that stainless  pipe  has its price  about 3 Euro a meter

Billi 

[Brandon]

In my experience here in Greece where we do not have any chimney regulations the heat created by the chimney is more than the fire. All those English woodstoves going directly into a double flue pipe and into the old sealed chimney are grossly inefficient. I think that a 5 kw fire will produce another 5 kw from the chimney if that heat is captured. Every house in Greece has a long single wall flue pipe curling around the rooms to capture this heat, my house has 8 meters indoors going up stairs and around 2 rooms before going outside and the heat gained is intense.

In my old house I put a large turbine fan to blow air down the existing chimney around the woodstove metal flue to capture this heat. The fan drew air from an upstairs bedroom and blew it back down into the living room and i measured air temperatures of over 80 degrees dont forget these chimneys glow red hot when there is a good fire roaring.

My current set up will heat 400 litres of water to 70 degrees in about 2 hours using pallet wood and heat captured from the chimney see photo

Rogeriko, I love that stove set up, glad to hear it works well, hows the innards of your flue looking? if nice and clean then that would certainly back up Ivans theory.

Looks like the the beginnings of a possible home brew gassifying boiler there...

[Chanireland]

Well what about the Cola can solar heater or faster roof sheeting style heatar with fan would give heat and Air circulation changes as days are longer now might dry it by summer. also i presume like with lime slow drying is probably less likely to cause cracks not sure with cob but def with lime...maby check the humidity levels, also think winter in Ireland have  humidity levels of 90% in winter and 70>80% in summer.
http://en.wikipedia.org/wiki/Cork_(city)#Climate

Damp Damp Damp 

[billi]

a few month gone past  and winter is here again .....

So same thoughts  come to my mind

A question i have is : "Does thermosyphoning (spelt it wrong ) needs 2 pipes " ? 

Or to explain  my brain   

I have 3 metres double walled insulated flue pipe and 3 metres normal pipe  from the stove to the roof , if i stick 7 metres  of finned flexible stainless steel 2 inch tube in , through the centre of the flue pipe  and seal the end that sticks into the flue pipe, connect that pipe to an insulated open   header tank  on top of the roof / flue pipe  and then run  the heating with a pump controlled by a  temp sensor  from this tank ....

Or do i need two pipes connected to the header tank to make thermosyphon happening ? 

Do you get me 

Thanks Billi