Can I retro-heat water from MF stove?

[rickw]

We have got a multi fuel small stove in our kitchen. How, or can I, heat some hot water via some plumbing to heat other rooms? Any links?

[dhaslam]

Do you know the make and model of the stove,  some stoves can retrofit  small internal  boilers.   

[billi]

here is a (translated ) link to one of the better designed flue heat exchangers

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

Billi

[rickw]

The stove is a 5Kw Sherborne, made by Arrow.

[dhaslam]

There is a boiler available for this stove about 2.5kw output.   

http://www.firesonline.co.uk/acatalog/Aarrow-Sherborne-Large-Multi-fuel-Stove.html

That size boiler won't produce a lot of heat but it would heat one or two radiators.   You would need to fit a header tank  as well as the radiators and   at least one radiator would need to be  fitted without valves  to act as a heat dump.   If you can arrange to have the radiators gravity fed you wouldn't need a pump.   

[energy from earth]

I have just tested a flue gas boiler that I have designed.
I had the boiler built specially after realising that I could not buy a wood fired flue boiler that I could directly regulate the heating of the water.
Wood fired stoves are renowned for boiling the water with little or no way of controlling the heat, therefore the one that I had made was designed to control the heat to the boiler.
When I first installed the boiler to my vented hot water system, I took heat readings with a digital thermometer with a thermocouple pipe reader, this takes a water temperature reading every two seconds and I could therefore test how effective the heat deflector was. It worked perfectly for the open vented system.
Even though I have had to pay for the cad design work and the engineering calculations and fabrication, not including the time I spent sketching designs (usually in the middle of the night) it was a well worth while unique prototype.

[dhaslam]

Any pictures and performance figures.

[energy from earth]

The patent is based on the principal of retrofit boiler that diverts exhaust gas to air or to boiler.
I managed to get an engineer who prepares wood stoves and boilers for CE approval to have a look at this.
He reckoned that the existing boiler would only give out about 3 kw to water, but with a properly designed boiler it could achieve 10kw.
Mark 2 has got (or will have when it arrives) a catalytic combustor.
The flue temperatures with the exhaust valve open where reaching 950 degrees f easily and quickly.
I only needed 500 to get the cat fired up when the valve was turned to boiler mode.
I have been looking at the American market regarding wood stoves, they are light years ahead and we could learn a lot from their strict codes.
I think most of the emission regulations where enforced because of all the neighbours that used to scrap over smoke wandering onto their yard.
I am keen to progress with this idea, when the driving force is not based on money, it is the dream of thinking about a design, doing endless sketches, looking to see if you can save a load of bother and buy it of somebody already, fabricating the design, big day of firing up the stove and testing it out, etc. etc and the ultimate achievment for me would be to see a finished product with MADE in BRITAIN laser cut in bold. What a journey.

[dhaslam]

Looks interesting.   Is the flue gas  diverted  downwards to heat  water and what kind of heat exchanger is used? 

[energy from earth]

The exhaust gases are forced down where they don`t want to go and then back up around the water jacket. This water jacket/heat exchanger is simply a 5mm plate steel box that holds 3 litres of water. This is a picture of the first prototype model. Version 2 has 1 and half inch BSP outlets to take big bore pipework, certainly for the flow, i`m thinking 35mm copper. This is why its only giving out 3kw. It needs the input from someone who knows about boilers to increase the power.

[dhaslam]

The surface area of the heat exchanger is important.   Too large and the gases cool  too much and draught  is reduced.  Too small and you don't get the heat output.   My stove in the last house had about  40sq' of boiler surface  and had an output of about 30kw.  Present stove only has something like  4sq' of boiler surface and outputs a miserable  3kw.    The firebox in the newer stove is about half of the size of the other one.   I think you need to be looking at  something like 10sq' of surface area  but ideally  with a way of adjusting the length of the  path according to flue temperature.   When you are dealing with a continuous water jacket this is  not an easy piece of construction.   

[energy from earth]

I suppose a cast iron boiler recycled from another system would be the best way to test it out.
How far can you send exhaust gases downward without using forced air?
I am hoping that when the CAT is installed, the temperatures are going to be a lot higher and this along with a revised boiler area should reach the required target kw.

[billi]

Nice one  have an applaud

I am thinking the same route  , but fair play  you are not only thinking 

http://www.navitron.org.uk/forum/index.php/topic,9074.0.html

Perhaps this design is quite clever (bad google translation)  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

Still tempted to get it  have a quote 

But again nothing beats homebrew ideas

Billi

[energy from earth]

Thanks for the vote of confidence,
Just like the flue boiler that charnwood have developed, the German ones aswell need quite a lot of height above the top of the stove to fit them in. If you notice they are all top mounted. When I spoke to the designer from Charnwood, he said that the boiler held 14 litres of water and made it heavy and it was still only producing about 3kw.
My main concern when designing this was not how much heat I could produce, it was how much heat can I divert from the boiler either because I didnt need it or to enable me to fire the stove up to at least 900 deg f before sending it down to the CAT and boiler.
My design can either be top or rear flue mounted, with or without boiler, with cat or not, totally dismantled for cleaning and inspection, basically it is everything I wanted from a wood stove boiler, the only problem is that I have had to make it myself, forcing me to be inventive when I didnt really have the time to be. Imagine being paid to be inventive, has anyone got such a job ?

[rickw]

Very nice piece of design, thats exactly the sort of thing I had in mind.