My multi-fuel stove history overview



It has been few years since I bought my standard multi-fuel stove. It was providing nice heat in the living room for many months. It was difficult to estimate the efficiency of the stove (meaning the amount of the heat which actually heats up the house), but the amount of the heat escaping through the chimney was greater than I've been able to accept. The stove is located on the ground floor and after and hour of burning of the wood and smokeless coal the brick wall of the chimney on the first floor was getting decently warm (too warm in my feeling). I didn't mind heating up the upper floor as wel,l but it made me wonder how to improve the stove to capture more heat and use it to heat the house more efficiently. After a bit of researching, brainstorming, sketching and designing I came up with the secondary burn air pre-heater. First I build a sample prototype pre-heater from thin 1mm metal sheet, then I re-designed it and created a final version from thicker 2mm plate (picture below).


Afterburner Air Pre-heater


The afterburner gave a significant improvement. Now I could close the bottom air feed door slightly more and as the result more air got sucked in through the secondary air pre-heater creating nice secondary flame. Comparatively, I could see the improvement in the level of generated heat from the same amount of wood. The picture below shows the secondary flames using the first, prototype pre-heater.



The afterburner improved the burning efficiency of the stove but unfortunately my chimney wall was still getting hot. The metal flue connecting the stove with the brick chimney was sizzling hot. I came up with an idea of building an air to water heat exchanger and to distribute the hot water through a central heating system. The heat exchanger was built from 2mm metal sheet and copper pipes and connected to my central heating using a PVC barrier pipe.



Obviously it required a "slight" modification of the central heating system to accommodate another source of the heat and to allow for reliable and safe functioning of the central heating. Now I was able to heat up not only the living room but the whole house as well. The amount of the recovered heat was beyond my words. Everything was working fine but sometimes when I tried to heat up the house using my stove as a side effect I was grossly overheating the living room. The temperature inside reached up to 32 centigrade peak. It was getting way too hot.  Now the challenge was how to heat up the house without the overheating the living room. I observed that the hottest part of the stove was the top plate so I decided to replace it with another 2nd stage heat exchanger (picture below).  I've made the allowance for bigger fume exit but attached an old heat exchanger (for now).


Heat Exchanger


I'd been using above set-up to heat the house for about two years when I decided to replace the first stage heater with the new one with some modifications (picture on the very top). Firstly, it is bigger with the bigger surface area of the copper pipes to extract even more heat. Secondly, the new heat exchanger have two parallel loops of the pipes instead of the one loop. It lets the water to flow with less resistance and makes the water circulations faster. Initial tests (summer 2014) confirmed the better heat transfer in comparison to an old exchanger but for now I have to wait till winter to confirm trial heat ups.