A site for some of my micro generation projects!

I should add, this site is not complete, and will be added to on an ad hock basis as and when I have time

Wood Burning Stove - Flue Heat Recovery

  • Contact Me
  • Home
  • As usual, click an image for a larger view (but not all).

    Our wood burner does not have a back boiler as the hot water tank is the other end of the house, however when we gutted the living room to add loads of wall insulation, this gave me the chance to run a pair of 28mm copper pipes from the fire place/alcove to the other end of the house where the hot water tank was sited.

    Its always worried me what heat I could be losing up the flue, which is lost without any gain. I had thought of various methods of heat recovery from the flue, however the easiest method I thought was to wrap the exposed bit of flue in copper pipe before it goes up the insulated chimney stack.

    Okay not the best of photos, but you'll get the idea/principle of what I did.

    Wrapping the pipe as tight as possible, and using large Jubilee/pipe clips to hold the pipe in position while we try and strangle it in to position.

    Three runs of pipe now in position ready to join the ends in to some three in to one manifolds.

    A good thick layer of fibre glass insulation held in place with MIG welding wire before being covered with a sheet of aluminium.

    Covering in place, job done, though it looks neater in the flesh.

    Finished job read to fill the sides up with wood.

    What's the box on top I hear you say... That's what wifey calls the 'spud box'! The WBS has hot plates for cooking, so over the one I made a bottomless steel box with a top opening lid where we cook bakes spuds, bread & butter puddings and so on :o)


    Before I added my heat recovery system I bought a cheap temperature reading gun (contact-less with the red laser beam) and did a few rough readings and was quite surprised how little heat seemed to be going up the flue as the front of the WBS seemed to be around 200C where as the flue was only around 50C.

    I've only been running the system for a week or so, so no extensive figures etc. Due to the length of pipe runs (approx 10 metres with an overall rise of about 1.5 metres) the flow of heat along the pipes was painfully slow with almost no heat getting to the hot water tank, though the pipe at the flue was quite hot at around 45C. Also I wasn't sure if I had any air locks due to the small rise in the pipes, so I added a small pump in the return pipe to the flue, this did get rid of some air and there is heat getting to the tank. As mentioned earlier there seems to be little waste heat in the flue, so wasn't expecting huge gains, but the hot water tank seems to gain around 1.5c per hour, so with the stove going most of the day it should help keep the water heating costs down.