Hi , I use olive-wood logs on my box fire in the winter . We had a small box fire which was fitted into a 15cm stainless steel flue , but we decided to change the fire for a much more powerful one that would heat 3 rooms .Its flue was 20 cms diameter , but we were assured that if we raised the height of the stack we would be fine .It works fine except on windless days - when you want to recharge the fire ,when its running low but still with some smoking wood on it - you open the door slowly , but at the last instant it coughs a little smoke into the room .Woodsmoke in the house stinks , and neighbours say if they run a kitchen fan , their fire coughs too .I am unable to do anything about the stack because it is stone built and carries another flue from the diesel boiler .My solution? and electric fan assist ,remotely controlled , which generates a high negative pressure on the flue gasses , and speeds up the chimney draught immensely.I made the whole thing for about 100 Euros , £75 English.Its useful too on windless days when the fire just will not burn up ,and also when de-ashing the grate ,the fine powder is sucked straight up the chimney
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Step 1: The Theory of Chimney Fans and Parts Required
The beauty of this idea , which you can find on the internet is the fan is always in the cool clean air , it never gets fouled up with tar and flue gasses , and the chimney is easy to rod out,either from the top or from the bottom with no obstruction to the cleaning brush .
You will need to buy
1. an appropriate size stainless tube with a 45 degree branch in it
2. odd pieces of stainless sheet
3. A small boiler fan
4 some power cable
5 a radio remote with 12/24v power supply mine came from www.quasaruk.co.uk or Maplins UK also stock these "radio remote controls"
Step 2: Your Parts and How to Assemble Them
Here you can see the stainless section with a branch arm , in my case it is 20cm diameter both main and branch.
you first need to cut with tinsnips or similar,a disc which mounts the motor and seals the branch .Dont worry if its a little gappy on the sides , a tube of high temperature silicon is run around the edge to seal the gaps.
You can then place the motor in its housing .for all of this metalwork I used small pop rivets which give a pleasing look , and make the shroud over the motor easy to work .
Step 3: Adding the Shroud for the Motor and the Remote Control
Work from the top of the branch leg, aiming to completely clad the motor top , to stop rain driving into the motor windings . you also need a 3 pin waterproof cable joiner to tuck up underneath this shroud , and a decent length of cable to get down to a nearby external mains socket. If you purchase a radio remote control to turn the fan on and off ,simply follow the directions on how to wire this up , it has a 12 or 24 v d.c. supply and can switch upto 5amps, and the range isup to 70 metres in air , but I am using it thru ferro-concrete walls and a floor and it still operates the fan without fail .at about 20 metres .
Step 4: Wiring the Motor to the Remote
The radio remote will close a loop on 2 wires, switching the live line to the motor , one press switches the fan on , the next press will switch it off .