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Wade

A practical cold smoker flue fan

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When you are cold smoking it is important to ensure that there is a good flow of air and smoke passing through the smoking chamber and over the food. In traditional smokeries this was/is achieved by placing the food inside a chimney and letting heat convection and the natural chimney draw maintain a good air flow. In modern smokeries this is achieved through the use of fans.

Using a fan on your smoker at home also makes it practical to locate your smoker in a protected shed or garage environment and have the smoke extracted to the outside.

Why is it important to ensure that the air keeps moving through the smoking chamber?

  • It helps to prevent the build-up of the heavier smoke tars on the food.
  • The increased air flow helps with the removal of water from the food. This is important when making traditional smoked salmon in conjunction with smoking at temperatures of between 20-24 C.
  • If the cold smoke generator finishes unexpectedly it ensures that air continues to flow through the smoking chamber preventing the build-up of condensation on the food and on the inside of the chamber walls - which can then drip onto the food. The build up of moisture is the main cause of some home smoked foods developing a "musty" smell and taste.
  • The flow of air also helps to ensure that the cold smoke generator continues to burn - especially when smoking in the winter and the nights are cooler. This is a balance though as too great a flow of air can result in the smoke generator flaring up and burning with a flame rather than smouldering.

Why place the fan in the flue?

By placing the fan above the large buffering volume of the smoking chamber it helps to maintain a gentle, steadier air flow through the smoker and prevents "gusting" across the cold smoke generator - which can result in it flaring up. In many multi-purpose smokers it is also often easier to attach a fan to the top of the unit than it would be to attach it to the bottom.

Placing the fan in the flue does have the disadvantage that the exhaust tars do pass through the blades of the fan and over time will deposit there. Although it is reasonably easy to clean the fan blades after each use when used infrequently, if the smoker is in constant use the tars do build up and eventually the fan will fail. In my commercial smoker I leave the flue fan running permanently 24x7 and expect to replace the fan every 6 months. With the low cost of the fans (~ £10 each) this rate of replacement is an acceptable running cost of the smoker. For low volume smokers you would expect the life of the fan to be several years.

Which type of fan?

It is important that the air is kept flowing, however it needs to be a gentle flow and so the use of a low speed fan is very important. This makes a variable speed large diameter computer case cooling fan ideal. They are readily available, are inexpensive and have standard fittings so are interchangeable. When first setting up my cold smoker i used a fully variable speed fan - the Silverstone FM121 however these are now no longer available in the UK. In the photos below you will see this fan being used.

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I have now moved to the Antec TrueQuiet 120, however most 120 mm fans that can be set to a fan speed of ~600 rpm would be fine.

529429317_AntecTrueQuiet120.jpg.ed3527465abc4ca11d15ce960d2cc872.jpg

An advantage of moving to the Antec fan was that the wiring was much simpler - just the + and - 12v DC power leads. The fan speed is controlled through a simple built in switch on the fan. Almost any 12 volt power supply can be used - I use a charger from an old discarded laptop.

Mounting the fan

In order to make the best use of readily available DIY components for the air management, the fan is easily mounted using standard 100 mm air ducting components. The fan module is made by adapting a Manrose ducting connector (available from B&Q

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With a sharp craft knife simply remove the "flat" adaptor side of the  connector and then remove the plastic from the round opening. Drill holes for fixing bolts in each corner of flat plate in line with the mounting holes on the fan.

1942008292_Manroseconnectoradapted.thumb.jpg.6ce891c4fe142c4044d9622877291bcb.jpg

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Repeat with a second adaptor and sandwich the fan between the two plates to make a fan "module". This can then be inserted in-line using any standard 100 mm off-the-shelf ducting components.

113851172_FanModuleinplace.thumb.jpg.d91f93edf65d3726af0756b703414bb2.jpg

** Note the complex wiring on this Silverstone fan. With the newer Antec fan you only have the two power leads.

In my smokery I have the smoke ducting to the outside

1278380362_Extracterfan2.thumb.jpg.68dc7d253b84fb5d1c9c8028787d83b5.jpg

If you do not need to duct the smoke away from the smoker you can simply slot the fan "module" directly into a 100 mm round hole cut into the top of your smoker. 

The fan can also be used with Kettle and Bullet smokers without needing to make any modifications to the smoker. Here the secret is Blu Tac - used to keep the fan in place over the top air vent.

291277149_KettleFan.thumb.jpg.299799fa3d1893069a70ae3725b0aba5.jpg430837173_KettleFan1.thumb.jpg.d2a2e4106d94821e0f38557a5f3d89d2.jpg

In order to maximise the life of your fan it is also a good idea to seal the cables leading to the fan motor with a little silicone sealant before the fan is bolted into the "module". Standard kitchen/bathroom sealant is fine for this.

1966710076_Fanrequiressealing.thumb.jpg.009c9e7089717687b97134d70ea0784c.jpg

 

 

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That is terrific. What cubic capacity is your smoking chamber as I imagine fan extraction rate must be related to this? 

In my metal box smoker the door is a vertical sliding unit and the smoke billows out either side, so I have now managed to pull this door forwards to almost stop escape of smoke. This smoker bought on eBay looked so good but it had so many design faults I wish I had built my own.

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Great write up Wade. Not sure I need this on a cardboard pro smoke smoker as smoke moves up fine but easy enough to set up  as a mod. I will see how results go and then consider if mod required.   Still too warm here to do cold smoke.

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At 600 rpm the fan will move 21.5 cubic feet/minute (608 Litres per minute). My smoker volume is 650 litres. For smaller volume smokers the air flow can be reduced further by either using a slower speed fan or by restricting the area of the pipe before or after it hits the fan. In the past I have used a pipe size reducer. Alternatively you can extend the pipe as it comes out of the top of the smoker with some 100 mm round ducting and drill some holes in the side. The holes will allow some air in a so reduce the volume of air passing through the smoking chamber.

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Maybe a small slow fan will be a good enhancements for the pro q box. Will investigate.

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With the smaller cardboard box smokers I am not sure that fan assistance would be much of a benefit, however if you want to try it I will be very interested in the results.

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for the future once i get the box working more regularly, when it gets cooler. At the mo I am getting electric fitted to garage then cold storage in garage will be sorted and a light, I have made the space.  Actually I might fit a tube to take the smoke  out the garage and let the smoker work there, At least there is no chance it will get wet there.  A small  fan will help there of course

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Ah my smoker is only about 72 litres, so a much smaller fan could be needed or quite a lot of restriction.  I have now using draught excluder , ply and a bit of ingenuity cured about 75% of the smoke escapement but it is too Heath Robinson  for my liking. A totally new door on the front will be needed. I think I will start a thread on the perils of buying (some) smokers on eBay....looks good but leak smoke like a colander. No good instructions at all and in my experience either no meaningful or no correspondence at all to questions. I will not definitively  identify the product for obvious legal reasons.....see my photo!!

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8 minutes ago, Ruedeleglise said:

my smoker is only about 72 litres

The computer fans come in a range of sizes - This 40 mm one gives a flow rate of 4.1 cubic feet per minute (113 litres per minute) at full speed (12 v) and you can probably make a simple adaptor to connect it to the top of your existing flue. If you run it at, say, 7.5 v you could probably reduce the air flow further.

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20 minutes ago, Wade said:

The computer fans come in a range of sizes - This 40 mm one gives a flow rate of 4.1 cubic feet per minute (113 litres per minute) at full speed (12 v) and you can probably make a simple adaptor to connect it to the top of your existing flue. If you run it at, say, 7.5 v you could probably reduce the air flow further.

Good advice. I will put my mind to that and the new door once I am back in the uk. Ah yes...thanks for the advice on the book. Got it in 12 hrs through Amazon. What a great read and so much advice.

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What a fantastic read Wade thank you so much...what about using a potentiometer...I use one on a element in my boiler works a treat.  On a 12v system it would be ok, you just dial in the speed you want.

https://m.ebay.co.uk/itm/1K-1M-ohm-Lin-Linear-Log-Logarithmic-Mono-Stereo-Pot-Potentiometer-Or-Knobs/170703080727?hash=item27beb24d17%3Am%3Am8lVZ4hvJCHBNbD1RCYU0PQ&var=470042112676

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16 minutes ago, Icefever said:

what about using a potentiometer...

Yes that should work.

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16 minutes ago, Justin said:

how does it connect to the fan.  

It would connect is series with the fan. You would have to pick the right size potentiometer though or it may not work. Yes it should still work with batteries.

Here is an interesting thread that helps explain how it all fits together.

https://electronics.stackexchange.com/questions/231947/why-cant-i-vary-the-speed-of-a-dc-motor-with-only-a-potentiometer

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series? the battery is fixed voltage and voltage drop in series will be more considerable, as sort of on off rather than variable?  Super low voltage fan if you have a smaller smoker will be a good idea , that will give you more fine control on the fan when using battery 

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