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Eco fan for top of woodburning stove

Started by Peter Wells

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  • #990725

     
    Peter WellsPeter Wells
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    A steel framed fan is placed on top of a wood burning stove and according to a Canadian University study, saves up to 18% of fuel. It does it by better distributing the heat around a room thus leading the owner to regulate the ‘burn’ better. 

    A blurb from Google reads. “The Ecofan generates its own electricity through the difference in temperature. The base must make contact with a heat source of at least 85C (150F) and the top of the fan must remain cool. The Ecofan needs to draw cooler air from behind in order to operate. The actual rotation of the blade as well as the cooler air and the heat source are the essential elements needed for the Ecofan to operate.”

    I bought one a year ago for my daughter’s wood burning stove and decided the other day to buy one for my own stove.

    Has anyone else tried them?

    #990726

     
    mursalmursal
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    Peter Wells

    The Ecofan generates its own electricity through the difference in temperature

    No Peter not yet, but really interested if it generates electricity for the fan motor? 

    Expensive? 

  • #990727

     
    Peter WellsPeter Wells
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    mursal

    really interested if it generates electricity for the fan motor?

     Mursal.

    The quotation below is the nearest I have got to an explanation as to how the Eco Fan works without batteries or connection to the mains. It is silent in operation and the blades spin so fast you cannot see the movement. It shifts a lot of air (without you feeling it) to the back of the room and so the Inglenook is not a ‘sink’ for the heat from the wood burner.

    “As you read this page, your computer is using a Peltier chip to cool its central processor unit. In this scenario, electricity is put into the chip to create a hot side & a cool side, and the cool side is attached to the CPU. An EcoFan does the reverse – using a hot & cool side of a Peltier chip to generate electricity & run the fan motor.

    The Eco fan  features an attractive black brushed aluminum finish, with lightweight brass, nickel blades or black painted blades.”. Made in Canada!  “

    I have an all black one as I didn’t want a silver or gold coloured disc whizzing around on top of the burner. I paid 95 inclusive of everything and hope to save that in the effort I need to put in to prepare the wood, including chainsaw, splitting, tractor time etc.

    #990728

     
    mursalmursal
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     Thanks Peter very interesting, I haven’t come across this system before.

    Sounds like free energy (to run the motor), but I must be missing something

    #990729

     
    JacobusJacobus
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    mursal

    Sounds like free energy (to run the motor), but I must be missing something

    It’s a thermopile (several thermocouples wired together).  If you google ‘thermopile’ you won’t get much but ‘thermoelectric generator’ will give you more.

    #990730

     
    henararhenarar
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    mursal

     Thanks Peter very interesting, I haven’t come across this system before.

    Sounds like free energy (to run the motor), but I must be missing something

    You don’t get free energy it must come for somewhere it must be using some of the heat from the wood burner to run the fan therefore the wood burner will give out less heat

     

    #990731

     
    2658336
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    henarar

    [quote user="mursal"]

     Thanks Peter very interesting, I haven’t come across this system before.

    Sounds like free energy (to run the motor), but I must be missing something

    You don’t get free energy it must come for somewhere it must be using some of the heat from the wood burner to run the fan therefore the wood burner will give out less heat

    [/quote] 

    Absolutely right, or almost.   The thermo-electric generator does absorb energy and turn it into electricity to turn the fan, but the electric energy all gets dissipated as heat again, so there’s no nett loss.  The whole point of the fan is to blow air across the stove, and therefore put more heat into the room for a given stove skin temperature, which means you get a bit more useful energy per unit fuel consumed.

    The word “thermopile” is usually reserved for arrays of metal thermocouples, most likely chromel-alumel types which will give about 10 millivolts with the cold side at 0C and the hot side at 50C.  You used to be able to buy cylindrical mounted stacks of these things in the US, designed for running a small electric motor to power a boat for fishing.  I think they were mostly gas fired, but I suppose in principle you could have used a small fire of sticks or something.  You’d certainly need a thousand or more separate thermocouples.

    The things on the ECO fan are slightly different in that they employ a semiconductor junction made of something horrible (to a semiconductor engineer such as myself)  like bismuth telluride rather than two metals.  The details of the physics are just a little different, but you get something over 100 millivolts for a 50C drop, so a lot less junctions are needed.  Identical devices are used in cold boxes for the car and suchlike.

    Are they worth while?  Quite possibly for a wood burning stove without water jacket, although if the latter does apply and radiators are run, I doubt it.

    Just in case anyone considered it, NEVER eat bismuth telluride: it’ll give you the most dreadful indigestion, possibly fatal.

    #990732

     
    Peter WellsPeter Wells
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    2658336

    Are they worth while?  Quite possibly for a wood burning stove without water jacket, although if the latter does apply and radiators are run, I doubt it.

    My wood burner is in an ingle nook and has no connections to water or radiators. Under those conditions I am glad you think the Fan useful.

    I think the point of henarar  “You don’t get free energy it must come for somewhere it must be using some of the heat from the wood burner to run the fan therefore the wood burner will give out less heat” is almost correct however, as 265………  implies, under the conditions specified, the wood burner doesn’t produce less heat, rather the heat produced is dissipated more effectively to where it is needed.  ‘Interestingly. the fan must be sited at the rear of the burner so that the relatively cooler air coming up from the back of the burner can be used as a contrast to the temperature of the base of the fan which is sitting on top of the burner itself. A difference of around c 150c.

     

    #990733

     
    mursalmursal
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    Thanks everyone for the information

    Note to self:

    Well that’s that knocked on the head ……….. [:^)]

    #990734

     
    Peter WellsPeter Wells
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    mursal

    Well that’s that knocked on the head ……….. Huh? 

    Why. What where you thinking?

     

    #990735

     
    mursalmursal
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     I wasn’t thinking Peter, got carried away with the thought of not having to plug the fan in

    #990736

     
    Janovich
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    We’ve got a black one sitting on top of our woodburner,…bought in from the same shop with purchased the woodburner from.

     It does indeed do a good job of sending the warm air out into the room and Yes, they are extremely quiet and worth it in my humble opinion.  Does the job well i’d say.

    #990737

     
    Back In Black
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    I’m sure it works but not sure how it would save fuel. I find our stove gives out most heat when it’s got really dry wood in it and it’s shut right down with minimal ventilation. Then it burns for hours and really pumps it out. The fan would be acting to more evenly distribute the heat horizontally I guess. But I can’t see a way I can burn more efficiently to save fuel. Opening up the vents just increases burn speed and pulls more air into the stove and up the chimney. It’s a good idea but practically I don’t think it’s going to save you on logs. It will just spread the heat your logs are producing more evenly and effectively.

    #990738

     
    Peter WellsPeter Wells
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    Back In Black

    But I can’t see a way I can burn more efficiently to save fuel

    I agree with you and I’m sure it doesn’t per see. As you say it does distribute the heat horizontally and I have found that with an Ingle Nook it shifts some of the heat from the Nook to the room. I have also found that it is during the evening hours, say seven to eleven, that you want the heat in the room and not in the nook or fireplace. The fan does that.

    As for saving logs. During those ‘core warming’ hours there is no need to raise the burn level of the fire as the fan is bringing the warm air forward.

    I believe the Canadian study involved a typical living room being built inside another room. The heat required to keep that inner room at the required temperature was then measured with and without the fan. Apparently, the fanless fire required some 14-18% more logs (calorific value)  to maintain the required temperature.

    PS. As one gets older one is looking for devices that will save not just money, but labour. Even if the saving in log felling, cutting, splitting, handling is 10%. I’ll take it.  

     

    #990739

     
    2658336
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     Putting a fan around the stove allows it to produce the same heat output for a lower surface temperature, and therefore a lower burn rate. QED.  Very simple physics if you look at it the right way.  The fan itself has to be energy neutral because it can’t store energy.

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