Does a Fan Produce More Heat or Just Blow the Air Around?

 
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lsayre
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Post by lsayre » Mon. Jan. 13, 2014 11:25 am

There is no doubt that in many applications the comfort provided by a fan means less heat needs to be produced to provide said comfort. That is not what the original poster is asking however. The original poster is specifically asking if a fan causes a coal burning stove to produce more heat than it would without the fan. It does not.


 
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Post by franco b » Mon. Jan. 13, 2014 11:55 am

lsayre wrote: That is not what the original poster is asking however. The original poster is specifically asking if a fan causes a coal burning stove to produce more heat than it would without the fan. It does not.
Even though that is correct it is misleading in that the purpose of the stove is to transfer heat to the room. Because a fan will increase the rate of heat transfer of the metal of the stove, the room will receive more heat than without it. The stove does not produce more heat but transfers it to the room more efficiently. Less heat goes up the chimney and more into the room as has been mentioned many times in this thread.

 
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Post by tony17112acst » Mon. Jan. 13, 2014 12:48 pm

franco b wrote:
lsayre wrote: That is not what the original poster is asking however. The original poster is specifically asking if a fan causes a coal burning stove to produce more heat than it would without the fan. It does not.
Even though that is correct it is misleading in that the purpose of the stove is to transfer heat to the room. Because a fan will increase the rate of heat transfer of the metal of the stove, the room will receive more heat than without it. The stove does not produce more heat but transfers it to the room more efficiently. Less heat goes up the chimney and more into the room as has been mentioned many times in this thread.
I'm the OP and franco is correct. My sole concern was: if I point a fan at my stove, will I get more heat in the room than if I did not have a fan at all.

 
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Post by Carbon12 » Mon. Jan. 13, 2014 1:07 pm

Adding additional convection air currents will provide additional heat transfer from the stove to the room

 
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Post by titleist1 » Mon. Jan. 13, 2014 1:28 pm

Lightning wrote:
windyhill4.2 wrote:So will the big fish fry faster with or without the fan running ????
Wouldn't ya know it. It depends.
Do you want that baked or fried?
I don't even have to ask a physicist for this one, according to my oven instructions if I use the convection fan it has then the food cooks faster!! :clap:

hmmmmmmm......... but in the 5 years or so since we have had that thing I don't think we ever used the convection fan, just think of all that energy we have wasted. :bang:

 
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Post by lsayre » Mon. Jan. 13, 2014 3:46 pm

tony17112acst wrote:I'm the OP and franco is correct. My sole concern was: if I point a fan at my stove, will I get more heat in the room than if I did not have a fan at all.
So a fan either noticably improves the overall efficiency of the stove itself (leading the old time hand fired stove guys who donlt have fans on their stoves [the ones that I was trying to help out] down the path of derision), or it mysteriously puts more heat out without burning more coal to do so. Hmmm???

I can possibly be dragged while screaming and be forced to accept the first possibility, the one about increased efficiency. But it seems more likely that the entire system (including the house itself) is made more efficient, and thus "potentially" require less coal with a fan than without in order for the occupants to reach a certain comfort level. We are all talking in circles now.
Last edited by lsayre on Mon. Jan. 13, 2014 5:09 pm, edited 1 time in total.

 
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Post by Lightning » Mon. Jan. 13, 2014 3:55 pm

Larry, with due respect sir, why are you choosing to ignore the drop in stack temperature that occurs when you scrub heat off the stove with moving air. I don't understand.

And where would said heat be disappearing to?
I don't mean to sound brash but are we trying to get to the bottom of this or help out the stove owners that don't have or use a means of circulating air??
Last edited by Lightning on Mon. Jan. 13, 2014 4:44 pm, edited 1 time in total.


 
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Post by Sunny Boy » Mon. Jan. 13, 2014 4:41 pm

lsayre wrote:
tony17112acst wrote:I'm the OP and franco is correct. My sole concern was: if I point a fan at my stove, will I get more heat in the room than if I did not have a fan at all.
So a fan either noticably improves the overall efficiency of the stove itself (leading the old time hand fired stove guys who donlt have fans on their stoces [the ones that I was trying to help out] down the path of derision), or it mysteriously puts more heat out without burning more coal to do so. Hmmm???

I can possibly be dragged while screaming and be forced to accept the first possibility, the one about increased efficiency. But it seems more likely that the entire system (including the house itself) is made more efficient, and thus "potentially" require less coal with a fan than without in order for the occupants to reach a certain comfort level. We are all talking in circles now.
Larry, also with due respect.

Your getting hung up on the fan's affect on the coal and that's taking you around in circles - not all others.

This has nothing to do with the fan impacting the heat output of coal inside the stove. It's about a fans affect on the outer surface of the stove. The coal is only providing a "set amount" of heat. Either that "set amount" goes up the chimney, or the fan can help a greater percentage of that "set amount" transfer through the stove casing out into the room faster than without a fan.

In the OP's stated instance and question, and just verified by the OP himself, the fan has no impact on how well the coal burns. He just wants to know if a fan will remove heat from the outside of the stove faster. And it will. ;)

Paul

 
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Post by Sunny Boy » Mon. Jan. 13, 2014 4:47 pm

Time for some humor. Next question.

Which produces more hot air ? A thread about fans blowing over stoves ? Or, . . . an actual stove ? :D

Paul

 
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Post by windyhill4.2 » Mon. Jan. 13, 2014 5:04 pm

The thread= :mad: just stop :bang: start :rofl: :clap:

 
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Post by lsayre » Mon. Jan. 13, 2014 5:20 pm

Sunny Boy wrote:Larry, also with due respect.

Your getting hung up on the fan's affect on the coal and that's taking you around in circles - not all others.

This has nothing to do with the fan impacting the heat output of coal inside the stove. It's about a fans affect on the outer surface of the stove. The coal is only providing a "set amount" of heat. Either that "set amount" goes up the chimney, or the fan can help a greater percentage of that "set amount" transfer through the stove casing out into the room faster than without a fan.

In the OP's stated instance and question, and just verified by the OP himself, the fan has no impact on how well the coal burns. He just wants to know if a fan will remove heat from the outside of the stove faster. And it will. ;)

Paul
There is a thing called equilibrium. You may get a brief sweep of heat off of the stove via turning on a fan, but now the stove is cooler and must be re-heated by something, which in effect either means that the equilibrium point of the system will be shifted downward to a continuing lower surface temp for the stove, or the stove will have to burn more coal to restore its original higher surface temp. It's all about heat transfer equilibrium and the coal being consumed. If there is a certified and sustained drop in stack temp via a fan that would certainly contribute to raising the efficiency of the stove, but I was the one who said that in my very first post to this thread.

But then what about the special case for the non-fan crowd that is already getting maximum efficiency and the worlds best low stack temperatures as a consequence. How do they benefit from adding a fan if they have already achieved blissful efficiency nirvana without one?

 
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Post by waldo lemieux » Mon. Jan. 13, 2014 6:20 pm

OMG , Seriously? :bang: :bang: :chop:

 
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Post by Lightning » Mon. Jan. 13, 2014 6:25 pm

lsayre wrote:There is a thing called equilibrium. You may get a brief sweep of heat off of the stove via turning on a fan, but now the stove is cooler and must be re-heated by something, which in effect either means that the equilibrium point of the system will be shifted downward to a continuing lower surface temp for the stove, or the stove will have to burn more coal to restore its original higher surface temp.
Yes the stove would reach an equilibrium of a lower surface temperature and then maintain that temperature as long as the coal heat output was steady and the air moving across it's surface is steady... Does that mean it would be removing any less heat? No, the lower surface temperature would be proof that you are effectively removing more heat, otherwise it would just get hot again.. :?
lsayre wrote:If there is a certified and sustained drop in stack temp via a fan that would certainly contribute to raising the efficiency of the stove, but I was the one who said that in my very first post to this thread.
Not a matter of if... There is a sustained drop of stack temperature. So sounds like we're all on the page then. :)
lsayre wrote:But then what about the special case for the non-fan crowd that is already getting maximum efficiency and the worlds best low stack temperatures as a consequence.
Well maybe and most likely, they would see a slight enhancement in efficiency by use of some kind of forced air circulation.

 
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Post by warminmn » Mon. Jan. 13, 2014 6:34 pm

maybe the fan is just blowing the heat back into the stove where it leaves thru the stove pipe Yes, Im joking, but we havent covered that angle yet! :P

 
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Post by lsayre » Mon. Jan. 13, 2014 6:36 pm

I would think that thermal destratification via a ceiling fan would do a lot to make a home more comfortable by taking heat that would normally be at the ceiling level and dispersing it into the lower living area. It doesn't make a stove more efficient, but it makes the heat the stove emits more beneficial to us ground dwellers. Freetown Fred has the right idea here. As I recall he stopped using his stoves fan, and switched to using a ceiling fan. He turns in some of the absolutely lowest coal consumption figures of any of us each year, and he lives in a large old house in an area that gets downright cold. And he has a simple box stove to boot.


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