Does a Fan Produce More Heat or Just Blow the Air Around?
- windyhill4.2
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Why have windows gone to muti-pane ?? heat/cold transfer, or the radiator on a car?? get rid of the fan on your car radiator,see what happens,fan blowing air on surface = greater heat transfer,plain & simple,transferring engine heat to the atmosphere is more effective WITH the fan running,turn fan off,let radiant heat do it's job,in the summer time the car engine will overheat,just my .0000000000000000001
- tony17112acst
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It just doesn't seem intuitive to me that heat transfer depends on ambient temperature. So you're saying if I have a constant BTU output say at 20,000 BTU, I'll get MORE BTU's if it's colder in the room? I don't see that, but I could be wrong.waldo lemieux wrote:I seem to remember something from physics class. That " the greater the differential in temp of water or air on each side of a surface the greater the rate of heat transfer across that surface.I believe that it also flows faster from high density to low. :
-Tony
- Lightning
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This...
and to prove it, this....waldo lemieux wrote:I seem to remember something from physics class. That " the greater the differential in temp of water or air on each side of a surface the greater the rate of heat transfer across that surface.
lsayre wrote:You would have to watch the stack temperature fall
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... I got to chime in
. if the fan was capable of actually decreasing the temperature of the side of the stove it's blowing on... then technically you are decreasing the rate of heat transfer of that metal..
.. because air is a poor conductor of heat... the fan helps distribute the heat better
. if the fan was capable of actually decreasing the temperature of the side of the stove it's blowing on... then technically you are decreasing the rate of heat transfer of that metal..
.. because air is a poor conductor of heat... the fan helps distribute the heat better
- lsayre
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Air has mass and moving air will assuredly take heat away from the surface of the stove, but if you don't subsequently burn more coal, all you will end up with in a hurry is a colder stove surface. Once the equilibrium of the wind blown system is restored, unless you are burning more coal or seeing a measurably lower flue pipe (stack) temp, the energy per unit of time evolving form the air blown stove surface (that is being cooled by the blowing air) is ultimately the same as the energy evolution without any air blowing across it.waldo lemieux wrote:I seem to remember something from physics class. That " the greater the differential in temp of water or air on each side of a surface the greater the rate of heat transfer across that surface.I believe that it also flows faster from high density to low. Its all kinda cloudy back there
- jpete
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Other than the heat produced through the use of electricity, a fan doesn't "MAKE" heat.
It moves the heat produced by the stove around more efficiently.
Heat moves from an area of high concentration to lower concentration and the greater the difference, the faster the rate of transfer.
So imagine your stove with no fan. It heats up the actual stove, then the area immediately around it, then the area around that and so on as it radiates out into the room. At some point, it heats up the outside walls which very quickly transfer the heat out of your house.
Maybe it makes it to the other side of your house, maybe it doesn't.
Think of the fan as a "conveyor belt" for heat, moving it out faster and further than it would otherwise naturally move. This distributes the heat to where you want it in the shortest time necessary.
Any hot air heating system is all about air management. What you'd want ideally is a high volume, low velocity fan because the faster you move the air, the faster it gives up its heat.
Do you blow on your soup vigorously when you want to cool it down or do you barely whisper at it?
HVAC systems use low speed for heat but high speed for cooling for this reason.
The ultimate answer is turn your fan off for a week and see if your house is still comfortable.
It moves the heat produced by the stove around more efficiently.
Heat moves from an area of high concentration to lower concentration and the greater the difference, the faster the rate of transfer.
So imagine your stove with no fan. It heats up the actual stove, then the area immediately around it, then the area around that and so on as it radiates out into the room. At some point, it heats up the outside walls which very quickly transfer the heat out of your house.
Maybe it makes it to the other side of your house, maybe it doesn't.
Think of the fan as a "conveyor belt" for heat, moving it out faster and further than it would otherwise naturally move. This distributes the heat to where you want it in the shortest time necessary.
Any hot air heating system is all about air management. What you'd want ideally is a high volume, low velocity fan because the faster you move the air, the faster it gives up its heat.
Do you blow on your soup vigorously when you want to cool it down or do you barely whisper at it?
HVAC systems use low speed for heat but high speed for cooling for this reason.
The ultimate answer is turn your fan off for a week and see if your house is still comfortable.
- tony17112acst
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I ague that the fan simply sends the heat off and away from the object, not that you get more of it. If you had no fan blowing air for heat in your car, yes, it would be cold for a while, but it would eventually get hot ...it would just take longer ...the heat was simply NOT MOVED from it's spot; it's hotter than hell where the heater coil would be.windyhill4.2 wrote:Why have windows gone to muti-pane ?? heat/cold transfer, or the radiator on a car?? get rid of the fan on your car radiator,see what happens,fan blowing air on surface = greater heat transfer,plain & simple,transferring engine heat to the atmosphere is more effective WITH the fan running,turn fan off,let radiant heat do it's job,in the summer time the car engine will overheat,just my .0000000000000000001
Last edited by tony17112acst on Sat. Jan. 11, 2014 7:39 pm, edited 1 time in total.
- Lightning
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Ultimately, If blowing air across the stove results in lower flue gas temperature then where is that heat going?? Its going in your house instead of out the chimney.. That's the bottom line...
- Lightning
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I can vouch for this since between blower cycles I see my flue pipe temperature rise and fall a couple degrees..Lightning wrote:Ultimately, If blowing air across the stove results in lower flue gas temperature then where is that heat going?? Its going in your house instead of out the chimney.. That's the bottom line...
- windyhill4.2
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I wasn't referring to heater core,i was referring to the engine radiator removing heat from the engine,by itself low heat removal,with fan running,high heat removal,simple to me ,but then I qualify as a simple minded person.
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... if it were even possible to lower the temperature of the outside of the stove with a fan... technically the flu temps would increase... not decreaseLightning wrote:Ultimately, If blowing air across the stove results in lower flue gas temperature then where is that heat going?? Its going in your house instead of out the chimney.. That's the bottom line...
... this is probably not even something we could measure without sophisticated equipment... but if you decrease the heat transfer rate on the outside... then technically the flue gas temp will increase
- Lightning
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The fan would definitely lower the stove temp some.. And why would the flue gas temp increase?? This doesn't make sense to me at all Bro...Rigar wrote:... if it were even possible to lower the temperature of the outside of the stove with a fan... technically the flu temps would increase... not decrease
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Blowing air across the heat exchange surface increases the efficiency of that surface and flue gas temp. will go down just as lightning has observed.
- oliver power
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OK, I finished off my sentence by adding "if any". I was going to say NO to getting more heat when fan blows across stove. Then, I too remember something about density, and heat transfer. Yes, I do believe you'll get more heat transfer if blowing fan across metal. But, not enough to make a difference that amounts to anything. I then went on to say if the stove has a bimetallic damper, it would open. Then you WILL get more heat off the stove.oliver power wrote:I agree Waldo. If the stove has fixed air control, pretty much you're just moving heat around. I'm sure taking heat off the surface would allow a faster rate of transfer. Not sure how much faster, if any. However, if the stove has a bi-metallic primary air damper, blowing heat off the stove would cool the stove mass. This would cause the flapper to open, and allow more air, which would create more heat.waldo lemieux wrote:OH,OHHH>>>> I got this one. It Depends
- lsayre
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Agreed, through burning more coal.oliver power wrote:I then went on to say if the stove has a bimetallic damper, it would open. Then you WILL get more heat off the stove.