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I got into an argument with someone who thinks that blowing air across a fireplace will make the room heat more slowly, but based upon the principles computer heat sinks use to get heat away the room would get warmer quicker because you're getting the heat away from the area faster. Which way is true for heating up the room with the fireplace in it along with the rest of the house?

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  • $\begingroup$ Blowing air across a fireplace will blow smoke into the room, unless all the blown air goes directly up the chimney. In that case, the blown air may make a difference due to radiant heat transfer, but not due to convective heat transfer. $\endgroup$ Jan 5 '19 at 17:12
  • $\begingroup$ @DavidWhite: Hmm, who said anything about smoke? ;-) Assuming the fireplace is e.g. electrical, blowing air on it will improve convection and the room will heat up slightly faster. I'm also assuming the power output of the fireplace is constant. $\endgroup$
    – Gert
    Jan 5 '19 at 17:29
  • $\begingroup$ @Gert, I agree with your point. The OP should be somewhat more specific on the physical situation that he is arguing about. $\endgroup$ Jan 5 '19 at 17:40
  • $\begingroup$ You need to be careful about what you mean by "heat the room". The walls are mostly heated by radiation from the fire, which is not affected by the air. But what you "feel" as warm or cold is the air temperature, and to make the room "feel warm" you need to mix the air to get the same temperature everywhere. $\endgroup$
    – alephzero
    Jan 5 '19 at 19:36
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It all depends on the fireplace. If the fireplace is in the center of the room, and you blow on the back side of it, you will increase convection currents , and yes, heat will be distributed faster. If you blow across the front of the fireplace, or you have a fireplace in the wall, you will be increasing the rate by which the air goes up the chimney, and thus most probably it will take more time to heat the room because half of the warm air circulates in the room and half goes up the chimney, in excess of the usual loss of heat in fireplaces. Fireplaces are very inefficient in heating, most of the heat goes to the wall and up the chimney.

There are special fans that can be installed in a fireplace that blow air towards the room, not allowing so much of the heat to go up the chimney and to the walls. So the answer depends on the geometry of how the fan is used.

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