Does a Hairdryer blow harder with heat on than it does with heat off ? and why? My feeling is the blowing force, or pressure that the air exhaust will exert on a surface that opposes it will stay the same whether the hairdryer is blowing hot or cold air. That the difference will be that the hot blown air will not be as dense as cold blown air. That would be because the heater which is in the air stream will be slowing down the air coming at it thereby making the air stream being dammed up a little, or raising the air pressure. Not as much air will get past the damn but the air that does get past the heater will have more Kinetic Energy. So since the heat radiates in all direction it lowers the mass/sec output of the hairdryer but the mass that comes out is more energetic.