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I've read this question and answer: How efficient is an electric heater? , but still don't understand.

If I have an electric radiator it heats the room with 1000 Watts of power. And I feel the room's getting warmer. In contrast, if I turn on a vacuum cleaner which consumes 1000 Watts as well as the radiator, it doesn't seem to heat the room as well.

Why? Won't all kind of energy transform into heat ultimately?

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    $\begingroup$ A 1kW heater and 1kW vacuum cleaner will heat the room at the same rate. However you're going to struggle to find a 1kW vacuum cleaner without going to industrial cleaning scales. $\endgroup$
    – John Rennie
    Commented Dec 18, 2013 at 12:20
  • $\begingroup$ Ah yes, hwlau makes a good point in his answer. Heaters tend to be directional so the heat they emit is concentrated in a certain direction. A vacuum cleaner will spread the heat evenly through the room so it will feel less intense even though the total amount of heat is the same. $\endgroup$
    – John Rennie
    Commented Dec 18, 2013 at 12:41
  • $\begingroup$ Maybe it's an illusion: Maybe you think that for all the noise it's making, the vacuum cleaner should heat the room more than it actually does. While maybe the radiator, which really is putting out exactly the same amount of heat, is so quiet that it seems remarkable to you that it puts out any heat at all. $\endgroup$
    – Solomon Slow
    Commented Aug 21, 2016 at 2:00

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It is because you wouldn't hide in the corners like your kitty does!

A electric radiator is designed to be directional and therefore it doesn't heat the unnecessary part of your room. It makes you feel warming in front of it, but some part of the room don't get heated like those corner and the ceiling. In comparison, a vacuum cleaner heating the gas instead, so it is much more uniform, but less efficient from your point of view because you don't feel it (Your kitty might be happy about it though).

As what @JohnRennie, they dissipate the same amount of heat (and some become noise).

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A more creative answer involves knowledge of statistical physics:

Using the vacuum cleaner will transfer the system (your room) in a state of less entropy (if the rising temperature is neglected) as the dust is compressed in a smaller volume (just like the mixed state of two gases has more entropy then the state where the gases are separated). This transfer costs energy (that follows from the second law of thermodynamics) and thus the vacuum cleaner needs to use some of the energy for this transition reducing the heating power. The heater doesn't reduce the entropy in any way.

Therefire the heater is a tiny bit more efficient.

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