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Could someone please explain why there are 2 types of space heaters-- one that is convective and one that is infrared? Why does the first one not radiate and why does the second one not heat the air?

I know also that a convective heater is built with a spiral wire over a ceramic core that act like a resistor that gets heated. How exactly is infrared heater built?

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The second part of your question "how is an infrared heater" built may be off topic. (anyway, it's preferable to keep that as a separate post) –  Manishearth Jan 11 '13 at 9:59
    
Definitely not a duplicate, but related: physics.stackexchange.com/questions/23048/… –  Chris White Jan 11 '13 at 16:05
    
Thanks, that's the post i read which made me visit this website at the first place :). I read and posted my question there , but someone said i have to post the question in a new post. –  Ronen Festinger Jan 11 '13 at 22:17
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3 Answers

A human body feels heat while in contact with the air, so it is desirable to heat the air. This is what convectional heaters do - they have a developed surface and relatively low temperature to transmit the heat to the air. The radiation power is proportional to the following temperature difference: $Q \propto (T_{heater} ^4 - T_{air} ^4)$, so it can be small. The heater transfers its heat mainly to the air and the air transfers it to the walls.

The radiating heater has small surface, but much higher temperature so its radiating power is the main heat transfer (it works just like a lamp). The infrared waves get on the skin and heat it. Otherwise they get on the walls and heat thick walls. The radiating heater heats the air too, but due to too high temperature this hot air goes straight up and heats the ceiling, so it is poorly mixes with the room air.

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May be you should add that to aid to the convection most convective heaters have a fan to circulate the air over the heating element.The article in wikipedia has a number of infrared heaters: en.wikipedia.org/wiki/Infrared_heater –  anna v Jan 11 '13 at 10:16
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Convective heaters do indeed radiate, but they radiate much less than an infrared heater because they are at a lower temperature. The amount of energy radiated by an object (strictly speaking a black body) is determined by Stefan's Law and varies as $T^4$ so a small increase in temperature makes a big difference.

Air is transparent to infrared radiation, so an infrared heater can't heat the air directly. Instead it heats anything it's radiation hits and that object then heats the air.

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Something is not clear to me,why does the convective heater use 2000W and reach less temperature than a radiative heater that use 800W? I'm talking about a convective heater like that: link and radiative heater like that: link –  Ronen Festinger Jan 11 '13 at 13:46
    
Or why can't we use a radiative heater and use it with less power causing it to reach lower temperature and make it operates like a convective heater? –  Ronen Festinger Jan 11 '13 at 13:53
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Almost all of you might have been told or learned about an infrared heater. It is innovatively manufactured to give heat by means of infrared light. This way of home heating is definitely effective since this is the same method that our great sun heats the entire world.

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This really doesn't answer the question, I'm afraid :/ –  Manishearth Jan 18 '13 at 13:11
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