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  1. #1

    Radiant vs Forced air convection

    I'm doing a little project and I'm comparing the difference of forced air convection to radiant heater. I would like to know which one would be more efficient heating up a room using a space heater. From my schooling I know that since both are electric that they are both 100% efficient. But, would one use less energy than the other? Also I did a little experiment using both heaters using two identical rooms. Placed the heaters in two different rooms and ran my little experiment. The convection heater was much quicker heating up the air which makes sense, and the radiant heater was quicker to heat just me up. Which makes sense because of how the heaters work. But what I'm mostly about is if there is a way to calculate the heat gain of the person or heat loss of the person assuming that I'm a cylinder. Using the churchill equation from my old heat transfer book I calculated a convection coefficient of about 13 and 11 for the convection and radiant respectively. So, then my q' was about 750 for the convection and 620 for the radiant W/m. I don't know if I am on the right track or if I'm totally wrong. If anyone has any kind of insight I would greatly appreciate any kind of insight.

  2. #2
    Join Date
    Jan 2006
    Near Atlanta, GA.

  3. #3
    Join Date
    Dec 2010
    Eaton Rapids, Mi
    Quote Originally Posted by tisoykid View Post
    I know that since both are electric that they are both 100% efficient.
    don't confuse 100% efficiency in converting electricity to heat with good efficiency.. it just means that for every watt in you get a watt out of heat.

    1000 watts is 3400 btus. that means for every 1000 watts in, the system heats 3400 btus per hour.

    from a standpoint of electrical efficiency they both should operate at the same, given the same wattage used by the unit. From a comfort standpoint i would think that the radiant heating would be perceived as more "efficient" at adjusting the comfort level.

    I'm sure someone will come along and expand on this more than i can.

  4. #4
    Both of the heaters are 1500 watts. If there was a group of people would the forced air convection heater be more efficient for a room vs a radiant? Meaning would more people be comfortable with the convection compared to the radiant?

  5. #5
    Join Date
    Jun 2010
    Philadelphia PA
    Convection warms the air that warms the "stuff" radiant warms the stuff without first warming the air. The one that skips a step and doesn't have the heat at the ceiling gets my vote RADIANT
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  6. #6
    Thanks for the post. Hi guys, Im a newbie. Nice to join this forum.

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  7. #7
    Join Date
    Sep 2002
    I don't know
    Most so called radiant heaters provide very little heat via radiation. (there are exceptions - ex: those electric dish heaters)

    The air in contact with the radiator fins warms up by conduction, the density drops as a result, and the cooler, denser air around the heater pushes the warm air out into the room. (convention)

    Forced air heaters simply aid the process with a fan.

    You can't stop warm air from rising (or more correctly being pushed up by cooler air) by using a "radiant" heating system; efficiency is dependent on the heat source, not the means of distribution - provided that the everything is in the conditioned space.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

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