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House Heatings question

  1. Aug 31, 2007 #1
    Imagine a house in a closed system. This house cannot lose heat or gain heat outside of itself. Now we have a heater that produces heat for the house. We also have a 60 watt light bulb that only supplies about 3 watts to actual light. 57 watts of it would be turned into heat and relatively a small amount of noise. Since this is a closed system, isn't all the heat transfer from the light bulb and the heater the same. All the light turns into heat and all the noise vibrates the walls and turns into heat. Is it true that everything is 100% efficient for heating as long as you are in this closed system. If this is true then inefficient light bulbs are the exact same as efficient ones and the exact same as the heater. Considering conservation of energy even the electromagnetic waves that exit the lightbulb and all sound waves will turn into heat when they strike the wall.

    Following that rational, if the house was not a closed system and the heater or lightbulb was at the center of the house. They would both have the same efficiency. As long as all the light from the bulbs does not exit a window. The heat will eventually get to the outside wall but before it gets there the light and noise has already been converted to heat in the center of the house.

    thanks in advance
    Last edited: Aug 31, 2007
  2. jcsd
  3. Sep 1, 2007 #2
    What is it (noting the absence in your post of any question mark) that you're thanking us in advance for?

    You're also giving a missimpression (is that a word?). Assuming that it is winter (ie. that you do actually want to heat the house), then you would obtain greater than 100% heating efficiency if you replaced the inefficient light-bulb with a CFC, and used the left over power to run a heat pump (ie. reverse cycle air conditioner). The resistive heater is a poor benchmark.

    In fact, it's probably best to use CFC lighting and gas heating. This way your heating stays decoupled from the lighting (so you can have light in the summer without needing excess air conditioning, and can vent heated air to the floor rather than have it stay floating around the light fittings), plus you don't have to worry about the conversion inefficiencies (burning coal to heat steam to generate and transport electricity to produce heat again).

    Ideally, you would probably feed the gas into a fuel cell (which in thermodynamic-principle should be able to extract more power than methods involving normal combustion), using the inevitable waste heat to start warming your home, and powering the most efficient devices for whatever further purpose you require.
  4. Sep 1, 2007 #3


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    Staff: Mentor

    We get this question every now and then. Yes, if you just look at the electric usage, an electric heater and an electric light bulb are both 100% efficient at heating your house. But the electricity comes from a power plant, most of which use a fossil fuel and thermodynamic cycle that is 45% efficient (nuclear is a little less, but the fuel is essentially limitless - hydro is renewable) while a gas or oil heater is up to 95% efficient.

    Also, if you are ever not running your heater, of course, then CFCs save you a lot of energy and money.
  5. Sep 2, 2007 #4
    What I'm really getting at is the fact that a light bulb could do the same amount of heating as a heater designed for heating.
  6. Sep 2, 2007 #5


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    Staff: Mentor

    Yes, that is correct.
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