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Do electric resistance heating devices loose efficiency w/ age?

I am working with a condominium HOA that is proposing to replace 6 25KW electric unit heaters in their common garage in hopes of reducing their electrical consumption. I am trying to find out whether electric resistance heaters loose efficiency with age. It is my understanding that electric resistance heating elements are theoretically 100% efficient - i.e. 1 KWH of electricity consumed by an electrical resistance heater will ALWAYS produce 3412.3 BTU of heat.

I am aware that some resistance heating elements will produce less heat as they age but I assume they also consume less electricity as their output drops. I also am aware that other factors may affect the EFFECTIVE efficiency of an electric resistance heater such as controls, fans, placement, buildup of lint, etc. I am really only trying to verify what I believe to be the fundamental physics of the issue - that a new electric heater will not inherently be less costly to operate per rate KWH.

I have advised the HOA they should not expect their energy cost to to down as a result of their simply replacing old wall mounted electric unit heaters with new electric heaters of the same output. I am looking for some backup that my advise is sound.


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  • shopper355 Jul 20, 2009

    This did not answer my question - whether electric resistance heaters loose efficiency (fewer BTU per KWH consumed) over time.

  • shopper355 Jul 20, 2009

    So you agree that basic physics dictates that 1 KWH of electricity consumed by an electrical resistance heater will ALWAYS produce 3412.3 BTU of heat (i.e. there is no other way for the electricity to be consumed)?

  • shopper355 Jul 20, 2009

    Yes, the response was helpful!



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Overall Natural Gas would be best but generally the efficiency in electric resistance heaters is not really lost (very minimum) as long as they are kept clean, aren't falling apart, and proper airflow is kept which it seems you are already aware of. All electric resistance heaters are considered 100 percent efficient because there is no heat loss through ducts or combustion. Remember that some space heaters deliver heat more quickly or more concentrated than others. Also again, using electric resistant heat to heat the entire house is generally more expensive than using other systems like a natural gas furnace or a heat pump.

So overall, it will probably not be any cheaper to operate the new systems to the old ones but if the old units are wearing down and falling apart, maybe it is time to replace. I hope this helps.


Posted on Jul 20, 2009

  • Benjamin Patri
    Benjamin Patri Jul 20, 2009

    yes, I agree with that statement. It may not be dissipated as well in the future but it should still produce the same as long as it is kept up.


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Don't know how much this will help. I agree with that replacing the heater will not do much help in the consumption of electricity, but it should be use in a much optimum way. The operation of electric resistance heaters to heat an area for a long period of time is generally considered to be costly. However intermittent or partial day use can be more cost efficient than whole building heating since there savings due to superior zonal control.
Example: A lunch room in an office setting has limited hours of operation. During low use periods a "monitor" level of heat (50 °F/10 °C) is provided by the central heating system. Peak use times between the hours of 11:00–14:00 are heated to "comfort levels" (70 °F/21 °C). Significant savings can be realized in overall energy consumption since infrared radiation losses through thermal conductivity are not as large with a smaller temperature gradient both between this space and unheated outside air as well as between the refrigerator and the (now cooler) lunch room.
Economically, electric heat is very efficient, and can be compared to other sources of home heating by calculating the cost per kilowatt hour multiplied by the efficiency of the heater, and then multiplied by the number of kilowatts the heater uses.

Posted on Jul 20, 2009


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