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New here, so apologies for the basic question.

My undergraduate-level physics understanding of efficiency is it is the % of energy input that is turned into useful work as opposed to heat. At the same time, I've been told that free-standing space heaters waste energy because they are "inefficient". How can something that is designed to produce heat be considered inefficient?

Similarly, is there any reason to care about the efficiency light bulbs if I live in a climate where it is always cold outside and both heat and light are desirable things for a light bulb to produce?

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up vote 7 down vote accepted

Electric heaters are darned near 100% efficient at what they do: convert the electric potential in your home's power to heat. Other heating appliances can't claim as high an efficiency (for example, an oil boiler might be somewhere in the mid 80-90% range for efficiency, loses being related to incomplete combustion). However, what you might have heard is that the relative cost of heating with electricity is greater than other means.

Here is a nice comparison/calculator of costs to produce the same amount of heat with various heating sources.

Regarding sources of light: I believe you are correct in your assumption. If you would be heating your home anyway, an "inefficient" incandescent bulb will provide you will useful heat. However, keep in might the cost of electric heat vs cost of other heat sources available. Also consider where the lights are relative to you. If they are all near the ceiling you might not sense much benefit from their heating.

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The statement about electric heating being “inefficient” may take into account the inefficiencies of generating the electricity at the power plant. Even modern combined-cycle natural-gas power plants only convert 50 to 60 of the thermal energy in the natural gas to electricity, so even though the efficiency of your space heater is near 100%, the combined efficiency is lower than the alternative, which is delivering the natural gas to your home and converting it to heat at more than 90% efficiency.

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The amount of energy required to generate a given number of BTUs is higher for electrical resistance heaters than for combustion heaters. In addition, there are "line losses" of approximately 6% in getting electricity to your house from a power plant.

Electrical heat generation is the least efficient in terms of energy required to produce each BTU.

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