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Is it OK to leave device chargers plugged in all the time? An expert explains
(theconversation.com)
this post was submitted on 27 May 2025
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Has any study been done on how efficient they are as heaters? The electricity they use when idle doesn't vanish; it's given off as heat. In the winter it might be worthwhile to not bother to unplug them because what they're giving off could offset what other, more conventional, heat sources might otherwise provide. i.e. you leave a charger plugged in, and your house heating goes off half a second sooner, saving you the pennies there that the charger costs otherwise.
Admittedly, this doesn't apply to summer and hotter climates, so most people, most of the time, probably ought to be unplugging them, but there's a small percentage of cases where the reverse might actually be beneficial.
100% is the typical claimed number as it is easy to measure watts of electric in and find that is exactly equal to watts of heat out - or if not the difference is easially explained by measurement error. There is no hypothesis (much less theory!) of where the energy could go it it isn't heat and conservation of energy is enough to also decide 100% efficient.
The above isn't the whole story though. If you could somehow measure watts from the power plant output you would discover that 4-12% (depending on a bunch of factors) of the energy is lost before it even gets to your house and so your efficiency goes down. If you measure fuel into the power plant, those range for 10% (old systems from the 1920s only run in emergencies) to 60% (combined cycle power plants) - I'm not sure how you would measure wind and solar. Eventually the universe will die a heat death and 0% long term.