I have heard that using a humidifier in the winter can help you save money in heating costs. If this is true, I was curious about the physics behind why this is.

My thoughts were that since water has a very high specific heat, adding more water into the air would actually require you to use more energy to raise the temperature of the air the same amount.

Is it that if you use a humidifier, the perceived temperature is higher?(so maybe 67 degrees F with a humidifier would feel like 70 without, thus saving because you can keep the thermostat down?) If so, then how does humidity affect perceived temperature?

Or is it that this claim is wrong?

My background: I am a graduate student in combinatorics, a branch of math not very related to physics. I have seen undergraduate physics 1 & 2 in a formal setting, and enjoy learning about physics.

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    $\begingroup$ i don't think it saves anything on heating. warm moist air doesn't feel warmer than dry air of the same warm temperature, unless maybe you're in a steam bath. the reason i had always thought that humidifiers were used in wintertime in the north was that the very cold air outside had a lower absolute humidity, because it's so cold. then, if the absolute humidity inside is the same as outside, the relative humidity inside will be very low and it will feel very dry. sometimes resulting in cracked skin or similar. $\endgroup$ – robert bristow-johnson Dec 13 '16 at 7:00
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    $\begingroup$ it has health benefits and in this sense may save you money in medical expences drfranklipman.com/… $\endgroup$ – anna v Dec 13 '16 at 7:17
  • $\begingroup$ Are confusing a humidifiers with a heat pump? it can save a lot on the energy bill. en.wikipedia.org/wiki/Air_conditioning#Heat_pump_unit $\endgroup$ – anna v Dec 13 '16 at 7:46
  • $\begingroup$ @annav No, I am talking specifically about humidifiers. There are many places online that suggest they will save you money e.g. centralhtg.com/blog/… I saw this, and couldn't figure out how they could be saving you money on heat, so I thought I would ask. $\endgroup$ – Sean English Dec 14 '16 at 14:05
  • $\begingroup$ well, the link you give explains the savings, it is about "feeling" more comfortable at a lower thermostat setting if there is higher humidity. Difference between heat "felt" and thermometer heat. $\endgroup$ – anna v Dec 14 '16 at 14:19

I don't think it results in any savings. Given some interior temperature and outside temperature, heat flows from inside to outside by conduction through walls. Even if humidity were to change conductivity of air, heat transfer in most cases (say from your body to air) is by turbulent convection, and so change in conductivity of air matters little. Having said that, I am not from a cold country, so it is possible that I have overlooked something subtle.

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