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Would a dehumidifier in a basement change the temperature of the room/basement?

  • Toshiba 45 Pint 115-Volt Dehumidifier
  • Continuous operation mode; draining into floor drain
  • 400 square ft basement; 8 ft ceilings; concrete floor and walls
  • 800 sq ft house; built in 1929; 1.5 stories
  • Greater Toronto Area, Ontario, Canada

My basement is hot. I'm wondering if the dehumidifier is warming it up.

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  • What's your concern, exactly? What problem are you trying to solve?
    – isherwood
    Commented Sep 19 at 17:45
  • What I find really strange about this (on Home Depot site via link but also on Toshiba site) is (a) it is "115-Volt". That changed to 120V around 40 years ago, and I assure you that dehumidifier was designed much more recently; (b) nowhere that I could find listed the power usage (e.g., Watts) or current (Amps). This is a heat pump, but like a refrigerator rather than an air conditioner because input and output are both indoors. So it should be a net balance on cooling vs. heating except for the heat generated from the compressor, etc. - which is unknown without knowing the power/current used.
    – manassehkatz-Moving 2 Codidact
    Commented Sep 19 at 17:45
  • @isherwood My basement is hot. I'm wondering if the dehumidifier is warming it up.
    – User1974
    Commented Sep 19 at 17:46
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    I run one all summer in Minnesota. I don't think it has a significant effect on room temperature. It doesn't really matter, though, because it's a necessity to prevent mustiness.
    – isherwood
    Commented Sep 19 at 17:48
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    They are very poor room heaters(maybe in a tiny cupboard with the door close). A hot basement/room will have other causes, warm air entering from somewhere, sunlight beating down on a wall.
    – crip659
    Commented Sep 19 at 17:55

4 Answers 4

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Yes. Or maybe. It depends on what ventilation or circulation practices you have in place.

A dehumidifier works by cooling a coil, on which water vapor then condenses. In order to cool something, you usually have to heat something else. In this case it's ultimately air exhausted out the back or side of the unit, just as with a refrigerator. This can raise room temperature if you don't have air circulation preventing it.

However, in my experience the net effect is a wash. The feel of dryer air is cooler, so even if the room warms a degree or two, it'll feel the same or cooler due to the improved function of body sweat.

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    That's very true in a warm humid environment. Those of us using dehumidifiers in cool damp climates are glad of the warmth (and the exhaust from mine does feel slightly warm especially on low fan speed)
    – Chris H
    Commented Sep 20 at 9:10
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    In order to cool something you have to heat something else, first law of thermodynamics, and you're going to end up with more heat, second law of thermodynamics.
    – user71659
    Commented Sep 21 at 19:54
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A dehumidifier converts vapor to liquid water - that releases heat.

It also has a electric motor that also releases heat.

It's basically the inverse of a swamp cooler.

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    We can work out how much heat. The latent heat of vaporisation of water is 2,260kJ/kg, so per litre (=1kg) of water condensed (at room temperature) you get 2.26 MJ (about 0.63kWh in more familiar units). The specific heat capacity of air is 1.005 kJ/kg/°C or about 1.3 kJ/m³/°C. The biggest question is the size of the room. Mine is in a room approx 10×4×2.5m (100m³). Excluding losses my room could warm by 17°C for each litre condensed. In practice that takes 12 hours, in which time there's a lot of air exchange with the rest of the house, heat soaks into the walls, etc. so in practice not much
    – Chris H
    Commented Sep 20 at 9:22
  • @ChrisH if you know the power draw of the dehumidifier, the calculation will be much simpler. The power used by the dehumidifier will all eventually be turned into heat.
    – Mark Ransom
    Commented Sep 20 at 19:46
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    @Mark, No. You have to add that to the latent heat. But the power consumption is far less than the latent heat recovered (hence my ignoring the electrical power, and the order and emphasis of Jasen's points)
    – Chris H
    Commented Sep 20 at 20:35
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Yes for sure. The more the humidifier works the greater the energy output. Unless it is dissipating the energy out a window and in only in that direction your basement will be warmer.

In a closed basement if you run fans continuously it will get warmer. We have ran fans to get rid of water and if the thermostat is on the first floor it is quite normal for the basement to be 2-3 degrees warmer after a day of running heavy fans.

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    This is the best answer. Unless heat is moved outside the building a self-contained dehumidifier simply moves heat from the air into the water that condenses into the drip pan. The mechanics of the dehumidifier requires electricity to operate. Some of that electricity will be converted to work (turning the compressor) but most of the electricity will be converted to heat.
    – pndfam05
    Commented Sep 21 at 0:33
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Yes, the dehumidifier compressor will exhaust heat in the room. However not much, more like a 150 Watt light bulb.

The main change in the temperature will be in the Feels like

They have "Feels Like" in the weather forecast.

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    @manassehkatz-Moving2Codidact thank you for your concern, the compressor consumes 400 Watt for the motor. Estimated no more than 30% is converted into heat.
    – DIY75
    Commented Sep 20 at 1:48
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    @manassehkatz-Moving2Codidact if all the 400 Watt would go in to heat and not motor function, that would be very bad design
    – DIY75
    Commented Sep 20 at 1:54
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    @Traveler That's not how efficiency works. All energy ends up as heat. All of that 400W will end up as heat, either in the air, or in the water. Just because 75% of it has done some useful work on the way there doesn't change the fact that it will ultimately be heat. a 400W humidifier will put 400W of heat into the environment. (Don't forget that the phase change of the water will also release latent heat)
    – SiHa
    Commented Sep 20 at 6:16
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    Just wanted to underline what @SiHa said - the process of condensing water releases stored heat, so something like 105% of the electric energy 'used' is converted to local heat - so an enclosed de-humidifier is a better room heater than an electric heater.
    – MikeB
    Commented Sep 20 at 10:11
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    @Traveler They do heat up, but by an insignificant amount by comparison. Not sure what point you're trying to make there. The circuit breaker and the wires aren't consuming the energy, the dehumidifier is.
    – Guy Incognito
    Commented Sep 21 at 10:34

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