To dehumidify or not to dehumidify - that is the question.

Someone asked me a question this summer and I thought it might be worth while to post the answer here too as I'm sure a lot of people wondered the same thing. She asked, "Why can't I run my dehumidifier in the bedroom in the hot summer - won't I be more comfortable with less humidity?

The answer is - yes and no. Let me explain.

The dehumidifier will do its thing in extracting humidity from the air making you feel more comfortable since the Relative Humidity will have been reduced, but there will be a downside as well. The room will heat up as you run the dehumidifier. I don't know which one will win in the comfort battle, the reduced humidity making you feel more comfortable or the increased temperature making you feel less comfortable. Here's the logic.

I like to use the old engineering black box analogy - if you run a wire into a black box (your living room in this case) and then measure the power going thorough the wire you can tell how much power (BTUs in thermal terms) is going into the box. A typical dehumidifier draws 7 or 8 amps. Multiply that times 120 volts and you get the power it uses (P=EI) so at 8 amps you are using 960 watts. Now picture your average toaster. It uses approximately 1000 watts (for a small one). So running a dehumidifier in the middle of your room will generate the equivalent heat as a small toaster.

On the good side, it is removing moisture from the air and we all know about THI or Temperature-Humidity Index numbers. As the humidity is lowered, the moisture on your skin can evaporate more readily and that has a definite cooling effect on your body. So I guess the only way to find out which is the overriding factor, the increased heat or the lower humidity, is to try it!! Engineering solutions are only good on paper. The real test is for you to try it and then let us all know which way it goes.

An air conditioner is very similar to a dehumidifier. The BIG difference is that the air in a dehumidifier first passes over a series of cooling coils (the evaporator) and then immediately over a set of heating coils (the condenser) and then back into the room as dryer air with its temperature elevated.

In an air conditioner, the air passes over the cooling coils (the evaporator) and then directly into the room. The heated Freon then goes thorough a tube outside the house and into the heating coils (the condenser) and OUTSIDE air passes over it and then stays outside, exiting to the environment. The water which condenses on the evaporator in a dehumidifier is caught in the drain pan (or, if you attach a hose to it, down the drain). The water which condenses on the evaporator in an air conditioner runs thorough a duct to the outside of the window where it is splashed onto the condenser coils and evaporates into steam outside the house. Soooooo, if you are going to spend the money for a device, and also the money for the electricity to operate it, to make you more comfortable it is better to buy an air conditioner, since it not only removes moisture from the room air, it also cools it!

I followed up with her and she did try it. She brought the dehumidifier up from the basement and ran it for two hours prior to going to bed. Then she hopped in the sack and tried to get to sleep. With all of the "engineering" explanation racing around in her head she just lay there with her eyes open trying to figure out if she was more or less comfortable, but she did decide on one thing - the damn thing was much too noisy, so she turned it off and opened the window. All the engineering thinking about heat flow and RH and I forgot the one problem that bothered here more than either - the noise!!

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