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I own a home in southern Wisconsin, USA, where we have a humid continental climate (emphasis on humid!).

There is no central air conditioning. This summer we are experimenting with cooling strategies as we'd prefer not to add air conditioning (to avoid the up-front cost, higher electric bills, and increased carbon emissions).

By keeping blinds and windows closed during the day, and open at night, we've been successful at keeping the house about 10 degrees F (5 degrees C) cooler inside than outside during the hottest part of the day.

The issue is the humidity. The night air is damp and stays inside. This makes the floors sticky, and the furniture feel clammy. Especially if there has been rain overnight, this can make the house feel very uncomfortable!

Without adding air conditioning (or other significant expenses or energy users), what are some steps we could take to reduce indoor humidity?

There is a related question, How to reduce humidity in the home?, but it focuses on winter-time. I'm interested in summer-time strategies.

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  • You probably want to rule out an electric dehumidifier for the same reasons as air conditioning, right?
    – Jean-Paul Calderone
    Commented Jul 19, 2019 at 0:31
  • @Jean-PaulCalderone that's correct -- a dehumidifier works on the same principle as air conditioning, but instead of exhausting heat outdoors, would leave it inside.
    – LShaver ♦
    Commented Jul 19, 2019 at 2:26

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Most folks don't know that their 'frost free fridge' can be easily hacked to act as a dehumidifier. As it runs continuously, it can be used to suck unwanted moisture out of a humid home 24 hours a day.

Frost free fridges actually have a heating element. This heating element comes on every-so-often to thaw out the cooling plate. Any frost/ice that has formed on the cooling plate melts, drips into a plastic trough, drains to the bottom-rear of your fridge via a small tube, and then ends up in a plastic bowl located on top of your compressor.

back of fridge

The compressor, as it helps pump heat out of your fridge and into the surrounding air, also heats up. Heat from the compressor warms the bowl and evaporates the water, returning the moisture back to the room where it originally came from. So, under normal circumstances, this operation is humidity-neutral.

Assuming your fridge is against an external wall, or above an accessible basement, or near a drain, you can get a short piece of scrap tubing, attach it onto the end of the drain tube (just above the bowl), and instead of the water ending up in the bowl, it can be redirected outside, to a closed container or a drain. In any case, since it is no longer being heated and evaporated back into the air, it is effectively removed from the humidity equation and your internal air becomes drier.

Depending on how easy it is to access the back of your fridge, this hack takes mere minutes. It doesn't require any extra electricity, and it doesn't harm your fridge in any way. It's just the free 24/7/365 dehumidifier that everyone has in their kitchen but isn't aware of.

The more warm/humid air you have in the house, and the more often you access the fridge, the more moisture will be removed in this manner and the drier the house will become. It would seem to be a nice fit for a humid continental climate with year-round precipitation.

If you expressly don't want moisture removed during part of the year, you can always spend a few bucks on a diverter valve and install it so that by simply turning the valve you can direct the condensate to either the bowl (and retain the moisture 'inside') or to a drain/container/through a wall (and send the moisture 'outside'). Direct the condensate to the bowl when the internal air is dry and you don't want to make it any drier. Direct the condensate outside for the rest of the year.

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  • Interesting. Any idea how much water this could remove?
    – LShaver ♦
    Commented Jul 19, 2019 at 15:48
  • @LShaver Assuming summer temp of 30°C, relative humidity of 80%, fridge size of 300L, fridge temp of 5°C, and 20 door openings per day, you would extract 105mL of water from the air every day. Not a huge amount, but perhaps part of a solution. Opening the fridge door more often, opening the freezer door, a larger fridge/freezer capacity, or a higher RH would all increase the amount removed, of course. Lots of variables — and not all of them scale linearly.
    – Tim
    Commented Jul 23, 2019 at 13:25
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One option is to place materials that absorb or adsorb water from the air into the house. Such materials include silica gel, clay and other mineral soils, and calcium chloride. The amount of water this materials can deal with likely makes them part of a solution, not a solution on their own. These materials may also need to be "recharged" or replaced regularly as they become saturated and ineffective.

Another option is houseplants. In particular, epiphytes, which are adapted to gather their water needs from the air and other non-soil sources, may be helpful. Some of this water will be used in photosynthesis to produce sugars. As long as the sugars aren't metabolized the water is removed from the environment (thus removing parts of the plant may be necessary). As with the above, this is probably not a solution by itself but can contribute somewhat to a solution.

Both of these may also provide some buffer for humidity. If there is a brief increase in outdoor humidity they may help slow the increase in humidity indoors. If outdoor humidity falls before indoor humidity catches up, that's a win as well. The reverse is also true, of course, which may or may not be desirable.

Additionally, make sure there aren't unnecessary sources of humidity inside the house. Driers, kitchens, and bathrooms should be vented to exhaust excessively humid air outdoors. If you have houseplants you water regularly, these may also contribute. Anything else that's sitting around and wet - towels, muddy boots or boot pans, compost buckets, etc, may all be contributing additional humidity.

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Nothing beats the classic dehumidifier and the water you can later use for whatever purpose enter image description here

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