Getting an Evaporative Cooler to Work in Humidity

Evaporative coolers don’t work in humid conditions, or so people tell you. But you can get them to work and blast cold air even when humidity is high indoors!

All you need to do is understand how these low cost air coolers work and use that knowledge to get more cooling ability from them even when the level of humidity rises to high levels in the room you are trying to stay cool in. This article will explain how to do that by using the simplest of tricks that you’ll probably kick yourself for not realizing after you read it!

Why is the Humidity So High?

First off, it’s pretty important to understand why the humidity in your room is rising so high as to stop the evaporative cooler from expelling cold air any more. The explanation is in the way the device works to create cold air.

It uses evaporation of moisture to create the cooling effect, just like your skin does when it perspires in the heat and a breeze feels nice and cool. The appliances have a big water tank that soaks a porous membrane through which air is passed by the fan. The air picks up the moisture and evaporation reduces the temperature rapidly.

That moist air is blasted into the room by the unit’s fan so you can enjoy a colder atmosphere. At the same time, all that cool, moist air is saturating the atmosphere in the room, artificially raising its humidity level. Eventually it will reach saturation point (100% humidity) and the evaporation process will no longer work, because the air cannot absorb any more moisture!

Cycle the Air

The way to prevent this happening is simplicity itself. All you have to do is open a window to let in dry air from outside and allow the moist air from inside to cycle out of the room.

You can open a door too. This will create a cross-draft in the room and allow moisture to escape, keeping the room’s atmosphere dry enough to allow the swamp cooler to keep creating cold air.

When told about this simple solution, many people are surprised that they should allow hot air from outside to get into the room. Won’t that make it hot in the room?

Actually, the room will stay cool because the cooler is still working and blasting out cold air, maintaining a cooler temperature than there would otherwise be in the room. This works very well and if you own a swamp cooler and were concerned it wasn’t working properly, please try this before discarding it!

Running Costs are Still Low

This is a big difference from running a portable air conditioner which needs all windows and doors to be closed to keep the coolness in and the heat out. AC still works with a window open, but because it costs so much to run and uses so much power, it would be extremely wasteful (and cost you a lot more in dollar terms) to run AC with a window open.

However, ventless evaporative air coolers cost around 1/20th of a comparable AC to run in terms of power consumption. So there is very little wastage by having a window open and in fact this is actually a necessity to ensure the unit keeps the room cool.

So now you know (if you didn’t already). You can run a swamp cooler in a humid room just by allowing air to cycle from outside to keep the moisture level low enough inside and you’ll still enjoy all the low cost benefits of this type of cooling process day after day!


25 thoughts on “Getting an Evaporative Cooler to Work in Humidity

  1. Amy says:

    Will this open window technique work if you live in the southeastern portion of the US, such as northern Mississippi? The outside air is also humid.

    Also, what if you have a central air unit but need to keep just one room cooler than the rest of the house at night? Would this unit work, preferably without window open?

    Thank you!!

    • cook says:

      Hey Amy, thanks for the question. Most of the areas in the southeastern states are very humid in summer and that’s not great for evaporative coolers. You need to know the humidity levels in your location to be really sure, but if outside air humidity is 70% or higher I would not recommend using an evaporative cooler, even with windows open. However, if you already have central AC running in your home and want to cool one room a bit more, they can work because AC dries the air a lot. You would need to keep windows closed in that case and let the AC act as a dehumidifier.

      • Nathan says:

        Thanks for wasting everyone’s time. I’m sure everyone that found this article did so because we live in humid areas like the southeast, looking for solutions for off-gridding and such, but have not yet found practical solutions to air conditioning.

        • cook says:

          You’re welcome Nathan, glad you took some more time to leave your thoughts.

          I’m sure you read through the article and realized it was aimed at why swamp coolers stop working in closed rooms with no way for the rising humidity in the air they create to escape and be replenished with dryer air from outside. Sure there are limits to what these devices can achieve and we can’t control the outside climate. But we can to some extent control the indoor climate without AC where it’s not insanely humid outside.

          One more thing. I lived off grid when I was younger and generated a lot of electricity using a combo of micro-hydro and wind. Photovoltaics were expensive and inefficient back in the 70s (in my day). So we used what we had. Living in a windy place with a pretty fast running river at the far end of the land made it possible to generate a steady 2Kw for a lot of the time. Enough to run a small overhead split A/C unit in the living room where we slept when it got too hot outside.

          Times change and technology moves forward. But for all the collected brain power the human race is capable of aiming at a solution to the problem of generating off grid electricity, we’ve come up woefully short. Or maybe Big Energy is holding out on us because they want us to use the grid power and not get it without paying their exorbitant bills! Maybe I should stop there before I get a visit from some guys in suits…

          • Prashant Sharma says:

            Lolss try story ????
            And yes unfortunately u cant have it all. These devices are awesome because they cost about ¼ or even less of an AC and electricity consumption is also very low. I mean cost of running an AC increases the electricity consumption to atleast 2 folds if suppose entire house with all the appliance including an evaporation cooler consumes about 500 units of ekectricity a month then using an AC increases it to minimum 1000 or1200 units a month and that too when it is not beings used entire day but in short durations.
            So ya no doubt that evaporative coolers are much greener but at the same time they aint as effective as AC
            I am from India and have humid sub tropical climate here temperature rises up to extreme 113°F or 45°C and using cooler gives cooling but also increases the inside humidity and eventually the discomforts associated with it.
            Coolers are good in month of may and june when there is less humidity outside. In month of July and August we recieve monsoon that is the rainy season that increases humidity to even 80-90 % and unfortunately coolers is of no use then and you cant do anything about it and last resort is to use an AC

      • Tirthanath Goswami says:

        There r varius types of aircooler in India. Can u suggest the type of cooler best suitable for high humid area, assan,india

  2. Elsie says:

    Okay, I live in Southern Louisiana, where it is very humid. I’m looking for something to cool my garage. Not necessarily as cool as the inside of my house, but at least something where I can breathe when I sit in my garage. I’m a smoker and do not smoke in my house and sometimes the weather isn’t cooperative for me to sit on my back patio (stormy, too hot, etc). I thought something like this would be a solution, but after reading some of the info provided here, I guess this is not the way to go. Any suggestions as to how I can cool it down enough to be bearable??

    • cook says:

      Hey Elsie, If you can close up the garage but have someplace to fit an AC exhaust hose, I’d suggest getting a portable AC and hooking it up. That will cool you down as humidity doesn’t affect AC but high humidity will stop a swamp cooler working. AC costs more to run, but what price comfort, right?

      • Joe says:

        A portable AC will do absolutely nothing about the insane heat load inside a closed garage. Even with the unit’s vents pointed directly at your bare buttocks.

  3. Kalim says:

    Hi, I have a question if someone can help. If the ambient temperature (DBT) is 120F and relative humidity is 50 %, how much an evaporative cooling will drop the temperature, ie WBT=?

    • Stephanie says:

      Around 30 degrees or to 90F could be possible with an evaporative cooler. The lower the humidity the better an evaporative cooler will work.

  4. Louise A Carasone says:

    I live in Connecticut. Would this type of cooling system work here. I don’t have a window in my bedroom, just a sliding glass door. I don’t want to be uncomfortable this summer.

  5. Mary says:

    Hey Louise, I live just outside of Harford CT and I have a free standing swamp cooler in the bedroom. It isn’t as powerful as the AC but it does drop the temp about 15 deg in summer when I turn off the AC. Its a little noisy but I like the hum it helps me sleep!

    Hey Kalim, that sounds too tech for me, but my own personal experience is a 15 deg drop in temp. It never gets as hot as 120 here in summer!

  6. Anthony says:

    I’m in Memphis very humid I have A/C but my bed room does not get as cool as other rooms very hot in peak summer days will a evaporative cooler help my bed room if so what size I priced some from $65 up help THANKS.

    • cook says:

      Anthony, if your AC isn’t cooling your bedroom enough, could be it needs to be serviced. You might be better spending that $65 on a service engineer to check over your system, clean out the ducts and get it working the way it should.

  7. Kathy says:

    I live in Southwest MO where the humidity sometimes in summer reaches very high levels. I have AC, but we built on a large 28×24 ft bedroom and only put in 2- 8 in. Vents next to a wall for AC and heat. (my husband was being very cheap) Consequently, it’s just not enough to heat or cool the air in that room to a real comfortable level. Since its getting some A.C., would a swamp cooler work here to finish cooling the room to a more comfortable level? Or should we just put in a window unit? Thanks

    • Zaak OConan says:

      There’s a good chance it would help. If your AC is dehumidifying the air enough.
      Measure the humidity. If 50% or below you will get results from evaporative coolers.

      Above 50% your milage will vary.
      Higher the humidity goes the less effective evaporative cooling will work.

  8. Skylur says:

    We live in phoenix. Very hot and dry, even during the rainy season the humidity is rarely above 40 for very long. We are leaving for a trip and having a discussion on leaving the cooler going 24/7 while we are gone or turning on the ac to 86 or so during the day. The whole issue is the dog who will be on guard while we are gone.

    The last trip we turned the water off on the cooler and just had the unit come on at night for 5 hours in order to get the cooler air in the house.

  9. Akosua says:

    I live in DC where the temp gets up to 100 degrees in July and August. I can’t fit a window a/c unit in my basement because of the window bars and no vent because the windows won’t hold it. Will the swamp cooler help keep the temperature down?

  10. Maggie McAuliffe says:

    I am trying to cool down a “crawl space” inside my daughter’s room so that we can turn it in to a little “clubhouse” type nook for her. There is a door to get in to it. There are no windows or vents in the space and it gets really hot in there during the summer. I live in Georgia so obviously it’s humid. Would a swamp cooler work if I also purchased a dehumidifier for the space? My only other alternative is to have a dormer window put in but frankly the price for something like that is crazy…

    • cook says:

      Hi Maggie, sorry I didn’t respond sooner. I was hoping someone with better specific buildings knowledge might chime in, but I guess not.

      From what I know of evaporative coolers, I’d be reluctant to try one on a small enclosed space like you’re describing with a total lack of ventilation. An evap + dehumidifier will work but the extra energy costs of specific units together can come close to that of a small 8,000 btu portable AC running on the lowest setting.

      The next part would need to be answered by a builder or ventilation engineer, but if it’s feasible to ventilate the space maybe with an extractor fan unit installed linking to the outside your options would be better.

  11. Lisa Hayes says:

    I live in south Orange County, California, about 4 miles from ocean. Today even though the temperature is 83 degrees the humidity is 60% and the dew pt is 63%.

    My home was built without A/C in 1970. But it is absolutely miserable here. I was looking into buying a New Air Portable evaporative cooler from Home Depot but now after reading some of your reviews it looks like that might not be smart. With the humidity level as high as it is right now would an evaporative cooler be ineffective? If so would a dehumidifier be a better choice? I know air conditioning would be the best solution but my windows won’t hold an air conditioner and the cost of electricity would be too high for me. :/ Any suggestions?

    • cook says:

      Hi Lisa, 60% is around the upper limit for evaporative coolers to be effective so you will still get some cooling from one with a window open. Adding a dehumidifier will help some, but they also consume electricity. In your situation, it would be worth working out the total consumption of each specific model of evap cooler + dehumidifier running together vs that of a portable AC to see which is a better choice on running costs.

  12. Ali McFall says:

    When running a swamp cooler do you need to close the air conditioning vents?

  13. Eddie Smith says:

    I live in an apartment, here in L.A. that has no AC. Being that my windows open sideways, like doors, a portable AC unit won’t work. I finally broke down an picked up a SPT swamp cooler and I cannot figure out why I didn’t think about this years ago. After all, as a kid, we had a old faux woodgrain version of one.

    Although a cooler won’t lower temps like an actual AC, it can make a substantial difference. When I tell most folks about swamp coolers, they’d never heard of them. If you’re in SoCal and heat’s a problem, I’d recommend trying out a cheap version of a cooler than doing without one at all.

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