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Cheap Evaporative Cooler

Hello everyone,

My goal in this hobby is to grow plants using cheap materials with minimal electrical power. I'm an eco-nut and just hate spending money on electric bills. So, here is my homemade swamp cooler. I made it for $25-30 and it draws about 50W. Hopefully, this will allow me to grow HL Nepenthes and Heliamphora, but my goal is to help everyone else out as well! Please comment with questions, ideas, and experiences.

I have confirmed that this cooler humidifies as well as chills air at least 10 degrees. My basement's air is typically 70F or 68F and 30% RH, and this cooler got the air down to 60F and the relative humidity up to 65%.

However, its effects in your conditions may be different. It will cool to a temperature very close to the dew point, so you can use this calculator to determine the temperature you could achieve. http://www.dpcalc.org/

-Sterilite tub (sizable, should hold 20 gallons I think)
-Fans (I used two Cooltron fans that can be found here: http://www.amazon.com/115V-AC-Cooli...1351817274&sr=8-1&keywords=cooltron+fans+115v)
-Evaporative cooling pad (also called humidifier filter pads, they should be water absorbant and porous)
-Nails (you can use screws and bolts)
-Drill and assorted bits
-Powerful cutting implement (I used tin snips and scissors)
-Duct tape
-Electrical Pump
-PVC tube (rigid and flexible)
-Meter stick or ruler


Assemble all necessary materials :)

<a href="http://www.flickr.com/photos/84442298@N03/8146337466/" title="DSC01726 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8473/8146337466_5b74cd2473.jpg" width="500" height="375" alt="DSC01726"></a>

Cut the evaporative cooling pad to a suitable size for your tub and trace it on one side. It should leave a few inches open beside it, and leave about 3-4 inches below it for the reservoir of water.

<a href="http://www.flickr.com/photos/84442298@N03/8146336204/" title="DSC01727 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8334/8146336204_5ca4f2a236.jpg" width="500" height="375" alt="DSC01727"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8146334918/" title="DSC01728 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8465/8146334918_5701085e1d.jpg" width="500" height="375" alt="DSC01728"></a>

Select a large bit for the drill, and make a hole in one corner of the trace. Using the tin-snips, cut out the hole for the evaporative cooling pad. BE SURE TO MAKE IT A LITTLE SMALLER THAN THE PAD ITSELF. I learned the hard way that no overlap will lead to leaking later. Also, I like to cut in chunks, to make sure I didn't stress the plastic so much that it would shatter.

<a href="http://www.flickr.com/photos/84442298@N03/8146300047/" title="DSC01729 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8189/8146300047_b3345e9cb7.jpg" width="500" height="375" alt="DSC01729"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8146331892/" title="DSC01730 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8323/8146331892_5a22ebe4ab.jpg" width="500" height="375" alt="DSC01730"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8146297137/" title="DSC01731 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8184/8146297137_606f72d71f.jpg" width="500" height="375" alt="DSC01731"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8146295907/" title="DSC01732 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8054/8146295907_e1c7a70ebd.jpg" width="500" height="375" alt="DSC01732"></a>

Drill six holes around the hole, one in each corner, one above the middle, and one below the middle. Cut six lengths of wire, about 4 inches long. Thread these through the pad and the holes and twist to secure the pad in place. There should be overlap between the pad and the tub.

<a href="http://www.flickr.com/photos/84442298@N03/8146276201/" title="DSC01747 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8336/8146276201_9221661212.jpg" width="375" height="500" alt="DSC01747"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8146294976/" title="DSC01762 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8474/8146294976_678bd12cf1.jpg" width="500" height="375" alt="DSC01762"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8146260467/" title="DSC01764 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8326/8146260467_8dd461a2df.jpg" width="375" height="500" alt="DSC01764"></a>

Flip the tub over and place the two fans on the tub. Position them however you like, just make sure they are well above the water line, and well spaced apart. Trace the fan blades to create the circle you need to cut out.

<a href="http://www.flickr.com/photos/84442298@N03/8146327928/" title="DSC01733 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8470/8146327928_1145ab5e81.jpg" width="500" height="375" alt="DSC01733"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8146293341/" title="DSC01734 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8467/8146293341_b65f768836.jpg" width="500" height="375" alt="DSC01734"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8146325412/" title="DSC01736 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8185/8146325412_b8cd7ba2c4.jpg" width="500" height="375" alt="DSC01736"></a>

Drill a few holes in the center, and use the tin snips to cut the two circles out.

<a href="http://www.flickr.com/photos/84442298@N03/8146324494/" title="DSC01737 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8194/8146324494_a4a1e4692a.jpg" width="500" height="375" alt="DSC01737"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8146290213/" title="DSC01738 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8331/8146290213_d17cac1898.jpg" width="500" height="375" alt="DSC01738"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8146321752/" title="DSC01739 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8333/8146321752_bba5fe91fb.jpg" width="500" height="375" alt="DSC01739"></a>

Place the fans over the holes, and trim to perfection. Then, select a nail (or screw and bolt) that fits snugly through the holes in the fan's corners. Stick this through the holes, then press down and twist to make a mark where a hole should be drilled. Do this for each corner, then remove the fan and clearly mark with the marker. Then drill these holes with a drillbit that is slightly larger than the nails.

<a href="http://www.flickr.com/photos/84442298@N03/8146287443/" title="DSC01742 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8334/8146287443_10b88dfcbf.jpg" width="500" height="375" alt="DSC01742"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8146319166/" title="DSC01743 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8323/8146319166_a6f251fd70.jpg" width="500" height="375" alt="DSC01743"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8146317862/" title="DSC01744 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8194/8146317862_b7003c9f5d.jpg" width="500" height="375" alt="DSC01744"></a>

Then, insert the nails into the holes. Thread the fans onto the nails. Screw on the bolt if you have them. Mine were perfectly snug, and I left them as is.

<a href="http://www.flickr.com/photos/84442298@N03/8146314900/" title="DSC01745 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8469/8146314900_8f9267b39c.jpg" width="500" height="375" alt="DSC01745"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8146311064/" title="DSC01746 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8466/8146311064_2e7886c5c9.jpg" width="500" height="375" alt="DSC01746"></a>

Now you're 80% done, but this last part is hard and will take some more time. Here's where you rig the pump and PVC tube.

Begin by cutting the PVC tube to the length you want. I used clear, 1/2" diameter tubing. I cut it to be about 3' long. If it is a little too small to fit over the pump outlet, try heating it with a lighter or something to stretch it. That's what I ended up having to do.

After you have the PVC attached to the pump, prepare the mounting equipment. You're going to need five pieces of wire, about 2.5" long. Hold one end down on a flat surface, and use the wire pliers to curl them into hooks. The hook should be just a little smaller than the tube. Then you want to drill five holes into the tub, directly above the cooling pad. Placement doesn't matter, just keep them even.

<a href="http://www.flickr.com/photos/84442298@N03/8194202080/" title="DSC01792 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8488/8194202080_26611f60d1.jpg" width="500" height="375" alt="DSC01792"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8194201634/" title="DSC01793 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8203/8194201634_8d3cfb2079.jpg" width="500" height="375" alt="DSC01793"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8194204278/" title="DSC01796 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8200/8194204278_79c445c844.jpg" width="500" height="375" alt="DSC01796"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8193114381/" title="DSC01797 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8200/8193114381_5d1e962594.jpg" width="500" height="375" alt="DSC01797"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8193113645/" title="DSC01798 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8200/8193113645_1044ac6016.jpg" width="500" height="375" alt="DSC01798"></a>

Now you want to thread the wire hooks onto the PVC tubing. Lay the tube flat against the tub and the holes you drilled. Mark with your finger where the hook should go, pinch down on the tube, and slide it on. It should stick on firmly. Once you have all of them attached, thread them through the holes, and use the wire pliers to make hooks on the other side, so that the wire stays in place.

<a href="http://www.flickr.com/photos/84442298@N03/8193113125/" title="DSC01799 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8067/8193113125_8b4428e09d.jpg" width="500" height="375" alt="DSC01799"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8193115433/" title="DSC01795 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8479/8193115433_bede4800ab.jpg" width="500" height="375" alt="DSC01795"></a>
<a href="http://www.flickr.com/photos/84442298@N03/8194201186/" title="DSC01804 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8348/8194201186_93ba130315.jpg" width="500" height="375" alt="DSC01804"></a>

Now that you have your tube in place, you can start drilling your holes. There is no easy way to do this, but what I did is lay the tub on it's side, pad facing down. I then reached the drill inside, and turned it so it faced the bottom of the PVC tube. I drilled about 8 little holes. MAKE SURE THEY ARE WELL-DRILLED HOLES WITH NO PVC DEBRIS IN THEM. THIS WILL BE A PAIN TO FIX LATER. Once everything is drilled, turn it right-side up and plug the end of the tube with something. I found that an aluminum foil ball stuffed in the end created enough resistance to make the water come out the holes, but also left enough of a gap so that nothing was spurting or exploding :)

Here's what it should look like:

<a href="http://www.flickr.com/photos/84442298@N03/8194156606/" title="DSC01821 by Sundrew, on Flickr"><img src="http://farm9.staticflickr.com/8487/8194156606_38351a4357_z.jpg" width="640" height="480" alt="DSC01821"></a>

Now you can place the tub's top back on (it should bend over the wires) and plug everything into a timer. Any odd holes you can re-drill. I had to fix the duct tape mess I made at the end of the tube and direct the spurting water down onto the pad. But otherwise, you're done the cooler! Fill it up with water every couple of weeks, and enjoy your highland plants!

I will post later this winter when I have the grow shelf and duct the cold air into the HL chamber. But thanks for looking, and comments are welcome!
Last edited:
Do you have a CFM reading? I could see this being more of a humidifier than a swamp cooler with just two small fans. Nice work though! :)
Very cool and thanks for sharing the info!
That looks like a great start! i cant wait to see the finished product.
Thanks everyone!

Do you have a CFM reading? I could see this being more of a humidifier than a swamp cooler with just two small fans. Nice work though! :)

Each fan has an output of 110CFM, which I think should be more than enough for most terrariums and growshelves. At least the one I'm building.
*updated* Video coming soon.
guess im going to have to try this too , need some cooling in the coming summer now that im growing at work too .
nice work, sundew

let us know how much air your getting it does seem a little shy of what you might need,what does the average cpu fan push.

(CFM ) whats this??:blush:
  • #10
Each of the two fans moves about 110 cubic feet per minute (CFM). They are plenty strong, as a 4' x 4' x 8' growtent is only 128 cubic feet in volume. But you can also use larger fans from Walmart or somewhere cheap if you would like more air. I liked this size though, because I will be able to use 5" aluminum ducts to guide the air.
  • #11
Now to keep Lil Stink's kitten out of it, somehow. Solve that, and I might build one. :lol:

Nice job, really! It's a cool build.
  • #12
Thanks Lil! lol I can imagine a kitten tearing apart the cooling pad.
  • #13
Nice work. I would recommend against the pads unless you don't mind running through your RO water and can manage to design a small water pump.
My attempt at a design like this last year didn't quite meet my expectations. I was either running through crazy amounts of DI water which I had to constantly re-fill or the minerals/sediments would very quickly clog my evaporative pads. Sponges didn't do the trick either.
I think you'll find that even with only RO/DI water, the fans will evaporate the water off quicker than the pad can pull. Ideally a pump to water the pad from the top would be best but I ended up going with a mist maker/pond fogger.

Not saying this won't work for you but I can recommend other threads if you decide to change your setup. Let us know how this works out for you in the long run.
  • #14
I do have this watering from the top, and I am currently using tap water for these tests. I don't want to buy distilled or RO water, so I use rain water, but that has too many microorganisms for it to be better than tap. I think that the minerals will be washed out of the pad as the water trickles down, but we will know in a few weeks. The pump is old and has worked in much worse conditions, so I'm not worried about it. And I think with a constant supply of water the pad should stay wet, although I can always turn off one fan if they pull too much air.

Thanks for the feedback! I appreciate it.
  • #15
Ahh my mistake, I should have looked at your last picture more carefully :)
You should be fine in regards to the mineral build up then. Maybe occasionally having to replace the pad depending on your water's hardness. But with RO water that shouldn't be a concern.
Regarding microoganisms, you can periodically add just a small amount of bleach to your water. I do this to mine to keep the algae and slime out. Good luck!!
  • #16
I didn't think I could use bleach for something like this, thanks for the advice! I'll let you know about the pad :)
  • #17
Looks great Drew! I am a huge fan of anything DIY and cheap, so will definitly try something like this. A word of caution on the use of bleach though: in tiny amounts no problem, but the chlorine is fairly volitile and could harm you or your plants in such an effective evaporator like this if you use it "heavy handedly". Though I'm sure you've thought about this idea already. Gonna try this for sure though, so thanks for sharing!
  • #18
Having a home RO unit will help with refills. Fantastic plan; please post a video of it in action.
The holes for the fans might work better if placed higher so there can be a larger reservoir.
  • #19
Thank you so much! It was more the pad that I placed too low, I had assumed that the PVC tubing would take up more space above it. That's absolutely something someone could improve upon, there is the potential here for it to hold a ton of water. I appreciate the feedback!

I will make a video today :)
  • #20
Cool project drew... curious as to what your temperature differential ends up being.