How to Build an Evaporative Cooler


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Categories: DIY

Which Swamp Cooler Pad to Buy?  Synthetic or Organic?

You can buy swamp cooler pad that is made of organic or synthetic fibers.  You can read the marketing stuff about which one is better, but here’s my experience from hosting a workshop where a bunch of people built 5 swamp coolers in my yard and some of them used organic and others used synthetic pad.  When you cut the pad, little bits will get everywhere.  The organic pad that got all over our garage and yard was quickly used by birds and squirrels to make energy-efficient nests in the trees.  The synthetic blue bits seemed to get ground into the floor and dirt by our feet.  The synthetic bits were difficult to remove with a shop vac or broom, perhaps because they had some static charge making them cling?  The organic fibers smell like wood chips or hay, and the synthetic pad has a slightly plastic smell.  Neither smell was offensive to me, but some folks didn’t like the  smell of hay when the swamp cooler was operating.

I recommend purchasing a roll of the organic Aspen Cooler Pad, and cut rectangles to share it with friends and neighbors.    We cut one piece of pad into a  33.5″ x 24″ rectangle and then folded it in half, and rolled it into a cylinder that fit inside our bucket.  The instructions on the ePlaya link explain how to cut two perfectly fitted rectangles using the synthetic pad by Duracool.

Battery Options and Solar Energy


For maximum portability, we used a 12 volt sealed lead acid battery for about ten to twenty dollars.  This type of battery is often used to run a computer backup uninterruptible power supply, or UPS.  You will want a battery which can give enough current to both the fan and the water pump, so 1.2 AH rating on the battery is quite sufficient.  AH stands for Amp Hours.  We ran our swamp cooler with the big 1.60 Amp fan for 6 hours and it ran down our battery enough that it wasn’t blowing very hard anymore.  Frys.com andAllElectronics.com sell batteries like this, however you’ll save money on shipping if you buy from a local hobby store, electronics store, or computer store.

If you’re traveling with a car or boat, then you can run your swamp cooler on your 12V vehicle battery.  When we go to Burning Man, we take a deep cycle marine battery that weighs about fifty pounds.  That huge battery runs our lights, a stereo, and our swamp coolers for 9 days.  The marine battery is easily recharged with a small (12″ x 4″) solar panel and a charge controller.

You could try using this solar-powered water pump for $25.  However you would still need a power source for the fan.

Steps to build your Evaporative Cooler

Generally, we followed the instructions for “Cooling your Tent or Van” by FigJam on the ePlaya website.  Here I will reference his instructions and add my own tips and alternatives.

Step 1 Drill Holes in your 5 gallon bucket

FigJam drilled one row of big holes, we drilled two rows of 2″ holes because that’s the size of hole saw that we already owned.  This step is messy and fun.  Use a shop vac to cleanup the mess.  The goal is to maximize air flow through the damp pad, and leave enough water in the bottom of the bucket to cover your water pump for the entire duration of the runtime (e.g. six hours of sleep).

Key considerations on where to drill the holes:

  • Your water pump must be completely submerged or it will run dry and break.  Mark your water line that gives you at least 2 inches of water above your pump intake.  Cut your ventilation holes above that water line.
  • The holes should be at least 4 or 5 inches from the lid of the bucket.  You want the air to come in through the holes, pass through the damp pad, then come out through the fan at the top.   If the air passes through more damp pad, then that’s great!  See pictures.

Step 2 Cut your Screen and Cooler Pad

Two rows of 2″ holes above the water line.

The optional window screen helps to keep the cooler pad and the drippy water inside of your bucket.  I tried gluing the screen to the inside of my bucket, but that didn’t work well, so don’t bother.  The screen and cooler pad should cover all of your ventilation holes.  Measure from the inside bottom of your bucket to at least 3 inches above your ventilation holes.  Leave an inch or two at the top section of the bucket for your PC fan and wires.

You want to force ALL the air through the damp pad.  If air can sneak in the air holes and out through the fan without going through the damp pad, then it won’t be cool!

Option A exact dimensions:  Measure and cut your screen in a trapezoid shape because the bottom circumference of your bucket is closer to 32″ and the top diameter of the bucket is about 33.5″ if you are using the same bucket that I did.    Measure the diameters of the inside of your bucket near the lid and near the bottom, and then do some math (diameter * 3.14 = circumference).  Now measure and cut your window screen and test the fit before measuring and cutting your cooler pad.  For the cooler pad, cut your trapezoid slightly smaller to allow for the thickness of the pad.

Option B Close Enough Engineering:  Cut your screen to a rectangle about 34″ x 13″ and it will overlap some when you stick it in your bucket.  Cut your swamp cooler pad about 33″ by 24″, fold it in half and shove it in your bucket.  Trim it if you have to.

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