How to Build an Evaporative Cooler

Categories: DIY

Portable Swamp Cooler. Click for larger image.

How to build a low-cost 12 volt evaporative cooler.  My husband and I built two swamp coolers that we use to air condition our tent when we camp in hot, dry weather at Burning Man.  These compact units blow cool air like an air conditioner, but they use just water for evaporation instead of using a compressor or toxic Freon. There are two great designs on the internet for making evaporative coolers for camping.  This blog post enhances one of those designs by providing lots of detail on sourcing parts, comparing options for parts, and a variety of power options.  We built ours for under $40 each and they worked great for cooling a tent and letting us nap in the Nevada desert.  After building one, we hosted a workshop where we helped neighbors build 5 coolers, which let us buy parts in batches and save on shipping costs.

Reference designs:

We used the following materials:

  • 5 gallon bucket from the local hardware store or recycled, $0 – $2.30
  • 12v water pump from, $18.50 + shipping = $20
  • Swamp cooler pad 33.5″ x 24″, $2 – $7
  • Drip irrigation tube 48″ long, Tee connector, diameter should fit your water pump, $5 – $10
  • Recycled PC fan, 12VDC and around 1 to 2 Amps, $0.50 – $4
  • Elbow duct 4″ diameter, $3
  • 12 volt battery, $10 – $20
  • Screws, 4 Short sheet metal screws, $0.50 – $1
  • Quick connect female crimp connectors, sized for your battery
  • Four to eight feet of small gauge wire (20 – 26 gauge)
  • Butt splice connectors, to connect the wires butt to butt, in the gauge of your wire
  • Optional: window screen 33.5″ x 13″, $0 – $6
  • Total:  $40 to $73

Tools that you will need to buy or borrow:

  • Drill
  • Hole saw drill bit, 2″ to 3″ , $13
  • Wire cutters and very small gauge wire strippers, 20 – 26 gage
  • Tin snips for cutting your elbow duct
  • Optional: silicone caulk

How do I choose a good recycled PC fan?

You can get a great deal if your town has a store where you can get recycled computer parts, or perhaps your local Goodwill has electronic stuff.  We got a bunch of fans for 50 cents each at PC Recycle in Seattle.  Or for a bit more money you can buy recycled PC fans off the internet from places like or  Or you could pay the full price for a new fan from your local computer store or  Shame on you for paying full price.  Retail is for chumps!

You want to read all those letters and numbers and find “12 VDC” which means 12 volts of direct current.  Direct current is what you get from a battery or solar panel.  Next you want to find a fan that will move a lot of air by drawing a lot of current, so you look at the number preceding the “A” for amps.  For example, “0.11A” or “0.20 Amps” are pathetically weak, and a “1.2A” or “1.6A” fan will blow a lot of air!    The bigger the number, the cooler you will be, and the faster it will drain your battery.  My fan was 1.6A and our little $10 battery ran the fan and pump for 5 hours before we noticed the battery getting low.

Recycled PC fan screwed to lid of bucket. Note the edges of the elbow duct. Click for larger image.

Online the listings will also describe the dimensions of the fan, such as 80mm or 120mm.  The size doesn’t really matter as long as it is in the ballpark of about 80 – 120 millimeters.  You’re going to drill your own mounting holes in the lid of your bucket so the exact size doesn’t matter.  Bring the fan with you to the store when you buy your elbow duct.  Your elbow duct diameter must be smaller than the distance between the corners of the fan’s mounting holes.

The number of wires coming out of the fan also don’t matter for this application.  You will only use power and ground, typically red and black.  The other wires control the speed of the fan if it were connected to a computer, but we don’t care.

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