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Evaporative Cooler Performance

Homeowners can use the cooler index to decide when to switch between evaporative cooling and air conditioning. As a general rule, if a cooler produces air colder than 70F, it will create a comfortable environment; if it produces air hotter than 75F, it will not. Between 70F and 75F is a gray range in which some people are comfortable and some are not.

Evaporative cooler index for standard aspen-pad coolers.

Evaporative Cooler Index - Relative Humidity vs. Air Temperature Comfort Chart

Enter the table from the left with outside air temperature and the top with outdoor humidity. Where the row and column meet is the temperature of air a typical evaporative cooler will produce. The cooler index can also be used to check the performance of cooler pads.

An alternate way to determine pad performance is to check the temperature of the air leaving the cooler against the cooler index. The cooler index is the anticipated temperature of the air leaving an aspen pad cooler and accounts for heat added to the air by the pump and fan motors and a cabinet exposed to the sun. The cooler index has the advantage of enabling the homeowner to check cooler performance by watching the news and checking the temperature of the air leaving the diffuser in the house.

If this temperature is 3F or more higher than the cooler index indicates as normal, the cooler is not operating as well as it should be, probably due to a malfunctioning water distribution system, sagging pads, or poorly manufactured aspen pads.

To Print An Evaporative cooler index

  1. Place the desired print material in the printer (magnetic sheet or paper/card stock). 
  2. Click Here.
  3. Right click the image and Select Print Picture.  
  • OR
  • Use the File Tab to print the image.
To turn your Evaporative Cooler Performance Chart into an easy reference refrigerator magnet; go to DIY Refrigerator Magnets at

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