Choosing Whether or Not To Install Evaporative Cooling

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(Also see “Trouble-Shooting” if your cooler is not performing well)

Evaporative Cooling
Refrigerated Air Conditioning??

A common question asked by many is “should I install an Evaporative Cooler or Refrigerated Air Conditioning?”

(Please note: The correct terminology is “Evaporative Cooler” and NOT “Swamp Cooler”)

If you live in a coastal or tropical region, you probably never hear the explanation below because “evap cooling” is not very efficient when your ambient air is full of humidity.
(except for use in greenhouses where high humidity is healthy for the plants)

If your wet bulb temperature is around 60% and higher, then refrigerated cooling is the correct answer.
In lower wet bulb regions a properly sized evaporative cooler can be a very cost- effective and comfortable choice.

Sizing the evaporative cooler is the key

A good “rule of thumb” is to have 1 air change every 3 minutes in northern states, 1 air change every 2 minutes in the mid section and 1 air change every 1-2 minutes in the southern states.

The Rule of Thumb formula for sizing your cooler is very simple;

Multiply the length by the width by the height of the area to be cooled to get the cubic footage for the area. Then divide by your air change factor minutes. The example below reflects a “2” minute air change.


A home that is 30′ wide, 40′ long and 8′ ceiling has a total of 9600 cubic feet of area to be cooled.
30 x 40 x 8 = 9600
Using the factor two (for an air change every two minutes),
divide 9600 by two to give you the CFM required, in this case, 4800 CFM.
9600 / 2 = 4800

In this case, you would want to use a 4800 CFM cooler.
(Note: It never hurts to go one size up. You might consider a 5500 CFM cooler here)
The cooler can be run on low speed, then cranked up to High on severe days.

Another important factor is “Exhaust Air’. A good cooler design is to exhaust slightly more air than your cooler is supplying, this can be done with windows or doors being open slightly or a sized exhaust fan inter-locked with the cooler.

Having enough air exhausted is important so that there is negative air pressure in the conditioned space, positive air will cut down your blower’s capacity. A big advantage to evap coolers is that the capacity can be changed easily by adjustable pulleys to increase or decrease air flow. If you open your front door and the pressure slams it shut then, you need more exhaust openings, such as a window or another door.

(Ample air exhausted also reduces the humidity build up)

Refrigerated air conditioning cools no matter what the humidity is and usually increases your home value (as well as your electric bill) more than an evap cooler, but with a well designed evaporative cooling system installed, cost is less to install and hardly noticeable on your utility bill.

A few notes for evaporative cooler maintenance:

The more frequent aspen cooler pads are changed the better – don’t try to get 2-3 years out of pads. Twice a season is best (although seldom done). Be sure to change aspen pads at the beginning of each season when starting up your cooler.
(An exception to this is using a cooler with a celdek type pad, such as our UltraCool)
The pads can easily be used for five years or more when the cooler is properly installed with a bleed off system.

A properly installed bleed off system can prolong the life of your pads and greatly reduce the corrosion affects on your cooler. Below are two types that can be used.

Bleed Off Kit System
Power Clean Purge Pump System
(Purge Pump Conserves More Water)

Oil the motor and bearings – Most evaporative cooler motors do have oil ports. Use SAE #20 non-detergent oil.
Do not use motor oil. It has detergent content. This will reduce the life of your bearings.

Check for proper belt tension, and amp draw. (Overloading the amp draw will burn the motor out)

(just a few tips – there are many more things to check out)
This should be done by a qualified technician

Cooler undersized
Replace with larger cooler
Clogged or dirty filters
Replace with new pads
Dry pads or lack of water while cooler is operating
Check water distributing system for possible obstruction in tubing. Check pump operation.
Replace Pump if necessary
Insufficient air discharge openings or inadequate exhaust from area being cooled, causing humidity building up and discomfort

Evaporative coolers must have large enough ductwork
Ductwork sized for refrigeration simply will not let the higher cfm from a cooler out.

Make sure there is adequate provision for exhausting air from area being cooled.
Excessive humidity.
(See also item above re: inadequate exhaust)
In some areas, there may be a few days during the summer when the relative humidity is high, resulting in poor cooling. (60% or higher) These are limitations of an evaporative cooler under conditions of high wet bulb temperature.
Blower turning backwards
Reconnect motor for correct direction.
Blower installed backward
Remove and reinstall blower wheel to turn in correct direction.
Blower running too slow
Check motor amps. If below nameplate amperage, readjust variable pitch motor pulley to increase blower speed. Do not increase amperage above motor rating. This will burn the motor out.
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