Buying Guide

How to Choose the Right Size Evaporative Cooler

How Do Evaporative Coolers Work?

Evaporative coolers lower indoor temperatures by combining the natural cooling properties of evaporating water with an efficient air moving system.

Evaporative coolers add moisture while water-filled pads act as a filter, removing dust and allergens from the air.

Evaporative coolers offer several benefits over air conditioning, including:

  • Lower installation and maintenance costs  
  • Up to 75 percent less electricity usage  
  • Helps prevent fabrics and wood from drying out 
  • Can be powered by standard 120-volt outlet  
  • No ozone damaging refrigerants  

Evaporative coolers are not as controllable as air conditioners and can use between 3.5 and 10 gallons of water per hour, a consideration for use in areas with limited water supplies.

Tip: Read our comprehensive guide if you’re still asking how does a swamp cooler work.

Types of Evaporative Coolers

Evaporative coolers are typically distinguished by where they are installed and the type of pads they use.

Most whole-house evaporative coolers are mounted on the roof and blow air downward, while others are mounted through windows or walls and blow air in from the side.

Down-flow installations are most popular, but window/wall-mounted horizontal units are more convenient for maintenance and reduce the chance of roof leaks.

Both down-draft and window-mounted units blow cooled air into the house either into a central location, which is effective for small homes, or through existing or specially installed ductwork in larger homes.

The following sections include a breakdown of swamp cooler sizing:

Portable Coolers
Portable coolers
Window/Through-the-Wall Coolers
Down Discharge Coolers
  • A whole-house cooler
  • Installed on roof  
  • Discharges cool air downward into the structure
Side Discharge Coolers
  • A whole-house cooler
  • Typically installed on the side of a building, directing into the attic area  
  • Can be installed on the roof using an elbow to direct the airflow through an opening in the roof
Types of Pads for Evaporative Coolers

The two types of pads for evaporative coolers are fiber (made of various materials) and rigid media pads.   

Fiber pads are inexpensive but require more maintenance and replacement, while rigid media pads are more expensive but require less maintenance and may last for years if properly maintained.

This chart details the best type of swamp cooler pads for different applications:

CFM Ratings

Tip: To ensure effective distribution, calculate know how much air the unit needs to move to cool your home, which is measured in cubic feet per minute. Read our guide on evaporative cooler installation for more information. 

Evaporative coolers are rated by CFM. Use this formula to calculate the CFM for cooling your home: 

  • Determine the square footage of space you want to cool.
  • Multiply this figure by the height of your ceilings.
  • Divide that number by 2.
  • The result is the swamp cooler CFM rating.
Evaporative Cooler Maintenance & Accessories

Keep the rust- and corrosion-resistant galvanized steel that most whole-house evaporative cooler housings are made of intact with monthly inspections.

Regular maintenance as instructed in the owner’s manual is the best way to keep your evaporative cooler working at peak efficiency.

Swamp cooler maintenance is usually centered on draining water to remove mineral buildup, and adjusting the belt and water levels.

If the unit isn’t going to be used for a few days it should be drained to reduce bacteria growth. This can also be controlled by adding one of several accessories before operation.

Pads should be inspected, cleaned or replaced, as needed.

Add any of these accessories to match your evaporative cooler to your specific needs: 

  • Purge pumps: Purge water automatically every six or eight hours, helping to avoid mineral buildup.
  • Ceiling vents: If open windows are a security issue, these ducts allow warm air to exhaust into the attic and out through the roof vents. This option may require additional ventilation in the attic.
  • Pre-filters: Help prevent water droplets from the pads from being pulled into the fan blades. Most evaporative coolers also have filters to remove dust from the incoming air.

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