How To Buy Evaporative Coolers

Low humidity and hot temps? Get an energy-efficient, portable evaporative cooler

Evaporative coolers, also called swamp coolers, combine the natural cooling properties of water with a steady breeze to lower indoor temperatures. This guide will help you determine which type is best suited for your needs.

Tip: Evaporative coolers are most effective in areas of low humidity and hot temperatures. They can be used as the sole cooling system, or to complement existing air conditioning systems. They should never be used at the same time, however, as evaporative coolers add humidity and A/C units remove it.

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, with the water-filled pads acting as a filter, removing dust and allergens from the air.

Evaporative coolers offer several benefits over air conditioning, including:
• Lower installation and maintenance costs

• 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.

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.

Tip: To ensure effective distribution, you’ll need to know how much air the unit needs to move to cool your home, which is measured in cubic feet per minute.  

Small Space Coolers

Portable Coolers

• Cools small spaces up to 300 sq. ft.

Small Space Coolers

Window/Through-the-Wall Coolers

• Can cool one room or a garage

Whole-House Coolers

Down Discharge Coolers

• Installed on roof
• Discharge cool air downward into the structure

Whole-House Coolers

Side Discharge Coolers

• Typically installed on side of building directly into the attic area
• Can be installed on roof using an elbow to direct the airflow through opening in roof

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.  

Type Materials Points to Consider


• Aspen wood
• Cellulose fiber
• Synthetic fibe

• For units with inlets on many sides
• Most economical
• Usually 1 to 2” thick
• Require regular maintenance/replacement
• Aspen wood is most durable; exact sizes
• Cellulose and synthetic may be cut-to-fit

Rigid Media

Stacked corrugated sheet material

• For units with single inlets
• Require larger upfront investment
• Usually 8 to 12” thick
• Lower maintenance
• Allows air to pass through at lower velocity, resulting in increased humidity
and air a few degrees cooler than with fiber pads
• Extremely long lifecycle if maintained

CFM Ratings

For the most cooling power, you’ll need to know how much air the unit needs to move to cool your home, which is measured in cubic feet per minute.

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 CFM rating for the evaporative cooler you need.

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 per the owner’s manual is the best way to keep your evaporative cooler working at peak efficiency.

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, which 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.