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Evaporative Coolers

Buying Guides: Evaporative Coolers
Evaporative coolers, also called swamp coolers, are well suited for climates where the air is hot and humidity is low. They combine the natural cooling properties of water with a steady breeze to lower indoor temperatures.

There are, however, several important factors to consider before making your selection. This guide explains the different types of evaporative coolers, their benefits and features, and how they can be most effective in your home. First, let’s take a look at how they work.

Evaporative Cooling

Evaporative coolers lower indoor temperatures by combining the natural cooling properties of evaporating water with an efficient air moving system. This combination of moisture and a steady breeze can lower indoor temperatures by as much as 30°F. Airflow is controlled by opening windows to allow the unit to push warm air outside. Evaporative coolers also add moisture, which helps keep fabrics and wood from drying out, and the water-filled pads act as a type of filter, removing dust and allergens from the air.

Evaporative Coolers vs. Air Conditioning

Evaporative coolers can be used as the sole cooling system, or to complement existing air conditioning systems. However, they should never be used at the same time, as one adds humidity while the other removes it. Evaporative coolers offer several benefits over air conditioning, including:

• Low installation and maintenance costs
• 75% less electricity usage
• Powered by a standard 120 volt outlet
• No ozone damaging refrigerants
• Fresh air flow pushes out warm air, smoke and pollution
• Breeze makes effective room temperature feel 4 to 6 degrees cooler

Evaporative coolers are most effective in areas of low humidity and hot temperatures. They are not effective in humid climates or during rainy seasons. They 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. The degree of humidity they deliver is a feature that distinguishes the two basic types of evaporative coolers.


Evaporative coolers fall into several different categories:

Portable Coolers cool small spaces or rooms, usually up to 300 square feet.
Mobile Coolers cool much larger, open spaces like warehouses or garages, and can be used 
  out-of-doors on patios or on job sites.
Window or Through-the-Wall units cool one room, an entire house or a garage.
Down Discharge coolers are installed on the roof, discharging the cooled air downward into the 
  structure and are designed to cool an entire home.
Side Discharge units are normally installed on the side of the building directly into the attic area, but  
  can be installed   on the roof, using an elbow to direct the airflow through an opening in the roof. 
  They can cool an entire house.

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


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

The table below explains their applications and features.



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

Evaporative coolers come in various sizes, from portable coolers that can be used in any room of the home, to whole-house units which require installation and distribute cool air through various means. The newer mobile units are designed to cool large, open areas like workshops, garages and even patios.

Installation and Flow

Most whole-house evaporative coolers are mounted on the roof and blow air downwards, while others are mounted through windows or walls and blow air in from the side. Down-flow installations are most popular, but the 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. 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.

CFM Ratings

Evaporative coolers are rated by the airflow the cooler can move through a space. This is measured by cubic feet per minute (CFM).
Use this formula to calculate the CFM for cooling your home:

1. Determine the square footage of space you want to cool.
2. Multiply this figure by the height of your ceilings.
3. Divide that number by 2.
4. The result is the CFM rating for the evaporative cooler you need.  

Example: If you have a 1,500 square foot home: 1,500 square feet X 8 ft. ceilings = 12,000 ÷ 2 = 6,000 CFM.
You need a unit rated at 6,000 CFM or higher.
Residential, whole-house models range from 3,000 to 8,500 CFM. Regular maintenance is the best way to keep your evaporative cooler working at peak efficiency.


Most whole-house evaporative cooler housings are made of sturdy rust and corrosion-resistant heavy gauge galvanized steel. You should perform maintenance per the directions in your unit’s owner’s manual, but a good, general rule of thumb is to inspect the units monthly. Maintenance is usually centered on draining water to remove any mineral build-up, 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 items available at The Home Depot before operation. Pads should be inspected, cleaned or replaced, as needed.

Accessories to Consider

Purge Pump

Purges 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.


Help prevent water droplets from the pads from being pulled into the fan blades.Other filters remove dust from incoming air.