How to Size an Evaporative Cooler

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For those living in hot, dry areas, a swamp cooler can provide effective and energy-efficient cooling. These devices lower temperatures by combining the natural process of evaporation with a simple air-moving system. Generally speaking, warm air is pulled through moist pads where it is cooled by evaporation and circulated throughout the air. As this occurs, temperatures can be lowered by as much as 20 degrees Fahrenheit.

When choosing an evaporative cooler, a few crucial considerations should be kept in mind, particularly environmental conditions. Because evaporative coolers rely on the process of evaporation to cool the air, they will only be effective in hot, arid climates. Moreover, unlike air conditioners which require a closed environment, evaporative coolers require some sort of fresh air in order to function properly. However, as long as your environment fits the above criteria, a swamp cooler can help you stay cool and comfortable in the summer heat. The map below illustrates the different parts of the United States in which swamp coolers are most effective (region A). To an extent, region B would also benefit from a swamp cooler (though the cooling capacity will be lower), but if you live in region C, a portable air conditioner will be better suited for your needs.

The next step to choosing an evaporative cooler is to find a correctly sized unit. Like air conditioners, evaporative coolers need to be the right size in order to adequately cool a room. When it comes to choosing a portable air conditioner, one of the most important factors to take into account is the model's BTU rating. This measurement describes the power and cooling capacity, and the higher the BTU value, the stronger the air conditioner. Furthermore, a portable air conditioner with too many BTUs will cycle off too quickly, and a unit without an insufficient number of BTUs will not adequately cool a room.

However, unlike air conditioners which rely on BTUs as a means of measuring cooling efficiency, the output of evaporative coolers is rated by CFMs. This measurement essentially describes the cubic feet per minute of air that the swamp cooler can blow into your home, and whether you're cooling a single room or entire home, a basic formula exists for determining the proper size swamp cooler you need. Simply take the cubic feet of the intended area you are cooling and divide that number by 2. For example, if you are trying to cool a bedroom that measures 100 square feet with 9 foot high ceilings, your cubic footage would be 900 feet. Divide that number by 2 and you will find out that you require a swamp cooler that offers approximately 450 CFMs, as shown by the formula below:

Room Square Footage: 100 square feet

Ceiling Height: 9 feet

Cubic Feet = 900 feet

CFM = Cubic Feet / 2

900 / 2 = 450

CFM = 450

Therefore, you can see that for a 100 square foot room with 9 foot high ceilings, the CFM requirement would be 450, and a suitable unit with optimal CFM ratings would be the Symphony Surround. As a general rule, choose the largest cooler (within reason) you can afford, and keep in mind that a large evaporative cooler with a big blower and low horsepower motor will sometimes perform better than a small model with a high horsepower motor.

Swamp Cooler Buying Tip:

Unlike a portable AC, there's no harm in choosing an evaporative cooler with a slightly greater cooling capacity than the space you're cooling.

However, also keep in mind that a swamp cooler's cooling efficiency will also depend on a few other factors such as the overall temperature and humidity levels. For reference, the chart below illustrates ambient temperatures, humidity levels, and the temperatures delivered by an evaporative cooler in optimal conditions:

Always keep in mind that portable evaporative coolers are meant for personal and spot cooling. For lowering the temperatures in larger, non-residential settings such as warehouses or garages, look to commercial evaporative coolers such as the Convair Mobile Max 3.

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