Can a swamp cooler be too big?

I personally think that it's best to buy a cooler that's a little above the rated CFM you actually need -- this will help ensure it actually cools your house to a comfortable level.

Where I live in Albuquerque, NM, I often find myself in people's houses where the performance of the evaporative cooler is quite inadequate. It's better than nothing, but not enough airflow to really be comfortable. Having a cooler that's a bit over spec will help to prevent this problem, especially as the system gets older and performance may deteriorate.

This often causes people to want to switch to refrigerated air, which I think is sad, because it uses SO much more energy, and an adequately-sized and well-performing evaporative cooler can do the job well for a fraction of the energy use.

That said, having one twice spec is a lot. I think you would be alright, though, as long as you keep in mind that you may have to increase the amount of window (or other) opening to accommodate the higher flow (and your ductwork is up to it).

From http://energy.gov/energysaver/evaporative-coolers:

Open the windows or vents on the leeward side of the house to provide 1 to 2 square feet of opening for each 1,000 cfm of cooling capacity. Experiment to find the right windows to open and the correct amount to open them. If the windows are open too far, hot air will enter. If the windows are not open far enough, humidity will build up in the home.

Also keep in mind you could always put in a smaller (lower horsepower-rated) motor in order to lower the effective CFM.

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 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

A higher RH will soften your cigars and can cause burn problems. A lower RH will make your cigars will feel a bit firmer. Be careful, too low of a temperature and humidity will eventually ruin your cigars with them be too dry and even cause tobacco beetles. Lastly, high end cigars and cigars with thick wrappers, like Cubans or Dominicans , say that they fare better at a lower RH, closer to around 65%. This is most likely due to the higher amount of oils in the wrapper leaf.

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.

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