Swamp coolers need a constant supply of water. As water keeps evaporating from the unit to cool the air, more water needs to replace it. Most water use estimates range from 3 to 15 gallons / 11 to 57 litres per hour, with averages between 7 and 11 gallons / 26.5 and 40 litres. But the amount of water an evaporative cooler will use varies depending on three major factors:
1. The combination of heat and humidity at any given time. A unit will use more water and provide more cooling on a dry day than on a more humid day.
2. Size of the unit. Smaller units use less water -- units under 100 watts and under 500 CFM may average less than 1 gallon / 4 litres per hour. Larger units may use as much as 20 gallons / 75 litres per hour or more . . . and again, this will depend on the heat and humidity levels.
3. How drain valves are used. Drain (or "dump" or "bleed") valves allow recirculated water to be removed and replaced with fresh water. Draining helps prevent damage and corrosion to swamp coolers from mineral deposits in the water supply. According to the Arizona Cooperative Extension, this damage can shorten a cooler's life by as much as 50%, so corrosion is a big concern. Mineral deposits can also interfere with a unit's cooling capacity, clogging water lines and pads. Periodically draining the tank can dramatically reduce this problem.
You can usually adjust the amount of water that drains. A continuous drain, while keeping the unit clean, could result in 50% more water use. Drained intermittently, additional water use can be held down to about 10% (Arizona Cooperative Extension).
You'll need to find a flexible balance of water use, cooling capacity, and unit care that you are comfortable with.
The drained waste-water can often be re-used to water plants, wash cars, etc. But if it has a high mineral content, it may not be good for certain uses. You can check with your local nursery for information on how your water's mineral content might affect certain plants and soils.
One way to prevent the build-up of minerals in your swamp cooler is with regular cleaning of the unit inside and out. We'll go over this in the maintenance section.
Some swamp coolers have hose connections, meaning you can use a constant supply of water without dealing with water storage tanks.
But it may be hard to find outdoor water lines exactly where you want to position your cooler. So units with water tanks may be your best bet for portability. You'll need to manage the water supply for these tank-fed units.
Consider the size of a unit's water tank. Most vary in size from 3 to 5 gallons / 11 to 20 litres, but some of the larger units may hold up to 50 gallons / 190 litres or more. Of course, these larger units will also use more water per hour. If you'll need to use the unit longer than the water tank will supply, prepare to have a backup water supply.
Fortunately many manufacturers sell portable water tanks, easily found up to 50 gallons / 190 litres and more. These let you take your own water supply with you. These tanks are mounted on frames with wheels and have a water line you can attach to your portable swamp cooler. These may be your best solution if water lines aren't easily available.
Some units may use ice trays, ice packs or gel packs. These are usually used to pre-cool the air in a two-stage system. (You can learn more about 1- and 2-stage systems at our swamp cooler types page.) When used in the water tank instead, they provide little additional cooling -- water evaporates at the same temperature whether it starts out room temperature or frozen. But the cold vapor from the ice and packs may add some cooling to the air being blown by the fan.
Swamp coolers use very little electricity. They only need enough energy to power the fan and a small pump. So they can almost always run on normal household currents.
Just be sure the cooler's electrical requirements are compatible with your electrical supply. Check a swamp cooler's CURRENT, FREQUENCY and VOLTAGE ratings. These will tell you before you purchase whether or not the cooler is compatible with your power supply.
You can learn more about these electrical terms and basic electrical concepts on our electricity basics page.
A swamp cooler needs a certain amount of electricity to do its job. It draws that amount from the voltage supply of a power line, but the actual amount taken is called AMPERES or "AMPS". Bigger, stronger coolers need more -- perhaps up to 15 amps. Smaller coolers need less than 1 amp. They both draw electricity from the same voltage supply (e.g., 115V), but they each draw a different amount of electricity from that supply.
There are a few big coolers that draw 20 amps or more. These won't work with standard household-type outlets and need special wiring.
At the simplest level you can estimate a swamp cooler's power by how many watts it uses. Just like a light bulb. A 60-watt bulb uses less electricity and puts out less light than a 100-watt bulb. A 60-watt cooler would use the same amount of electricity as a 60 watt bulb and be about as powerful. That's less electricity and power than a 100-watt cooler and much less than a 560-watt cooler.
A wattage rating is among the most helpful and universal measurements, and is supplied by almost all manufacturers. It will help you estimate electricity costs to run it.
Some manufacturers will only give you voltage and ampere ratings. You can use these to figure out how many watts the cooler uses. Simply multiply the number of amps by the number of volts. A cooler that uses 2.8 amps and runs on 115 volts uses 322 watts (2.8 × 115 = 322).
Some evaporative coolers are measured by horsepower (HP). Horsepower can give you a general idea of a swamp cooler's capability.
1 HP equals about 750 watts (746 to be exact)
1 HP equals about 2,544 BTU
HP doesn't take into account the voltage supply. An evaporative cooler operating at, say 115 VAC (Volts of Alternating Current) will have a different horsepower than the very same cooler operating at 220 VAC.
Even at that, not all horsepower ratings are measured the same. Some are rated under load (average amount of work long-term, "marathon"), some are rated at peak capacity (the most work they can do for a short time, "sprint"). Two two-horsepower motors may not be equal in actual power. But horsepower can be helpful to give you a general understanding of a swamp cooler's power and energy use.
Portable evaporative coolers use as much as 75% less energy to operate than portable air conditioners.
But unlike air conditioners they also need a steady supply of water.