Swamp Cooler vs. Air Conditioner: Which Is Right for a Southwest Home?
In the dry Southwest, a swamp cooler can cool a house for a fraction of what central air costs to buy and run, but humidity cuts into how well it works. This guide compares the two on cost, comfort, water use and upkeep, using published figures and a chart of what a cooler delivers as humidity rises.
Updated
The short version
- A swamp cooler uses about a quarter of the energy of central air and costs less than half as much to install.
- It works best in dry heat. As humidity rises, the air it delivers gets warmer, and in muggy weather it barely helps.
- It uses water, adds humidity indoors and needs open windows; central air doesn't.
- Dry heat in Arizona, New Mexico, Nevada, Utah and Colorado suits a cooler well. Humid monsoon weeks are the hard part.
How each one cools
Central air moves heat out of the house with refrigerant. It recirculates the same indoor air, pulls moisture out of it, and works the same whether it's dry or humid outside, as long as the house stays closed up.
A swamp cooler, or evaporative cooler, pulls outdoor air through wet pads. Water evaporating from the pads absorbs heat, which can drop the air temperature by 15°F to 40°F before it enters the house. That air isn't recirculated: a cooler replaces all the air in the house every 2 to 3 minutes, so windows or vents have to be open to let it out (PNNL).
Why humidity decides it
Evaporation can only cool air down to its wet-bulb temperature, the reading you'd get from a thermometer wrapped in a wet cloth. In dry air the wet bulb is far below the ordinary temperature, so a cooler has a lot of room to work. As humidity rises, the wet bulb climbs and that room shrinks.
The chart shows what a cooler with good rigid pads delivers in four sets of conditions. On a dry 105°F day it puts out 70°F air, 35 degrees cooler than outside. On a humid 95°F monsoon afternoon the same cooler manages 81°F, and in Gulf Coast humidity the drop is down to 8 degrees.
A useful rule of thumb from the Department of Energy's Building America program: places where the summer design wet-bulb temperature is 70°F or lower are good fits for evaporative cooling. Phoenix's design condition is 108°F with a 70°F wet bulb, a 38-degree gap a cooler can use. Sarasota, Florida, at 92°F and a 79°F wet bulb, leaves only 13 degrees, and a cooler there would not work very well (PNNL).
Side by side
| Swamp cooler | Central air | |
|---|---|---|
| Energy use | About a quarter of central air | The baseline |
| Cost to install | Less than half of central air | Higher |
| Dry heat | Very effective | Effective |
| Humid days | Weakens; little help in muggy weather | Unaffected |
| Indoor humidity | Adds moisture | Removes moisture |
| Air | Fresh outdoor air; windows open | Recirculated; house closed |
| Water | Thousands of gallons a year | None at the house |
| Upkeep | Twice a year: pads, belt, drain, winter cover | Filters and periodic service |
| Smart thermostat | Needs an adapter (how it works) | Works directly |
Energy and installation figures are from PNNL's evaporative cooling guide.
Running cost
A cooler runs a fan motor and a small water pump instead of a compressor, which is why it can use about a quarter of the energy of central air. Water and replacement pads add some cost back, so count those too when you compare.
Coolers are common in the region. The Energy Information Administration's 2020 housing survey counted more than 620,000 owner-occupied homes across Arizona, New Mexico, Nevada, Utah and Colorado that use one (EIA).
Water use
How much water a cooler uses depends on how many hours it runs and how dry the air is. For a 1,500-square-foot home, one estimate puts annual use at about 2,980 gallons in Santa Fe, 7,261 in Albuquerque and 12,457 in Las Cruces. A bleed-off valve, which flushes minerals out, can add up to half again. An auto-flush (dump pump) that refreshes the pan every 8 to 12 hours of running is a more efficient way to keep scale down (PNNL).
Which one fits your home
A swamp cooler suits a home in the dry Southwest where low summer bills and fresh air matter, and where someone will keep up with spring and fall maintenance. Central air suits a household that needs drier air, can't leave windows open, or lives where humid summers are normal.
Some homes keep both, using the cooler through the dry months and central air in the muggiest weeks. If you do, close the cooler's dampers or cover its duct while the air conditioner runs so cold air doesn't escape through it (PNNL).
Getting more from a cooler
A modern cooler should have at least two fan speeds and a vent-only setting, which runs the fan without water so it works like a whole-house fan on mild days (PNNL). Rigid pads rated 75% to 93% effective cool better than aspen pads at about 70%. Air flows toward open windows, so open them in the rooms you want cooled.
A rotary switch can't hold a temperature or follow a schedule, so the house tends to swing between too cold and warming up. A thermostat holds a set temperature, and with an adapter it can be a smart thermostat you control from your phone. Our guide to smart thermostats for swamp coolers covers how, and the monsoon season guide covers what to change when humidity arrives.