Swamp Cooler Operating Cost: What It Really Costs to Run (Power, Water and vs AC)

A swamp cooler's running cost has two parts: electricity for the fan motor and pump, and water for evaporation and bleed-off. For a typical whole-house unit, both are modest, and together they usually come to well under half of what central air conditioning costs to run in the same house. The exact figure depends on motor size, how many hours you run it, how dry your air is, your water hardness, and your local rates. This page shows the math so you can plug in your own numbers, or use the operating cost calculator to do it automatically.

All dollar figures below use example rates: $0.15 per kWh for electricity and $0.006 per gallon (about $6 per 1,000 gallons) for water. Check your own utility bills for actual rates.

Power draw by cooler type

An evaporative cooler's electrical load is just a blower motor and a small recirculating pump. Pumps typically draw well under 100 W. The blower is the main load.

The AC figure follows a useful rule of thumb: central air in the SEER2 13 to 16 range draws roughly 1 kW per ton of capacity when the compressor runs on a hot day, including the outdoor fan and indoor blower. A 3 ton system is therefore about 3 to 3.5 kW.

Water cost: the part people forget

A cooler cools by evaporating water, and the amount evaporated is set by physics, not by the brand:

The 8,186 comes from the sensible cooling equation (1.08 x CFM x temperature drop in BTU/h) divided by the latent heat of water (about 1,060 BTU per pound) and the weight of a gallon (8.34 pounds). On top of evaporation, bleed-off removes mineral-laden water, typically adding 25 to 100 percent depending on hardness. See swamp cooler water usage for the full breakdown.

Notice that this is close to the electricity cost of the same cooler. In water-expensive cities, it can exceed it.

Monthly cost: swamp cooler vs central AC

The fairest comparison uses the same house and the same hours. Assume a hot month with 10 hours of operation a day for 30 days.

Two caveats keep this honest. First, an AC compressor cycles, so on milder days it runs fewer hours than the cooler's fan; a cooler is also often run longer to hold comfort. Second, the cooler can only match the AC's comfort where the climate is dry enough. Check your city in the climate index and the full comparison in swamp cooler vs air conditioner.

How electricity rates change the picture

Using the same monthly energy (cooler 240 kWh, AC 975 kWh) and the same $29.70 of cooler water:

The pattern is clear: the higher your electric rate, the more a cooler saves. Time-of-use plans that charge peak rates in late afternoon favor coolers even more, because that is exactly when AC load peaks. Where water is very expensive, or where the water bill also adds a sewer charge per gallon, the cooler's advantage shrinks, so check how your utility bills sewer in summer.

Cost by daily runtime

The 24-hour row overstates reality, because temperature drop and therefore evaporation fall sharply at night when the air is cooler. Many homes switch to low speed or vent overnight.

Seasonal cost by climate

A month is useful, but the season is what you budget for. The cooling season length, daily hours and average temperature drop all change with climate. The scenarios below use the same 4,500 CFM cooler at 0.8 kW, 50 percent bleed-off and the example rates. They are illustrations, not forecasts for any particular city.

Two things stand out. In the hottest, driest places, water becomes roughly half of the cooler's running cost, so bleed-off tuning matters as much as motor efficiency. And in every scenario the cooler stays at around half the AC's cost or less, even after counting water. For your own location, the water usage calculator and operating cost calculator take your actual temperatures and rates.

Seven ways to cut running costs

1. Run on low whenever it holds comfort. Low speed draws roughly half to two-thirds of high-speed power and evaporates less water.
2. Tune bleed-off. A continuous bleed set for very hard water on a soft-water system can double water use for no benefit. See bleed-off and water quality.
3. Fix float valve leaks. A float that never quite shuts off sends water down the overflow 24 hours a day. See float valve adjustment.
4. Keep pads fresh. Scaled or clogged pads cool less, so the cooler runs longer for the same comfort.
5. Adjust the belt and pulley. A slipping belt wastes power; an over-tight belt loads the motor bearings. See belt and pulley adjustment.
6. Vent properly. Too little relief air reduces airflow and comfort, which leads to longer run times.
7. Use a thermostat. Automatic cycling and speed staging prevent hours of unneeded running.

When a cooler costs more than expected

If your bill looks high, isolate the cause before blaming the cooler. Read the water meter before and after an hour of operation with all other water off; compare with the evaporation formula plus your bleed-off setting. A result far above the estimate points to an overflow leak or excessive bleed. On the electric side, measure motor amps on high; a reading well above nameplate suggests a failing motor, a dragging blower bearing or an over-tightened belt. For longer-term planning, including purchase and maintenance, see cost of a swamp cooler.