Swamp Cooler vs. AC Running Cost Calculator

This calculator answers a narrower question than most: what does it cost in electricity to cool your house for one summer month, and what would the same month cost on refrigerated air? Pick the house size, how many hours the cooler actually runs in July, and what you want to compare against. There is no email gate and the number updates as you change the dropdowns.

The starting range is a whole-house evaporative cooler in a 1,200 to 2,000 square foot Pueblo home running about 12 hours a day, priced on Black Hills Energy rates. Everything the math assumes is written on the tool itself rather than buried, because a cooling-cost calculator with hidden assumptions is a sales tool, not a calculator.

What each answer changes

House size scales the cooler. A window or small side-draft unit is a smaller motor and a smaller pump; a big two-speed down-draft on a 3,000 square foot house moves far more air and draws accordingly. The multiplier tracks motor size, not floor area directly.
Hours per day is the honest variable, and the one people underestimate. A Pueblo cooler that gets switched on at noon and off at bedtime is running twelve hours. During a heat wave a lot of them never go off at all, and that doubles the number.
Comparison target swaps the equipment while holding the house and the hours constant. A one-zone mini-split is counted at about 1 kW while it modulates. Central air is counted at about 3.2 kW with the compressor cycling roughly two thirds of the hours, which is why it lands near three and a half times the cooler rather than five.

Reading the result honestly

Three things this number does not include. It does not include water, which the cooler uses and refrigerated air does not. It does not include seasonal labor: a cooler needs a spring start-up and a fall shutdown every year, plus pads, and central air does not. And it does not include the installed cost of the equipment, which is where the real gap sits: $6,000 to $15,000 for central air or $3,500 to $8,000 for a one-zone mini-split against $1,500 to $4,000 for a new cooler.

It also does not price comfort. A cooler cannot pull air much below the wet-bulb temperature, so during the monsoon weeks in late July and August the running-cost winner is also the system sitting in a 78 degree living room. That is a real trade, and the conversion page walks it through without pushing anyone in either direction.

If what you actually want to know is what a repair costs rather than what a month costs, use the repair cost calculator instead, and the pricing page has every published range on one screen.

Running cost

What does it cost to cool this house for a month?

Three questions. The starting number is a whole-house evaporative cooler on Black Hills Energy rates in a Pueblo July. Switch the last dropdown to see what the same house costs on refrigerated air.

How big is the house? Hours run per day in July Compare against

Estimated monthly running cost July electricity only, before any repair or maintenance

Assumptions, stated plainly. The cooler is a 1/3 to 3/4 horsepower two-speed blower plus a small submersible pump, about 400 to 800 watts in normal use. Phoenix Manufacturing's AeroCool tables list those motor sizes at 7.4 to 11.5 nameplate amps on 120 volts, which is the high-speed maximum rather than the usual draw. Electricity is priced at about 20 cents per kilowatt-hour all in, which is what Black Hills Colorado Electric's own PUC filing implies: an average residential bill of $123.37 a month on 600 kWh under Rate Schedule RS-1. San Isabel Electric members should use 16.07 cents for the first 800 kWh and 13.07 above.

Send this comparison to the quote form

An estimate of electricity only, not a quote, and not a promise about your bill. It does not include water, pads, pumps, seasonal service, or the installed cost of new equipment. Ranges are rounded to the nearest $25.

Frequently Asked Questions

Where does the 20 cents per kilowatt-hour come from?

From Black Hills Colorado Electric's own filing with the Colorado PUC, which describes an average residential customer on Rate Schedule RS-1 using 600 kWh a month with a bill of $123.37. That works out to roughly 20.6 cents per kilowatt-hour all in, including the fixed charge and the cost adjustments. It is the number to use for marginal summer cooling, because the residential tariff charges more per kilowatt-hour above 500 kWh a month.

Why does the cooler use so much less?

Because it runs a fan and a small pump instead of a compressor. A whole-house evaporative cooler is a 1/3 to 3/4 horsepower blower motor and a submersible pump; a 3-ton central air system is a compressor plus an indoor blower. The physics gap is about five to one on draw, and about three and a half to one once you account for the compressor cycling rather than running continuously.

Does this include the water the cooler uses?

No, and it is worth knowing why. A cooler evaporates water and bleeds more off to keep mineral out of the pan, which is a real cost, but on a Pueblo Water bill it is small next to the electricity. In Beulah, where the water district has posted Stage 3 drought restrictions, water is the binding constraint rather than the cost, and that page covers it.

Should I convert to refrigerated air based on this?

Not on running cost alone. Running cost is the half where the cooler wins by a wide margin, every year, forever. The half it loses is comfort during the monsoon weeks in late July and August, when Pueblo's dew point climbs and a cooler cannot pull air much below the wet bulb. Read the conversion page for the installed costs and the honest trade.