Knowledge · 6 min read
What a portable cooler really costs to run all night
A small evaporative cooler and a window air conditioner are not in the same financial category. Here is the arithmetic, with real rate numbers.
By Marcus Reyes · EPA 608 Certified HVAC Technician · 17 years in residential cooling
The formula, once
Watts divided by 1,000 gives kilowatts. Kilowatts times hours gives kilowatt-hours. Kilowatt-hours times your rate gives dollars. Every energy argument in this category is that one line, applied honestly.
Find the wattage on the label or the power adapter, not in the marketing copy. If a product page gives you BTU but no watts, that is a compressor unit and its running cost is in a different league.
Worked example: personal evaporative cooler
Most USB-powered personal coolers draw somewhere between 8 and 15 watts on a mid fan speed. Take 12 watts and eight hours: 0.012 kW × 8 h = 0.096 kWh. At the 2026 US residential average of roughly 17 cents per kWh, that is under two cents a night.
Eight hours a night for a 90-night summer comes out around $1.50. That is not a typo, and it is the entire economic argument for the category.
Worked example: window unit and central air
A small 6,000 BTU window air conditioner draws around 550 watts running. Eight hours is 4.4 kWh, or roughly 75 cents a night at the same rate — call it $65 for the summer if it runs every night.
Central air is a different animal again. A 3-ton system with an older SEER rating can pull 3,000-3,500 watts while the compressor runs. Cycling roughly half the night puts you near 13 kWh, or about $2.20 a night, plus the fan. Cooling a whole house to fix one hot bedroom is the most expensive way to solve the problem.
Where the small numbers stop being small
Rates are not averages everywhere. In parts of California and New England, 30-40 cents per kWh is normal, and peak-time pricing can double that in the late afternoon. Multiply the examples above accordingly — the personal cooler goes from two cents to five, and the central-air night goes from $2.20 to well over $5.
If you are on a time-of-use plan, shifting cooling load to off-peak hours is worth more than any equipment swap. Pre-cool before the peak window starts and coast through it.
The cost nobody puts on the spreadsheet
Replacement pads and cartridges are the real recurring cost of evaporative cooling. Budget one or two cartridges a season depending on water hardness and hours of use. That is usually somewhere between $10 and $30 a year and it still leaves the category far cheaper than compressor cooling.
Water use is trivial by comparison — a tank a night is a fraction of a shower.
How to decide
If your problem is one person in one room, the running-cost maths makes a personal cooler almost free by comparison and the decision is about whether the cooling is enough for your climate.
If your problem is a whole floor in a humid climate, pay for the compressor and stop optimising pennies. Buying the wrong category to save money is how people end up owning both.