How Much Does It Cost to Run AC on Oahu?

A SEER2 rating is the cooling an air conditioner delivers for each watt-hour of electricity over a cooling season. Divide the unit's size in BTU per hour by its SEER2 rating and you get an estimate of the watts it draws at full output; divide by 1,000 for kilowatts. Multiply by the hours it runs and by your price per kWh, and you have the cost. The calculator shows each step with your numbers.

It uses 30-day months and counts every hour you enter as a full-output hour. Inverter units spend much of the day below full output once the room is cool, so a unit that is on all day can use less than the hours suggest. For its own savings estimates, Hawaii Energy's engineering manual assumes 2,528 full-output hours a year for a ductless or room unit under 30,000 BTU, about seven a day, and 1,884 for central AC and larger ductless units, about five a day.

Federal efficiency minimums have climbed. A split system made between 1993 and January 2006 only had to reach 10 SEER, which is why the calculator starts an older unit at 10. Since January 1, 2023, a split-system AC installed in Hawaii must be rated at least 14.3 SEER2 below 45,000 BTU, or 13.8 SEER2 at 45,000 BTU and up, because the U.S. Department of Energy places Hawaii in its hot-humid Southeast region.

SEER and SEER2 are measured under different test conditions, and the Department of Energy notes they are not directly comparable. A savings figure that compares an old SEER label with a new SEER2 label is therefore a fair estimate, not an exact one. To find your unit's rating, look up the outdoor unit's model number in the AHRI Directory or on the manufacturer's spec sheet.

Hawaii Energy compared three ways to cool a home with at least two bedrooms, each with about 36,000 BTU of capacity at the minimum efficiency that qualifies for its rebates. In its figures, shown in the table near the top of this page, three window units used far more electricity in a year than one mini-split of the same total size and were expected to last fewer years. Central AC came in close to the mini-split.

A window unit can still be the right call for a room you cool only now and then. For rooms you cool most nights, compare our window and wall AC and split AC installation options. In a condo, what you can install depends on your building's rules; see condo AC.

Hawaiian Electric's price per kWh changes from month to month as fuel and purchased-power costs pass through to customers, so no published average matches your bill for long. On the standard residential rate, the energy charge also steps up in blocks as your monthly use grows, and AC use adds to the top of that total. For the closest estimate, type the per-kWh charge from your latest bill into the rate box.

Customers on Hawaiian Electric's residential time-of-use rate pay far more per kWh in the 5 pm to 9 pm evening peak than in the 9 am to 5 pm daytime period. On that rate, cooling the house in the afternoon and easing off in the evening peak lowers the bill. The current rates for both plans are in the questions below.

A few habits change the hours in the calculator more than anything else:

If the calculator shows a big gap between your unit and a new one, we can size a replacement for the room, quote it line by line and show which Hawaii Energy rebate tier the new unit falls in. Installed price ranges are in our mini-split cost guide, and the instant estimate gives a range for your home in a few minutes. Prefer to talk it through? Call (808) 400-6593.