What size AC for Honolulu, HI? 3.5 tons for 2,000 sq ft

What size AC a 2,000 sq ft house in Honolulu needs

3.5 tons central AC or heat pump, about 37,400 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.1 tons. This is one of the climates the chart was written for.

If a contractor quotes you more than 3.5 tons for an average 2,000 sq ft house here, ask to see the Manual J load calculation behind it before you sign. That works out to one ton per 641 square feet in this climate. For a single room, size by the room: 18.7 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Honolulu International Airport (5.9 mi away). Aug is the hottest month, averaging a high of 88.8°F and a low of 75.6°F, with about 32 days a year at 90°F or more. That gives a design temperature of 94°F against 75°F inside.

What it costs to run

About 7,489 kWh a year at SEER2 14.3, or roughly $3,475 at Hawaii's average residential rate of 46.41¢ per kWh. Cooling runs 12 months of the year here.

What drives the load in Honolulu

Of the 37,400 BTU/hr, 13,680 comes through walls, roof and windows on a 94°F afternoon (37%), 13,000 is sun on the house (35%), 2,120 is four people and their appliances, and 8,600 is moisture the coil has to wring out of Honolulu's summer air (23%).

Heat through the shell is the biggest share here, so insulation and air sealing cut the size you need more than shading would. Sensible heat totals 28,800 BTU/hr before the moisture allowance.

Other house sizes in Honolulu

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,800 BTU/hr; a 350 sq ft living room needs about 6,500 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 11,200 BTU/hr.

Month by month in Honolulu

Aug alone uses 11% of the year's cooling energy. The unit runs the equivalent of 2,860 hours a year at full output.

Honolulu against nearby cities

Honolulu is the only Hawaii city in this set.

Where Honolulu's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Honolulu International Airport, 5.9 miles from the center of Honolulu at 6 ft above sea level. That is close enough that the station's summers are Honolulu's summers.

No other city in this set uses Honolulu International Airport, so this sizing is Honolulu's alone.

The sun over Honolulu in late July

At 21.32°N, the noon sun on 21 July stands 89.1° above the horizon over Honolulu and the day runs 13 h 07 min from sunrise to sunset. With the sun that close to overhead, the roof takes most of the heat at midday and the west wall takes the rest after 3 pm. Shorter days give the house a longer night to shed the day's heat.

344,967 people live in Honolulu. Coordinates used: 21.3243, -157.8476.

Honolulu AC sizing questions