What size AC for Twentynine Palms, CA? 5 tons for 2,000 sq ft

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

5 tons central AC or heat pump, about 54,300 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, which falls short here. On a design day the unit runs flat out and the house still drifts above 75°F by late afternoon.

If a contractor quotes you more than 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 442 square feet in this climate. For a single room, size by the room: 27.1 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Twentynine Palms (2.1 mi away). Jul is the hottest month, averaging a high of 104°F and a low of 77.4°F, with about 154 days a year at 90°F or more. That gives a design temperature of 112°F against 75°F inside.

What it costs to run

About 5,470 kWh a year at SEER2 14.3, or roughly $1,782 at California's average residential rate of 32.58¢ per kWh. Cooling runs 7 months of the year here.

What drives the load in Twentynine Palms

Of the 54,300 BTU/hr, 26,640 comes through walls, roof and windows on a 112°F afternoon (49%), 13,000 is sun on the house (24%), 2,120 is four people and their appliances, and 12,500 is moisture the coil has to wring out of Twentynine Palms'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 41,760 BTU/hr before the moisture allowance.

Other house sizes in Twentynine Palms

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 4,100 BTU/hr; a 350 sq ft living room needs about 9,500 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 16,300 BTU/hr.

Month by month in Twentynine Palms

Jul alone uses 23% of the year's cooling energy. The unit runs the equivalent of 1,441 hours a year at full output.

Twentynine Palms against nearby cities

Of 376 California cities here, Twentynine Palms has the 15th highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where Twentynine Palms's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Twentynine Palms, 2.1 miles from the center of Twentynine Palms at 1,975 ft above sea level. That is close enough that the station's summers are Twentynine Palms's summers.

No other city in this set uses Twentynine Palms, so this sizing is Twentynine Palms's alone.

The sun over Twentynine Palms in late July

At 34.15°N, the noon sun on 21 July stands 76.3° above the horizon over Twentynine Palms and the day runs 13 h 57 min from sunrise to sunset. A lower noon sun puts more of the day's heat on east and west walls than on the roof, which is why shading west glass pays off here. Shorter days give the house a longer night to shed the day's heat.

26,563 people live in Twentynine Palms, the 260th largest of the 376 California cities sized on this site. Coordinates used: 34.1478, -116.0660.

Twentynine Palms AC sizing questions