What size AC for Alhambra, CA? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 29,000 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 45% more than this climate needs. An oversized unit cools the air fast, shuts off before it pulls moisture out, and leaves the house cold and clammy.

If a contractor quotes you more than 2.5 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 828 square feet in this climate. For a single room, size by the room: 14.5 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Los Angeles Downtown/Usc (9.8 mi away). Aug is the hottest month, averaging a high of 84°F and a low of 65.4°F, with about 26 days a year at 90°F or more. That gives a design temperature of 89°F against 75°F inside.

What it costs to run

About 1,801 kWh a year at SEER2 14.3, or roughly $587 at California's average residential rate of 32.58¢ per kWh. Cooling runs 6 months of the year here.

What drives the load in Alhambra

Of the 29,000 BTU/hr, 10,080 comes through walls, roof and windows on a 89°F afternoon (35%), 13,000 is sun on the house (45%), 2,120 is four people and their appliances, and 3,800 is moisture the coil has to wring out of Alhambra's summer air (13%).

Sun is the biggest share here, more than heat through the walls, so shading west windows and a light roof cut the size you need more than extra insulation would. Sensible heat totals 25,200 BTU/hr before the moisture allowance.

Other house sizes in Alhambra

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,200 BTU/hr; a 350 sq ft living room needs about 5,100 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 8,700 BTU/hr.

Month by month in Alhambra

Aug alone uses 23% of the year's cooling energy. The unit runs the equivalent of 888 hours a year at full output.

Alhambra against nearby cities

Of 376 California cities here, Alhambra has the 199th highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where Alhambra's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Los Angeles Downtown/Usc, 9.8 miles from the center of Alhambra at 179 ft above sea level. That is close enough that the station's summers are Alhambra's summers.

18 other cities use the same station and get the same climate inputs. The closest to Alhambra: South Pasadena (2 mi away, 9.7 mi from the station), San Gabriel (2 mi away, 12.1 mi from the station), Monterey Park (2 mi away, 9.2 mi from the station), San Marino (3 mi away, 12.3 mi from the station), Rosemead (3 mi away, 12.3 mi from the station). Alhambra is farther from the station than 9 of them.

The sun over Alhambra in late July

At 34.08°N, the noon sun on 21 July stands 76.3° above the horizon over Alhambra 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.

80,279 people live in Alhambra, the 107th largest of the 376 California cities sized on this site. Coordinates used: 34.0836, -118.1364.

Alhambra AC sizing questions