What size AC for Piedmont, CA? 1.5 tons for 2,000 sq ft

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

1.5 tons central AC or heat pump, about 18,000 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 134% 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 1.5 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 1,335 square feet in this climate. For a single room, size by the room: 9 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Oakland International Airport (7.2 mi away). Sep is the hottest month, averaging a high of 74.1°F and a low of 55.5°F, with about 6 days a year at 90°F or more. That gives a design temperature of 78°F against 75°F inside.

What it costs to run

About 220 kWh a year at SEER2 14.3, or roughly $72 at California's average residential rate of 32.58¢ per kWh. Cooling runs 1 month of the year here.

What drives the load in Piedmont

Of the 18,000 BTU/hr, 2,160 comes through walls, roof and windows on a 78°F afternoon (12%), 13,000 is sun on the house (72%), 2,120 is four people and their appliances, and 700 is moisture the coil has to wring out of Piedmont's summer air (4%).

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 17,280 BTU/hr before the moisture allowance.

Other house sizes in Piedmont

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 1,400 BTU/hr; a 350 sq ft living room needs about 3,200 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 5,400 BTU/hr.

Month by month in Piedmont

Sep alone uses 29% of the year's cooling energy. The unit runs the equivalent of 175 hours a year at full output.

Piedmont against nearby cities

Of 376 California cities here, Piedmont has the 356th highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where Piedmont's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Oakland International Airport, 7.2 miles from the center of Piedmont at 5 ft above sea level. That is close enough that the station's summers are Piedmont's summers.

3 other cities use the same station and get the same climate inputs. The closest to Piedmont: Oakland (4 mi away, 3.6 mi from the station), Alameda (6 mi away, 2.2 mi from the station), Moraga (6 mi away, 10.7 mi from the station). Piedmont is farther from the station than 2 of them.

The sun over Piedmont in late July

At 37.82°N, the noon sun on 21 July stands 72.6° above the horizon over Piedmont and the day runs 14 h 14 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.

10,816 people live in Piedmont, the 366th largest of the 376 California cities sized on this site. Coordinates used: 37.8225, -122.2300.

Piedmont AC sizing questions