What size AC for Walnut, CA? 3 tons for 2,000 sq ft

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

3 tons central AC or heat pump, about 31,500 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 33% 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 3 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 763 square feet in this climate. For a single room, size by the room: 15.7 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Fullerton Municipal Airport (13.6 mi away). Aug is the hottest month, averaging a high of 86.7°F and a low of 66.4°F, with about 39 days a year at 90°F or more. That gives a design temperature of 92°F against 75°F inside.

What it costs to run

About 2,094 kWh a year at SEER2 14.3, or roughly $682 at California's average residential rate of 32.58¢ per kWh. Cooling runs 6 months of the year here.

What drives the load in Walnut

Of the 31,500 BTU/hr, 12,240 comes through walls, roof and windows on a 92°F afternoon (39%), 13,000 is sun on the house (41%), 2,120 is four people and their appliances, and 4,100 is moisture the coil has to wring out of Walnut'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 27,360 BTU/hr before the moisture allowance.

Other house sizes in Walnut

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,400 BTU/hr; a 350 sq ft living room needs about 5,500 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 9,400 BTU/hr.

Month by month in Walnut

Aug alone uses 24% of the year's cooling energy. The unit runs the equivalent of 952 hours a year at full output.

Walnut against nearby cities

Of 376 California cities here, Walnut has the 174th highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where Walnut's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Fullerton Municipal Airport, 13.6 miles from the center of Walnut at 86 ft above sea level. That is close enough that the station's summers are Walnut's summers.

24 other cities use the same station and get the same climate inputs. The closest to Walnut: West Covina (3 mi away, 13.4 mi from the station), Covina (4 mi away, 16.2 mi from the station), La Puente (6 mi away, 11.2 mi from the station), Baldwin Park (7 mi away, 14.6 mi from the station), Azusa (8 mi away, 18.9 mi from the station). Walnut is farther from the station than 19 of them.

The sun over Walnut in late July

At 34.04°N, the noon sun on 21 July stands 76.4° above the horizon over Walnut and the day runs 13 h 56 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.

27,250 people live in Walnut, the 255th largest of the 376 California cities sized on this site. Coordinates used: 34.0372, -117.8556.

Walnut AC sizing questions