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

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

3 tons central AC or heat pump, about 35,200 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 19% 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 682 square feet in this climate. For a single room, size by the room: 17.6 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Paso Robles Municipal Airport (13.1 mi away). Aug is the hottest month, averaging a high of 94°F and a low of 53.2°F, with about 92 days a year at 90°F or more. That gives a design temperature of 101°F against 75°F inside.

What it costs to run

About 1,205 kWh a year at SEER2 14.3, or roughly $392 at California's average residential rate of 32.58¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Atascadero

Of the 35,200 BTU/hr, 18,720 comes through walls, roof and windows on a 101°F afternoon (53%), 13,000 is sun on the house (37%), 2,120 is four people and their appliances, and 1,400 is moisture the coil has to wring out of Atascadero's summer air (4%).

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 33,840 BTU/hr before the moisture allowance.

Other house sizes in Atascadero

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,600 BTU/hr; a 350 sq ft living room needs about 6,200 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 10,600 BTU/hr.

Month by month in Atascadero

Aug alone uses 28% of the year's cooling energy. The unit runs the equivalent of 489 hours a year at full output.

Atascadero against nearby cities

Of 376 California cities here, Atascadero has the 137th highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where Atascadero's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Paso Robles Municipal Airport, 13.1 miles from the center of Atascadero at 820 ft above sea level. That is close enough that the station's summers are Atascadero's summers.

1 other city uses the same station and get the same climate inputs. The closest to Atascadero: El Paso de Robles (Paso Robles) (10 mi away, 3.1 mi from the station). Atascadero is farther from the station than 1 of them.

The sun over Atascadero in late July

At 35.49°N, the noon sun on 21 July stands 74.9° above the horizon over Atascadero and the day runs 14 h 03 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.

29,743 people live in Atascadero, the 246th largest of the 376 California cities sized on this site. Coordinates used: 35.4857, -120.6879.

Atascadero AC sizing questions