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

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

2.5 tons central AC or heat pump, about 26,200 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 60% 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 916 square feet in this climate. For a single room, size by the room: 13.1 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Santa Rosa Sonoma County Airport (12.3 mi away). Aug is the hottest month, averaging a high of 84.1°F and a low of 51.9°F, with about 34 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 516 kWh a year at SEER2 14.3, or roughly $168 at California's average residential rate of 32.58¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Rohnert Park

Of the 26,200 BTU/hr, 10,080 comes through walls, roof and windows on a 89°F afternoon (38%), 13,000 is sun on the house (50%), 2,120 is four people and their appliances, and 1,000 is moisture the coil has to wring out of Rohnert Park'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 25,200 BTU/hr before the moisture allowance.

Other house sizes in Rohnert Park

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,000 BTU/hr; a 350 sq ft living room needs about 4,600 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 7,900 BTU/hr.

Month by month in Rohnert Park

Aug alone uses 26% of the year's cooling energy. The unit runs the equivalent of 281 hours a year at full output.

Rohnert Park against nearby cities

Of 376 California cities here, Rohnert Park has the 235th highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where Rohnert Park's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Santa Rosa Sonoma County Airport, 12.3 miles from the center of Rohnert Park at 119 ft above sea level. That is close enough that the station's summers are Rohnert Park's summers.

3 other cities use the same station and get the same climate inputs. The closest to Rohnert Park: Santa Rosa (7 mi away, 6.9 mi from the station), Windsor (15 mi away, 2.7 mi from the station), Healdsburg (21 mi away, 8.7 mi from the station). Rohnert Park is farther from the station than 3 of them.

The sun over Rohnert Park in late July

At 38.35°N, the noon sun on 21 July stands 72.1° above the horizon over Rohnert Park and the day runs 14 h 17 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.

44,894 people live in Rohnert Park, the 197th largest of the 376 California cities sized on this site. Coordinates used: 38.3476, -122.7009.

Rohnert Park AC sizing questions