What size AC for Mission Viejo, CA? 2 tons for 2,000 sq ft

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

2 tons central AC or heat pump, about 25,700 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 64% 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 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 935 square feet in this climate. For a single room, size by the room: 12.8 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Santa Ana John Wayne Airport (13.1 mi away). Aug is the hottest month, averaging a high of 80.4°F and a low of 67.1°F, with about 13 days a year at 90°F or more. That gives a design temperature of 85°F against 75°F inside.

What it costs to run

About 1,494 kWh a year at SEER2 14.3, or roughly $487 at California's average residential rate of 32.58¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Mission Viejo

Of the 25,700 BTU/hr, 7,200 comes through walls, roof and windows on a 85°F afternoon (28%), 13,000 is sun on the house (51%), 2,120 is four people and their appliances, and 3,300 is moisture the coil has to wring out of Mission Viejo'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 22,320 BTU/hr before the moisture allowance.

Other house sizes in Mission Viejo

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 1,900 BTU/hr; a 350 sq ft living room needs about 4,500 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 7,700 BTU/hr.

Month by month in Mission Viejo

Aug alone uses 25% of the year's cooling energy. The unit runs the equivalent of 832 hours a year at full output.

Mission Viejo against nearby cities

Of 376 California cities here, Mission Viejo has the 243rd highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where Mission Viejo's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Santa Ana John Wayne Airport, 13.1 miles from the center of Mission Viejo at 43 ft above sea level. That is close enough that the station's summers are Mission Viejo's summers.

17 other cities use the same station and get the same climate inputs. The closest to Mission Viejo: Laguna Hills (3 mi away, 11.5 mi from the station), Lake Forest (3 mi away, 11.2 mi from the station), Rancho Santa Margarita (4 mi away, 15.8 mi from the station), Laguna Woods (4 mi away, 9.2 mi from the station), Aliso Viejo (5 mi away, 10.6 mi from the station). Mission Viejo is farther from the station than 13 of them.

The sun over Mission Viejo in late July

At 33.61°N, the noon sun on 21 July stands 76.8° above the horizon over Mission Viejo and the day runs 13 h 54 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.

91,601 people live in Mission Viejo, the 86th largest of the 376 California cities sized on this site. Coordinates used: 33.6093, -117.6565.

Mission Viejo AC sizing questions