What size AC for Simi Valley, CA? 3.5 tons for 2,000 sq ft

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

3.5 tons central AC or heat pump, about 38,100 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.2 tons. This is one of the climates the chart was written for.

If a contractor quotes you more than 3.5 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 630 square feet in this climate. For a single room, size by the room: 19 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Van Nuys Airport (15.2 mi away). Aug is the hottest month, averaging a high of 93.1°F and a low of 64.9°F, with about 77 days a year at 90°F or more. That gives a design temperature of 100°F against 75°F inside.

What it costs to run

About 2,553 kWh a year at SEER2 14.3, or roughly $832 at California's average residential rate of 32.58¢ per kWh. Cooling runs 7 months of the year here.

What drives the load in Simi Valley

Of the 38,100 BTU/hr, 18,000 comes through walls, roof and windows on a 100°F afternoon (47%), 13,000 is sun on the house (34%), 2,120 is four people and their appliances, and 5,000 is moisture the coil has to wring out of Simi Valley's summer air (13%).

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 33,120 BTU/hr before the moisture allowance.

Other house sizes in Simi Valley

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,900 BTU/hr; a 350 sq ft living room needs about 6,700 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 11,400 BTU/hr.

Month by month in Simi Valley

Aug alone uses 24% of the year's cooling energy. The unit runs the equivalent of 958 hours a year at full output.

Simi Valley against nearby cities

Of 376 California cities here, Simi Valley has the 86th highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where Simi Valley's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Van Nuys Airport, 15.2 miles from the center of Simi Valley at 785 ft above sea level. That is close enough that the station's summers are Simi Valley's summers.

4 other cities use the same station and get the same climate inputs. The closest to Simi Valley: Agoura Hills (8 mi away, 16.2 mi from the station), Calabasas (10 mi away, 11.4 mi from the station), Santa Clarita (18 mi away, 14.1 mi from the station), San Fernando (18 mi away, 6.2 mi from the station). Simi Valley is farther from the station than 3 of them.

The sun over Simi Valley in late July

At 34.27°N, the noon sun on 21 July stands 76.1° above the horizon over Simi Valley and the day runs 13 h 57 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.

125,778 people live in Simi Valley, the 48th largest of the 376 California cities sized on this site. Coordinates used: 34.2669, -118.7485.

Simi Valley AC sizing questions