What size AC for King City, CA? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 27,000 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 56% 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 890 square feet in this climate. For a single room, size by the room: 13.5 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at King City (0.7 mi away). Aug is the hottest month, averaging a high of 85.2°F and a low of 53.7°F, with about 39 days a year at 90°F or more. That gives a design temperature of 90°F against 75°F inside.

What it costs to run

About 726 kWh a year at SEER2 14.3, or roughly $237 at California's average residential rate of 32.58¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in King City

Of the 27,000 BTU/hr, 10,800 comes through walls, roof and windows on a 90°F afternoon (40%), 13,000 is sun on the house (48%), 2,120 is four people and their appliances, and 1,000 is moisture the coil has to wring out of King City'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 25,920 BTU/hr before the moisture allowance.

Other house sizes in King City

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 4,700 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 8,100 BTU/hr.

Month by month in King City

Aug alone uses 24% of the year's cooling energy. The unit runs the equivalent of 385 hours a year at full output.

King City against nearby cities

Of 376 California cities here, King City has the 233rd highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where King City's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is King City, 0.7 miles from the center of King City at 320 ft above sea level. That is close enough that the station's summers are King City's summers.

1 other city uses the same station and get the same climate inputs. The closest to King City: Greenfield (10 mi away, 10 mi from the station). King City sits closer to the station than any of them, so its numbers are the best measured of the group.

The sun over King City in late July

At 36.22°N, the noon sun on 21 July stands 74.2° above the horizon over King City and the day runs 14 h 06 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.

13,920 people live in King City, the 333rd largest of the 376 California cities sized on this site. Coordinates used: 36.2163, -121.1320.

King City AC sizing questions