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

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

2 tons central AC or heat pump, about 22,400 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 88% 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 1,074 square feet in this climate. For a single room, size by the room: 11.2 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at N Is NAS (6.7 mi away). Aug is the hottest month, averaging a high of 76.7°F and a low of 66.5°F, with about 4 days a year at 90°F or more. That gives a design temperature of 81°F against 75°F inside.

What it costs to run

About 1,056 kWh a year at SEER2 14.3, or roughly $344 at California's average residential rate of 32.58¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in National City

Of the 22,400 BTU/hr, 4,320 comes through walls, roof and windows on a 81°F afternoon (19%), 13,000 is sun on the house (58%), 2,120 is four people and their appliances, and 2,900 is moisture the coil has to wring out of National City'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 19,440 BTU/hr before the moisture allowance.

Other house sizes in National City

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 1,700 BTU/hr; a 350 sq ft living room needs about 3,900 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 6,700 BTU/hr.

Month by month in National City

Aug alone uses 27% of the year's cooling energy. The unit runs the equivalent of 675 hours a year at full output.

National City against nearby cities

Of 376 California cities here, National City has the 290th highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where National City's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is N Is NAS, 6.7 miles from the center of National City at 14 ft above sea level. That is close enough that the station's summers are National City's summers.

1 other city uses the same station and get the same climate inputs. The closest to National City: Coronado (3 mi away, 4 mi from the station). National City is farther from the station than 1 of them.

The sun over National City in late July

At 32.67°N, the noon sun on 21 July stands 77.7° above the horizon over National City and the day runs 13 h 50 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.

58,460 people live in National City, the 158th largest of the 376 California cities sized on this site. Coordinates used: 32.6652, -117.0988.

National City AC sizing questions