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

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

2 tons central AC or heat pump, about 23,200 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 81% 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 1,034 square feet in this climate. For a single room, size by the room: 11.6 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Napa County Airport (6.3 mi away). Sep is the hottest month, averaging a high of 80.3°F and a low of 51°F, with about 16 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 395 kWh a year at SEER2 14.3, or roughly $129 at California's average residential rate of 32.58¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Napa

Of the 23,200 BTU/hr, 7,200 comes through walls, roof and windows on a 85°F afternoon (31%), 13,000 is sun on the house (56%), 2,120 is four people and their appliances, and 900 is moisture the coil has to wring out of Napa'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 22,320 BTU/hr before the moisture allowance.

Other house sizes in Napa

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 4,100 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 7,000 BTU/hr.

Month by month in Napa

Aug alone uses 27% of the year's cooling energy. The unit runs the equivalent of 243 hours a year at full output.

Napa against nearby cities

Of 376 California cities here, Napa has the 279th highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where Napa's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Napa County Airport, 6.3 miles from the center of Napa at 16 ft above sea level. That is close enough that the station's summers are Napa's summers.

6 other cities use the same station and get the same climate inputs. The closest to Napa: American Canyon (9 mi away, 2.3 mi from the station), Sonoma (9 mi away, 11.3 mi from the station), Vallejo (13 mi away, 7 mi from the station), Hercules (19 mi away, 12.9 mi from the station), Novato (20 mi away, 16.8 mi from the station). Napa is farther from the station than 1 of them.

The sun over Napa in late July

At 38.30°N, the noon sun on 21 July stands 72.1° above the horizon over Napa 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.

76,921 people live in Napa, the 115th largest of the 376 California cities sized on this site. Coordinates used: 38.2979, -122.3007.

Napa AC sizing questions