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

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

3.5 tons central AC or heat pump, about 37,300 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.1 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 643 square feet in this climate. For a single room, size by the room: 18.7 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Vacaville/Nut Tree Airport Asos (8.9 mi away). Jul is the hottest month, averaging a high of 95°F and a low of 59°F, with about 88 days a year at 90°F or more. That gives a design temperature of 102°F against 75°F inside.

What it costs to run

About 1,816 kWh a year at SEER2 14.3, or roughly $592 at California's average residential rate of 32.58¢ per kWh. Cooling runs 6 months of the year here.

What drives the load in Fairfield

Of the 37,300 BTU/hr, 19,440 comes through walls, roof and windows on a 102°F afternoon (52%), 13,000 is sun on the house (35%), 2,120 is four people and their appliances, and 2,800 is moisture the coil has to wring out of Fairfield's summer air (8%).

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 34,560 BTU/hr before the moisture allowance.

Other house sizes in Fairfield

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,800 BTU/hr; a 350 sq ft living room needs about 6,500 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 11,200 BTU/hr.

Month by month in Fairfield

Jul alone uses 27% of the year's cooling energy. The unit runs the equivalent of 696 hours a year at full output.

Fairfield against nearby cities

Of 376 California cities here, Fairfield has the 97th highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where Fairfield's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Vacaville/Nut Tree Airport Asos, 8.9 miles from the center of Fairfield at 104 ft above sea level. That is close enough that the station's summers are Fairfield's summers.

4 other cities use the same station and get the same climate inputs. The closest to Fairfield: Suisun City (2 mi away, 9.4 mi from the station), Vacaville (8 mi away, 1.4 mi from the station), Dixon (17 mi away, 8.7 mi from the station), Rio Vista (19 mi away, 19.6 mi from the station). Fairfield is farther from the station than 2 of them.

The sun over Fairfield in late July

At 38.26°N, the noon sun on 21 July stands 72.1° above the horizon over Fairfield and the day runs 14 h 16 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.

122,646 people live in Fairfield, the 52nd largest of the 376 California cities sized on this site. Coordinates used: 38.2620, -122.0324.

Fairfield AC sizing questions