What size AC for Somerton, AZ? 5 tons for 2,000 sq ft

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

5 tons central AC or heat pump, about 57,100 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, which falls short here. On a design day the unit runs flat out and the house still drifts above 75°F by late afternoon.

If a contractor quotes you more than 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 420 square feet in this climate. For a single room, size by the room: 28.5 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Yuma Mcas (5.7 mi away). Jul is the hottest month, averaging a high of 106.7°F and a low of 82.6°F, with about 181 days a year at 90°F or more. That gives a design temperature of 115°F against 75°F inside.

What it costs to run

About 7,391 kWh a year at SEER2 14.3, or roughly $1,135 at Arizona's average residential rate of 15.36¢ per kWh. Cooling runs 9 months of the year here.

What drives the load in Somerton

Of the 57,100 BTU/hr, 28,800 comes through walls, roof and windows on a 115°F afternoon (50%), 13,000 is sun on the house (23%), 2,120 is four people and their appliances, and 13,200 is moisture the coil has to wring out of Somerton's summer air (23%).

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 43,920 BTU/hr before the moisture allowance.

Other house sizes in Somerton

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 4,300 BTU/hr; a 350 sq ft living room needs about 10,000 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 17,100 BTU/hr.

Month by month in Somerton

Aug alone uses 20% of the year's cooling energy. The unit runs the equivalent of 1,851 hours a year at full output.

Somerton against nearby cities

Of 44 Arizona cities here, Somerton has the 17th highest cooling load. The range runs from Flagstaff at 24,000 BTU/hr to Bullhead City at 60,800.

Where Somerton's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Yuma Mcas, 5.7 miles from the center of Somerton at 213 ft above sea level. That is close enough that the station's summers are Somerton's summers.

2 other cities use the same station and get the same climate inputs. The closest to Somerton: San Luis (8 mi away, 12.9 mi from the station), Yuma (12 mi away, 10.8 mi from the station). Somerton sits closer to the station than any of them, so its numbers are the best measured of the group.

The sun over Somerton in late July

At 32.60°N, the noon sun on 21 July stands 77.8° above the horizon over Somerton 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.

14,902 people live in Somerton, the 38th largest of the 44 Arizona cities sized on this site. Coordinates used: 32.6018, -114.6963.

Somerton AC sizing questions