What size AC for Marana, AZ? 4 tons for 2,000 sq ft

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

4 tons central AC or heat pump, about 47,400 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 4 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 506 square feet in this climate. For a single room, size by the room: 23.7 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Tucson 11 W (15.8 mi away). Jun is the hottest month, averaging a high of 100.4°F and a low of 69.7°F, with about 149 days a year at 90°F or more. That gives a design temperature of 108°F against 75°F inside.

What it costs to run

About 4,713 kWh a year at SEER2 14.3, or roughly $724 at Arizona's average residential rate of 15.36¢ per kWh. Cooling runs 7 months of the year here.

What drives the load in Marana

Of the 47,400 BTU/hr, 23,760 comes through walls, roof and windows on a 108°F afternoon (50%), 13,000 is sun on the house (27%), 2,120 is four people and their appliances, and 8,600 is moisture the coil has to wring out of Marana's summer air (18%).

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 38,880 BTU/hr before the moisture allowance.

Other house sizes in Marana

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 3,600 BTU/hr; a 350 sq ft living room needs about 8,300 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 14,200 BTU/hr.

Month by month in Marana

Jul alone uses 21% of the year's cooling energy. The unit runs the equivalent of 1,421 hours a year at full output.

Marana against nearby cities

Of 44 Arizona cities here, Marana has the 30th highest cooling load. The range runs from Flagstaff at 24,000 BTU/hr to Bullhead City at 60,800.

Where Marana's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Tucson 11 W, 15.8 miles from the center of Marana at 2,733 ft above sea level. That is close enough that the station's summers are Marana's summers.

1 other city uses the same station and get the same climate inputs. The closest to Marana: Oro Valley (10 mi away, 16.8 mi from the station). Marana sits closer to the station than any of them, so its numbers are the best measured of the group.

The sun over Marana in late July

At 32.47°N, the noon sun on 21 July stands 77.9° above the horizon over Marana and the day runs 13 h 49 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.

62,380 people live in Marana, the 19th largest of the 44 Arizona cities sized on this site. Coordinates used: 32.4659, -111.1354.

Marana AC sizing questions