What size AC for San Juan, TX? 4 tons for 2,000 sq ft

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

4 tons central AC or heat pump, about 50,500 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 475 square feet in this climate. For a single room, size by the room: 25.3 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Mcallen Miller International Airport (5.8 mi away). Aug is the hottest month, averaging a high of 99.6°F and a low of 78.9°F, with about 177 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 7,837 kWh a year at SEER2 14.3, or roughly $1,256 at Texas's average residential rate of 16.03¢ per kWh. Cooling runs 12 months of the year here.

What drives the load in San Juan

Of the 50,500 BTU/hr, 23,760 comes through walls, roof and windows on a 108°F afternoon (47%), 13,000 is sun on the house (26%), 2,120 is four people and their appliances, and 11,700 is moisture the coil has to wring out of San Juan'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 38,880 BTU/hr before the moisture allowance.

Other house sizes in San Juan

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 3,800 BTU/hr; a 350 sq ft living room needs about 8,900 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 15,200 BTU/hr.

Month by month in San Juan

Aug alone uses 15% of the year's cooling energy. The unit runs the equivalent of 2,217 hours a year at full output.

San Juan against nearby cities

Of 252 Texas cities here, San Juan has the 8th highest cooling load. The range runs from Levelland at 37,300 BTU/hr to Laredo at 51,500.

Where San Juan's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Mcallen Miller International Airport, 5.8 miles from the center of San Juan at 99 ft above sea level. That is close enough that the station's summers are San Juan's summers.

10 other cities use the same station and get the same climate inputs. The closest to San Juan: Alamo (2 mi away, 7.9 mi from the station), Pharr (3 mi away, 3.3 mi from the station), McAllen (6 mi away, 3.2 mi from the station), Donna (7 mi away, 12.8 mi from the station), Hidalgo (8 mi away, 4.9 mi from the station). San Juan is farther from the station than 4 of them.

The sun over San Juan in late July

At 26.19°N, the noon sun on 21 July stands 84.2° above the horizon over San Juan and the day runs 13 h 24 min from sunrise to sunset. With the sun that close to overhead, the roof takes most of the heat at midday and the west wall takes the rest after 3 pm. Shorter days give the house a longer night to shed the day's heat.

37,341 people live in San Juan, the 102nd largest of the 252 Texas cities sized on this site. Coordinates used: 26.1894, -98.1518.

San Juan AC sizing questions