What size AC for Las Cruces, NM? 3.5 tons for 2,000 sq ft

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

3.5 tons central AC or heat pump, about 38,900 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.2 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 617 square feet in this climate. For a single room, size by the room: 19.4 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at State University (3.5 mi away). Jun is the hottest month, averaging a high of 96.2°F and a low of 63.7°F, with about 109 days a year at 90°F or more. That gives a design temperature of 104°F against 75°F inside.

What it costs to run

About 2,687 kWh a year at SEER2 14.3, or roughly $412 at New Mexico's average residential rate of 15.34¢ per kWh. Cooling runs 6 months of the year here.

What drives the load in Las Cruces

Of the 38,900 BTU/hr, 20,880 comes through walls, roof and windows on a 104°F afternoon (54%), 13,000 is sun on the house (33%), 2,120 is four people and their appliances, and 2,900 is moisture the coil has to wring out of Las Cruces's summer air (7%).

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 36,000 BTU/hr before the moisture allowance.

Other house sizes in Las Cruces

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,900 BTU/hr; a 350 sq ft living room needs about 6,800 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 11,600 BTU/hr.

Month by month in Las Cruces

Jul alone uses 26% of the year's cooling energy. The unit runs the equivalent of 988 hours a year at full output.

Las Cruces against nearby cities

Of 19 New Mexico cities here, Las Cruces has the 7th highest cooling load. The range runs from Las Vegas at 25,500 BTU/hr to Sunland Park at 44,800.

Where Las Cruces's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is State University, 3.5 miles from the center of Las Cruces at 3,886 ft above sea level. That is close enough that the station's summers are Las Cruces's summers.

No other city in this set uses State University, so this sizing is Las Cruces's alone.

The sun over Las Cruces in late July

At 32.33°N, the noon sun on 21 July stands 78.1° above the horizon over Las Cruces 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.

116,998 people live in Las Cruces, the 2nd largest of the 19 New Mexico cities sized on this site. Coordinates used: 32.3264, -106.7897.

Las Cruces AC sizing questions