What size AC for Los Lunas, NM? 3 tons for 2,000 sq ft

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

3 tons central AC or heat pump, about 35,800 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 17% more than this climate needs. An oversized unit cools the air fast, shuts off before it pulls moisture out, and leaves the house cold and clammy.

If a contractor quotes you more than 3 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 671 square feet in this climate. For a single room, size by the room: 17.9 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Los Lunas 3 Ssw (2.8 mi away). Jul is the hottest month, averaging a high of 93.3°F and a low of 62.2°F, with about 92 days a year at 90°F or more. That gives a design temperature of 100°F against 75°F inside.

What it costs to run

About 1,555 kWh a year at SEER2 14.3, or roughly $239 at New Mexico's average residential rate of 15.34¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Los Lunas

Of the 35,800 BTU/hr, 18,000 comes through walls, roof and windows on a 100°F afternoon (50%), 13,000 is sun on the house (36%), 2,120 is four people and their appliances, and 2,700 is moisture the coil has to wring out of Los Lunas'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 33,120 BTU/hr before the moisture allowance.

Other house sizes in Los Lunas

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,700 BTU/hr; a 350 sq ft living room needs about 6,300 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 10,700 BTU/hr.

Month by month in Los Lunas

Jul alone uses 33% of the year's cooling energy. The unit runs the equivalent of 622 hours a year at full output.

Los Lunas against nearby cities

Of 19 New Mexico cities here, Los Lunas has the 13th highest cooling load. The range runs from Las Vegas at 25,500 BTU/hr to Sunland Park at 44,800.

Where Los Lunas's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Los Lunas 3 Ssw, 2.8 miles from the center of Los Lunas at 4,840 ft above sea level. That is close enough that the station's summers are Los Lunas's summers.

No other city in this set uses Los Lunas 3 Ssw, so this sizing is Los Lunas's alone.

The sun over Los Lunas in late July

At 34.80°N, the noon sun on 21 July stands 75.6° above the horizon over Los Lunas and the day runs 13 h 60 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.

19,907 people live in Los Lunas, the 12th largest of the 19 New Mexico cities sized on this site. Coordinates used: 34.8009, -106.7887.

Los Lunas AC sizing questions