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

What size AC a 2,000 sq ft house in Farmington 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 Farmington Four Corners Regional A (2.8 mi away). Jul is the hottest month, averaging a high of 93.3°F and a low of 60.9°F, with about 69 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 1,298 kWh a year at SEER2 14.3, or roughly $199 at New Mexico's average residential rate of 15.34¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Farmington

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 Farmington'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 Farmington

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 Farmington

Jul alone uses 38% of the year's cooling energy. The unit runs the equivalent of 519 hours a year at full output.

Farmington against nearby cities

Of 19 New Mexico cities here, Farmington has the 12th highest cooling load. The range runs from Las Vegas at 25,500 BTU/hr to Sunland Park at 44,800.

Where Farmington's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Farmington Four Corners Regional A, 2.8 miles from the center of Farmington at 5,499 ft above sea level. That is close enough that the station's summers are Farmington's summers.

No other city in this set uses Farmington Four Corners Regional A, so this sizing is Farmington's alone.

The sun over Farmington in late July

At 36.75°N, the noon sun on 21 July stands 73.6° above the horizon over Farmington and the day runs 14 h 09 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.

46,262 people live in Farmington, the 6th largest of the 19 New Mexico cities sized on this site. Coordinates used: 36.7538, -108.1805.

Farmington AC sizing questions