What size AC for Farmington, UT? 3.5 tons for 2,000 sq ft

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

3.5 tons central AC or heat pump, about 40,400 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.4 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 594 square feet in this climate. For a single room, size by the room: 20.2 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Salt Lake City International Airport (15.1 mi away). Jul is the hottest month, averaging a high of 94°F and a low of 68.2°F, with about 62 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 2,093 kWh a year at SEER2 14.3, or roughly $276 at Utah's average residential rate of 13.19¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Farmington

Of the 40,400 BTU/hr, 18,000 comes through walls, roof and windows on a 100°F afternoon (45%), 13,000 is sun on the house (32%), 2,120 is four people and their appliances, and 7,300 is moisture the coil has to wring out of Farmington'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 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 3,000 BTU/hr; a 350 sq ft living room needs about 7,100 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 12,100 BTU/hr.

Month by month in Farmington

Jul alone uses 35% of the year's cooling energy. The unit runs the equivalent of 741 hours a year at full output.

Farmington against nearby cities

Of 67 Utah cities here, Farmington has the 22nd highest cooling load. The range runs from Heber at 30,700 BTU/hr to St. George at 49,200.

Where Farmington's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Salt Lake City International Airport, 15.1 miles from the center of Farmington at 4,227 ft above sea level. That is close enough that the station's summers are Farmington's summers.

20 other cities use the same station and get the same climate inputs. The closest to Farmington: Centerville (4 mi away, 11.6 mi from the station), Woods Cross (8 mi away, 7.5 mi from the station), Bountiful (8 mi away, 8.9 mi from the station), North Salt Lake (10 mi away, 5.8 mi from the station), Salt Lake City (14 mi away, 1.8 mi from the station). Farmington is farther from the station than 18 of them.

The sun over Farmington in late July

At 40.98°N, the noon sun on 21 July stands 69.4° above the horizon over Farmington and the day runs 14 h 31 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. Long days mean the house keeps gaining heat into the evening, well after the outdoor peak.

26,163 people live in Farmington, the 39th largest of the 67 Utah cities sized on this site. Coordinates used: 40.9847, -111.9063.

Farmington AC sizing questions