What size AC for Washington, UT? 4 tons for 2,000 sq ft

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

4 tons central AC or heat pump, about 49,200 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 488 square feet in this climate. For a single room, size by the room: 24.6 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at St. George (6.6 mi away). Jul is the hottest month, averaging a high of 101.9°F and a low of 71.7°F, with about 128 days a year at 90°F or more. That gives a design temperature of 110°F against 75°F inside.

What it costs to run

About 3,562 kWh a year at SEER2 14.3, or roughly $470 at Utah's average residential rate of 13.19¢ per kWh. Cooling runs 6 months of the year here.

What drives the load in Washington

Of the 49,200 BTU/hr, 25,200 comes through walls, roof and windows on a 110°F afternoon (51%), 13,000 is sun on the house (26%), 2,120 is four people and their appliances, and 8,900 is moisture the coil has to wring out of Washington'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 40,320 BTU/hr before the moisture allowance.

Other house sizes in Washington

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 3,700 BTU/hr; a 350 sq ft living room needs about 8,600 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 14,800 BTU/hr.

Month by month in Washington

Jul alone uses 28% of the year's cooling energy. The unit runs the equivalent of 1,035 hours a year at full output.

Washington against nearby cities

Of 67 Utah cities here, Washington has the 2nd highest cooling load. The range runs from Heber at 30,700 BTU/hr to St. George at 49,200.

Where Washington's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is St. George, 6.6 miles from the center of Washington at 2,857 ft above sea level. That is close enough that the station's summers are Washington's summers.

2 other cities use the same station and get the same climate inputs. The closest to Washington: St. George (6 mi away, 3.3 mi from the station), Ivins (11 mi away, 5.6 mi from the station). Washington is farther from the station than 2 of them.

The sun over Washington in late July

At 37.13°N, the noon sun on 21 July stands 73.3° above the horizon over Washington and the day runs 14 h 11 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.

35,501 people live in Washington, the 32nd largest of the 67 Utah cities sized on this site. Coordinates used: 37.1267, -113.4878.

Washington AC sizing questions