What size AC for Williston, ND? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 26,200 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 60% 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 2.5 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 916 square feet in this climate. For a single room, size by the room: 13.1 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Williston Sloulin Field (1.2 mi away). Jul is the hottest month, averaging a high of 84.5°F and a low of 56.3°F, with about 21 days a year at 90°F or more. That gives a design temperature of 89°F against 75°F inside.

What it costs to run

About 574 kWh a year at SEER2 14.3, or roughly $72 at North Dakota's average residential rate of 12.46¢ per kWh. Cooling runs 3 months of the year here.

What drives the load in Williston

Of the 26,200 BTU/hr, 10,080 comes through walls, roof and windows on a 89°F afternoon (38%), 13,000 is sun on the house (50%), 2,120 is four people and their appliances, and 1,000 is moisture the coil has to wring out of Williston's summer air (4%).

Sun is the biggest share here, more than heat through the walls, so shading west windows and a light roof cut the size you need more than extra insulation would. Sensible heat totals 25,200 BTU/hr before the moisture allowance.

Other house sizes in Williston

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,000 BTU/hr; a 350 sq ft living room needs about 4,600 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 7,900 BTU/hr.

Month by month in Williston

Jul alone uses 41% of the year's cooling energy. The unit runs the equivalent of 313 hours a year at full output.

Williston against nearby cities

Of 9 North Dakota cities here, Williston has the 3rd highest cooling load. The range runs from Grand Forks at 23,200 BTU/hr to Minot at 26,400.

Where Williston's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Williston Sloulin Field, 1.2 miles from the center of Williston at 1,902 ft above sea level. That is close enough that the station's summers are Williston's summers.

No other city in this set uses Williston Sloulin Field, so this sizing is Williston's alone.

The sun over Williston in late July

At 48.19°N, the noon sun on 21 July stands 62.2° above the horizon over Williston and the day runs 15 h 17 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.

28,821 people live in Williston, the 6th largest of the 9 North Dakota cities sized on this site. Coordinates used: 48.1895, -103.6491.

Williston AC sizing questions