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

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

2 tons central AC or heat pump, about 24,900 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 69% 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 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 965 square feet in this climate. For a single room, size by the room: 12.4 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Jamestown Municipal Airport (1.8 mi away). Jul is the hottest month, averaging a high of 81.2°F and a low of 58.1°F, with about 9 days a year at 90°F or more. That gives a design temperature of 86°F against 75°F inside.

What it costs to run

About 547 kWh a year at SEER2 14.3, or roughly $68 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 Jamestown

Of the 24,900 BTU/hr, 7,920 comes through walls, roof and windows on a 86°F afternoon (32%), 13,000 is sun on the house (52%), 2,120 is four people and their appliances, and 1,800 is moisture the coil has to wring out of Jamestown's summer air (7%).

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 23,040 BTU/hr before the moisture allowance.

Other house sizes in Jamestown

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 1,900 BTU/hr; a 350 sq ft living room needs about 4,300 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 7,400 BTU/hr.

Month by month in Jamestown

Jul alone uses 39% of the year's cooling energy. The unit runs the equivalent of 314 hours a year at full output.

Jamestown against nearby cities

Of 9 North Dakota cities here, Jamestown has the 8th highest cooling load. The range runs from Grand Forks at 23,200 BTU/hr to Minot at 26,400.

Where Jamestown's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Jamestown Municipal Airport, 1.8 miles from the center of Jamestown at 1,495 ft above sea level. That is close enough that the station's summers are Jamestown's summers.

No other city in this set uses Jamestown Municipal Airport, so this sizing is Jamestown's alone.

The sun over Jamestown in late July

At 46.91°N, the noon sun on 21 July stands 63.5° above the horizon over Jamestown and the day runs 15 h 07 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.

15,789 people live in Jamestown, the 9th largest of the 9 North Dakota cities sized on this site. Coordinates used: 46.9059, -98.6936.

Jamestown AC sizing questions