What size AC for Harrisburg, SD? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 28,000 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 50% 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 857 square feet in this climate. For a single room, size by the room: 14 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Sioux Falls (10.6 mi away). Jul is the hottest month, averaging a high of 85.3°F and a low of 63.4°F, with about 15 days a year at 90°F or more. That gives a design temperature of 90°F against 75°F inside.

What it costs to run

About 1,106 kWh a year at SEER2 14.3, or roughly $161 at South Dakota's average residential rate of 14.58¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Harrisburg

Of the 28,000 BTU/hr, 10,800 comes through walls, roof and windows on a 90°F afternoon (39%), 13,000 is sun on the house (46%), 2,120 is four people and their appliances, and 2,100 is moisture the coil has to wring out of Harrisburg's summer air (8%).

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 25,920 BTU/hr before the moisture allowance.

Other house sizes in Harrisburg

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,100 BTU/hr; a 350 sq ft living room needs about 4,900 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 8,400 BTU/hr.

Month by month in Harrisburg

Jul alone uses 35% of the year's cooling energy. The unit runs the equivalent of 565 hours a year at full output.

Harrisburg against nearby cities

Of 14 South Dakota cities here, Harrisburg has the 10th highest cooling load. The range runs from Watertown at 24,900 BTU/hr to Pierre at 31,100.

Where Harrisburg's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Sioux Falls, 10.6 miles from the center of Harrisburg at 1,495 ft above sea level. That is close enough that the station's summers are Harrisburg's summers.

2 other cities use the same station and get the same climate inputs. The closest to Harrisburg: Sioux Falls (7 mi away, 3.3 mi from the station), Brandon (13 mi away, 7.3 mi from the station). Harrisburg is farther from the station than 2 of them.

The sun over Harrisburg in late July

At 43.43°N, the noon sun on 21 July stands 67.0° above the horizon over Harrisburg and the day runs 14 h 45 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.

10,203 people live in Harrisburg, the 14th largest of the 14 South Dakota cities sized on this site. Coordinates used: 43.4343, -96.7124.

Harrisburg AC sizing questions