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

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

2 tons central AC or heat pump, about 25,500 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 65% 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 943 square feet in this climate. For a single room, size by the room: 12.7 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Spearfish (2.8 mi away). Jul is the hottest month, averaging a high of 83.6°F and a low of 57.6°F, with about 26 days a year at 90°F or more. That gives a design temperature of 88°F against 75°F inside.

What it costs to run

About 636 kWh a year at SEER2 14.3, or roughly $93 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 Spearfish

Of the 25,500 BTU/hr, 9,360 comes through walls, roof and windows on a 88°F afternoon (37%), 13,000 is sun on the house (51%), 2,120 is four people and their appliances, and 1,000 is moisture the coil has to wring out of Spearfish'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 24,480 BTU/hr before the moisture allowance.

Other house sizes in Spearfish

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 4,400 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 7,600 BTU/hr.

Month by month in Spearfish

Jul alone uses 39% of the year's cooling energy. The unit runs the equivalent of 357 hours a year at full output.

Spearfish against nearby cities

Of 14 South Dakota cities here, Spearfish has the 12th highest cooling load. The range runs from Watertown at 24,900 BTU/hr to Pierre at 31,100.

Where Spearfish's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Spearfish, 2.8 miles from the center of Spearfish at 3,633 ft above sea level. That is close enough that the station's summers are Spearfish's summers.

No other city in this set uses Spearfish, so this sizing is Spearfish's alone.

The sun over Spearfish in late July

At 44.49°N, the noon sun on 21 July stands 65.9° above the horizon over Spearfish and the day runs 14 h 51 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.

13,803 people live in Spearfish, the 10th largest of the 14 South Dakota cities sized on this site. Coordinates used: 44.4914, -103.8163.

Spearfish AC sizing questions