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

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

2.5 tons central AC or heat pump, about 31,100 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 35% 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 772 square feet in this climate. For a single room, size by the room: 15.6 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Pierre Regional Airport (1.7 mi away). Jul is the hottest month, averaging a high of 88.3°F and a low of 61.6°F, with about 38 days a year at 90°F or more. That gives a design temperature of 94°F against 75°F inside.

What it costs to run

About 1,092 kWh a year at SEER2 14.3, or roughly $159 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 Pierre

Of the 31,100 BTU/hr, 13,680 comes through walls, roof and windows on a 94°F afternoon (44%), 13,000 is sun on the house (42%), 2,120 is four people and their appliances, and 2,300 is moisture the coil has to wring out of Pierre's summer air (7%).

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 28,800 BTU/hr before the moisture allowance.

Other house sizes in Pierre

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,300 BTU/hr; a 350 sq ft living room needs about 5,500 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 9,400 BTU/hr.

Month by month in Pierre

Jul alone uses 38% of the year's cooling energy. The unit runs the equivalent of 502 hours a year at full output.

Pierre against nearby cities

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

Where Pierre's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Pierre Regional Airport, 1.7 miles from the center of Pierre at 1,719 ft above sea level. That is close enough that the station's summers are Pierre's summers.

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

The sun over Pierre in late July

At 44.38°N, the noon sun on 21 July stands 66.0° above the horizon over Pierre 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.

13,788 people live in Pierre, the 11th largest of the 14 South Dakota cities sized on this site. Coordinates used: 44.3752, -100.3200.

Pierre AC sizing questions