What size AC for South St. Paul, MN? 2.5 tons for 2,000 sq ft

What size AC a 2,000 sq ft house in South St. Paul needs

2.5 tons central AC or heat pump, about 27,300 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 54% 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 878 square feet in this climate. For a single room, size by the room: 13.7 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at St. Paul Dwtn Airport (3.1 mi away). Jul is the hottest month, averaging a high of 82.6°F and a low of 64°F, with about 12 days a year at 90°F or more. That gives a design temperature of 87°F against 75°F inside.

What it costs to run

About 1,007 kWh a year at SEER2 14.3, or roughly $165 at Minnesota's average residential rate of 16.44¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in South St. Paul

Of the 27,300 BTU/hr, 8,640 comes through walls, roof and windows on a 87°F afternoon (32%), 13,000 is sun on the house (48%), 2,120 is four people and their appliances, and 3,600 is moisture the coil has to wring out of South St. Paul's summer air (13%).

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 23,760 BTU/hr before the moisture allowance.

Other house sizes in South St. Paul

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 4,800 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 8,200 BTU/hr.

Month by month in South St. Paul

Jul alone uses 36% of the year's cooling energy. The unit runs the equivalent of 527 hours a year at full output.

South St. Paul against nearby cities

Of 103 Minnesota cities here, South St. Paul has the 33rd highest cooling load. The range runs from Hibbing at 20,200 BTU/hr to Winona at 29,000.

Where South St. Paul's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is St. Paul Dwtn Airport, 3.1 miles from the center of South St. Paul at 700 ft above sea level. That is close enough that the station's summers are South St. Paul's summers.

18 other cities use the same station and get the same climate inputs. The closest to South St. Paul: West St. Paul (2 mi away, 2.5 mi from the station), Inver Grove Heights (4 mi away, 7.1 mi from the station), St. Paul (5 mi away, 2.6 mi from the station), Woodbury (6 mi away, 6.7 mi from the station), Oakdale (8 mi away, 5.9 mi from the station). South St. Paul is farther from the station than 2 of them.

The sun over South St. Paul in late July

At 44.89°N, the noon sun on 21 July stands 65.5° above the horizon over South St. Paul and the day runs 14 h 54 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.

20,590 people live in South St. Paul, the 61st largest of the 103 Minnesota cities sized on this site. Coordinates used: 44.8880, -93.0405.

South St. Paul AC sizing questions