What size AC for St. Peter, MN? 2 tons for 2,000 sq ft

What size AC a 2,000 sq ft house in St. Peter 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 St. Peter (0.5 mi away). Jul is the hottest month, averaging a high of 81.9°F and a low of 61.2°F, with about 11 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 753 kWh a year at SEER2 14.3, or roughly $124 at Minnesota's average residential rate of 16.44¢ per kWh. Cooling runs 3 months of the year here.

What drives the load in St. Peter

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 St. Peter'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 St. Peter

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 St. Peter

Jul alone uses 37% of the year's cooling energy. The unit runs the equivalent of 433 hours a year at full output.

St. Peter against nearby cities

Of 103 Minnesota cities here, St. Peter has the 88th highest cooling load. The range runs from Hibbing at 20,200 BTU/hr to Winona at 29,000.

Where St. Peter's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is St. Peter, 0.5 miles from the center of St. Peter at 795 ft above sea level. That is close enough that the station's summers are St. Peter's summers.

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

The sun over St. Peter in late July

At 44.33°N, the noon sun on 21 July stands 66.1° above the horizon over St. Peter and the day runs 14 h 50 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.

12,456 people live in St. Peter, the 92nd largest of the 103 Minnesota cities sized on this site. Coordinates used: 44.3293, -93.9677.

St. Peter AC sizing questions