What size AC for St. Joseph, MO? 3 tons for 2,000 sq ft

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

3 tons central AC or heat pump, about 32,300 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 30% 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 3 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 743 square feet in this climate. For a single room, size by the room: 16.1 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at St. Joseph Rosecrans Mem Airport (4.7 mi away). Jul is the hottest month, averaging a high of 88.1°F and a low of 67.3°F, with about 39 days a year at 90°F or more. That gives a design temperature of 93°F against 75°F inside.

What it costs to run

About 1,789 kWh a year at SEER2 14.3, or roughly $256 at Missouri's average residential rate of 14.28¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in St. Joseph

Of the 32,300 BTU/hr, 12,960 comes through walls, roof and windows on a 93°F afternoon (40%), 13,000 is sun on the house (40%), 2,120 is four people and their appliances, and 4,200 is moisture the coil has to wring out of St. Joseph'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 28,080 BTU/hr before the moisture allowance.

Other house sizes in St. Joseph

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,400 BTU/hr; a 350 sq ft living room needs about 5,600 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 9,700 BTU/hr.

Month by month in St. Joseph

Jul alone uses 31% of the year's cooling energy. The unit runs the equivalent of 792 hours a year at full output.

St. Joseph against nearby cities

Of 80 Missouri cities here, St. Joseph has the 70th highest cooling load. The range runs from Hannibal at 30,600 BTU/hr to Sikeston at 37,800.

Where St. Joseph's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is St. Joseph Rosecrans Mem Airport, 4.7 miles from the center of St. Joseph at 807 ft above sea level. That is close enough that the station's summers are St. Joseph's summers.

No other city in this set uses St. Joseph Rosecrans Mem Airport, so this sizing is St. Joseph's alone.

The sun over St. Joseph in late July

At 39.76°N, the noon sun on 21 July stands 70.6° above the horizon over St. Joseph and the day runs 14 h 24 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. Shorter days give the house a longer night to shed the day's heat.

71,098 people live in St. Joseph, the 9th largest of the 80 Missouri cities sized on this site. Coordinates used: 39.7595, -94.8211.

St. Joseph AC sizing questions