What size AC for Alton, IL? 3 tons for 2,000 sq ft

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

3 tons central AC or heat pump, about 36,000 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 17% 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 666 square feet in this climate. For a single room, size by the room: 18 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at St. Charles County Airport (15.3 mi away). Jul is the hottest month, averaging a high of 89.1°F and a low of 68.1°F, with about 44 days a year at 90°F or more. That gives a design temperature of 95°F against 75°F inside.

What it costs to run

About 2,159 kWh a year at SEER2 14.3, or roughly $415 at Illinois's average residential rate of 19.23¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Alton

Of the 36,000 BTU/hr, 14,400 comes through walls, roof and windows on a 95°F afternoon (40%), 13,000 is sun on the house (36%), 2,120 is four people and their appliances, and 6,500 is moisture the coil has to wring out of Alton's summer air (18%).

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 29,520 BTU/hr before the moisture allowance.

Other house sizes in Alton

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,700 BTU/hr; a 350 sq ft living room needs about 6,300 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 10,800 BTU/hr.

Month by month in Alton

Jul alone uses 29% of the year's cooling energy. The unit runs the equivalent of 857 hours a year at full output.

Alton against nearby cities

Of 225 Illinois cities here, Alton has the 3rd highest cooling load. The range runs from Fox Lake at 24,900 BTU/hr to Granite City at 36,000.

Where Alton's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is St. Charles County Airport, across the line in Missouri, 15.3 miles from the center of Alton at 432 ft above sea level. That is close enough that the station's summers are Alton's summers.

1 other city uses the same station and get the same climate inputs. The closest to Alton: Godfrey (5 mi away, 11.4 mi from the station). Alton is farther from the station than 1 of them.

The sun over Alton in late July

At 38.90°N, the noon sun on 21 July stands 71.5° above the horizon over Alton and the day runs 14 h 20 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.

24,967 people live in Alton, the 89th largest of the 225 Illinois cities sized on this site. Coordinates used: 38.9039, -90.1512.

Alton AC sizing questions