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

What size AC a 2,000 sq ft house in Cahokia Heights 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 Cahokia St. Louis Dwtn Airport (0.7 mi away). Jul is the hottest month, averaging a high of 89°F and a low of 68.8°F, with about 46 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 2,176 kWh a year at SEER2 14.3, or roughly $418 at Illinois's average residential rate of 19.23¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Cahokia Heights

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 Cahokia Heights'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 Cahokia Heights

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 Cahokia Heights

Jul alone uses 29% of the year's cooling energy. The unit runs the equivalent of 864 hours a year at full output.

Cahokia Heights against nearby cities

Of 225 Illinois cities here, Cahokia Heights has the 7th highest cooling load. The range runs from Fox Lake at 24,900 BTU/hr to Granite City at 36,000.

Where Cahokia Heights's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Cahokia St. Louis Dwtn Airport, 0.7 miles from the center of Cahokia Heights at 405 ft above sea level. That is close enough that the station's summers are Cahokia Heights's summers.

12 other cities use the same station and get the same climate inputs. The closest to Cahokia Heights: East St. Louis (3 mi away, 3.8 mi from the station), St. Louis (7 mi away, 7.2 mi from the station), Fairview Heights (8 mi away, 8.1 mi from the station), Columbia (9 mi away, 8.2 mi from the station), Collinsville (11 mi away, 10.9 mi from the station). Cahokia Heights sits closer to the station than any of them, so its numbers are the best measured of the group.

The sun over Cahokia Heights in late July

At 38.57°N, the noon sun on 21 July stands 71.8° above the horizon over Cahokia Heights and the day runs 14 h 18 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.

17,052 people live in Cahokia Heights, the 150th largest of the 225 Illinois cities sized on this site. Coordinates used: 38.5721, -90.1553.

Cahokia Heights AC sizing questions