What size AC for Rock Island, IL? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 30,600 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 37% 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 783 square feet in this climate. For a single room, size by the room: 15.3 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Moline Quad City International Airport (3.5 mi away). Jul is the hottest month, averaging a high of 86.1°F and a low of 64.9°F, with about 22 days a year at 90°F or more. That gives a design temperature of 91°F against 75°F inside.

What it costs to run

About 1,446 kWh a year at SEER2 14.3, or roughly $278 at Illinois's average residential rate of 19.23¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Rock Island

Of the 30,600 BTU/hr, 11,520 comes through walls, roof and windows on a 91°F afternoon (38%), 13,000 is sun on the house (42%), 2,120 is four people and their appliances, and 4,000 is moisture the coil has to wring out of Rock Island'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 26,640 BTU/hr before the moisture allowance.

Other house sizes in Rock Island

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,300 BTU/hr; a 350 sq ft living room needs about 5,400 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 9,200 BTU/hr.

Month by month in Rock Island

Jul alone uses 31% of the year's cooling energy. The unit runs the equivalent of 675 hours a year at full output.

Rock Island against nearby cities

Of 225 Illinois cities here, Rock Island has the 34th highest cooling load. The range runs from Fox Lake at 24,900 BTU/hr to Granite City at 36,000.

Where Rock Island's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Moline Quad City International Airport, 3.5 miles from the center of Rock Island at 576 ft above sea level. That is close enough that the station's summers are Rock Island's summers.

2 other cities use the same station and get the same climate inputs. The closest to Rock Island: Moline (5 mi away, 2.8 mi from the station), East Moline (11 mi away, 8.6 mi from the station). Rock Island is farther from the station than 1 of them.

The sun over Rock Island in late July

At 41.47°N, the noon sun on 21 July stands 68.9° above the horizon over Rock Island and the day runs 14 h 34 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.

36,434 people live in Rock Island, the 51st largest of the 225 Illinois cities sized on this site. Coordinates used: 41.4694, -90.5853.

Rock Island AC sizing questions