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

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

2.5 tons central AC or heat pump, about 29,000 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 45% 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 828 square feet in this climate. For a single room, size by the room: 14.5 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Romeoville WFO (1.8 mi away). Jul is the hottest month, averaging a high of 84.7°F and a low of 64.5°F, with about 16 days a year at 90°F or more. That gives a design temperature of 89°F against 75°F inside.

What it costs to run

About 1,316 kWh a year at SEER2 14.3, or roughly $253 at Illinois's average residential rate of 19.23¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Romeoville

Of the 29,000 BTU/hr, 10,080 comes through walls, roof and windows on a 89°F afternoon (35%), 13,000 is sun on the house (45%), 2,120 is four people and their appliances, and 3,800 is moisture the coil has to wring out of Romeoville'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 25,200 BTU/hr before the moisture allowance.

Other house sizes in Romeoville

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,200 BTU/hr; a 350 sq ft living room needs about 5,100 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 8,700 BTU/hr.

Month by month in Romeoville

Jul alone uses 32% of the year's cooling energy. The unit runs the equivalent of 649 hours a year at full output.

Romeoville against nearby cities

Of 225 Illinois cities here, Romeoville has the 113th highest cooling load. The range runs from Fox Lake at 24,900 BTU/hr to Granite City at 36,000.

Where Romeoville's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Romeoville WFO, 1.8 miles from the center of Romeoville at 660 ft above sea level. That is close enough that the station's summers are Romeoville's summers.

2 other cities use the same station and get the same climate inputs. The closest to Romeoville: Crest Hill (4 mi away, 2.5 mi from the station), Lockport (4 mi away, 3 mi from the station). Romeoville sits closer to the station than any of them, so its numbers are the best measured of the group.

The sun over Romeoville in late July

At 41.63°N, the noon sun on 21 July stands 68.8° above the horizon over Romeoville 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.

41,177 people live in Romeoville, the 38th largest of the 225 Illinois cities sized on this site. Coordinates used: 41.6279, -88.1012.

Romeoville AC sizing questions