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

What size AC a 2,000 sq ft house in Mount Prospect 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 Chicago Palwaukee Airport (4.3 mi away). Jul is the hottest month, averaging a high of 84°F and a low of 65.8°F, with about 17 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 1,297 kWh a year at SEER2 14.3, or roughly $249 at Illinois's average residential rate of 19.23¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Mount Prospect

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 Mount Prospect'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 Mount Prospect

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 Mount Prospect

Jul alone uses 33% of the year's cooling energy. The unit runs the equivalent of 640 hours a year at full output.

Mount Prospect against nearby cities

Of 225 Illinois cities here, Mount Prospect has the 107th highest cooling load. The range runs from Fox Lake at 24,900 BTU/hr to Granite City at 36,000.

Where Mount Prospect's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Chicago Palwaukee Airport, 4.3 miles from the center of Mount Prospect at 629 ft above sea level. That is close enough that the station's summers are Mount Prospect's summers.

22 other cities use the same station and get the same climate inputs. The closest to Mount Prospect: Prospect Heights (3 mi away, 1.7 mi from the station), Arlington Heights (3 mi away, 4.3 mi from the station), Rolling Meadows (5 mi away, 7 mi from the station), Wheeling (5 mi away, 1.1 mi from the station), Glenview (6 mi away, 4.7 mi from the station). Mount Prospect is farther from the station than 4 of them.

The sun over Mount Prospect in late July

At 42.06°N, the noon sun on 21 July stands 68.3° above the horizon over Mount Prospect and the day runs 14 h 37 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.

55,460 people live in Mount Prospect, the 23rd largest of the 225 Illinois cities sized on this site. Coordinates used: 42.0642, -87.9374.

Mount Prospect AC sizing questions