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

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

2.5 tons central AC or heat pump, about 27,200 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 54% 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 882 square feet in this climate. For a single room, size by the room: 13.6 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Mc Henry -Wg Stratton L&d (2.7 mi away). Jul is the hottest month, averaging a high of 84.2°F and a low of 61.5°F, with about 11 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 978 kWh a year at SEER2 14.3, or roughly $188 at Illinois's average residential rate of 19.23¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in McHenry

Of the 27,200 BTU/hr, 10,080 comes through walls, roof and windows on a 89°F afternoon (37%), 13,000 is sun on the house (48%), 2,120 is four people and their appliances, and 2,000 is moisture the coil has to wring out of McHenry's summer air (7%).

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 McHenry

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,000 BTU/hr; a 350 sq ft living room needs about 4,800 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 8,200 BTU/hr.

Month by month in McHenry

Jul alone uses 34% of the year's cooling energy. The unit runs the equivalent of 514 hours a year at full output.

McHenry against nearby cities

Of 225 Illinois cities here, McHenry has the 169th highest cooling load. The range runs from Fox Lake at 24,900 BTU/hr to Granite City at 36,000.

Where McHenry's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Mc Henry -Wg Stratton L&d, 2.7 miles from the center of McHenry at 736 ft above sea level. That is close enough that the station's summers are McHenry's summers.

No other city in this set uses Mc Henry -Wg Stratton L&d, so this sizing is McHenry's alone.

The sun over McHenry in late July

At 42.34°N, the noon sun on 21 July stands 68.1° above the horizon over McHenry and the day runs 14 h 38 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.

28,825 people live in McHenry, the 69th largest of the 225 Illinois cities sized on this site. Coordinates used: 42.3362, -88.2917.

McHenry AC sizing questions