What size AC for Mount Airy, NC? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 28,800 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 46% 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 834 square feet in this climate. For a single room, size by the room: 14.4 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Mount Airy 2 W (2.3 mi away). Jul is the hottest month, averaging a high of 86.3°F and a low of 63.3°F, with about 24 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 1,270 kWh a year at SEER2 14.3, or roughly $190 at North Carolina's average residential rate of 14.94¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Mount Airy

Of the 28,800 BTU/hr, 11,520 comes through walls, roof and windows on a 91°F afternoon (40%), 13,000 is sun on the house (45%), 2,120 is four people and their appliances, and 2,100 is moisture the coil has to wring out of Mount Airy'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 26,640 BTU/hr before the moisture allowance.

Other house sizes in Mount Airy

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 5,000 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 8,600 BTU/hr.

Month by month in Mount Airy

Jul alone uses 31% of the year's cooling energy. The unit runs the equivalent of 631 hours a year at full output.

Mount Airy against nearby cities

Of 91 North Carolina cities here, Mount Airy has the 88th highest cooling load. The range runs from Boone at 21,700 BTU/hr to Lumberton at 40,200.

Where Mount Airy's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Mount Airy 2 W, 2.3 miles from the center of Mount Airy at 1,080 ft above sea level. That is close enough that the station's summers are Mount Airy's summers.

No other city in this set uses Mount Airy 2 W, so this sizing is Mount Airy's alone.

The sun over Mount Airy in late July

At 36.51°N, the noon sun on 21 July stands 73.9° above the horizon over Mount Airy and the day runs 14 h 08 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.

10,583 people live in Mount Airy, the 90th largest of the 91 North Carolina cities sized on this site. Coordinates used: 36.5085, -80.6145.

Mount Airy AC sizing questions