What size AC for Rocky Mount, NC? 3.5 tons for 2,000 sq ft

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

3.5 tons central AC or heat pump, about 36,900 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.1 tons. This is one of the climates the chart was written for.

If a contractor quotes you more than 3.5 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 651 square feet in this climate. For a single room, size by the room: 18.4 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Rocky Mount Wilson Airport (9.5 mi away). Jul is the hottest month, averaging a high of 90.5°F and a low of 69°F, with about 54 days a year at 90°F or more. That gives a design temperature of 96°F against 75°F inside.

What it costs to run

About 2,478 kWh a year at SEER2 14.3, or roughly $370 at North Carolina's average residential rate of 14.94¢ per kWh. Cooling runs 6 months of the year here.

What drives the load in Rocky Mount

Of the 36,900 BTU/hr, 15,120 comes through walls, roof and windows on a 96°F afternoon (41%), 13,000 is sun on the house (35%), 2,120 is four people and their appliances, and 6,700 is moisture the coil has to wring out of Rocky Mount's summer air (18%).

Heat through the shell is the biggest share here, so insulation and air sealing cut the size you need more than shading would. Sensible heat totals 30,240 BTU/hr before the moisture allowance.

Other house sizes in Rocky Mount

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,800 BTU/hr; a 350 sq ft living room needs about 6,400 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 11,000 BTU/hr.

Month by month in Rocky Mount

Jul alone uses 27% of the year's cooling energy. The unit runs the equivalent of 961 hours a year at full output.

Rocky Mount against nearby cities

Of 91 North Carolina cities here, Rocky Mount has the 32nd highest cooling load. The range runs from Boone at 21,700 BTU/hr to Lumberton at 40,200.

Where Rocky Mount's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Rocky Mount Wilson Airport, 9.5 miles from the center of Rocky Mount at 150 ft above sea level. That is close enough that the station's summers are Rocky Mount's summers.

2 other cities use the same station and get the same climate inputs. The closest to Rocky Mount: Wilson (18 mi away, 8.5 mi from the station), Zebulon (30 mi away, 23.5 mi from the station). Rocky Mount is farther from the station than 1 of them.

The sun over Rocky Mount in late July

At 35.97°N, the noon sun on 21 July stands 74.4° above the horizon over Rocky Mount and the day runs 14 h 05 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.

54,541 people live in Rocky Mount, the 21st largest of the 91 North Carolina cities sized on this site. Coordinates used: 35.9685, -77.8083.

Rocky Mount AC sizing questions