What size AC for North Charleston, SC? 3.5 tons for 2,000 sq ft

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

3.5 tons central AC or heat pump, about 40,200 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.4 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 596 square feet in this climate. For a single room, size by the room: 20.1 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Charleston International Airport (1.9 mi away). Jul is the hottest month, averaging a high of 91.3°F and a low of 73.7°F, with about 64 days a year at 90°F or more. That gives a design temperature of 97°F against 75°F inside.

What it costs to run

About 3,824 kWh a year at SEER2 14.3, or roughly $608 at South Carolina's average residential rate of 15.9¢ per kWh. Cooling runs 7 months of the year here.

What drives the load in North Charleston

Of the 40,200 BTU/hr, 15,840 comes through walls, roof and windows on a 97°F afternoon (39%), 13,000 is sun on the house (32%), 2,120 is four people and their appliances, and 9,300 is moisture the coil has to wring out of North Charleston's summer air (23%).

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 30,960 BTU/hr before the moisture allowance.

Other house sizes in North Charleston

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 3,000 BTU/hr; a 350 sq ft living room needs about 7,000 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 12,100 BTU/hr.

Month by month in North Charleston

Jul alone uses 22% of the year's cooling energy. The unit runs the equivalent of 1,359 hours a year at full output.

North Charleston against nearby cities

Of 42 South Carolina cities here, North Charleston has the 17th highest cooling load. The range runs from Gaffney at 32,300 BTU/hr to Columbia at 43,100.

Where North Charleston's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Charleston International Airport, 1.9 miles from the center of North Charleston at 39 ft above sea level. That is close enough that the station's summers are North Charleston's summers.

3 other cities use the same station and get the same climate inputs. The closest to North Charleston: Hanahan (4 mi away, 3.1 mi from the station), Goose Creek (6 mi away, 6.8 mi from the station), Summerville (9 mi away, 10.9 mi from the station). North Charleston sits closer to the station than any of them, so its numbers are the best measured of the group.

The sun over North Charleston in late July

At 32.92°N, the noon sun on 21 July stands 77.5° above the horizon over North Charleston and the day runs 13 h 51 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.

126,005 people live in North Charleston, the 3rd largest of the 42 South Carolina cities sized on this site. Coordinates used: 32.9179, -80.0650.

North Charleston AC sizing questions