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

What size AC a 2,000 sq ft house in Sumter 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 Sumter (2.8 mi away). Jul is the hottest month, averaging a high of 90.2°F and a low of 69.6°F, with about 58 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 2,647 kWh a year at SEER2 14.3, or roughly $421 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 Sumter

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 Sumter'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 Sumter

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 Sumter

Jul alone uses 26% of the year's cooling energy. The unit runs the equivalent of 1,026 hours a year at full output.

Sumter against nearby cities

Of 42 South Carolina cities here, Sumter has the 29th highest cooling load. The range runs from Gaffney at 32,300 BTU/hr to Columbia at 43,100.

Where Sumter's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Sumter, 2.8 miles from the center of Sumter at 174 ft above sea level. That is close enough that the station's summers are Sumter's summers.

No other city in this set uses Sumter, so this sizing is Sumter's alone.

The sun over Sumter in late July

At 33.94°N, the noon sun on 21 July stands 76.5° above the horizon over Sumter and the day runs 13 h 56 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.

42,958 people live in Sumter, the 10th largest of the 42 South Carolina cities sized on this site. Coordinates used: 33.9408, -80.3955.

Sumter AC sizing questions