What size AC for Athens-Clarke County, GA? 3.5 tons for 2,000 sq ft

What size AC a 2,000 sq ft house in Athens-Clarke County needs

3.5 tons central AC or heat pump, about 38,700 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.2 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 621 square feet in this climate. For a single room, size by the room: 19.3 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Athens Ben Epps Airport (2.5 mi away). Jul is the hottest month, averaging a high of 92°F and a low of 70°F, with about 62 days a year at 90°F or more. That gives a design temperature of 98°F against 75°F inside.

What it costs to run

About 2,882 kWh a year at SEER2 14.3, or roughly $446 at Georgia's average residential rate of 15.48¢ per kWh. Cooling runs 7 months of the year here.

What drives the load in Athens-Clarke County

Of the 38,700 BTU/hr, 16,560 comes through walls, roof and windows on a 98°F afternoon (43%), 13,000 is sun on the house (34%), 2,120 is four people and their appliances, and 7,000 is moisture the coil has to wring out of Athens-Clarke County'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 31,680 BTU/hr before the moisture allowance.

Other house sizes in Athens-Clarke County

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,900 BTU/hr; a 350 sq ft living room needs about 6,800 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 11,600 BTU/hr.

Month by month in Athens-Clarke County

Jul alone uses 25% of the year's cooling energy. The unit runs the equivalent of 1,066 hours a year at full output.

Athens-Clarke County against nearby cities

Of 101 Georgia cities here, Athens-Clarke County has the 24th highest cooling load. The range runs from Cumming at 33,100 BTU/hr to Albany at 44,000.

Where Athens-Clarke County's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Athens Ben Epps Airport, 2.5 miles from the center of Athens-Clarke County at 784 ft above sea level. That is close enough that the station's summers are Athens-Clarke County's summers.

No other city in this set uses Athens Ben Epps Airport, so this sizing is Athens-Clarke County's alone.

The sun over Athens-Clarke County in late July

At 33.95°N, the noon sun on 21 July stands 76.5° above the horizon over Athens-Clarke County 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.

128,691 people live in Athens-Clarke County, the 6th largest of the 101 Georgia cities sized on this site. Coordinates used: 33.9496, -83.3701.

Athens-Clarke County AC sizing questions