What size AC for Athens, TN? 3 tons for 2,000 sq ft

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

3 tons central AC or heat pump, about 33,100 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 27% 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 3 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 725 square feet in this climate. For a single room, size by the room: 16.6 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Athens (2.1 mi away). Jul is the hottest month, averaging a high of 88.4°F and a low of 67.5°F, with about 39 days a year at 90°F or more. That gives a design temperature of 94°F against 75°F inside.

What it costs to run

About 2,055 kWh a year at SEER2 14.3, or roughly $284 at Tennessee's average residential rate of 13.8¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Athens

Of the 33,100 BTU/hr, 13,680 comes through walls, roof and windows on a 94°F afternoon (41%), 13,000 is sun on the house (39%), 2,120 is four people and their appliances, and 4,300 is moisture the coil has to wring out of Athens's summer air (13%).

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 28,800 BTU/hr before the moisture allowance.

Other house sizes in Athens

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,500 BTU/hr; a 350 sq ft living room needs about 5,800 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 10,000 BTU/hr.

Month by month in Athens

Jul alone uses 27% of the year's cooling energy. The unit runs the equivalent of 887 hours a year at full output.

Athens against nearby cities

Of 65 Tennessee cities here, Athens has the 49th highest cooling load. The range runs from Crossville at 27,300 BTU/hr to Memphis at 41,200.

Where Athens's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Athens, 2.1 miles from the center of Athens at 940 ft above sea level. That is close enough that the station's summers are Athens's summers.

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

The sun over Athens in late July

At 35.46°N, the noon sun on 21 July stands 74.9° above the horizon over Athens and the day runs 14 h 03 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.

15,050 people live in Athens, the 42nd largest of the 65 Tennessee cities sized on this site. Coordinates used: 35.4568, -84.6045.

Athens AC sizing questions