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

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

3 tons central AC or heat pump, about 33,400 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 26% 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 719 square feet in this climate. For a single room, size by the room: 16.7 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Oak Ridge Atdd (4.5 mi away). Jul is the hottest month, averaging a high of 87°F and a low of 68.1°F, with about 39 days a year at 90°F or more. That gives a design temperature of 92°F against 75°F inside.

What it costs to run

About 2,084 kWh a year at SEER2 14.3, or roughly $288 at Tennessee's average residential rate of 13.8¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Oak Ridge

Of the 33,400 BTU/hr, 12,240 comes through walls, roof and windows on a 92°F afternoon (37%), 13,000 is sun on the house (39%), 2,120 is four people and their appliances, and 6,000 is moisture the coil has to wring out of Oak Ridge's summer air (18%).

Sun is the biggest share here, more than heat through the walls, so shading west windows and a light roof cut the size you need more than extra insulation would. Sensible heat totals 27,360 BTU/hr before the moisture allowance.

Other house sizes in Oak Ridge

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 Oak Ridge

Jul alone uses 27% of the year's cooling energy. The unit runs the equivalent of 893 hours a year at full output.

Oak Ridge against nearby cities

Of 65 Tennessee cities here, Oak Ridge has the 43rd highest cooling load. The range runs from Crossville at 27,300 BTU/hr to Memphis at 41,200.

Where Oak Ridge's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Oak Ridge Atdd, 4.5 miles from the center of Oak Ridge at 1,019 ft above sea level. That is close enough that the station's summers are Oak Ridge's summers.

2 other cities use the same station and get the same climate inputs. The closest to Oak Ridge: Farragut (9 mi away, 8.7 mi from the station), Lenoir City (10 mi away, 13.1 mi from the station). Oak Ridge sits closer to the station than any of them, so its numbers are the best measured of the group.

The sun over Oak Ridge in late July

At 35.97°N, the noon sun on 21 July stands 74.4° above the horizon over Oak Ridge 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.

34,039 people live in Oak Ridge, the 25th largest of the 65 Tennessee cities sized on this site. Coordinates used: 35.9665, -84.2905.

Oak Ridge AC sizing questions