What size AC for Marietta, GA? 3.5 tons for 2,000 sq ft

What size AC a 2,000 sq ft house in Marietta 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 Atlanta Fulton County Airport (12.2 mi away). Jul is the hottest month, averaging a high of 90°F and a low of 70.2°F, with about 54 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 2,691 kWh a year at SEER2 14.3, or roughly $417 at Georgia's average residential rate of 15.48¢ per kWh. Cooling runs 6 months of the year here.

What drives the load in Marietta

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 Marietta'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 Marietta

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 Marietta

Jul alone uses 26% of the year's cooling energy. The unit runs the equivalent of 1,043 hours a year at full output.

Marietta against nearby cities

Of 101 Georgia cities here, Marietta has the 43rd highest cooling load. The range runs from Cumming at 33,100 BTU/hr to Albany at 44,000.

Where Marietta's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Atlanta Fulton County Airport, 12.2 miles from the center of Marietta at 804 ft above sea level. That is close enough that the station's summers are Marietta's summers.

6 other cities use the same station and get the same climate inputs. The closest to Marietta: Smyrna (6 mi away, 5.9 mi from the station), Mableton (10 mi away, 3.9 mi from the station), Powder Springs (10 mi away, 10.8 mi from the station), Atlanta (15 mi away, 5.9 mi from the station), Douglasville (18 mi away, 10.5 mi from the station). Marietta is farther from the station than 5 of them.

The sun over Marietta in late July

At 33.95°N, the noon sun on 21 July stands 76.4° above the horizon over Marietta 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.

63,122 people live in Marietta, the 15th largest of the 101 Georgia cities sized on this site. Coordinates used: 33.9536, -84.5425.

Marietta AC sizing questions