What size AC for Selma, AL? 3.5 tons for 2,000 sq ft

What size AC a 2,000 sq ft house in Selma 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 Selma 6 Sse (6.6 mi away). Jul is the hottest month, averaging a high of 91.2°F and a low of 70.7°F, with about 75 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 3,075 kWh a year at SEER2 14.3, or roughly $508 at Alabama's average residential rate of 16.51¢ per kWh. Cooling runs 7 months of the year here.

What drives the load in Selma

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 Selma'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 Selma

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 Selma

Jul alone uses 24% of the year's cooling energy. The unit runs the equivalent of 1,138 hours a year at full output.

Selma against nearby cities

Of 66 Alabama cities here, Selma has the 30th highest cooling load. The range runs from Boaz at 30,600 BTU/hr to Montgomery at 44,000.

Where Selma's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Selma 6 Sse, 6.6 miles from the center of Selma at 157 ft above sea level. That is close enough that the station's summers are Selma's summers.

No other city in this set uses Selma 6 Sse, so this sizing is Selma's alone.

The sun over Selma in late July

At 32.42°N, the noon sun on 21 July stands 78.0° above the horizon over Selma and the day runs 13 h 49 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.

16,312 people live in Selma, the 43rd largest of the 66 Alabama cities sized on this site. Coordinates used: 32.4170, -87.0357.

Selma AC sizing questions