What size AC for Florence, SC? 3.5 tons for 2,000 sq ft

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

3.5 tons central AC or heat pump, about 41,200 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.4 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 583 square feet in this climate. For a single room, size by the room: 20.6 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Florence Regional Airport (3.6 mi away). Jul is the hottest month, averaging a high of 92°F and a low of 72.4°F, with about 70 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 3,545 kWh a year at SEER2 14.3, or roughly $564 at South Carolina's average residential rate of 15.9¢ per kWh. Cooling runs 7 months of the year here.

What drives the load in Florence

Of the 41,200 BTU/hr, 16,560 comes through walls, roof and windows on a 98°F afternoon (40%), 13,000 is sun on the house (32%), 2,120 is four people and their appliances, and 9,500 is moisture the coil has to wring out of Florence's summer air (23%).

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 Florence

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 3,100 BTU/hr; a 350 sq ft living room needs about 7,200 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 12,400 BTU/hr.

Month by month in Florence

Jul alone uses 24% of the year's cooling energy. The unit runs the equivalent of 1,231 hours a year at full output.

Florence against nearby cities

Of 42 South Carolina cities here, Florence has the 11th highest cooling load. The range runs from Gaffney at 32,300 BTU/hr to Columbia at 43,100.

Where Florence's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Florence Regional Airport, 3.6 miles from the center of Florence at 141 ft above sea level. That is close enough that the station's summers are Florence's summers.

No other city in this set uses Florence Regional Airport, so this sizing is Florence's alone.

The sun over Florence in late July

At 34.18°N, the noon sun on 21 July stands 76.2° above the horizon over Florence and the day runs 13 h 57 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.

40,923 people live in Florence, the 11th largest of the 42 South Carolina cities sized on this site. Coordinates used: 34.1789, -79.7922.

Florence AC sizing questions