What size AC for Lumberton, NC? 3.5 tons for 2,000 sq ft

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

3.5 tons central AC or heat pump, about 40,200 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 596 square feet in this climate. For a single room, size by the room: 20.1 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Lumberton Regional Airport (2.8 mi away). Jul is the hottest month, averaging a high of 91°F and a low of 72.3°F, with about 67 days a year at 90°F or more. That gives a design temperature of 97°F against 75°F inside.

What it costs to run

About 3,279 kWh a year at SEER2 14.3, or roughly $490 at North Carolina's average residential rate of 14.94¢ per kWh. Cooling runs 7 months of the year here.

What drives the load in Lumberton

Of the 40,200 BTU/hr, 15,840 comes through walls, roof and windows on a 97°F afternoon (39%), 13,000 is sun on the house (32%), 2,120 is four people and their appliances, and 9,300 is moisture the coil has to wring out of Lumberton'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 30,960 BTU/hr before the moisture allowance.

Other house sizes in Lumberton

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 3,000 BTU/hr; a 350 sq ft living room needs about 7,000 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 12,100 BTU/hr.

Month by month in Lumberton

Jul alone uses 25% of the year's cooling energy. The unit runs the equivalent of 1,165 hours a year at full output.

Lumberton against nearby cities

Of 91 North Carolina cities here, Lumberton has the highest cooling load. The range runs from Boone at 21,700 BTU/hr to Lumberton at 40,200.

Where Lumberton's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Lumberton Regional Airport, 2.8 miles from the center of Lumberton at 121 ft above sea level. That is close enough that the station's summers are Lumberton's summers.

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

The sun over Lumberton in late July

At 34.63°N, the noon sun on 21 July stands 75.8° above the horizon over Lumberton and the day runs 13 h 59 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.

18,882 people live in Lumberton, the 56th largest of the 91 North Carolina cities sized on this site. Coordinates used: 34.6306, -79.0186.

Lumberton AC sizing questions