What size AC for Martinsburg, WV? 3 tons for 2,000 sq ft

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

3 tons central AC or heat pump, about 31,500 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 33% 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 763 square feet in this climate. For a single room, size by the room: 15.7 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Martinsburg E W Virginia Regional (3.7 mi away). Jul is the hottest month, averaging a high of 86.9°F and a low of 64.5°F, with about 26 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 1,407 kWh a year at SEER2 14.3, or roughly $219 at West Virginia's average residential rate of 15.58¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Martinsburg

Of the 31,500 BTU/hr, 12,240 comes through walls, roof and windows on a 92°F afternoon (39%), 13,000 is sun on the house (41%), 2,120 is four people and their appliances, and 4,100 is moisture the coil has to wring out of Martinsburg's summer air (13%).

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 Martinsburg

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,400 BTU/hr; a 350 sq ft living room needs about 5,500 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 9,400 BTU/hr.

Month by month in Martinsburg

Jul alone uses 33% of the year's cooling energy. The unit runs the equivalent of 640 hours a year at full output.

Martinsburg against nearby cities

Of 13 West Virginia cities here, Martinsburg has the 2nd highest cooling load. The range runs from Beckley at 24,100 BTU/hr to Parkersburg at 31,500.

Where Martinsburg's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Martinsburg E W Virginia Regional, 3.7 miles from the center of Martinsburg at 541 ft above sea level. That is close enough that the station's summers are Martinsburg's summers.

No other city in this set uses Martinsburg E W Virginia Regional, so this sizing is Martinsburg's alone.

The sun over Martinsburg in late July

At 39.46°N, the noon sun on 21 July stands 70.9° above the horizon over Martinsburg and the day runs 14 h 23 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.

19,047 people live in Martinsburg, the 6th largest of the 13 West Virginia cities sized on this site. Coordinates used: 39.4578, -77.9782.

Martinsburg AC sizing questions