What size AC for Christiansburg, VA? 2 tons for 2,000 sq ft

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

2 tons central AC or heat pump, about 24,900 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 69% 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 2 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 965 square feet in this climate. For a single room, size by the room: 12.4 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Christiansburg (0.9 mi away). Jul is the hottest month, averaging a high of 81.6°F and a low of 61.8°F, with about 6 days a year at 90°F or more. That gives a design temperature of 86°F against 75°F inside.

What it costs to run

About 828 kWh a year at SEER2 14.3, or roughly $140 at Virginia's average residential rate of 16.95¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Christiansburg

Of the 24,900 BTU/hr, 7,920 comes through walls, roof and windows on a 86°F afternoon (32%), 13,000 is sun on the house (52%), 2,120 is four people and their appliances, and 1,800 is moisture the coil has to wring out of Christiansburg's summer air (7%).

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 23,040 BTU/hr before the moisture allowance.

Other house sizes in Christiansburg

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 1,900 BTU/hr; a 350 sq ft living room needs about 4,300 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 7,400 BTU/hr.

Month by month in Christiansburg

Jul alone uses 33% of the year's cooling energy. The unit runs the equivalent of 476 hours a year at full output.

Christiansburg against nearby cities

Of 39 Virginia cities here, Christiansburg has the lowest cooling load. The range runs from Christiansburg at 24,900 BTU/hr to Chesapeake at 42,100.

Where Christiansburg's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Christiansburg, 0.9 miles from the center of Christiansburg at 2,100 ft above sea level. That is close enough that the station's summers are Christiansburg's summers.

No other city in this set uses Christiansburg, so this sizing is Christiansburg's alone.

The sun over Christiansburg in late July

At 37.14°N, the noon sun on 21 July stands 73.3° above the horizon over Christiansburg and the day runs 14 h 11 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.

22,632 people live in Christiansburg, the 27th largest of the 39 Virginia cities sized on this site. Coordinates used: 37.1407, -80.4045.

Christiansburg AC sizing questions