What size AC for Alexandria, VA? 3.5 tons for 2,000 sq ft

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

3.5 tons central AC or heat pump, about 38,400 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 625 square feet in this climate. For a single room, size by the room: 19.2 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Washington Reagan Natl Airport (3.3 mi away). Jul is the hottest month, averaging a high of 89.6°F and a low of 72.4°F, with about 40 days a year at 90°F or more. That gives a design temperature of 95°F against 75°F inside.

What it costs to run

About 2,730 kWh a year at SEER2 14.3, or roughly $463 at Virginia's average residential rate of 16.95¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Alexandria

Of the 38,400 BTU/hr, 14,400 comes through walls, roof and windows on a 95°F afternoon (38%), 13,000 is sun on the house (34%), 2,120 is four people and their appliances, and 8,900 is moisture the coil has to wring out of Alexandria'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 29,520 BTU/hr before the moisture allowance.

Other house sizes in Alexandria

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 6,700 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 11,500 BTU/hr.

Month by month in Alexandria

Jul alone uses 29% of the year's cooling energy. The unit runs the equivalent of 1,017 hours a year at full output.

Alexandria against nearby cities

Of 39 Virginia cities here, Alexandria has the 2nd highest cooling load. The range runs from Christiansburg at 24,900 BTU/hr to Chesapeake at 42,100.

Where Alexandria's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Washington Reagan Natl Airport, 3.3 miles from the center of Alexandria at 13 ft above sea level. That is close enough that the station's summers are Alexandria's summers.

7 other cities use the same station and get the same climate inputs. The closest to Alexandria: Falls Church (7 mi away, 8 mi from the station), Washington (7 mi away, 4.1 mi from the station), Takoma Park (12 mi away, 9.4 mi from the station), Hyattsville (12 mi away, 9 mi from the station), College Park (15 mi away, 11.6 mi from the station). Alexandria sits closer to the station than any of them, so its numbers are the best measured of the group.

The sun over Alexandria in late July

At 38.82°N, the noon sun on 21 July stands 71.6° above the horizon over Alexandria and the day runs 14 h 19 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.

159,102 people live in Alexandria, the 6th largest of the 39 Virginia cities sized on this site. Coordinates used: 38.8193, -77.0837.

Alexandria AC sizing questions