What size AC for Washington, DC? 3.5 tons for 2,000 sq ft

What size AC a 2,000 sq ft house in Washington 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 (4.1 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 $679 at District of Columbia's average residential rate of 24.86¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Washington

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 Washington'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 Washington

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 Washington

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

Washington against nearby cities

Washington is the only District of Columbia city in this set.

Where Washington's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Washington Reagan Natl Airport, across the line in Virginia, 4.1 miles from the center of Washington at 13 ft above sea level. That is close enough that the station's summers are Washington's summers.

7 other cities use the same station and get the same climate inputs. The closest to Washington: Hyattsville (5 mi away, 9 mi from the station), Takoma Park (5 mi away, 9.4 mi from the station), Alexandria (7 mi away, 3.3 mi from the station), College Park (8 mi away, 11.6 mi from the station), New Carrollton (9 mi away, 11.8 mi from the station). Washington is farther from the station than 1 of them.

The sun over Washington in late July

At 38.90°N, the noon sun on 21 July stands 71.5° above the horizon over Washington and the day runs 14 h 20 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.

702,250 people live in Washington. Coordinates used: 38.9042, -77.0165.

Washington AC sizing questions