What size AC for New Carrollton, MD? 3.5 tons for 2,000 sq ft

What size AC a 2,000 sq ft house in New Carrollton 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 (11.8 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 $582 at Maryland's average residential rate of 21.31¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in New Carrollton

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 New Carrollton'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 New Carrollton

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 New Carrollton

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

New Carrollton against nearby cities

Of 23 Maryland cities here, New Carrollton has the 6th highest cooling load. The range runs from Westminster at 28,000 BTU/hr to Baltimore at 39,300.

Where New Carrollton'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, 11.8 miles from the center of New Carrollton at 13 ft above sea level. That is close enough that the station's summers are New Carrollton's summers.

7 other cities use the same station and get the same climate inputs. The closest to New Carrollton: Greenbelt (2 mi away, 13 mi from the station), College Park (4 mi away, 11.6 mi from the station), Hyattsville (4 mi away, 9 mi from the station), Takoma Park (7 mi away, 9.4 mi from the station), Washington (9 mi away, 4.1 mi from the station). New Carrollton is farther from the station than 6 of them.

The sun over New Carrollton in late July

At 38.97°N, the noon sun on 21 July stands 71.4° above the horizon over New Carrollton 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.

13,645 people live in New Carrollton, the 20th largest of the 23 Maryland cities sized on this site. Coordinates used: 38.9656, -76.8775.

New Carrollton AC sizing questions