What size AC for Plum, PA? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 27,300 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 54% 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 2.5 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 878 square feet in this climate. For a single room, size by the room: 13.7 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Pittsburgh Allegheny County Airport (13.6 mi away). Jul is the hottest month, averaging a high of 83°F and a low of 64.1°F, with about 8 days a year at 90°F or more. That gives a design temperature of 87°F against 75°F inside.

What it costs to run

About 1,148 kWh a year at SEER2 14.3, or roughly $243 at Pennsylvania's average residential rate of 21.13¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Plum

Of the 27,300 BTU/hr, 8,640 comes through walls, roof and windows on a 87°F afternoon (32%), 13,000 is sun on the house (48%), 2,120 is four people and their appliances, and 3,600 is moisture the coil has to wring out of Plum'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 23,760 BTU/hr before the moisture allowance.

Other house sizes in Plum

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,100 BTU/hr; a 350 sq ft living room needs about 4,800 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 8,200 BTU/hr.

Month by month in Plum

Jul alone uses 32% of the year's cooling energy. The unit runs the equivalent of 601 hours a year at full output.

Plum against nearby cities

Of 68 Pennsylvania cities here, Plum has the 34th highest cooling load. The range runs from St. Marys at 21,700 BTU/hr to Philadelphia at 34,300.

Where Plum's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Pittsburgh Allegheny County Airport, 13.6 miles from the center of Plum at 1,244 ft above sea level. That is close enough that the station's summers are Plum's summers.

13 other cities use the same station and get the same climate inputs. The closest to Plum: New Kensington (5 mi away, 17.4 mi from the station), Monroeville (5 mi away, 9.8 mi from the station), Murrysville (6 mi away, 15.1 mi from the station), Wilkinsburg (8 mi away, 6.7 mi from the station), Munhall (11 mi away, 2.9 mi from the station). Plum is farther from the station than 10 of them.

The sun over Plum in late July

At 40.50°N, the noon sun on 21 July stands 69.9° above the horizon over Plum and the day runs 14 h 28 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.

26,420 people live in Plum, the 22nd largest of the 68 Pennsylvania cities sized on this site. Coordinates used: 40.5019, -79.7482.

Plum AC sizing questions