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

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

2 tons central AC or heat pump, about 22,600 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 86% 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 1,064 square feet in this climate. For a single room, size by the room: 11.3 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Johnstown Cambria County Airport (4.7 mi away). Jul is the hottest month, averaging a high of 78.6°F and a low of 61.2°F, with about 0 days a year at 90°F or more. That gives a design temperature of 83°F against 75°F inside.

What it costs to run

About 625 kWh a year at SEER2 14.3, or roughly $132 at Pennsylvania's average residential rate of 21.13¢ per kWh. Cooling runs 3 months of the year here.

What drives the load in Johnstown

Of the 22,600 BTU/hr, 5,760 comes through walls, roof and windows on a 83°F afternoon (25%), 13,000 is sun on the house (58%), 2,120 is four people and their appliances, and 1,700 is moisture the coil has to wring out of Johnstown's summer air (8%).

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 20,880 BTU/hr before the moisture allowance.

Other house sizes in Johnstown

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 1,700 BTU/hr; a 350 sq ft living room needs about 4,000 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 6,800 BTU/hr.

Month by month in Johnstown

Jul alone uses 35% of the year's cooling energy. The unit runs the equivalent of 396 hours a year at full output.

Johnstown against nearby cities

Of 68 Pennsylvania cities here, Johnstown has the 67th highest cooling load. The range runs from St. Marys at 21,700 BTU/hr to Philadelphia at 34,300.

Where Johnstown's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Johnstown Cambria County Airport, 4.7 miles from the center of Johnstown at 2,277 ft above sea level. That is close enough that the station's summers are Johnstown's summers.

No other city in this set uses Johnstown Cambria County Airport, so this sizing is Johnstown's alone.

The sun over Johnstown in late July

At 40.33°N, the noon sun on 21 July stands 70.1° above the horizon over Johnstown and the day runs 14 h 27 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.

17,853 people live in Johnstown, the 33rd largest of the 68 Pennsylvania cities sized on this site. Coordinates used: 40.3261, -78.9191.

Johnstown AC sizing questions