What size AC for South Portland, ME? 2 tons for 2,000 sq ft

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

2 tons central AC or heat pump, about 23,300 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 80% 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 1,029 square feet in this climate. For a single room, size by the room: 11.7 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Portland Jetport (1.2 mi away). Jul is the hottest month, averaging a high of 79.5°F and a low of 61.2°F, with about 5 days a year at 90°F or more. That gives a design temperature of 84°F against 75°F inside.

What it costs to run

About 583 kWh a year at SEER2 14.3, or roughly $176 at Maine's average residential rate of 30.23¢ per kWh. Cooling runs 3 months of the year here.

What drives the load in South Portland

Of the 23,300 BTU/hr, 6,480 comes through walls, roof and windows on a 84°F afternoon (28%), 13,000 is sun on the house (56%), 2,120 is four people and their appliances, and 1,700 is moisture the coil has to wring out of South Portland's summer air (7%).

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 21,600 BTU/hr before the moisture allowance.

Other house sizes in South Portland

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 1,800 BTU/hr; a 350 sq ft living room needs about 4,100 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 7,000 BTU/hr.

Month by month in South Portland

Jul alone uses 39% of the year's cooling energy. The unit runs the equivalent of 357 hours a year at full output.

South Portland against nearby cities

Of 11 Maine cities here, South Portland has the 5th highest cooling load. The range runs from Waterville at 23,300 BTU/hr to Sanford at 24,900.

Where South Portland's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Portland Jetport, 1.2 miles from the center of South Portland at 44 ft above sea level. That is close enough that the station's summers are South Portland's summers.

4 other cities use the same station and get the same climate inputs. The closest to South Portland: Portland (5 mi away, 6 mi from the station), Westbrook (6 mi away, 5.1 mi from the station), Saco (10 mi away, 9.8 mi from the station), Biddeford (14 mi away, 14.8 mi from the station). South Portland sits closer to the station than any of them, so its numbers are the best measured of the group.

The sun over South Portland in late July

At 43.63°N, the noon sun on 21 July stands 66.8° above the horizon over South Portland and the day runs 14 h 46 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. Long days mean the house keeps gaining heat into the evening, well after the outdoor peak.

26,994 people live in South Portland, the 4th largest of the 11 Maine cities sized on this site. Coordinates used: 43.6314, -70.2860.

South Portland AC sizing questions