What size AC for Lawrence, MA? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 26,400 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 59% 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 908 square feet in this climate. For a single room, size by the room: 13.2 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Lawrence Municipal Airport (2 mi away). Jul is the hottest month, averaging a high of 83.2°F and a low of 63.2°F, with about 15 days a year at 90°F or more. That gives a design temperature of 88°F against 75°F inside.

What it costs to run

About 927 kWh a year at SEER2 14.3, or roughly $280 at Massachusetts's average residential rate of 30.19¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Lawrence

Of the 26,400 BTU/hr, 9,360 comes through walls, roof and windows on a 88°F afternoon (35%), 13,000 is sun on the house (49%), 2,120 is four people and their appliances, and 2,000 is moisture the coil has to wring out of Lawrence'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 24,480 BTU/hr before the moisture allowance.

Other house sizes in Lawrence

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,000 BTU/hr; a 350 sq ft living room needs about 4,600 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 7,900 BTU/hr.

Month by month in Lawrence

Jul alone uses 36% of the year's cooling energy. The unit runs the equivalent of 501 hours a year at full output.

Lawrence against nearby cities

Of 58 Massachusetts cities here, Lawrence has the 31st highest cooling load. The range runs from Pittsfield at 22,600 BTU/hr to Framingham at 28,000.

Where Lawrence's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Lawrence Municipal Airport, 2 miles from the center of Lawrence at 136 ft above sea level. That is close enough that the station's summers are Lawrence's summers.

5 other cities use the same station and get the same climate inputs. The closest to Lawrence: Methuen (3 mi away, 3.4 mi from the station), Haverhill (7 mi away, 5.2 mi from the station), Lowell (9 mi away, 11.2 mi from the station), Amesbury (15 mi away, 12.9 mi from the station), Newburyport (16 mi away, 13.9 mi from the station). Lawrence sits closer to the station than any of them, so its numbers are the best measured of the group.

The sun over Lawrence in late July

At 42.70°N, the noon sun on 21 July stands 67.7° above the horizon over Lawrence and the day runs 14 h 41 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.

89,332 people live in Lawrence, the 12th largest of the 58 Massachusetts cities sized on this site. Coordinates used: 42.7003, -71.1614.

Lawrence AC sizing questions