What size AC for Nashua, NH? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 27,200 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 882 square feet in this climate. For a single room, size by the room: 13.6 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Manchester Airport (12.8 mi away). Jul is the hottest month, averaging a high of 84.1°F and a low of 63.6°F, with about 16 days a year at 90°F or more. That gives a design temperature of 89°F against 75°F inside.

What it costs to run

About 1,008 kWh a year at SEER2 14.3, or roughly $271 at New Hampshire's average residential rate of 26.91¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Nashua

Of the 27,200 BTU/hr, 10,080 comes through walls, roof and windows on a 89°F afternoon (37%), 13,000 is sun on the house (48%), 2,120 is four people and their appliances, and 2,000 is moisture the coil has to wring out of Nashua'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 25,200 BTU/hr before the moisture allowance.

Other house sizes in Nashua

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 4,800 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 8,200 BTU/hr.

Month by month in Nashua

Jul alone uses 36% of the year's cooling energy. The unit runs the equivalent of 530 hours a year at full output.

Nashua against nearby cities

Of 11 New Hampshire cities here, Nashua has the 2nd highest cooling load. The range runs from Claremont at 24,000 BTU/hr to Manchester at 27,200.

Where Nashua's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Manchester Airport, 12.8 miles from the center of Nashua at 229 ft above sea level. That is close enough that the station's summers are Nashua's summers.

1 other city uses the same station and get the same climate inputs. The closest to Nashua: Manchester (16 mi away, 3.8 mi from the station). Nashua is farther from the station than 1 of them.

The sun over Nashua in late July

At 42.75°N, the noon sun on 21 July stands 67.7° above the horizon over Nashua 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.

91,851 people live in Nashua, the 2nd largest of the 11 New Hampshire cities sized on this site. Coordinates used: 42.7491, -71.4905.

Nashua AC sizing questions