What size AC for Juneau, AK? 1.5 tons for 2,000 sq ft

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

1.5 tons central AC or heat pump, about 15,700 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 167% 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 1.5 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 1,526 square feet in this climate. For a single room, size by the room: 7.9 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Juneau Airport (6.1 mi away). Jul is the hottest month, averaging a high of 64°F and a low of 50.1°F, with about 0 days a year at 90°F or more. That gives a design temperature of 68°F against 75°F inside.

What it costs to run

About 4 kWh a year at SEER2 14.3, or roughly $1 at Alaska's average residential rate of 27.32¢ per kWh. Cooling runs 0 months of the year here.

What drives the load in Juneau

Of the 15,700 BTU/hr, 0 comes through walls, roof and windows on a 68°F afternoon (0%), 13,000 is sun on the house (83%), 2,120 is four people and their appliances, and 600 is moisture the coil has to wring out of Juneau's summer air (4%).

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 15,120 BTU/hr before the moisture allowance.

Other house sizes in Juneau

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 1,200 BTU/hr; a 350 sq ft living room needs about 2,800 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 4,700 BTU/hr.

Month by month in Juneau

Jun alone uses 50% of the year's cooling energy. The unit runs the equivalent of 4 hours a year at full output.

Juneau against nearby cities

Of 4 Alaska cities here, Juneau has the 3rd highest cooling load. The range runs from Wasilla at 15,700 BTU/hr to Fairbanks at 17,200.

Where Juneau's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Juneau Airport, 6.1 miles from the center of Juneau at 19 ft above sea level. That is close enough that the station's summers are Juneau's summers.

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

The sun over Juneau in late July

At 58.30°N, the noon sun on 21 July stands 52.1° above the horizon over Juneau and the day runs 16 h 56 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.

31,572 people live in Juneau, the 3rd largest of the 4 Alaska cities sized on this site. Coordinates used: 58.3019, -134.4197.

Juneau AC sizing questions