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

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

2 tons central AC or heat pump, about 25,700 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 64% 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 935 square feet in this climate. For a single room, size by the room: 12.8 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Portland International Airport (4.5 mi away). Aug is the hottest month, averaging a high of 82.3°F and a low of 58.9°F, with about 15 days a year at 90°F or more. That gives a design temperature of 87°F against 75°F inside.

What it costs to run

About 663 kWh a year at SEER2 14.3, or roughly $102 at Oregon's average residential rate of 15.46¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Portland

Of the 25,700 BTU/hr, 8,640 comes through walls, roof and windows on a 87°F afternoon (34%), 13,000 is sun on the house (51%), 2,120 is four people and their appliances, and 1,900 is moisture the coil has to wring out of 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 23,760 BTU/hr before the moisture allowance.

Other house sizes in Portland

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 1,900 BTU/hr; a 350 sq ft living room needs about 4,500 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 7,700 BTU/hr.

Month by month in Portland

Aug alone uses 36% of the year's cooling energy. The unit runs the equivalent of 369 hours a year at full output.

Portland against nearby cities

Of 57 Oregon cities here, Portland has the 18th highest cooling load. The range runs from North Bend at 15,700 BTU/hr to Ontario at 36,500.

Where Portland's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Portland International Airport, 4.5 miles from the center of Portland at 22 ft above sea level. That is close enough that the station's summers are Portland's summers.

2 other cities use the same station and get the same climate inputs. The closest to Portland: Milwaukie (7 mi away, 10.4 mi from the station), Vancouver (7 mi away, 2.9 mi from the station). Portland is farther from the station than 1 of them.

The sun over Portland in late July

At 45.54°N, the noon sun on 21 July stands 64.9° above the horizon over Portland and the day runs 14 h 58 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.

635,749 people live in Portland, the largest of the 57 Oregon cities sized on this site. Coordinates used: 45.5370, -122.6500.

Portland AC sizing questions