What size AC for Eugene, OR? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 26,200 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 60% 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 916 square feet in this climate. For a single room, size by the room: 13.1 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Eugene-Mahlon Sweet Field (7.1 mi away). Aug is the hottest month, averaging a high of 84.3°F and a low of 51.5°F, with about 18 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 368 kWh a year at SEER2 14.3, or roughly $57 at Oregon's average residential rate of 15.46¢ per kWh. Cooling runs 2 months of the year here.

What drives the load in Eugene

Of the 26,200 BTU/hr, 10,080 comes through walls, roof and windows on a 89°F afternoon (38%), 13,000 is sun on the house (50%), 2,120 is four people and their appliances, and 1,000 is moisture the coil has to wring out of Eugene'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 25,200 BTU/hr before the moisture allowance.

Other house sizes in Eugene

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 Eugene

Aug alone uses 39% of the year's cooling energy. The unit runs the equivalent of 201 hours a year at full output.

Eugene against nearby cities

Of 57 Oregon cities here, Eugene has the 16th highest cooling load. The range runs from North Bend at 15,700 BTU/hr to Ontario at 36,500.

Where Eugene's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Eugene-Mahlon Sweet Field, 7.1 miles from the center of Eugene at 358 ft above sea level. That is close enough that the station's summers are Eugene's summers.

1 other city uses the same station and get the same climate inputs. The closest to Eugene: Springfield (7 mi away, 12.9 mi from the station). Eugene sits closer to the station than any of them, so its numbers are the best measured of the group.

The sun over Eugene in late July

At 44.06°N, the noon sun on 21 July stands 66.3° above the horizon over Eugene and the day runs 14 h 49 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.

178,786 people live in Eugene, the 3rd largest of the 57 Oregon cities sized on this site. Coordinates used: 44.0568, -123.1190.

Eugene AC sizing questions