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

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

2.5 tons central AC or heat pump, about 27,700 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 52% 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 866 square feet in this climate. For a single room, size by the room: 13.9 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Roseburg Regional Airport (0.7 mi away). Aug is the hottest month, averaging a high of 85.9°F and a low of 57.1°F, with about 31 days a year at 90°F or more. That gives a design temperature of 91°F against 75°F inside.

What it costs to run

About 763 kWh a year at SEER2 14.3, or roughly $118 at Oregon's average residential rate of 15.46¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Roseburg

Of the 27,700 BTU/hr, 11,520 comes through walls, roof and windows on a 91°F afternoon (42%), 13,000 is sun on the house (47%), 2,120 is four people and their appliances, and 1,100 is moisture the coil has to wring out of Roseburg'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 26,640 BTU/hr before the moisture allowance.

Other house sizes in Roseburg

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,100 BTU/hr; a 350 sq ft living room needs about 4,900 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 8,300 BTU/hr.

Month by month in Roseburg

Jul alone uses 35% of the year's cooling energy. The unit runs the equivalent of 394 hours a year at full output.

Roseburg against nearby cities

Of 57 Oregon cities here, Roseburg has the 13th highest cooling load. The range runs from North Bend at 15,700 BTU/hr to Ontario at 36,500.

Where Roseburg's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Roseburg Regional Airport, 0.7 miles from the center of Roseburg at 502 ft above sea level. That is close enough that the station's summers are Roseburg's summers.

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

The sun over Roseburg in late July

At 43.22°N, the noon sun on 21 July stands 67.2° above the horizon over Roseburg and the day runs 14 h 44 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.

23,795 people live in Roseburg, the 26th largest of the 57 Oregon cities sized on this site. Coordinates used: 43.2236, -123.3520.

Roseburg AC sizing questions