What size AC for Hermiston, OR? 3 tons for 2,000 sq ft

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

3 tons central AC or heat pump, about 34,200 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 23% 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 3 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 701 square feet in this climate. For a single room, size by the room: 17.1 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Hermiston Municipal Airport (1.2 mi away). Jul is the hottest month, averaging a high of 92.7°F and a low of 58.6°F, with about 50 days a year at 90°F or more. That gives a design temperature of 98°F against 75°F inside.

What it costs to run

About 1,097 kWh a year at SEER2 14.3, or roughly $170 at Oregon's average residential rate of 15.46¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Hermiston

Of the 34,200 BTU/hr, 16,560 comes through walls, roof and windows on a 98°F afternoon (48%), 13,000 is sun on the house (38%), 2,120 is four people and their appliances, and 2,500 is moisture the coil has to wring out of Hermiston's summer air (7%).

Heat through the shell is the biggest share here, so insulation and air sealing cut the size you need more than shading would. Sensible heat totals 31,680 BTU/hr before the moisture allowance.

Other house sizes in Hermiston

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,600 BTU/hr; a 350 sq ft living room needs about 6,000 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 10,300 BTU/hr.

Month by month in Hermiston

Jul alone uses 40% of the year's cooling energy. The unit runs the equivalent of 459 hours a year at full output.

Hermiston against nearby cities

Of 57 Oregon cities here, Hermiston has the 4th highest cooling load. The range runs from North Bend at 15,700 BTU/hr to Ontario at 36,500.

Where Hermiston's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Hermiston Municipal Airport, 1.2 miles from the center of Hermiston at 640 ft above sea level. That is close enough that the station's summers are Hermiston's summers.

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

The sun over Hermiston in late July

At 45.83°N, the noon sun on 21 July stands 64.6° above the horizon over Hermiston and the day runs 15 h 00 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.

19,746 people live in Hermiston, the 32nd largest of the 57 Oregon cities sized on this site. Coordinates used: 45.8329, -119.2848.

Hermiston AC sizing questions