What size AC for Walla Walla, WA? 3 tons for 2,000 sq ft

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

3 tons central AC or heat pump, about 32,700 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 29% 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 735 square feet in this climate. For a single room, size by the room: 16.3 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Walla Walla Regional Airport (3.1 mi away). Jul is the hottest month, averaging a high of 90.1°F and a low of 62.4°F, with about 42 days a year at 90°F or more. That gives a design temperature of 96°F against 75°F inside.

What it costs to run

About 1,222 kWh a year at SEER2 14.3, or roughly $176 at Washington's average residential rate of 14.42¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Walla Walla

Of the 32,700 BTU/hr, 15,120 comes through walls, roof and windows on a 96°F afternoon (46%), 13,000 is sun on the house (40%), 2,120 is four people and their appliances, and 2,400 is moisture the coil has to wring out of Walla Walla'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 30,240 BTU/hr before the moisture allowance.

Other house sizes in Walla Walla

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,400 BTU/hr; a 350 sq ft living room needs about 5,700 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 9,800 BTU/hr.

Month by month in Walla Walla

Jul alone uses 38% of the year's cooling energy. The unit runs the equivalent of 535 hours a year at full output.

Walla Walla against nearby cities

Of 91 Washington cities here, Walla Walla has the 5th highest cooling load. The range runs from Burlington at 15,700 BTU/hr to Kennewick at 32,900.

Where Walla Walla's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Walla Walla Regional Airport, 3.1 miles from the center of Walla Walla at 1,170 ft above sea level. That is close enough that the station's summers are Walla Walla's summers.

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

The sun over Walla Walla in late July

At 46.07°N, the noon sun on 21 July stands 64.3° above the horizon over Walla Walla and the day runs 15 h 02 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.

33,901 people live in Walla Walla, the 38th largest of the 91 Washington cities sized on this site. Coordinates used: 46.0670, -118.3370.

Walla Walla AC sizing questions