What size AC for Lake Stevens, WA? 1.5 tons for 2,000 sq ft

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

1.5 tons central AC or heat pump, about 17,200 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 144% 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 1.5 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 1,394 square feet in this climate. For a single room, size by the room: 8.6 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Everett Snohomish County Airport (10.2 mi away). Aug is the hottest month, averaging a high of 73°F and a low of 55.4°F, with about 1 day a year at 90°F or more. That gives a design temperature of 77°F against 75°F inside.

What it costs to run

About 121 kWh a year at SEER2 14.3, or roughly $17 at Washington's average residential rate of 14.42¢ per kWh. Cooling runs 0 months of the year here.

What drives the load in Lake Stevens

Of the 17,200 BTU/hr, 1,440 comes through walls, roof and windows on a 77°F afternoon (8%), 13,000 is sun on the house (76%), 2,120 is four people and their appliances, and 700 is moisture the coil has to wring out of Lake Stevens'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 16,560 BTU/hr before the moisture allowance.

Other house sizes in Lake Stevens

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 1,300 BTU/hr; a 350 sq ft living room needs about 3,000 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 5,200 BTU/hr.

Month by month in Lake Stevens

Aug alone uses 39% of the year's cooling energy. The unit runs the equivalent of 101 hours a year at full output.

Lake Stevens against nearby cities

Of 91 Washington cities here, Lake Stevens has the 78th highest cooling load. The range runs from Burlington at 15,700 BTU/hr to Kennewick at 32,900.

Where Lake Stevens's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Everett Snohomish County Airport, 10.2 miles from the center of Lake Stevens at 548 ft above sea level. That is close enough that the station's summers are Lake Stevens's summers.

8 other cities use the same station and get the same climate inputs. The closest to Lake Stevens: Everett (5 mi away, 5.2 mi from the station), Snohomish (5 mi away, 8.8 mi from the station), Marysville (6 mi away, 12.4 mi from the station), Mill Creek (11 mi away, 5.2 mi from the station), Monroe (11 mi away, 14.5 mi from the station). Lake Stevens is farther from the station than 6 of them.

The sun over Lake Stevens in late July

At 48.00°N, the noon sun on 21 July stands 62.4° above the horizon over Lake Stevens and the day runs 15 h 15 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.

41,350 people live in Lake Stevens, the 31st largest of the 91 Washington cities sized on this site. Coordinates used: 48.0034, -122.0968.

Lake Stevens AC sizing questions