What size AC for Port Townsend, WA? 1.5 tons for 2,000 sq ft

What size AC a 2,000 sq ft house in Port Townsend 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 Port Townsend (1.4 mi away). Aug is the hottest month, averaging a high of 73.1°F and a low of 53.5°F, with about 0 days 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 77 kWh a year at SEER2 14.3, or roughly $11 at Washington's average residential rate of 14.42¢ per kWh. Cooling runs 0 months of the year here.

What drives the load in Port Townsend

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 Port Townsend'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 Port Townsend

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 Port Townsend

Jul alone uses 39% of the year's cooling energy. The unit runs the equivalent of 64 hours a year at full output.

Port Townsend against nearby cities

Of 91 Washington cities here, Port Townsend has the 84th highest cooling load. The range runs from Burlington at 15,700 BTU/hr to Kennewick at 32,900.

Where Port Townsend's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Port Townsend, 1.4 miles from the center of Port Townsend at 100 ft above sea level. That is close enough that the station's summers are Port Townsend's summers.

No other city in this set uses Port Townsend, so this sizing is Port Townsend's alone.

The sun over Port Townsend in late July

At 48.12°N, the noon sun on 21 July stands 62.3° above the horizon over Port Townsend and the day runs 15 h 16 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.

10,649 people live in Port Townsend, the 90th largest of the 91 Washington cities sized on this site. Coordinates used: 48.1218, -122.7879.

Port Townsend AC sizing questions