What size AC for Morro Bay, CA? 2 tons for 2,000 sq ft

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

2 tons central AC or heat pump, about 22,500 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 87% 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 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 1,068 square feet in this climate. For a single room, size by the room: 11.2 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at San Luis Obispo Mcchesney Field (15.5 mi away). Sep is the hottest month, averaging a high of 79.5°F and a low of 53.4°F, with about 15 days a year at 90°F or more. That gives a design temperature of 84°F against 75°F inside.

What it costs to run

About 420 kWh a year at SEER2 14.3, or roughly $137 at California's average residential rate of 32.58¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Morro Bay

Of the 22,500 BTU/hr, 6,480 comes through walls, roof and windows on a 84°F afternoon (29%), 13,000 is sun on the house (58%), 2,120 is four people and their appliances, and 900 is moisture the coil has to wring out of Morro Bay'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 21,600 BTU/hr before the moisture allowance.

Other house sizes in Morro Bay

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 1,700 BTU/hr; a 350 sq ft living room needs about 3,900 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 6,700 BTU/hr.

Month by month in Morro Bay

Sep alone uses 24% of the year's cooling energy. The unit runs the equivalent of 267 hours a year at full output.

Morro Bay against nearby cities

Of 376 California cities here, Morro Bay has the 289th highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where Morro Bay's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is San Luis Obispo Mcchesney Field, 15.5 miles from the center of Morro Bay at 183 ft above sea level. That is close enough that the station's summers are Morro Bay's summers.

3 other cities use the same station and get the same climate inputs. The closest to Morro Bay: San Luis Obispo (13 mi away, 2.4 mi from the station), Grover Beach (22 mi away, 8.2 mi from the station), Arroyo Grande (23 mi away, 8.6 mi from the station). Morro Bay is farther from the station than 3 of them.

The sun over Morro Bay in late July

At 35.37°N, the noon sun on 21 July stands 75.0° above the horizon over Morro Bay and the day runs 14 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. Shorter days give the house a longer night to shed the day's heat.

10,591 people live in Morro Bay, the 370th largest of the 376 California cities sized on this site. Coordinates used: 35.3668, -120.8683.

Morro Bay AC sizing questions