What size AC for Diamond Bar, CA? 3.5 tons for 2,000 sq ft

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

3.5 tons central AC or heat pump, about 38,900 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.2 tons. This is one of the climates the chart was written for.

If a contractor quotes you more than 3.5 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 617 square feet in this climate. For a single room, size by the room: 19.4 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Chino Airport (11.2 mi away). Aug is the hottest month, averaging a high of 96.3°F and a low of 63.2°F, with about 99 days a year at 90°F or more. That gives a design temperature of 104°F against 75°F inside.

What it costs to run

About 2,371 kWh a year at SEER2 14.3, or roughly $772 at California's average residential rate of 32.58¢ per kWh. Cooling runs 6 months of the year here.

What drives the load in Diamond Bar

Of the 38,900 BTU/hr, 20,880 comes through walls, roof and windows on a 104°F afternoon (54%), 13,000 is sun on the house (33%), 2,120 is four people and their appliances, and 2,900 is moisture the coil has to wring out of Diamond Bar'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 36,000 BTU/hr before the moisture allowance.

Other house sizes in Diamond Bar

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,900 BTU/hr; a 350 sq ft living room needs about 6,800 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 11,600 BTU/hr.

Month by month in Diamond Bar

Aug alone uses 25% of the year's cooling energy. The unit runs the equivalent of 872 hours a year at full output.

Diamond Bar against nearby cities

Of 376 California cities here, Diamond Bar has the 80th highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where Diamond Bar's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Chino Airport, 11.2 miles from the center of Diamond Bar at 636 ft above sea level. That is close enough that the station's summers are Diamond Bar's summers.

8 other cities use the same station and get the same climate inputs. The closest to Diamond Bar: Pomona (5 mi away, 9.7 mi from the station), Chino Hills (7 mi away, 6.2 mi from the station), Yorba Linda (8 mi away, 10.3 mi from the station), Chino (9 mi away, 2.4 mi from the station), Anaheim (11 mi away, 11.3 mi from the station). Diamond Bar is farther from the station than 7 of them.

The sun over Diamond Bar in late July

At 34.00°N, the noon sun on 21 July stands 76.4° above the horizon over Diamond Bar and the day runs 13 h 56 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.

52,292 people live in Diamond Bar, the 173rd largest of the 376 California cities sized on this site. Coordinates used: 34.0016, -117.8176.

Diamond Bar AC sizing questions