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

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

3.5 tons central AC or heat pump, about 39,700 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.3 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 604 square feet in this climate. For a single room, size by the room: 19.9 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Ontario International Airport (2 mi away). Aug is the hottest month, averaging a high of 94.9°F and a low of 65.2°F, with about 93 days a year at 90°F or more. That gives a design temperature of 102°F against 75°F inside.

What it costs to run

About 2,738 kWh a year at SEER2 14.3, or roughly $892 at California's average residential rate of 32.58¢ per kWh. Cooling runs 7 months of the year here.

What drives the load in Ontario

Of the 39,700 BTU/hr, 19,440 comes through walls, roof and windows on a 102°F afternoon (49%), 13,000 is sun on the house (33%), 2,120 is four people and their appliances, and 5,200 is moisture the coil has to wring out of Ontario's summer air (13%).

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 34,560 BTU/hr before the moisture allowance.

Other house sizes in Ontario

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 3,000 BTU/hr; a 350 sq ft living room needs about 7,000 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 11,900 BTU/hr.

Month by month in Ontario

Aug alone uses 24% of the year's cooling energy. The unit runs the equivalent of 985 hours a year at full output.

Ontario against nearby cities

Of 376 California cities here, Ontario has the 55th highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where Ontario's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Ontario International Airport, 2 miles from the center of Ontario at 924 ft above sea level. That is close enough that the station's summers are Ontario's summers.

9 other cities use the same station and get the same climate inputs. The closest to Ontario: Montclair (6 mi away, 7.1 mi from the station), Upland (6 mi away, 6.4 mi from the station), Rancho Cucamonga (7 mi away, 5.4 mi from the station), Claremont (9 mi away, 9.3 mi from the station), Fontana (10 mi away, 7.6 mi from the station). Ontario sits closer to the station than any of them, so its numbers are the best measured of the group.

The sun over Ontario in late July

At 34.04°N, the noon sun on 21 July stands 76.4° above the horizon over Ontario 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.

185,285 people live in Ontario, the 25th largest of the 376 California cities sized on this site. Coordinates used: 34.0370, -117.6060.

Ontario AC sizing questions