What size AC for Grass Valley, CA? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 30,300 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 38% 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 2.5 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 791 square feet in this climate. For a single room, size by the room: 15.2 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Grass Valley #2 (1.4 mi away). Jul is the hottest month, averaging a high of 88°F and a low of 58.2°F, with about 36 days a year at 90°F or more. That gives a design temperature of 93°F against 75°F inside.

What it costs to run

About 978 kWh a year at SEER2 14.3, or roughly $319 at California's average residential rate of 32.58¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Grass Valley

Of the 30,300 BTU/hr, 12,960 comes through walls, roof and windows on a 93°F afternoon (43%), 13,000 is sun on the house (43%), 2,120 is four people and their appliances, and 2,200 is moisture the coil has to wring out of Grass Valley's summer air (7%).

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 28,080 BTU/hr before the moisture allowance.

Other house sizes in Grass Valley

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,300 BTU/hr; a 350 sq ft living room needs about 5,300 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 9,100 BTU/hr.

Month by month in Grass Valley

Jul alone uses 34% of the year's cooling energy. The unit runs the equivalent of 461 hours a year at full output.

Grass Valley against nearby cities

Of 376 California cities here, Grass Valley has the 189th highest cooling load. The range runs from Corte Madera at 15,700 BTU/hr to Palm Desert at 59,000.

Where Grass Valley's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Grass Valley #2, 1.4 miles from the center of Grass Valley at 2,400 ft above sea level. That is close enough that the station's summers are Grass Valley's summers.

No other city in this set uses Grass Valley #2, so this sizing is Grass Valley's alone.

The sun over Grass Valley in late July

At 39.22°N, the noon sun on 21 July stands 71.2° above the horizon over Grass Valley and the day runs 14 h 21 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.

14,085 people live in Grass Valley, the 332nd largest of the 376 California cities sized on this site. Coordinates used: 39.2203, -121.0527.

Grass Valley AC sizing questions