What size AC for Castle Pines, CO? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 29,500 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 42% 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 812 square feet in this climate. For a single room, size by the room: 14.8 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Denver Centennial Airport (6.8 mi away). Jul is the hottest month, averaging a high of 87.3°F and a low of 58.6°F, with about 32 days a year at 90°F or more. That gives a design temperature of 92°F against 75°F inside.

What it costs to run

About 830 kWh a year at SEER2 14.3, or roughly $139 at Colorado's average residential rate of 16.8¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Castle Pines

Of the 29,500 BTU/hr, 12,240 comes through walls, roof and windows on a 92°F afternoon (41%), 13,000 is sun on the house (44%), 2,120 is four people and their appliances, and 2,200 is moisture the coil has to wring out of Castle Pines'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 27,360 BTU/hr before the moisture allowance.

Other house sizes in Castle Pines

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,200 BTU/hr; a 350 sq ft living room needs about 5,200 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 8,900 BTU/hr.

Month by month in Castle Pines

Jul alone uses 39% of the year's cooling energy. The unit runs the equivalent of 402 hours a year at full output.

Castle Pines against nearby cities

Of 53 Colorado cities here, Castle Pines has the 42nd highest cooling load. The range runs from Boulder at 15,700 BTU/hr to Grand Junction at 36,500.

Where Castle Pines's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Denver Centennial Airport, 6.8 miles from the center of Castle Pines at 5,870 ft above sea level. That is close enough that the station's summers are Castle Pines's summers.

7 other cities use the same station and get the same climate inputs. The closest to Castle Pines: Lone Tree (5 mi away, 2.3 mi from the station), Parker (6 mi away, 5.4 mi from the station), Castle Rock (6 mi away, 12.7 mi from the station), Centennial (9 mi away, 2.3 mi from the station), Greenwood Village (11 mi away, 5.1 mi from the station). Castle Pines is farther from the station than 4 of them.

The sun over Castle Pines in late July

At 39.46°N, the noon sun on 21 July stands 70.9° above the horizon over Castle Pines and the day runs 14 h 23 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.

15,162 people live in Castle Pines, the 39th largest of the 53 Colorado cities sized on this site. Coordinates used: 39.4625, -104.8706.

Castle Pines AC sizing questions