What size AC for Firestone, CO? 3 tons for 2,000 sq ft

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

3 tons central AC or heat pump, about 31,500 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 34% 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 3 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 763 square feet in this climate. For a single room, size by the room: 15.7 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Longmont 2 Ese (6.9 mi away). Jul is the hottest month, averaging a high of 90.8°F and a low of 55.4°F, with about 49 days a year at 90°F or more. That gives a design temperature of 96°F against 75°F inside.

What it costs to run

About 826 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 Firestone

Of the 31,500 BTU/hr, 15,120 comes through walls, roof and windows on a 96°F afternoon (48%), 13,000 is sun on the house (41%), 2,120 is four people and their appliances, and 1,200 is moisture the coil has to wring out of Firestone's summer air (4%).

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 30,240 BTU/hr before the moisture allowance.

Other house sizes in Firestone

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,400 BTU/hr; a 350 sq ft living room needs about 5,500 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 9,400 BTU/hr.

Month by month in Firestone

Jul alone uses 39% of the year's cooling energy. The unit runs the equivalent of 375 hours a year at full output.

Firestone against nearby cities

Of 53 Colorado cities here, Firestone has the 29th highest cooling load. The range runs from Boulder at 15,700 BTU/hr to Grand Junction at 36,500.

Where Firestone's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Longmont 2 Ese, 6.9 miles from the center of Firestone at 4,950 ft above sea level. That is close enough that the station's summers are Firestone's summers.

3 other cities use the same station and get the same climate inputs. The closest to Firestone: Frederick (4 mi away, 7 mi from the station), Longmont (8 mi away, 1.2 mi from the station), Berthoud (9 mi away, 9.9 mi from the station). Firestone is farther from the station than 1 of them.

The sun over Firestone in late July

At 40.16°N, the noon sun on 21 July stands 70.2° above the horizon over Firestone and the day runs 14 h 26 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.

19,396 people live in Firestone, the 35th largest of the 53 Colorado cities sized on this site. Coordinates used: 40.1557, -104.9486.

Firestone AC sizing questions