What size AC for Casper, WY? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 30,000 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 40% 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 801 square feet in this climate. For a single room, size by the room: 15 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Casper-Natrona County Airport (8.6 mi away). Jul is the hottest month, averaging a high of 89°F and a low of 53°F, with about 38 days a year at 90°F or more. That gives a design temperature of 94°F against 75°F inside.

What it costs to run

About 557 kWh a year at SEER2 14.3, or roughly $78 at Wyoming's average residential rate of 14.01¢ per kWh. Cooling runs 3 months of the year here.

What drives the load in Casper

Of the 30,000 BTU/hr, 13,680 comes through walls, roof and windows on a 94°F afternoon (46%), 13,000 is sun on the house (43%), 2,120 is four people and their appliances, and 1,200 is moisture the coil has to wring out of Casper'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 28,800 BTU/hr before the moisture allowance.

Other house sizes in Casper

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 9,000 BTU/hr.

Month by month in Casper

Jul alone uses 45% of the year's cooling energy. The unit runs the equivalent of 266 hours a year at full output.

Casper against nearby cities

Of 11 Wyoming cities here, Casper has the highest cooling load. The range runs from Jackson at 21,700 BTU/hr to Casper at 30,000.

Where Casper's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Casper-Natrona County Airport, 8.6 miles from the center of Casper at 5,319 ft above sea level. That is close enough that the station's summers are Casper's summers.

No other city in this set uses Casper-Natrona County Airport, so this sizing is Casper's alone.

The sun over Casper in late July

At 42.84°N, the noon sun on 21 July stands 67.6° above the horizon over Casper and the day runs 14 h 41 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. Long days mean the house keeps gaining heat into the evening, well after the outdoor peak.

58,823 people live in Casper, the 2nd largest of the 11 Wyoming cities sized on this site. Coordinates used: 42.8421, -106.3213.

Casper AC sizing questions