What size AC for Altus, OK? 4 tons for 2,000 sq ft

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

4 tons central AC or heat pump, about 44,800 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.7 tons. This is one of the climates the chart was written for.

If a contractor quotes you more than 4 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 536 square feet in this climate. For a single room, size by the room: 22.4 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Altus Irig Research Station (4.8 mi away). Jul is the hottest month, averaging a high of 97.2°F and a low of 71°F, with about 100 days a year at 90°F or more. That gives a design temperature of 105°F against 75°F inside.

What it costs to run

About 3,317 kWh a year at SEER2 14.3, or roughly $458 at Oklahoma's average residential rate of 13.81¢ per kWh. Cooling runs 6 months of the year here.

What drives the load in Altus

Of the 44,800 BTU/hr, 21,600 comes through walls, roof and windows on a 105°F afternoon (48%), 13,000 is sun on the house (29%), 2,120 is four people and their appliances, and 8,100 is moisture the coil has to wring out of Altus's summer air (18%).

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 36,720 BTU/hr before the moisture allowance.

Other house sizes in Altus

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 3,400 BTU/hr; a 350 sq ft living room needs about 7,800 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 13,400 BTU/hr.

Month by month in Altus

Jul alone uses 26% of the year's cooling energy. The unit runs the equivalent of 1,059 hours a year at full output.

Altus against nearby cities

Of 45 Oklahoma cities here, Altus has the 3rd highest cooling load. The range runs from Miami at 35,600 BTU/hr to Ardmore at 44,900.

Where Altus's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Altus Irig Research Station, 4.8 miles from the center of Altus at 1,380 ft above sea level. That is close enough that the station's summers are Altus's summers.

No other city in this set uses Altus Irig Research Station, so this sizing is Altus's alone.

The sun over Altus in late July

At 34.66°N, the noon sun on 21 July stands 75.7° above the horizon over Altus and the day runs 13 h 59 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.

18,543 people live in Altus, the 29th largest of the 45 Oklahoma cities sized on this site. Coordinates used: 34.6571, -99.3090.

Altus AC sizing questions