What size AC for Ruston, LA? 3.5 tons for 2,000 sq ft

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

3.5 tons central AC or heat pump, about 39,500 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.3 tons. This is one of the climates the chart was written for.

If a contractor quotes you more than 3.5 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 607 square feet in this climate. For a single room, size by the room: 19.8 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Ruston La Tech (1.8 mi away). Aug is the hottest month, averaging a high of 92.6°F and a low of 71°F, with about 85 days a year at 90°F or more. That gives a design temperature of 99°F against 75°F inside.

What it costs to run

About 3,391 kWh a year at SEER2 14.3, or roughly $450 at Louisiana's average residential rate of 13.27¢ per kWh. Cooling runs 7 months of the year here.

What drives the load in Ruston

Of the 39,500 BTU/hr, 17,280 comes through walls, roof and windows on a 99°F afternoon (44%), 13,000 is sun on the house (33%), 2,120 is four people and their appliances, and 7,100 is moisture the coil has to wring out of Ruston'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 32,400 BTU/hr before the moisture allowance.

Other house sizes in Ruston

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 3,000 BTU/hr; a 350 sq ft living room needs about 6,900 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 11,900 BTU/hr.

Month by month in Ruston

Jul alone uses 23% of the year's cooling energy. The unit runs the equivalent of 1,227 hours a year at full output.

Ruston against nearby cities

Of 35 Louisiana cities here, Ruston has the 33rd highest cooling load. The range runs from Covington at 37,800 BTU/hr to Natchitoches at 45,900.

Where Ruston's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Ruston La Tech, 1.8 miles from the center of Ruston at 295 ft above sea level. That is close enough that the station's summers are Ruston's summers.

No other city in this set uses Ruston La Tech, so this sizing is Ruston's alone.

The sun over Ruston in late July

At 32.53°N, the noon sun on 21 July stands 77.9° above the horizon over Ruston and the day runs 13 h 50 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.

22,330 people live in Ruston, the 15th largest of the 35 Louisiana cities sized on this site. Coordinates used: 32.5330, -92.6353.

Ruston AC sizing questions