What size AC for Gretna, LA? 4 tons for 2,000 sq ft

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

4 tons central AC or heat pump, about 44,900 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 534 square feet in this climate. For a single room, size by the room: 22.5 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at New Orleans Audubon (4.7 mi away). Aug is the hottest month, averaging a high of 94°F and a low of 76.9°F, with about 106 days a year at 90°F or more. That gives a design temperature of 102°F against 75°F inside.

What it costs to run

About 5,527 kWh a year at SEER2 14.3, or roughly $733 at Louisiana's average residential rate of 13.27¢ per kWh. Cooling runs 9 months of the year here.

What drives the load in Gretna

Of the 44,900 BTU/hr, 19,440 comes through walls, roof and windows on a 102°F afternoon (43%), 13,000 is sun on the house (29%), 2,120 is four people and their appliances, and 10,400 is moisture the coil has to wring out of Gretna's summer air (23%).

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 34,560 BTU/hr before the moisture allowance.

Other house sizes in Gretna

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 7,900 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 13,500 BTU/hr.

Month by month in Gretna

Aug alone uses 18% of the year's cooling energy. The unit runs the equivalent of 1,759 hours a year at full output.

Gretna against nearby cities

Of 35 Louisiana cities here, Gretna has the 4th highest cooling load. The range runs from Covington at 37,800 BTU/hr to Natchitoches at 45,900.

Where Gretna's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is New Orleans Audubon, 4.7 miles from the center of Gretna at 20 ft above sea level. That is close enough that the station's summers are Gretna's summers.

No other city in this set uses New Orleans Audubon, so this sizing is Gretna's alone.

The sun over Gretna in late July

At 29.91°N, the noon sun on 21 July stands 80.5° above the horizon over Gretna and the day runs 13 h 39 min from sunrise to sunset. With the sun that close to overhead, the roof takes most of the heat at midday and the west wall takes the rest after 3 pm. Shorter days give the house a longer night to shed the day's heat.

17,185 people live in Gretna, the 19th largest of the 35 Louisiana cities sized on this site. Coordinates used: 29.9109, -90.0517.

Gretna AC sizing questions