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

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

4 tons central AC or heat pump, about 42,100 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.5 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 570 square feet in this climate. For a single room, size by the room: 21.1 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Lafayette Regional Airport (2.4 mi away). Aug is the hottest month, averaging a high of 92.3°F and a low of 74.7°F, with about 91 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 4,724 kWh a year at SEER2 14.3, or roughly $627 at Louisiana's average residential rate of 13.27¢ per kWh. Cooling runs 9 months of the year here.

What drives the load in Lafayette

Of the 42,100 BTU/hr, 17,280 comes through walls, roof and windows on a 99°F afternoon (41%), 13,000 is sun on the house (31%), 2,120 is four people and their appliances, and 9,700 is moisture the coil has to wring out of Lafayette'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 32,400 BTU/hr before the moisture allowance.

Other house sizes in Lafayette

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 3,200 BTU/hr; a 350 sq ft living room needs about 7,400 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 12,700 BTU/hr.

Month by month in Lafayette

Aug alone uses 19% of the year's cooling energy. The unit runs the equivalent of 1,604 hours a year at full output.

Lafayette against nearby cities

Of 35 Louisiana cities here, Lafayette has the 9th highest cooling load. The range runs from Covington at 37,800 BTU/hr to Natchitoches at 45,900.

Where Lafayette's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Lafayette Regional Airport, 2.4 miles from the center of Lafayette at 35 ft above sea level. That is close enough that the station's summers are Lafayette's summers.

3 other cities use the same station and get the same climate inputs. The closest to Lafayette: Broussard (6 mi away, 4.7 mi from the station), Carencro (7 mi away, 8.4 mi from the station), Youngsville (8 mi away, 7.1 mi from the station). Lafayette sits closer to the station than any of them, so its numbers are the best measured of the group.

The sun over Lafayette in late July

At 30.21°N, the noon sun on 21 July stands 80.2° above the horizon over Lafayette and the day runs 13 h 40 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.

122,280 people live in Lafayette, the 4th largest of the 35 Louisiana cities sized on this site. Coordinates used: 30.2056, -92.0281.

Lafayette AC sizing questions