What size AC for Bay St. Louis, MS? 3.5 tons for 2,000 sq ft

What size AC a 2,000 sq ft house in Bay St. Louis needs

3.5 tons central AC or heat pump, about 38,400 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.2 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 625 square feet in this climate. For a single room, size by the room: 19.2 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Waveland (2.5 mi away). Aug is the hottest month, averaging a high of 89°F and a low of 74°F, with about 48 days a year at 90°F or more. That gives a design temperature of 95°F against 75°F inside.

What it costs to run

About 3,863 kWh a year at SEER2 14.3, or roughly $582 at Mississippi's average residential rate of 15.06¢ per kWh. Cooling runs 7 months of the year here.

What drives the load in Bay St. Louis

Of the 38,400 BTU/hr, 14,400 comes through walls, roof and windows on a 95°F afternoon (38%), 13,000 is sun on the house (34%), 2,120 is four people and their appliances, and 8,900 is moisture the coil has to wring out of Bay St. Louis'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 29,520 BTU/hr before the moisture allowance.

Other house sizes in Bay St. Louis

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,900 BTU/hr; a 350 sq ft living room needs about 6,700 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 11,500 BTU/hr.

Month by month in Bay St. Louis

Aug alone uses 21% of the year's cooling energy. The unit runs the equivalent of 1,440 hours a year at full output.

Bay St. Louis against nearby cities

Of 41 Mississippi cities here, Bay St. Louis has the 36th highest cooling load. The range runs from Brookhaven at 36,900 BTU/hr to Columbus at 44,000.

Where Bay St. Louis's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Waveland, 2.5 miles from the center of Bay St. Louis at 8 ft above sea level. That is close enough that the station's summers are Bay St. Louis's summers.

No other city in this set uses Waveland, so this sizing is Bay St. Louis's alone.

The sun over Bay St. Louis in late July

At 30.32°N, the noon sun on 21 July stands 80.1° above the horizon over Bay St. Louis and the day runs 13 h 41 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.

10,526 people live in Bay St. Louis, the 40th largest of the 41 Mississippi cities sized on this site. Coordinates used: 30.3234, -89.3588.

Bay St. Louis AC sizing questions