What size AC for St. Matthews, KY? 3 tons for 2,000 sq ft

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

3 tons central AC or heat pump, about 34,300 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 23% more than this climate needs. An oversized unit cools the air fast, shuts off before it pulls moisture out, and leaves the house cold and clammy.

If a contractor quotes you more than 3 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 701 square feet in this climate. For a single room, size by the room: 17.1 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Louisville Bowman Field (1.9 mi away). Jul is the hottest month, averaging a high of 87.9°F and a low of 69.3°F, with about 38 days a year at 90°F or more. That gives a design temperature of 93°F against 75°F inside.

What it costs to run

About 2,275 kWh a year at SEER2 14.3, or roughly $323 at Kentucky's average residential rate of 14.2¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in St. Matthews

Of the 34,300 BTU/hr, 12,960 comes through walls, roof and windows on a 93°F afternoon (38%), 13,000 is sun on the house (38%), 2,120 is four people and their appliances, and 6,200 is moisture the coil has to wring out of St. Matthews's summer air (18%).

Sun is the biggest share here, more than heat through the walls, so shading west windows and a light roof cut the size you need more than extra insulation would. Sensible heat totals 28,080 BTU/hr before the moisture allowance.

Other house sizes in St. Matthews

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,600 BTU/hr; a 350 sq ft living room needs about 6,000 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 10,300 BTU/hr.

Month by month in St. Matthews

Jul alone uses 27% of the year's cooling energy. The unit runs the equivalent of 950 hours a year at full output.

St. Matthews against nearby cities

Of 42 Kentucky cities here, St. Matthews has the 14th highest cooling load. The range runs from Versailles at 29,000 BTU/hr to Paducah at 36,900.

Where St. Matthews's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Louisville Bowman Field, 1.9 miles from the center of St. Matthews at 540 ft above sea level. That is close enough that the station's summers are St. Matthews's summers.

7 other cities use the same station and get the same climate inputs. The closest to St. Matthews: Lyndon (3 mi away, 4.7 mi from the station), Jeffersontown (5 mi away, 5.4 mi from the station), Louisville/Jefferson County (6 mi away, 4.6 mi from the station), Jeffersonville (7 mi away, 7.7 mi from the station), Clarksville (9 mi away, 8.5 mi from the station). St. Matthews sits closer to the station than any of them, so its numbers are the best measured of the group.

The sun over St. Matthews in late July

At 38.25°N, the noon sun on 21 July stands 72.2° above the horizon over St. Matthews and the day runs 14 h 16 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.

17,806 people live in St. Matthews, the 25th largest of the 42 Kentucky cities sized on this site. Coordinates used: 38.2493, -85.6378.

St. Matthews AC sizing questions