What size AC for Mountain Brook, AL? 3.5 tons for 2,000 sq ft

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

3.5 tons central AC or heat pump, about 40,200 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.4 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 596 square feet in this climate. For a single room, size by the room: 20.1 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Birmingham Airport (5.2 mi away). Jul is the hottest month, averaging a high of 91°F and a low of 72.1°F, with about 65 days a year at 90°F or more. That gives a design temperature of 97°F against 75°F inside.

What it costs to run

About 3,420 kWh a year at SEER2 14.3, or roughly $565 at Alabama's average residential rate of 16.51¢ per kWh. Cooling runs 7 months of the year here.

What drives the load in Mountain Brook

Of the 40,200 BTU/hr, 15,840 comes through walls, roof and windows on a 97°F afternoon (39%), 13,000 is sun on the house (32%), 2,120 is four people and their appliances, and 9,300 is moisture the coil has to wring out of Mountain Brook'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 30,960 BTU/hr before the moisture allowance.

Other house sizes in Mountain Brook

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 7,000 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 12,100 BTU/hr.

Month by month in Mountain Brook

Jul alone uses 24% of the year's cooling energy. The unit runs the equivalent of 1,215 hours a year at full output.

Mountain Brook against nearby cities

Of 66 Alabama cities here, Mountain Brook has the 15th highest cooling load. The range runs from Boaz at 30,600 BTU/hr to Montgomery at 44,000.

Where Mountain Brook's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Birmingham Airport, 5.2 miles from the center of Mountain Brook at 616 ft above sea level. That is close enough that the station's summers are Mountain Brook's summers.

11 other cities use the same station and get the same climate inputs. The closest to Mountain Brook: Vestavia Hills (2 mi away, 7.1 mi from the station), Birmingham (4 mi away, 4 mi from the station), Homewood (5 mi away, 8.3 mi from the station), Irondale (5 mi away, 5.3 mi from the station), Hoover (9 mi away, 13.7 mi from the station). Mountain Brook is farther from the station than 1 of them.

The sun over Mountain Brook in late July

At 33.49°N, the noon sun on 21 July stands 76.9° above the horizon over Mountain Brook and the day runs 13 h 54 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.

21,701 people live in Mountain Brook, the 31st largest of the 66 Alabama cities sized on this site. Coordinates used: 33.4915, -86.7345.

Mountain Brook AC sizing questions