What size AC for Martin, TN? 3.5 tons for 2,000 sq ft

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

3.5 tons central AC or heat pump, about 36,900 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.1 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 651 square feet in this climate. For a single room, size by the room: 18.4 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Martin U Of T Branch E (0.8 mi away). Jul is the hottest month, averaging a high of 89.8°F and a low of 69.7°F, with about 59 days a year at 90°F or more. That gives a design temperature of 96°F against 75°F inside.

What it costs to run

About 2,513 kWh a year at SEER2 14.3, or roughly $347 at Tennessee's average residential rate of 13.8¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Martin

Of the 36,900 BTU/hr, 15,120 comes through walls, roof and windows on a 96°F afternoon (41%), 13,000 is sun on the house (35%), 2,120 is four people and their appliances, and 6,700 is moisture the coil has to wring out of Martin's summer air (18%).

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 30,240 BTU/hr before the moisture allowance.

Other house sizes in Martin

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,800 BTU/hr; a 350 sq ft living room needs about 6,400 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 11,000 BTU/hr.

Month by month in Martin

Jul alone uses 27% of the year's cooling energy. The unit runs the equivalent of 974 hours a year at full output.

Martin against nearby cities

Of 65 Tennessee cities here, Martin has the 27th highest cooling load. The range runs from Crossville at 27,300 BTU/hr to Memphis at 41,200.

Where Martin's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Martin U Of T Branch E, 0.8 miles from the center of Martin at 340 ft above sea level. That is close enough that the station's summers are Martin's summers.

No other city in this set uses Martin U Of T Branch E, so this sizing is Martin's alone.

The sun over Martin in late July

At 36.34°N, the noon sun on 21 July stands 74.1° above the horizon over Martin and the day runs 14 h 07 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.

10,989 people live in Martin, the 58th largest of the 65 Tennessee cities sized on this site. Coordinates used: 36.3379, -88.8514.

Martin AC sizing questions