What size AC for Montgomery, OH? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 30,600 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 37% 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 2.5 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 783 square feet in this climate. For a single room, size by the room: 15.3 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Cincinnati Municipal Airport Lunken Field (10.7 mi away). Jul is the hottest month, averaging a high of 86.6°F and a low of 65.3°F, with about 27 days a year at 90°F or more. That gives a design temperature of 91°F against 75°F inside.

What it costs to run

About 1,564 kWh a year at SEER2 14.3, or roughly $294 at Ohio's average residential rate of 18.81¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Montgomery

Of the 30,600 BTU/hr, 11,520 comes through walls, roof and windows on a 91°F afternoon (38%), 13,000 is sun on the house (42%), 2,120 is four people and their appliances, and 4,000 is moisture the coil has to wring out of Montgomery's summer air (13%).

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 26,640 BTU/hr before the moisture allowance.

Other house sizes in Montgomery

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,300 BTU/hr; a 350 sq ft living room needs about 5,400 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 9,200 BTU/hr.

Month by month in Montgomery

Jul alone uses 30% of the year's cooling energy. The unit runs the equivalent of 730 hours a year at full output.

Montgomery against nearby cities

Of 176 Ohio cities here, Montgomery has the 18th highest cooling load. The range runs from Conneaut at 24,100 BTU/hr to Hamilton at 31,500.

Where Montgomery's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Cincinnati Municipal Airport Lunken Field, 10.7 miles from the center of Montgomery at 475 ft above sea level. That is close enough that the station's summers are Montgomery's summers.

9 other cities use the same station and get the same climate inputs. The closest to Montgomery: Blue Ash (2 mi away, 9.8 mi from the station), Loveland (4 mi away, 13.7 mi from the station), Reading (5 mi away, 8.2 mi from the station), Norwood (8 mi away, 4.3 mi from the station), Cincinnati (11 mi away, 5.4 mi from the station). Montgomery is farther from the station than 8 of them.

The sun over Montgomery in late July

At 39.25°N, the noon sun on 21 July stands 71.1° above the horizon over Montgomery and the day runs 14 h 22 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.

10,952 people live in Montgomery, the 164th largest of the 176 Ohio cities sized on this site. Coordinates used: 39.2512, -84.3480.

Montgomery AC sizing questions