What size AC for Mason City, IA? 2 tons for 2,000 sq ft

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

2 tons central AC or heat pump, about 25,700 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 64% 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 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 935 square feet in this climate. For a single room, size by the room: 12.8 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Mason City Municipal Airport (6.4 mi away). Jul is the hottest month, averaging a high of 82.5°F and a low of 60.5°F, with about 12 days a year at 90°F or more. That gives a design temperature of 87°F against 75°F inside.

What it costs to run

About 787 kWh a year at SEER2 14.3, or roughly $114 at Iowa's average residential rate of 14.55¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Mason City

Of the 25,700 BTU/hr, 8,640 comes through walls, roof and windows on a 87°F afternoon (34%), 13,000 is sun on the house (51%), 2,120 is four people and their appliances, and 1,900 is moisture the coil has to wring out of Mason City's summer air (7%).

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 23,760 BTU/hr before the moisture allowance.

Other house sizes in Mason City

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 1,900 BTU/hr; a 350 sq ft living room needs about 4,500 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 7,700 BTU/hr.

Month by month in Mason City

Jul alone uses 35% of the year's cooling energy. The unit runs the equivalent of 438 hours a year at full output.

Mason City against nearby cities

Of 41 Iowa cities here, Mason City has the 38th highest cooling load. The range runs from Dubuque at 24,900 BTU/hr to Council Bluffs at 34,300.

Where Mason City's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Mason City Municipal Airport, 6.4 miles from the center of Mason City at 1,188 ft above sea level. That is close enough that the station's summers are Mason City's summers.

No other city in this set uses Mason City Municipal Airport, so this sizing is Mason City's alone.

The sun over Mason City in late July

At 43.15°N, the noon sun on 21 July stands 67.3° above the horizon over Mason City and the day runs 14 h 43 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. Long days mean the house keeps gaining heat into the evening, well after the outdoor peak.

26,948 people live in Mason City, the 18th largest of the 41 Iowa cities sized on this site. Coordinates used: 43.1478, -93.2004.

Mason City AC sizing questions