What size AC for Ottawa, KS? 3 tons for 2,000 sq ft

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

3 tons central AC or heat pump, about 33,900 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 24% 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 707 square feet in this climate. For a single room, size by the room: 17 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Ottawa (1.4 mi away). Jul is the hottest month, averaging a high of 89.3°F and a low of 67.6°F, with about 47 days a year at 90°F or more. That gives a design temperature of 95°F against 75°F inside.

What it costs to run

About 1,858 kWh a year at SEER2 14.3, or roughly $283 at Kansas's average residential rate of 15.26¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Ottawa

Of the 33,900 BTU/hr, 14,400 comes through walls, roof and windows on a 95°F afternoon (42%), 13,000 is sun on the house (38%), 2,120 is four people and their appliances, and 4,400 is moisture the coil has to wring out of Ottawa's summer air (13%).

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 29,520 BTU/hr before the moisture allowance.

Other house sizes in Ottawa

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 10,200 BTU/hr.

Month by month in Ottawa

Jul alone uses 31% of the year's cooling energy. The unit runs the equivalent of 783 hours a year at full output.

Ottawa against nearby cities

Of 38 Kansas cities here, Ottawa has the 37th highest cooling load. The range runs from Pittsburg at 33,100 BTU/hr to Wichita at 39,500.

Where Ottawa's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Ottawa, 1.4 miles from the center of Ottawa at 905 ft above sea level. That is close enough that the station's summers are Ottawa's summers.

No other city in this set uses Ottawa, so this sizing is Ottawa's alone.

The sun over Ottawa in late July

At 38.60°N, the noon sun on 21 July stands 71.8° above the horizon over Ottawa and the day runs 14 h 18 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.

12,733 people live in Ottawa, the 28th largest of the 38 Kansas cities sized on this site. Coordinates used: 38.5982, -95.2628.

Ottawa AC sizing questions