What size AC for Lisbon, WI? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 26,400 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 59% 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 908 square feet in this climate. For a single room, size by the room: 13.2 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Richfield 3 Ssw (4.3 mi away). Jul is the hottest month, averaging a high of 83.1°F and a low of 60.4°F, with about 13 days a year at 90°F or more. That gives a design temperature of 88°F against 75°F inside.

What it costs to run

About 757 kWh a year at SEER2 14.3, or roughly $144 at Wisconsin's average residential rate of 19.05¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Lisbon

Of the 26,400 BTU/hr, 9,360 comes through walls, roof and windows on a 88°F afternoon (35%), 13,000 is sun on the house (49%), 2,120 is four people and their appliances, and 2,000 is moisture the coil has to wring out of Lisbon's summer air (8%).

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 24,480 BTU/hr before the moisture allowance.

Other house sizes in Lisbon

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,000 BTU/hr; a 350 sq ft living room needs about 4,600 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 7,900 BTU/hr.

Month by month in Lisbon

Jul alone uses 38% of the year's cooling energy. The unit runs the equivalent of 409 hours a year at full output.

Lisbon against nearby cities

Of 98 Wisconsin cities here, Lisbon has the 30th highest cooling load. The range runs from Two Rivers at 20,200 BTU/hr to La Crosse at 29,800.

Where Lisbon's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Richfield 3 Ssw, 4.3 miles from the center of Lisbon at 1,069 ft above sea level. That is close enough that the station's summers are Lisbon's summers.

2 other cities use the same station and get the same climate inputs. The closest to Lisbon: Sussex (2 mi away, 5.4 mi from the station), Richfield (6 mi away, 2.3 mi from the station). Lisbon is farther from the station than 1 of them.

The sun over Lisbon in late July

At 43.16°N, the noon sun on 21 July stands 67.2° above the horizon over Lisbon 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.

11,127 people live in Lisbon, the 90th largest of the 98 Wisconsin cities sized on this site. Coordinates used: 43.1576, -88.2504.

Lisbon AC sizing questions