What size AC for Kalispell, MT? 2 tons for 2,000 sq ft

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

2 tons central AC or heat pump, about 24,700 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 70% 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 971 square feet in this climate. For a single room, size by the room: 12.4 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Kalispell Glacier Airport (6.7 mi away). Jul is the hottest month, averaging a high of 82.2°F and a low of 47.6°F, with about 14 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 180 kWh a year at SEER2 14.3, or roughly $25 at Montana's average residential rate of 14.13¢ per kWh. Cooling runs 2 months of the year here.

What drives the load in Kalispell

Of the 24,700 BTU/hr, 8,640 comes through walls, roof and windows on a 87°F afternoon (35%), 13,000 is sun on the house (53%), 2,120 is four people and their appliances, and 1,000 is moisture the coil has to wring out of Kalispell's summer air (4%).

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 Kalispell

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 4,300 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 7,400 BTU/hr.

Month by month in Kalispell

Jul alone uses 50% of the year's cooling energy. The unit runs the equivalent of 104 hours a year at full output.

Kalispell against nearby cities

Of 8 Montana cities here, Kalispell has the 7th highest cooling load. The range runs from Butte-Silver Bow at 24,000 BTU/hr to Billings at 29,500.

Where Kalispell's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Kalispell Glacier Airport, 6.7 miles from the center of Kalispell at 2,963 ft above sea level. That is close enough that the station's summers are Kalispell's summers.

No other city in this set uses Kalispell Glacier Airport, so this sizing is Kalispell's alone.

The sun over Kalispell in late July

At 48.22°N, the noon sun on 21 July stands 62.2° above the horizon over Kalispell and the day runs 15 h 17 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.

31,296 people live in Kalispell, the 7th largest of the 8 Montana cities sized on this site. Coordinates used: 48.2162, -114.3276.

Kalispell AC sizing questions