What size AC for Jerome, ID? 3 tons for 2,000 sq ft

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

3 tons central AC or heat pump, about 31,900 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 32% 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 753 square feet in this climate. For a single room, size by the room: 15.9 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Jerome County Airport (3.2 mi away). Jul is the hottest month, averaging a high of 89.6°F and a low of 58.7°F, with about 35 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 932 kWh a year at SEER2 14.3, or roughly $121 at Idaho's average residential rate of 13.02¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Jerome

Of the 31,900 BTU/hr, 14,400 comes through walls, roof and windows on a 95°F afternoon (45%), 13,000 is sun on the house (41%), 2,120 is four people and their appliances, and 2,400 is moisture the coil has to wring out of Jerome's summer air (8%).

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 Jerome

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,400 BTU/hr; a 350 sq ft living room needs about 5,600 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 9,500 BTU/hr.

Month by month in Jerome

Jul alone uses 41% of the year's cooling energy. The unit runs the equivalent of 418 hours a year at full output.

Jerome against nearby cities

Of 26 Idaho cities here, Jerome has the 12th highest cooling load. The range runs from Sandpoint at 24,000 BTU/hr to Mountain Home at 36,500.

Where Jerome's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Jerome County Airport, 3.2 miles from the center of Jerome at 4,024 ft above sea level. That is close enough that the station's summers are Jerome's summers.

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

The sun over Jerome in late July

At 42.72°N, the noon sun on 21 July stands 67.7° above the horizon over Jerome and the day runs 14 h 41 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.

13,481 people live in Jerome, the 20th largest of the 26 Idaho cities sized on this site. Coordinates used: 42.7176, -114.5158.

Jerome AC sizing questions