What size AC for Westminster, MD? 2.5 tons for 2,000 sq ft

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

2.5 tons central AC or heat pump, about 28,000 BTU/hr of load

The 20 BTU per square foot chart would put in 3.5 tons, about 50% 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 857 square feet in this climate. For a single room, size by the room: 14 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at York Airport (24.5 mi away). Jul is the hottest month, averaging a high of 85.2°F and a low of 63.1°F, with about 16 days a year at 90°F or more. That gives a design temperature of 90°F against 75°F inside.

What it costs to run

About 1,113 kWh a year at SEER2 14.3, or roughly $237 at Maryland's average residential rate of 21.31¢ per kWh. Cooling runs 4 months of the year here.

What drives the load in Westminster

Of the 28,000 BTU/hr, 10,800 comes through walls, roof and windows on a 90°F afternoon (39%), 13,000 is sun on the house (46%), 2,120 is four people and their appliances, and 2,100 is moisture the coil has to wring out of Westminster'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 25,920 BTU/hr before the moisture allowance.

Other house sizes in Westminster

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 2,100 BTU/hr; a 350 sq ft living room needs about 4,900 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 8,400 BTU/hr.

Month by month in Westminster

Jul alone uses 33% of the year's cooling energy. The unit runs the equivalent of 568 hours a year at full output.

Westminster against nearby cities

Of 23 Maryland cities here, Westminster has the lowest cooling load. The range runs from Westminster at 28,000 BTU/hr to Baltimore at 39,300.

Where Westminster's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is York Airport, across the line in Pennsylvania, 24.5 miles from the center of Westminster at 464 ft above sea level. That is close enough that the station's summers are Westminster's summers.

2 other cities use the same station and get the same climate inputs. The closest to Westminster: Hanover (16 mi away, 9.3 mi from the station), York (30 mi away, 8.3 mi from the station). Westminster is farther from the station than 2 of them.

The sun over Westminster in late July

At 39.58°N, the noon sun on 21 July stands 70.8° above the horizon over Westminster and the day runs 14 h 23 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.

20,662 people live in Westminster, the 13th largest of the 23 Maryland cities sized on this site. Coordinates used: 39.5792, -77.0067.

Westminster AC sizing questions