What size AC for Baltimore, MD? 3.5 tons for 2,000 sq ft

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

3.5 tons central AC or heat pump, about 39,300 BTU/hr of load

Here the 20 BTU per square foot chart lands close: 3.5 tons against a load of 3.3 tons. This is one of the climates the chart was written for.

If a contractor quotes you more than 3.5 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 611 square feet in this climate. For a single room, size by the room: 19.7 BTU/hr per square foot.

The climate it is sized for

Climate from NOAA's 1991 to 2020 normals at Maryland Sci Ctr (1.3 mi away). Jul is the hottest month, averaging a high of 90.1°F and a low of 72.9°F, with about 43 days a year at 90°F or more. That gives a design temperature of 96°F against 75°F inside.

What it costs to run

About 2,747 kWh a year at SEER2 14.3, or roughly $585 at Maryland's average residential rate of 21.31¢ per kWh. Cooling runs 5 months of the year here.

What drives the load in Baltimore

Of the 39,300 BTU/hr, 15,120 comes through walls, roof and windows on a 96°F afternoon (38%), 13,000 is sun on the house (33%), 2,120 is four people and their appliances, and 9,100 is moisture the coil has to wring out of Baltimore's summer air (23%).

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 30,240 BTU/hr before the moisture allowance.

Other house sizes in Baltimore

Single rooms with a window or mini-split unit: a 150 sq ft bedroom needs about 3,000 BTU/hr; a 350 sq ft living room needs about 6,900 BTU/hr; a 600 sq ft open plan kitchen and family room needs about 11,800 BTU/hr.

Month by month in Baltimore

Jul alone uses 29% of the year's cooling energy. The unit runs the equivalent of 999 hours a year at full output.

Baltimore against nearby cities

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

Where Baltimore's weather numbers come from

The nearest NOAA station with full 1991 to 2020 normals is Maryland Sci Ctr, 1.3 miles from the center of Baltimore at 20 ft above sea level. That is close enough that the station's summers are Baltimore's summers.

No other city in this set uses Maryland Sci Ctr, so this sizing is Baltimore's alone.

The sun over Baltimore in late July

At 39.30°N, the noon sun on 21 July stands 71.1° above the horizon over Baltimore and the day runs 14 h 22 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.

568,271 people live in Baltimore, the largest of the 23 Maryland cities sized on this site. Coordinates used: 39.3000, -76.6105.

Baltimore AC sizing questions