Size is one of the biggest factors when installing a new air conditioner. If the unit’s capacity is too small, it will run continuously and use more energy, increasing your electric bill. Also, it won’t cool your home very well. And if the AC unit is too large, your space may cool more quickly, but the system won’t run long enough to remove moisture. Your home may then become humid, damp, and clammy, while frequent cycling will burn more energy.
Choosing the right size air conditioner requires knowing the area that needs to be cooled, among other factors.
Measure Your Space
To start, accurately measure the square footage of your home, room, or space you intend to cool. Multiplying the length of a room by its width gives you its square footage, or area, in square feet (ft2). This value is then multiplied by 25 to estimate the proper air conditioner size in British Thermal Units (BTUs). Using this example, a 12 x 15 foot room is 180 square feet; multiplied by 25 this yields 4,500 BTU of required cooling capacity.
By following this rule, you get ample cooling on a rainy or hot, sunny day. But you can also determine size by considering an A/C needs 20 BTU per square foot. Another method calculates BTU capacity by multiplying square footage by 35, which would yield:
- 100 to 150 ft2: 3,500 to 5,250 BTUs
- 300 to 350 ft2: 10,500 to 12,250 BTUs
- 450 to 550 ft2: 15,750 to 19,250 BTUs
- 1,000 to 1,200 ft2: 35,000 to 42,000 BTUs
- 1,500 to 2,000 ft2: 52,700 to 70,000 BTUs
When estimating capacity, combine the size of rooms not separated by doors. Also consider factors such as ceiling height and window/doorway size; higher values may call for increased cooling capacity. There are other factors as well; per ENERGY STAR recommendations, consider the following:
- Bright Sunlight: Increase the capacity calculation by 10%.
- Heavy Shading: Reduce your capacity calculation by 10%.
- Kitchen Installation: The A/C’s capacity should be 4,000 BTU higher.
- Rooms Used by >2 People: +600 BTU for each additional person.
Manual J Calculation
A professional measurement is the most precise. Whether you work with an HVAC company or energy auditor, a Manual J calculation for you home determines the exact HVAC unit size it needs. It takes square footage into account, among many other factors, such as climate zone, ductwork design and condition, and the number and style of windows in your home. Insulation, shade or sunlight, presence of heat-generating appliances, and the number of people using the space in question are considered as well. All these details are inputted to determine the exact BTU heating and cooling capacity needed.
Does Optimal Size Guarantee Efficiency?
There are more considerations than size when it comes to efficiency. One is the type of air conditioner; window units, for example, sit low, while a wall-mounted unit delivers cool air from a higher point. This cools a room more thoroughly. A system’s energy-efficiency ratio (EER) counts as well; and always look for the ENERGY STAR label. Cleaning your filters, setting an optimal temperature, and using timers for cooling when it’s most needed also help improve efficiency.
Let Us Help Choose the Right AC for You
The professional technicians at Sky Heating & Air Conditioning can make all the calculations and recommend the best air conditioner for you. Our high-quality services are depended upon throughout Portland and The Dalles, OR. Call 503-235-9083 or contact us online to request a consultation.