What Size Air Conditioner Do I Need for My House?
- A room's size is measured in square feet; calculating the square footage requires measuring each room that will need to be cooled individually. Multiply the length of the room by the width of the room, and do not include closet space in the calculation. You need to calculate all rooms that will be cooled, including hallways, laundry rooms and bathrooms. Exclude rooms or areas that are not or will not be connected to the system, such as basements and attics.
- Converting the square footage to British Thermal Units (BTUs) determines the basic cooling needs of the room. One hundred- to 150-square foot rooms need 5,000 BTUs to be cooled. One hundred fifty- to 250-square feet convert to 6,000 BTUs. Two hundred fifty- to 350-square feet convert to 7,000 BTUs. Multiply the area for rooms larger than 350 square feet by 25 to determine the estimated BTUs. Add each room together to determine the whole house BTU needs. Divide the total BTUs by 12,000 to identify the tonnage needs. AC units are measured by either BTUs or tonnage, depending upon the type.
- Choosing and installing a split system has several benefits. The unit will impact the whole house for a more even distribution of air and a greater reduction of humidity within the house. A properly sized unit will have the least impact to the monthly electric bill than any other option, especially if you choose Energy Star-rated appliances. The downside to the split system is the installation costs. Installing a split system often requires updating the circuit breaker box, installing ductwork and installing the unit directly. Total costs for a split-system installation could easily exceed $10,000.
- Ductless units operate similarly to split systems and are often called miniature split systems. The system routes refrigerant through pipes from an outside unit into room-specific control boxes. The room-specific boxes actually cool the room. Window units operate in a similar manner but house the different elements into one basic cabinet. Both units can be cost effective if used properly and are cheaper to install. The ductless and window units are better for zone control, whereas specific areas are cooled as opposed to the whole dwelling. Monthly costs can be a little higher depending upon the amount of cooling the units produce.