Homeowner satisfaction using a whole-house air conditioning system is dependent upon proper system sizing. A correctly sized air-conditioning program will keep temperatures and humidity in the conditioned space at comfortable levels despite high exterior heat and heat. Air conditioner cooling size generally is expressed in tons. 1 ton of cooling capacity equals removal of 12,000 British thermal units of heat per hour, an amount of heat that could melt a 1-ton block of ice in 24 hours.
Rule of Thumb
There is no single “average” cooling figure that’s valid anywhere in the United States. But there’s a general guideline given by the American Society of Home Inspectors that you can use to produce a quick but rough estimate of the cooling capability you will need, depending on the square footage of your floor area. In the temperate northern half of the continental United States, 1 ton of cooling capacity should be sufficient to cool between 700 and 1,000 square feet of ground area. In the hot southern half of the country, 1 ton of cooling capacity can cool between 450 and 700 square feet of ground area, presuming the house has 8-foot ceilings, insulation in ceilings and walls and tight-fitting windows.
Cooling Load Factors
There are at least nine factors affecting the residential cooling capability necessary for a specific home in a specific site. They are general climate for the area; average outdoor temperatures and humidity; insulation amount; air leakage; compass orientation of windows; glazing size and kind; existence and use of awnings, blinds or drapes; amount of shading from trees or overhangs; and amount of heat produced by equipment and individuals in the home.
Selecting the right size of cooling equipment is essential for optimal performance. Oversizing an air-conditioning system means higher setup costs and inefficient operation. An air conditioner not only cools the air but dehumidifies as well. But an oversized air conditioner cools the air so fast that the unit does not run long enough to dehumidify the air. The outcome would be a clammy feeling for the occupants and encouragement of unhealthy mold development. An undersized system will not trendy effectively about the hottest days when you really require cooling. A contractor shouldn’t only assume the existing system’s cooling capability was right and sell you just like it. Manual J released by the Air Conditioning Contractors of America comprises proven procedures for contractors to follow when calculating air conditioner size.
A good estimate of the needed air conditioner size requires the contractor to measure the volume of each room and determine the amount of air leakage and the insulating R-value of the house’s building materials, insulation and windows. Other factors include the size, condition and location of supply ducts, positioning of the home and consequent heat gain through windows. Also be sure the contractor uses outdoor temperature and humidity averages particular to your area of the condition when designing the new program. Use of overall statewide figures could result in oversizing or undersizing the air conditioner.