How to Size a Central Air Conditioner
Whether you are looking to install a new central air conditioning unit or replacing a current unit, it is important to use the correct size unit. A central AC that is too small will run continuously without adequately cooling the house, while a unit that is too big is overly costly and, due to frequent on/off cycles, can cause humidity problems. Does this Spark an idea?
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Things You'll Need
- paper
- writing utensil
- tape measure (or other measuring device)
- computer with internet access
Instructions
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When trying to determine the appropriate size central air conditioner for your home, the first step you want to take is to look at your windows. Using your tape measure, find the length and width (in feet) of all the windows in your house. Be sure to include any glass doors or skylights. Multiply the length times the width to find the area in square feet for each window. Then add the areas for the windows on the same side of the house so you have the total area of all the windows for each side of your house.
You also want to look to see if your windows are single pane (one sheet of glass) or double pane (two sheets of glass). If single pane, determine if your windows are in good or poor condition.
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After you measure your windows, check to see how much shading is offered for each of your windows. Shading could include curtains that are closed during the day, an overhang, or trees and other vegetation blocking the sun from reaching the window. If the sun can't directly heat your home, you won't need as big of a central AC.
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The next factor to determine the size of your central air conditioning unit is your house. Determine if you live in the southern, middle, or northern latitudes. Check the age of your house and how many inches of insulation you have in your roof/attic and walls (if any). Are there any noticeable air leaks in you house and, if so, how much air do they let in?
As a side note, if you have little to no insulation and/or have air leaks in your house, it will save you money and require a smaller central AC unit if you add insulation and seal the air leaks before you purchase a new unit. A Do-It-Yourself Guide to Home Sealing link can be found below in the resources section.
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The last major factor in determining the size of your central air conditioner is your ductwork. Check to see if your ducts are located primarily in your basement, walls, or attic. If in the attic, verify if your ducts are insulated or not. For the duct work you can see, are there any leaks allowing air to escape before it reaches the intended room?
As mentioned above, if you have leaks in your ducts, it will save you money and require a smaller central AC unit if you seal the air leaks before you purchase a new unit. A Duct Sealing brochure link can be found below in the resources section.
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With all this information in hand, go to the Central Air Conditioner Sizing Tutorial (link below) at the EnergyStar.gov website to help you determine what size central AC unit you need.
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Once you have an idea of the size of unit you will need and begin to contact contractors to install your unit, they will probably want to take their own measurements to determine the correct size. Be sure to ask them to perform a Manual J analysis of your needs. Manual J is the current industry standard and may be required by your housing code.
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Resources
- Photo Credit energystar.gov
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Comments
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jenng
Mar 10, 2009
Very important you need the right size 5*
