How to Measure for a Wall Fan Vent
Measuring the dimensions of your home is a vital step in order to determine the right size for your wall ventilation fan. When you have the right size vent fan, this ensures that your home is being ventilated with a healthy quality of indoor air. In order to determine the measurements, it depends on the location of your fan, whether you plan on ventilating your entire home with one fan or one room with one fan. Does this Spark an idea?
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Instructions
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Application and Sizing Chart Method
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Choose the application for the ventilation fan between intermittent --- or spot --- ventilation, or continuous --- or whole house --- ventilation. This is vital because it helps you determine the recommended Air Changes per Hour (ACH). For instance, the industry standard for spot ventilation depends on the room where you are installing the vent. Kitchens are 15 ACH or 2 Cubic Feet per Minute (CFM) per square foot; bathrooms are 8 ACH or for cubic feet, 1 CFM per square foot. Every other room is 6 ACH or, for cubic feet, .75 CFM per square foot. For continuous ventilation, the standard is 7.5 CFM for each person, as well as 1 CFM for every 100 square feet.
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Calculate the square footage for the space and application you are using.
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Calculate the duct run by determining the material your duct is made of, the number of roof jacks, elbows and wall caps it has, and then calculate it using the standard figures. Your duct is made of either flex aluminum or insulated flex. For flex aluminum you multiply the duct length by 1.25 for duct with a 4-inch diameter, and 1.5 for a 6-inch diameter. With an insulated flex duct, you multiply the duct length by 1.5 for a 4-inch diameter duct, and 1.75 or 2 for a 6-inch diameter. For each wall cap and each roof jack, you add 30 feet, and for every elbow you add 15 feet. For instance, with a 12-foot flex aluminum duct that has one elbow and one roof jack, your calculation is: 12 x 1.25 = 15 + 15 + 30 = 60. Your Equivalent Duct Length (EDL) is 60 feet.
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Check the sizing chart for the brand you are considering and use the square footage and the EDL figures you calculated to find the ventilation fan you need.
Performance Curve Method
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Calculate the cubic feet for the space and application you are using and divide that figure by 60 to determine the CFM figure.
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Multiply the CFM figure by the ACH value for the space you are calculating for. For instance, if you have a bathroom that is 768 cubic feet, you divide 768 by 60 to get 12.5 CFM and multiply it by industry standard, which is 8 ACH, to get the resulting 102 CFM for a bathroom ventilation measurement.
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Calculate the EDL in the same manner as stated with the sizing chart method, and locate the two figures on the curve chart to determine the size vent fan you need.
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Tips & Warnings
Check to make sure the methods described are accepted in your area with a local building inspector.
If you have cathedral ceilings, to find the square footage for a 10 to 12-foot cathedral ceiling, you multiply length-by-width-by-1.25, or for a 12- to 16-foot cathedral ceiling, you multiply length-by-width-by-1.5.
References
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