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Which Ventilation Fan Should I Choose?
- 1st You Will Need To Size UpYour Fan:
The first step when sizing for a ventilating fan is to determine the application. Decide whether you are sizing for intermittent or continuous ventilation (see pages 6 and 7). If intermittent, determine which application, (i.e. bathroom, kitchen or other). Use the following industry recommendations to determine Air Changes per Hour (ACH) for your specific application.
Intermittent (spot) ventilation:
The Home Ventilating Institute (HVI) recommends the following Air Changes per Hour (ACH).
I. Bathrooms - 8 ACH or 1 CFM/sq ft
II. Kitchens - 15 ACH or 2 CFM/sq ft
Other Rooms - 6 ACH or .75 CFM/sq ft
Continuous (Whole House) Ventilation:
Most building codes have adopted the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) Standard 62. The most current version, ASHRAE 62.2-2004, calls for continuous mechanical ventilation as shown below.
I. House or apartment - 7.5 CFM per person plus 1 CFM per 100 square feet
- Calculate the Area Being Ventilated:
The following method for selecting the proper fans follows industry standards and will give you the recommended fan for your application. The Sizing Chart Method is easier. The Performance Curve Method is often preferred by engineers.
Note: You should check with your local building inspector to confirm that these methods are accepted in your area.
Sizing Chart Method:
|Sizing Chart Method:|
Sizing and selecting a Ceiling Mounted Fan: Proper sizing requires that you determine the needed CFM, the square footage of the room or home, and the length and type of duct.
Sizing for an 8 ft x 10 ft x 8 ft ceiling bathroom using 12 foot long, 4 inch diameter aluminum flex duct, one elbow, one wall cap.
|•||Bathroom = 1 CFM/square foot.|
Calculate the area to be ventilated in square feet. Assuming an 8 ft ceiling: room length x width = area in square feet.
|•||8 ft x 10 ft = 80 sq ft|
Calculate your required CFM.
|•||1 CFM x 80 sq ft = 80 CFM|
See the Fan Sizing Charts Use the Equivalent Duct Length chart below to calculate duct run.
12 ft aluminum flex duct x 1.25 = 15 ft
FOne elbow = 15 ft EDL
One roof jack = 30 ft EDL
15 ft + 15 ft + 30 ft = 60 ft EDL
This is the equivalent duct length (or resistance) the fan must overcome to move air through the duct to the outside.
Select a properly sized fan using the sizing chart below.
Identify the column with 60 ft EDL
Identify the color with 80 CFM
Identify the proper models with their duct size
FV-08VKS1 4" duct
FV-08VKM1 4" duct
FV-08VK1 4" duct
FV-08VKL1 4" duct
FV-11VQ3 4" duct
FV-11VQL4 4" duct
FV-11VF2 4" duct
FV-11VFL2 4" duct
FV-11VQD2 4" duct
FV-11VH1 4" duct
FV-11VHL1 4" duct
Sizing and Selecting a Ceiling Mounted Fan Steps to Select A Fan:
1. Calculate the CFM needed for your application
2. Calculate the Equivalent Duct Length (EDL) for your installation
- Measure the Equivalent Duct Length (EDL):
Static Pressure and Duct Run:
A ventilating fan must overcome resistance when pushing air from the inlet, through the duct, to the outside of the building. This resistance is known as static pressure. The amount of static pressure depends on the duct length, type of duct, elbows and the roof jack or wall cap.
Equivalent Duct Length (EDL):
Static pressure in a typical duct run is caused by the type of duct material, elbows, exterior wall cap, etc. The Equivalent Duct Length Table (Figure B) shows the standard values for duct components. The EDL chart allows you to calculate the equivalent straight duct length in order to overcome static pressure caused by each component in a duct run. The EDL helps assure the fan performs as expected under the airfl ow resistance caused by the components listed in this chart.
A ventilating fan's performance is plotted on a graph called a performance curve. The performance curve shows airflow in cubic feet per minute (CFM) along the horizontal axis and the vertical axis. Figure A shows how a performance curve works. The fan with a "Closed Duct" has high static pressure and no airflow; and the fan with "No Duct" has low static pressure and high airfl ow. In reality, an installed fan will be somewhere in between these two points.
|Equivalent Duct Length|
|Duct||Smooth Metal||Same as measured duct length|
|Material||Flex Aluminum||1.25 x duct length||1.25 X duct length||1.5 X duct length||1.5 X duct length|
|Insulated Flex||1.5 X duct length||1.5 X duct length||1.75 X duct length||1.75 X duct length|
|Terminal||Wall Cap||30 feet||30 feet||40 feet||40 feet|
|Device||Roof Jack||30 feet||30 feet||40 feet||40 feet|
|Elbow||Adjustable||15 feet||15 feet||20 feet||20 feet|