Brochure

3534
Fan Selection Guide
1. What is the size of the bathroom?
a. Need 1 CFM (cubic foot per minute) per square
foot
b. Length x Width = CFM
(length) x (width) = (Total CFM needed)
c. Example: 8 ft length x 10 ft wide = 80 CFM is
needed to properly ventilate the bathroom
2. What features are needed/wanted?
Fan only? Light? Heat? Variable speed? Motion?
Humidity? Time delay?
3. What type of construction is available?
Truss size is necessary if it is smaller than 2 x 8
construction so the selected fan housing size will t
the installation.
a. 2 x 8 construction – can use any fan
combination that we have
b. 2 x 6 construction – can use our fan
combinations that t 2 x 6 or 2 x 4 construction
c. 2 x 4 construction – can use our fan
combinations that t 2 x 4 construction
4. Now that you know the CFM needed, the
features wanted and the construction size, you are
ready to nd your fan combination.
Equivalent Duct Length (EDL)
The Equivalent Duct Length Table (Figure B) shows
you how to calculate the equivalent straight duct
length in order to overcome static pressure. The
EDL chart helps ensure fan performs as expected
under the airow resistance caused by the listed
components.
A ventilating fan’s performance is plotted on
a graph called a performance curve. The
performance curve shows airow in cubic feet per
minute (CFM) along the horizontal axis and static
pressure (resistance) along the vertical axis. Figure
A shows how a performance curve works. The
fan with a “Closed Duct” has high static pressure
and no airow; and the fan with “No Duct” has
low static pressure and high airow. In reality, an
installed fan will be somewhere in between these
two points.
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.
Example: Sizing for an 8 ft x 10 ft x 8 ft ceiling
bathroom using 12 foot long, 4 inch diameter
aluminum ex duct, one elbow, one wall cap.
Step 1: Determine application
Bathroom = 1 CFM/square foot
Step 2: 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
Step 3: Calculate your required CFM
1 CFM x 80 sq ft = 80 CFM
Step 4: Use the Equivalent Duct Length chart
above to calculate duct run.
4a. 12 ft aluminum ex duct x 1.25 = 15 ft
4b. One elbow = 15 ft EDL
4c. One wall cap = 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.
Step 5: Review models in catalog pages to nd a
model with desired feature. Features may include
light xture, heater or low-prole housing.
Note: Check with your local building inspector to
conrm that these methods are accepted in your
area.
Sizing
Information and Instructions
FIG. A
Closed or Blocked duct work —A closed or blocked exhaust
port results in highest static pressure and zero air ow.
Extended Duct work —Long duct length and
elbows increase static pressure and reduce air ow.
Duct work —Duct increases static
pressure and reduces air ow.
Short Duct work —Short
duct allows low static
pressure and higher air ow.
No Duct work —
No duct equals
zero static pressure
and maximum
air ow.
Air Flow (CFM)
Static Pressure (Resistance)
FIG. B
Equivalent Duct Length
Duct Diameter
3" 4" 6" 8"
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