National Oilheat Research Alliance 27
Table 1
Table 2
To estimate the equivalent feet length of the Reducer/
Increaser, find the figure at the intersection of the
small pipe size and the large pipe size.
Sizing the Power Venter
Power vents are sized based on the
input firing rate of the appliance AND
the equivalent feet of vent pipe for the
installation. If the power vent is being used for
multiple appliances, it must be sized based on
the total firing rate and total equivalent feet of
all connected appliances.
Calculating the Equivalent Feet
of a Venting System
To determine the total equivalent feet:
1. Determine the total equivalent feet for
each type of fitting used in the venting system
from Tables 1 and 2.
2. Calculate the total length of the straight
lengths of pipe.
3. Add the equivalent feet of the fittings
to the total length of the straight pipe to
determine the total equivalent feet of the vent
system.
4. Find the total equivalent feet in Table
3 to determine the proper model for the
installation.
For example, for a vent system
made up of 6" pipe:
Step 1: Two 6" 90° elbows
Table 3
equivalent to 11'
each = 22'
Step 2: Five 4' lengths
of 6" pipe = 20'
Step 3: One 6" x 4"
reducer = 4'
Step 4: 22' + 20' + 4' = 46'
total equivalent
feet.
If the calculated
equivalent feet is greater
than what is specified for
the power vent, increase
the diameter of the vent
pipe or use the next larger
size power vent.
Note: The maximum equivalent footage allowable for the vent pipe is given for
two points: 1) the maximum BTU/hr venting capacity and 2) at 60% of the maxi-mum.
This allows for estimating values between the two given points.