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100309035_2000560888_Rev. A www. reliancewaterheaters .com 31
Calculating Equivalent Feet
WATER
HEATER
MODEL
HEATER
INPUT
(Btu/hr)
VENT SIZE
(Inside
Diam.)
PRESSURE
SWITCH
SETTING
MAXIMUM EQUIVALENT
VENT LENGTH
MINIMUM EQUIVALENT VENT
LENGTH
75 gal. 76,000
3”
-0.90 in. w.c.
50’ + termination elbow and
screen*
7’ + termination elbow and
screen*
4”
125’ + termination elbow
and screen*
50’ + termination elbow and
screen*
* see Figure 32, “Venting terminations and sizing” and “Vent screen installation”.
Equivalent lengths of straight pipe for various elbows using Schedule 40 PVC, CPVC, ABS and polypropylene.
Size Type
Short Sweep/
Short Radius
Long Sweep/
Long Radius
Notes:
1. Use long radius elbows where possible. Minimum
distance between 90º elbows should be 6 in.
wherever possible.
2. Venting systems may use a maximum of five (5)
90° elbows.
3. Use proper screen termination (see Figure 32).
3"
4"
90° elbow 8’ 5’
3"
4"
45° elbow 4’ 2.5’
Table 2.
Example for calculating equivalent feet.
Section “A” 0.5 ft.
90° elbow 8.0 ft.
Section B 1.0 ft.
45° elbow 4.0 ft.
Section C 1.5 ft.
45° elbow 4.0 ft.
Section D 15.0 ft.
Total Equivalent 34.0 ft.
Based on this example use the (fully open) rodent
screen for vent length greater than 20 equivalent ft.
(see Figure 32).
Note: The vent pipe must be supported every 4 ft. . To prevent vibration and sagging, it is recommended to use
isolation pads when attaching straps to floor joists, walls or ceilings. PVC and CPVC vent pipe should be sloped
upwards away from the blower assembly at a pitch of 1/8 in. rise per 4 ft. . Polypropylene vent systems require a
1/4 in. per 1 ft. upward slope to ensure proper drainage.
STRAP
45° SHORT
ELBOW
90° SHORT
ELBOW
RODENT
SCREEN
(INSTALL INTO
ELBOW)
TERMINATION
ELBOW
GROUND LEVEL
12 in. MIN. OR ABOVE
ANTICIPATED SNOW
LEVEL.
COVER PLATE
(OPTIONAL)
RUBBER
COUPLING
Figure 33.
Important: All heaters equipped with the 181°F thermostat
control require that the first 5 ft. of the outlet vent pipe be
installed using the CPVC venting that is supplied with
the heater. If the first elbow is within this 5 ft. length, it
is required to be of CPVC material (field supplied) also.
Use of cellular core PVC (ASTM F891), cellular core
CPVC, or Radel
®
(polyphenylsulfone) in non-metallic
venting systems is prohibited.
Important: The exhaust vent piping must be connected
to the blower using the rubber coupling supplied with this
heater. This coupling contains the condensate trap and
is sized for the efficient flow of the exhaust gases. Failure
to use the coupling can result in an unsafe operating
condition and poor heater performance.
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