331432-001
27
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’ (15m) + termination
elbow and screen*
7’ (2m) + termination elbow and
screen*
4”
125’ (38m) + termination
elbow and screen*
50’ (15m) + termination elbow
and screen*
* see Figure 26, “Venting terminations and sizing” and “Vent screen installation”.
Equivalent lengths of straight pipe for various elbows using Schedule 40 PVC, CPVC 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 150mm
(6 in.) wherever possible.
2. Venting systems may use a maximum of
fi
ve (5)
90° elbows.
3. Use proper screen termination (see Figure 26).
3"
4"
90° elbow
8’ (2.44m)
5’ (1.5m)
3"
4"
45° elbow
4’ (1.22m)
2.5’ (0.76m)
Table 2
Note:
Use only Schedule 40 CPVC piping and
fi
ttings for the
fi
rst linear 1.5m (5 ft.) of the outlet vent system.
Example for calculating equivalent feet.
Section “A”
305mm
(0.5 ft.)
90° elbow
2.4m
(8.0 ft.)
Section B
610mm
(1.0 ft.)
45° elbow
1.2m
(4.0 ft.)
Section C
450mm
(1.5 ft.)
45° elbow
1.2m
(4.0 ft.)
Section D
4.5m
(15.0 ft.)
Total Equivalent 10.7m
(34.0 ft.)
Based on this example use the (fully open) rodent
screen for vent length greater than 6 equivalent
metres (20 equivalent ft.) (see Figure 26).
Note:
The vent pipe must be supported every 1.2m (4 ft.). To prevent vibration and sagging, it is recommended
to use isolation pads when attaching straps to
fl
oor joists, walls or ceilings. PVC and CPVC vent pipe should be
sloped upwards away from the blower assembly at a pitch of 3mm (1/8 in.) rise per 1.2m (4 ft.). Polypropylene
vent systems require a 6.5mm (1/4 in.) per 305mm (1 ft.) upward slope to ensure proper drainage.
STRAP
45° SHORT
ELBOW
90° SHORT
ELBOW
RODENT
SCREEN
(INSTALL INTO
ELBOW)
TERMINATION
ELBOW
GROUND LEVEL
305mm (12 in.)
MIN. OR ABOVE
ANTICIPATED SNOW
LEVEL.
COVER PLATE
(OPTIONAL)
Figure 28
