Calculating Equivalent Feet - A.O. Smith GPVX 75L Series Installation And Operating Manual

Calculating Equivalent Feet

WATER HEATER VENT SIZE
HEATER INPUT
MODEL (Btu/hr)
75 gal. 76,000
* 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
3"
90° elbow
4"
3"
45° elbow
4"
COVER PLATE
(OPTIONAL)
TERMINATION
ELBOW
RODENT
SCREEN
(INSTALL INTO
ELBOW)
300mm (12 in.)
MIN. OR ABOVE
Example for calculating equivalent feet.
ANTICIPATED SNOW
Section "A"
LEVEL.
90° elbow
Section B
45° elbow
Section C
45° elbow
Section D
Total Equivalent 10.2m
Based on this example use the (fully open) rodent
GROUND LEVEL
screen for vent length greater than 6 equivalent
metres (20 equivalent ft.) (see Figure 26).
Important: All heaters equipped with the 181°F thermostat control require that the first 1.5m (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 1.5m (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
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.
100271597
PRESSURE
(Inside SWITCH
Diam.) SETTING
3"
-0.90 in. w.c.
4"
Short Sweep/ Long Sweep/
Short Radius Long Radius
8' (2.44m)
4' (1.22m) 2.5' (0.76m)
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 floor 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 300mm (1 ft.) upward slope to ensure proper drainage.
150mm (0.5 ft.)
2.4m (8.0 ft.)
300mm (1.0 ft.)
1.2m (4.0 ft.)
450mm (1.5 ft.)
1.2m (4.0 ft.)
4.5m (15.0 ft.)
(34.0 ft.)
MAXIMUM EQUIVALENT
VENT LENGTH
50' (15m) + termination
elbow and screen*
125' (38m) + termination
elbow and screen*
Notes:
1. Use long radius elbows where possible. Minimum
distance between 90º elbows should be 150mm
5' (1.5m)
(6 in.) wherever possible.
2. Venting systems may use a maximum of five (5)
90° elbows.
3. Use proper screen termination (see Figure 26).
Table 2
STRAP
Figure 27
® (polyphenylsulfone) in non-metallic venting
MINIMUM EQUIVALENT VENT
LENGTH
7' (2m) + termination elbow and
screen*
50' (15m) + termination elbow
and screen*
45° SHORT
ELBOW
90° SHORT
ELBOW
RUBBER
COUPLING
27