Raypak MVB 503-2003 User Manual
Page 26
26
Common Venting
The NFGC does not address sizing guidelines for the
common venting of multiple Category IV heaters. This
is covered in the NFGC under “Engineered Vent Sys-
tems”. Table M provides boiler discharge vent
pressures at vent pressure switch and volumes of flue
products at full fire for the calculation of appropriate
vent and extractor sizing for common venting.
WARNING: Vent connectors serving any other
appliances shall not be connected into any portion of
mechanical draft systems operating under a positive
pressure. If an MVB heater is installed to replace an
existing heater, the vent system MUST be verified to
be of the correct size and of Category IV AL29-4C
vent material construction. If it is NOT, it MUST be
replaced.
NOTE: For extractor sizing, typical CO
2
levels are
8.5% for natural gas and 9.5% for propane gas and
flue temperature of 300° F.
Model
Vent
Size (in.)
Vent
Pressure
(in. WC)
Volume of
Flue Products
(CFM)
503
0.1
160
753
0.2
240
1003
6
0.3
320
1253
0.2
400
1503
0.3
480
1753
0.4
560
2003
8
0.5
640
* NOTE: Data for 100% firing rate.
Table M: Typical Vent Pressure and Volume
of Flue Products
Fig. 24: Typical Common Venting