Raypak 503-2003 manual Common Venting, Volume of, Model, Pressure, Flue Products, in. WC

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 CO2 levels are 8.5% for natural gas and 9.5% for propane gas and flue temperature of 300° F.

	Vent	Vent	Volume of
Model		Pressure	Flue Products
	Size (in.)
		(in. WC)	(CFM)
503		0.1	160
	6
753		0.2	240
1003		0.3	320
1253		0.2	400
1503	8	0.3	480
1753		0.4	560
2003		0.5	640

* NOTE: Data for 100% firing rate.

Table M: Typical Vent Pressure and Volume

of Flue Products

Fig. 24: Typical Common Venting

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