Horizontally VENTED, Category III Figure

STANDARD COMBUSTION

HORIZONTALLY VENTED, CATEGORY III - Figure 15

Vent Systems

Termination Clearance Requirements

			Minimum
	Structure		Clearances for
			Termination
			Locations

			4 feet
			below

	Door, window or		4 feet
	any gravity air inlet		horizontally

			1 foot
			above

	Forced air inlet within 10 ft.		3 feet
	Forced air inlet within 10 ft.		above
			above

	Adjoining building or parapet		6 feet

	Adjacent public walkways		7 feet
	Adjacent public walkways		above grade
			above grade

Observe the following precautions when venting the unit:

1.Use ﬂue pipe of the same size as the ﬂue connection(s) on the gas unit heater, 4" (102mm). All heaters must be vented with a single or double wall pipe listed for category III positive pressure vent systems.

Type B double wall pipe can be used with limitations as shown in Figure 15B. As illustrated, a single 5 foot (1.52m) section of Type B vent pipe with a draft hood connector may be used between the appliance vent connection and the vent terminal. Use Metalbestos Type B gas vent with a Metalbestos 4RV-DH draft hood connector, or, an Amerivent Type B gas vent with an Amerivent 4EDC draft hood connector.

2.Each unit must have an individual vent pipe and vent terminal. Unit MUST NOT be connected to other vent systems or to a chimney.

3.Category III units are limited to a maximum of 40 feet (12.19m) equivalent length of vent pipe. Equivalent length is the total length of straight sections PLUS 5 feet (1.5m) for each 90 degree elbow and 2.5 feet (.75m) for each 45 degree elbow.

4.If using a single section of Type B vent pipe, seal the annular space between the inner and outer sections of the draft hood connector with a high temper- ature silicone sealant. Use General Electric RTV-108, Dow- Corning RTV-732, or equivalent silicone sealant with a temper- ature rating of 500 deg. F. See Figure 15C. Attach the draft hood connector to the appliance vent connection with screws (3 minimum) and seal the joint with silicone sealant. Install a Type B vent thimble in the wall. Insert the vent pipe through the thimble and attach it to the adapter on the appliance. Seal the joint with silicone sealant or two wraps of aluminum foil tape. Install a vent cap on the outlet pipe and secure with screws (3 minimum).

5.An Amerivent Americap or Metalbestos vent cap must be supplied by the customer for

each power vented unit. The vent pipe diameter must be 4 inches (102mm).

6.Through the wall venting for these appliances shall not terminate over public walkways, or over an area where the condensate or vapor could create a nuisance, hazard, or could be detrimental to the operation of regulators, relief valves, or other equipment, see Figures 15A, 16 and 18.

7.The vent terminal must be at least 3 feet (1m) above grade, or in snow areas, at least 3 feet above the snow line to prevent blockage by snow.

8.The vent terminal must be at least 12 inches (305mm) from the exterior of the wall that it passes through to prevent degradation of the building materials by ﬂue gasses.

9.Maintain 1 - inch (25 . 4mm) clearance between the vent pipe and combustible materials.

10.Seal all vent pipe joints and seams to prevent leakage. Use General Electric RTV-108, Dow- Corning RTV-732, or equivalent silicone sealant with a temper- ature rating of 500 deg.F, or 3M #425 aluminum foil tape (or equivalent). The vent system must be installed to prevent collection of condensate. Pitch horizontal pipes downward 1/4 inch per foot (21mm per meter) toward the outlet for condensate drainage. Install a tee with a condensate drain at the low point of the pipe (see Figure 15A). As an alternate, a 3/8 inch diameter hole may be drilled at the low point of the pipe for condensate drainage.

11.Horizontal portions of the venting system shall be supported at minimum intervals of 4 feet (1.2m) to prevent sagging (in Canada, support at 3 foot (1m) minimum intervals).

12.Avoid running vent pipe through unheated spaces. When this cannot be avoided, insulate the pipe to prevent condensation of moisture on the walls of the pipe.