Venting, Vertically Vented Unit Heaters Category

VENTING

ANSI now organizes vented appliances into four categories.

Venting Categories

	Non
	Condensing	Condensing
Negative
Vent	I	II
Pressure
Positive
Vent	III	IV
Pressure

Category I

Includes non-condensing appliances with negative vent pressure, like the traditional atmospheric unit heater.

Category II

Groups condensing appliances with negative vent pressure.

Category III

Appliances are non-condensing and operate with a positive vent pressure.

Category IV

Covers condensing appliances with positive vent pressure.

NOTICE: Category II and IV do not apply to equipment speciﬁed within this manual.

All unit heaters must be vented! All Venting installations shall be in accordance with the latest edition of Part 7, Venting of Equipment of the National Fuel Gas Code, ANSI Z223.1, or applicable provisions of local building codes. Refer to page 15 for Canadian installations. Refer to Figures 6, 7, 8A, 8B, 9A and 9B.

CARBON MONOXIDE! Your venting system must not be blocked by any snow, snow drifts, or any foreign matter. Inspect your venting system to ensure adequate ventilation exists at all times! Failure to heed these warnings could result in Carbon Monoxide Poisoning (symptoms include grogginess, lethargy, inappropriate tiredness, or ﬂu-like symptoms).

VERTICALLY VENTED UNIT HEATERS (CATEGORY I)

Observe the following precautions when venting the unit:

1.Use flue pipe of the same size as the flue connections on the gas unit heater (See Table #1). All heaters should be vented with UL Listed Type B vent, a factory built chimney, or a lined brick and mortar chimney that has been constructed in accordance with the National Building Code.

2.Provide as long a vertical run of ﬂue pipe at the gas unit heater as possible. A minimum of 5 feet (1.5m) of vertical ﬂue is required. The top of the vent pipe should extend at least 2 feet (0.61m) above the highest point on the roof. Install a weather cap over the vent opening.

3.Slope horizontal runs upward from the gas unit heater at least 1/4-inch per foot (21mm/m) minimum. Horizontal runs should not exceed 75% of the vertical height of the vent pipe, or chimney, above the ﬂue pipe connection, up to a maximum length of 10 feet (3m). Horizontal portions of the venting system shall be supported at maximum intervals of 4 feet (1.2m). (See Figure 6)

4.Use as few elbows as possible.

5.Tape ﬂue pipe joints with high-temp, RTV or foil face tape.

6.Avoid running vent pipe through unheated spaces.

7.When this cannot be avoided, insulate the pipe to prevent condensation of moisture on the walls of the pipe.

8.Do not damper the ﬂue piping. Failure to open such a damper prior to operating the gas unit heater will result in the spillage of flue gas into the occupied space.

9.Avoid installing units in areas under negative pressure due to large exhaust fans or air conditioning. When required, a ﬂue vent fan should be installed in accordance with the instructions included with the fan.

10.Vent connectors serving Category I and Category II heaters shall not be connected into any portion of mechanical draft systems operating under positive pressure.