Thomas & Betts UDAS Combustion Air applies to Model Udap and Model, Model Udap and Model UDAP-CV

9.Combustion Air - applies to Model UDAP and Model

UDAP-CV

(Note: For Model UDAS, see Venting Manual for combustion air requirements.)

This heater must be supplied with the air that enters into the combustion process and is then vented to the outdoors. Sufficient air must enter the equipment location to replace that exhausted through the heater vent system. In the past, the infiltra- tion of outside air assumed in heat loss calculations (one air change per hour) was assumed to be sufficient. However, current construction methods using more insu- lation, vapor barriers, tighter fitting and gasketed doors and windows, weather- stripping, and/or mechanical exhaust fans may now require the introduction of outside air through wall openings or ducts.

The requirements for combustion and ventilation air depend upon whether the unit is located in a confined or unconfined space. An "unconfined space" is defined as a space whose volume is not less than 50 cubic feet per 1000 BTUH of the installed appliance. Under ALL conditions, enough air must be provided to ensure there will not be a negative pressure condition within the equipment room or space.

WARNING: Model UDAP and UDAP-CV power-vented unit heaters are designed to take combustion air from the space in which the unit is installed and are not designed for connection to outside combustion air intake ducts. Connecting outside air ducts voids the warranty and could cause hazardous operation. See Hazard Levels, page 2.

Combustion Air Requirements for a Heater Located in a Confined Space - applies to

Do not install a unit in a confined space without providing wall openings leading to and from the space. Provide openings near the floor and ceiling for ventilation and air for combustion as shown in FIGURE 5, depending on the combustion air source as noted in Items 1, 2, and 3 below.

Add total BTUH of all appliances in the confined space and divide by figures below for square inch free area size of each (top and bottom) opening.

Model UDAP and Model UDAP-CV

FIGURE 5 - Definition of Confined Space and Required Openings for Combustion Air

Confined Space:

A space whose volume is less than 50 cubic feet per 1000 BTUH of the installed appliance input rating

(3) (1) (2)

Confined

Space

(3) (1) (2)

1.Air from inside the building -- openings 1 square inch free area per 1000 BTUH. Never less than 100 square inches free area for each opening. See (1) in FIGURE 5.

2.Air from outside through duct -- openings 1 square inch free area per 2000 BTUH. See (2) in FIGURE 5.

3.Air direct from outside -- openings 1 square inch free area per 4000 BTUH. See (3) in FIGURE 5.

NOTE: For further details on supplying combustion air to a confined space, see the National Fuel Gas Code ANSI Z223.1a (latest edition).

Form RZ-NA I-UDA, P/N 195673 Rev 5, Page 8