Thomas & Betts UDAP - Manual (Page 8)

Form RZ-NA I-UDA, P/N 195673 Rev 5, Page 8
Confined Space:
A space whose volume is
less than 50 cubic feet
per 1000 BTUH of the
installed appliance input
rating
Combustion Air
Requirements for
a Heater Located
in a Confined
Space - applies to
Model UDAP and
Model UDAP-CV
FIGURE 5 - Definition of
Confined Space and
Required Openings for
Combustion Air
(3)
(3)
(1)
(1)
(2)
(2)
Confined
Space
9. Combustion
Air - applies to
Model UDAP
and Model
UDAP-CV
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.
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.
(Note: For Model
UDAS, see Venting
Manual for
combustion air
requirements.)
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).