Form I-VR (10-14), P/N 205202 R14, Page 30
DANGER: The fresh air requirement of 4 CFM per 1000 BTUH
for natural gas and 5 CFM per 1000 BTUH for propane gas is
mandatory when operating a heater in the unvented mode. See
Hazard Levels, page 2.
•
Do not
operate in the unvented mode if there is any doubt about the qual
-
ity of the insulation in the building. Unvented operation in a building that
has an uninsulated roof or that may have uninsulated structural members
partially exposed to the outdoors may result in condensation. The conden
-
sation may be severe enough to drip and/or cause corrosion.
•
Do not
install in the unvented mode with outside combustion air unless the
inlet air cap is at or below the plane of the heater.
When installing a heater in the unvented mode, a vent cap must be used and
must be inverted as illustrated in
FIGURE 29
. Install the elbow as shown in
FIG-
URE 25
but in addition to securing the elbow with one screw on the top, secure
it to the compression coupling using two additional non-corrosive sheetmetal
screws with all three screws spaced approximately 120° apart. Attach the vent
cap to the 90° elbow in the same manner with three sheetmetal screws.
When a heater is operated without being vented to the outdoors,
the TOP
clearance to combustibles is 18” (457mm); see Paragraph 4.3.
The burner is equipped with a centrifugal blower to provide combustion air. The
air for combustion can come either from the heated space or be piped directly
from the outside. Combustion air should be piped from the outside if (1) the
pressure in the building is negative, (2) the atmosphere is dirt laden, (3) the
atmosphere contains any substance that will cause toxic gas when passed
through a flame, or (4) the heater is installed in a tightly closed room that does
not provide required air for combustion.
If drawing combustion air from the heated space,
the screened combus
-
tion air opening on the burner box must be kept clean. Maintain a minimum 12”
clearance from the combustion air inlet opening. If the heater is located in a
tightly closed room and is not equipped with a combustion air inlet pipe, provi
-
sion must be made to supply air for combustion to the room.
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 aggregate input rating of all appliances installed in that space. Under all
conditions, enough air must be provided to ensure there will not be a negative
pressure condition within the equipment room or space.
Do not install a unit in a confined space without providing wall openings lead
-
ing to and from this space. Provide adequate openings near floor and ceiling
for ventilation and air for combustion, as shown in
FIGURE 30
, depending on
combustion air source as noted below.
6.4.4 Combustion Air
FIGURE 30 -
Combustion Air
and Ventilation
Requirements for a
Confined Space
Confined Space: A space whose
volume is less than 50 cubic feet
per 1000 BTUH of the aggregate
input rating of all appliances
installed in that space.
6.4 Venting and
Combustion Air
(cont’d)
6. Mechanical
(cont’d)
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.
6.4.3 Unvented Installation (cont’d)