Form RZ-NA-I-FT, Mfg No. 173473 Rev 8, Page 3
Pressure Switch
Figure 1 - Pressure Switch Location (above 6000 ft,
replace with a pressure switch set for high altitude
operation)
5. Clearances and
Combustion Air
Units must be installed so that the clearances in the table are
provided for combustion air space, inspection and service, and
for proper spacing from combustible construction. Clearance to
combustibles is defined as the minimum distance from the heater
to a surface or object that is necessary to ensure that a surface
temperature of 90°F above the surrounding ambient tempera-
ture is not exceeded.
This fuel-burning heater must be supplied with the air that en-
ters into the combustion process and is then vented to the out-
doors. Sufficient air must enter the equipment location to re-
place that exhausted through the heater vent system. In the past,
the infiltration of outside air assumed in heat loss calculations
(one air change per hour) was assumed to be sufficient. How-
ever, current construction methods using more insulation, 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 ap-
pliance.
Under all
conditions
, enough air must be provided to
ensure there will not be a negative pressure condition within the
equipment room or space. For specific requirements for con-
fined space installation, see Paragraph 6.
WARNING: These 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 1.
6. Combustion Air Requirements for
a Heater Located in a Confined
Space
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 2, 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.
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 2.
2. Air from outside through duct
-- openings 1 square inch free area per
2000 BTUH. See (2) in Figure 2.
3. Air direct from outside
-- openings 1 square inch free area per 4000 BTUH.
See (3) in Figure 2.
NOTE:
For further details on supplying combustion air to a confined space,
see the National Fuel Gas Code ANSI Z223.1a (latest edition).
7. Unit Heater Location
Suspend the heater so that it is a minimum of five feet (1.5M) above the floor.
Other clearances are listed in Paragraph 5.
WARNING: If touched, the vent pipe and certain
internal heater surfaces that are accessible from
outside the heater will cause burns. Suspend the heater
a minimum of 5' (1.5M) above the floor.
For best results, the heater should be placed with certain rules in mind. In
general, a unit should be located from 8 to 12 feet (2.4-3.7M) above the floor.
Units should always be arranged to blow toward or along exposed wall sur-
faces, if possible. Where two or more units are installed in the same room, a
general scheme of air circulation should be maintained for best results.
Suspended heaters are most effective when located as close to the working
zone as possible, and this fact should be kept in mind when determining the
mounting heights to be used. However, care should be exercised to avoid
directing the discharged air directly on the room occupants.
Partitions, columns, counters, or other obstructions should be taken into con-
sideration when locating the unit heater so that a minimum quantity of airflow
will be deflected by such obstacles.
When units are located in the center of the space to be heated, the air should
be discharged toward the exposed walls. In large areas, units should be lo-
cated to discharge air along exposed walls with extra units provided to dis-
charge air in toward the center of the area.
At those points where infiltration of cold air is excessive, such as at entrance
doors and shipping doors, it is desirable to locate the unit so that it will dis-
charge directly toward the source of cold air from a distance of 15 to 20 feet
(4.6-6.1M).
CAUTION: Do not locate the heater where it may be
exposed to water spray, rain or dripping water.
Figure 2 - Confined
Space: A space
whose volume is less
than 50 cubic feet
per 1000 BTUH of
the installed
appliance input
rating
Confined
Space
Required Clearances - inches and millimeters
Model S izes
inche s mm inche s mm inche s mm
Top
1
25
6
152
6
152
Flue Connector
6
152
6
152
6
152
Access Panel
18
457
24
610
24
610
Non-Access S ide
1
25
6
152
6
152
Bottom*
1
25
1
25
1
25
Rear
18
457
18
457
24
610
30, 45, 60,
75
100, 125,
150, 200
250, 300
*A Model FT 30, 45, 60, 75 installed in a residential garage
must be installed a minimum clearance above the floor of 18
inches (457mm). Sizes 100-300 are not certified for residential
installation.
