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Vermont Castings UVS27 Vent-Free Gas Heater
20005004
Example:
A room that is 18' x 12' x 8' has a volume of 1728
cubic feet, ( length x width x height). An adjoining open
kitchen that is 10' x 12' x 8' has a volume of 960 cubic
feet. An adjoining open dining room is 12' x 12' x 8'
with a volume of 1152 cubic feet. The total space
volume is 3840 cubic feet. (1728 + 960 + 1152).
2. Divide the volume of space by 50 cubic feet. The
result is the maximum BTU/Hr that the space can
support.
Example:
3840 divided by 50 = 76.8 or 76,800 BTU/Hr.
3. Add the BTU/Hr ratings of all fuel-burning appli-
ances installed in the same space, including the
following:
Gas Water Heater Gas Furnace
Gas Fireplace Logs Unvented Gas Heater
Vented Gas Heater* Other Gas Appliances*
* Do not include Direct Vent appliances as these
utilize outside air for combustion and vent to the
outdoors.
Example:
Gas Range 55,000 BTU/Hr
Unvented Heater +33,000 BTU/Hr
Total 88,000 BTU/Hr
4. Compare the maximum BTU/Hr rating the space can
support with the total BTU/Hr used by the appliances.
Example:
76,800 BTU/Hr - max. the space can support
88,000 BTU/Hr - total used by appliances
In this example, the maximum BTU/Hr that the space
can support is less than the total used by the appli-
ances, the space is considered to be
Confined space
.
Additional air must be provided to meet the require-
ments of the Unvented heater.
WARNING
This heater shall not be installed in a confined
space or unusually tight construction unless
provisions are made for adequate combustion
and ventilation air.
WARNING
If the area in which the heater may be operated
is smaller than that defined as an unconfined
spaceof if the building is of unusually tight
constructins, provide adequate combustion and
ventilation air by one of the methods described
in the National Fuel Gas Code, ANSI Z223.1,
NFPA 54, Section 5.3 or applicable codes.
A confined space may be ventilated in two ways:
A) Open up or provide at least two ventilating grilles
to an adjoining unconfined space. Use any of the
options illustrated in Figure 8.
Each of the two grilles must provide an opening of
at least 50 square inches, with all opening dimensions
being at least 3". One grille must be located within 12"
of the ceiling; the other within 12" of the floor. (If the
total exceeds 100,000 BTU/Hr, additional grilles will be
required.)
B) Vent the room directly to the outdoors. (Provide
one square inch of opening for each 4,000 BTU/hr.
If the total BTU/Hr used by the appliances is less than
the maximum BTU/Hr the space is able to support, the
room meets the Unconfined space
criteria and no
further ventilation is required.
For further information on ventilation guidelines and
sizing specifications follow the National Fuel Gas Code
NFPA 54/ANSI Z223.1 Section 5.3.
12”
12”
Option 3 -
Vents to
Adjoining
Room
Option 1
Vents to
Adjoining
Room
Option 2 -
Remove
Door to
Adjoining
Rooms
VO370-2
Fig. 8 Vent options to provide additional air.