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Confined and Unconfined Space
The National Fuel gas Code, ANSI
Z223.1/NFPA 54 defines a confined space as
a space whose volume is less than 50 cubic
feet per 1,000 Btu per hour (4,8 m
3
per kw) of
the aggregate input rating of all appliances
installed in that space and an unconfined
space as a space whose volume is not less
than 50 cubic feet per 1,000 Btu per hour (4,8
m
3
per kw) of the aggregate input rating of all
apliances installed in that space. Rooms com-
municating directly with the space in which the
appliances are installed*, through openings
not furnished with doors, are considered a
part of the unconfined space.
*Adjoining rooms are communicating only if
there are doorless passageways or ventilation
grilles between them.
DETERMINING FRESH-AIR FLOW FOR
HEATER LOCATION.
Determining if you have a confined or uncon-
fined space.
Use this work sheet to determine if you have a
confined or unconfined space.
Space: includes the room in which you will
install heater plus any adjoining rooms with
doorless passageways or ventilation grilles
between the rooms.
1. Determine the volume of the space (length
x width x height).
length x width x height =________ cu.ft.
(volume of space)
Example: space size 20ft. (length) x 16 ft
(width) x 8ft (ceiling height) = 2560 cu. ft.
(volume of space)
If additional ventilation to adjoining room
is supplied with grilles or openings, add
the
volume of these rooms to the total volume
of the space.
2. Multiply the space volume by 20 to deter-
mine the maximum Btu/Hr the space can
support.
________ (volume of space) x 20= 51.200
(maximum Btu/Hr the space can support)
Example:2560 cu. ft (volume of space) x
20= 51.200 (maximum Btu/Hr the space
can support)
3. Add the Btu/Hr of all fuel burning appli-
ances in the space.
Vent-free heater ____________ Btu/Hr
Gas water heater* ____________ Btu/Hr
Gas furnace ____________ Btu/Hr
Vented gas heater ____________ Btu/Hr
Gas fireplace logs ____________Btu/Hr
Other gas appliances* +________Btu/Hr
Total =___________ Btu/Hr
* Do not include direct-vent gas appliances. Direct-
vent draws combustion air from the outdoors and
vents to the outdoors.
Example
Gas water heater* 40,000
Btu/Hr
Vent-free heater + 20,000
Btu/Hr
Total = 60,000
Btu/Hr
4. Compare the maximum Btu/Hr the space
can support with the actual amount of
Btu/Hr used.
Btu/Hr (maximum the space can
support)
Btu/Hr (actual amount of Btu/Hr used)
Example: 51,200 Btu/Hr (maximum the space
can support)
60,000 Btu/Hr (actual amount of Btu/Hr
used)
The space in the above example is a confined
space because the actual Btu/Hr used is more
than the maximum Btu/Hr the space can sup-
port. You must provide additional fresh air.
Your options are as follows:
A. Rework worksheet, adding the space of an
adjoining room. If the extra space pro-
vides an unconfined space, remove door
to adjoining room or add ventilation grills
between rooms. See ventilation air from
inside building, page 4
B. Vent room directly to outdoors. See ventila-
tion air from outdoors, page 4
C. Install a lower Btu/Hr heater, if lower
Btu/Hr size makes room unconfined.
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WIR 2 26-06-2003 18:21 Pagina 5