5
Adequate Combustion And Ventilation Air Options:
• Increase
the
Maximum Supportable Btu/Hr
by adding to the number of rooms which comprise the "Space".
To do this you must ether completely remove the door to an adjoining room or provide two permanent ventilation
grills; one within 12" of the ceiling and another within 12" of the floor.
• Increase
the
Maximum Supportable Btu/Hr
by providing extra fresh air using ventilation grills and ducts to the
outdoors. You must provide two permanent openings, one within 12" of the ceiling and another within 12" of the
floor. Connect these directly to the outdoors or spaces open to the outdoors, e.g., attics or crawl spaces.
• Follow
the
National Fuel Gas Code NFPA 54/ANSI Z223.1, Section 5.3, Air for Combustion and Ventilation
for
required size of ventilation grills or ducts.
• Lower
the
Actual Btu/Hr Used
by relocating other gas burning appliances outside the "space" or installing a
lower Btu/Hr heater. In the example, the maximum Btu/Hr of the heater could be no more than 28,160 Btu/Hr.
For our example, we have chosen to add to our
Total Volume of the Space
by removing the door to an adjoining
study and increasing our
Maximum Supportable Btu/Hr
by the volume of the additional room. The new "space"
calculations, including the additional adjoining room are:
Living room/dining room & Kitchen
3008 cu ft
Study (9' x 10' x 8')
720 cu ft
Total volume of space
3728 cu ft
The new Maximum Supportable Btu/Hr = (3728 cu ft ÷ 50 cu ft ) x 1000 = 74,560 Btu/Hr
74,560
Btu/Hr
=
Maximum
Supportable
Btu/Hr
-
72,000 Btu/Hr = Actual Btu/Hr Used
2,560
Btu/Hr
=
Remaining
Supportable
Btu/Hr
Because the
Actual Btu/Hr
used is now less than the
Maximum Supportable Btu/Hr
, the space is
considered an
Unconfined Space
. No additional fresh combustion and ventilation air would be required.
VENT FREE OPERATION
COMBUSTION AIR CALCULATIONS WORKSHEET
1.
Room Width Length Height W
x
L
x
H=Vol. (ft3)
1a.
1b.
1c.
1d.
2. Total Volume (ft3)
sum of Volume (ft3) of all rooms (sum lines 1a. thru
1d.)
2.
3. Max Supportable BTu/Hr
=Total Volume (ft3) ÷ 50 x 1000 (line 2 ÷ 50 x1000)
3.
4. 4a.
3
Btu/hr
4b.
3
Btu/hr
4c.
3
Btu/hr
4d.
3
Btu/hr
Actual Btu/hr used
= Sum Btu/hr of all fuel burning appliances inside the space
identified as rooms 1a. thru 1.b (sum
line 4a thru 4d.)
4.
5. (Maximum Supportable BTu/Hr)
minus
(Actual BTu/hr Used)
(Line 3 - line 4)
5. *
* If
Line
5
is greater than zero, the
Actual BTu/Hr Used
is
less
than the
Maximum Supportable BTu/Hr
and
the space is considered
UNCONFINED
.
No additional fresh combustion and ventilation is required.
* If
Line
5
is zero or less, the
Actual BTu/Hr Used
is
greater
than
Maximum Supportable BTu/Hr
and the
space is
CONFINED.
You must either
increase
the
Maximum Supportable BTu/Hr, decrease
the
Actual
BTu/Hr Used
or
operate as a Vented Appliance
(see page 4).
WARNING: If the area in which the heater may be operated is smaller than that defined as an
unconfined space or if the building is of unusually tight construction, provide adequate
combustion and ventilation air by one of the methods described in the National Fuel Gas Code,
ANSI Z223.1, 1992, Section 5.3 or applicable local codes.
Unusually tight construction is construction where:
a) Walls and ceilings exposed to the outside atmosphere have a continuous water vapor retarder
with a rating of 1 perm or less with openings gasketed or sealed, and
b) Weather stripping has been added on openable windows and doors, and
c) Caulking or sealants are applied to areas such as joints around window and door frames,
between sole plates and floors, between wall panels, at penetrations for plumbing, electrical, and
gas lines, and at other openings.
