Monessen Hearth DFX24C - Manual (Page 8)

8 33D4047
DFX & DBX Series Vent Free Fireplaces
ADEQUATE COMBUSTION AND VENTILATION AIR
This heater shall not be installed in a confined space or unusually tight construction unless
provisions are provided for adequate combustion and ventilation air.
The National Fuel Gas Code, (ANSI Z223.1/NFPA54), 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 aggre-
gate 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 appliances installed in that space. Rooms communicating directly
with the space in which the appliances are installed, through openings not furnished with doors,
are considered a part of the unconfined space.
UNUSUALLY TIGHT CONSTRUCTION IS DEFINED AS CONSTRUCTION
WHERE:
a) walls and ceilings exposed to the outside atmosphere have a continuous water vapor
retarder with a rating of 1 perm
(6 x 10
11 kg per pa/sec-m  ) or less with openings gasketed or sealed;
b) weather striping 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-ceiling joints, between wall panels, at pen-
etrations for plumbing, electrical, and gas lines, and at other openings.
The following formula can be used to determine the maximum heater rating per the definition
of unconfined space:
(L
1
+ L

) Ft x (W) Ft x (H) Ft
50
Consider two connecting rooms with an open area between, with the following dimensions:
L
1
= 15Z\x Ft., L

= 1 Ft., W = 1 Ft., H = 8 Ft.
(15Z\x + 1) x (1) x (8)
50
If there were a door between the two rooms the calculation would be based only on the room
with the heater.
(15Z\x) x (1) x (8)
50
x 1000
x 1000 = 5800 BTU/hr
x 1000 = 9,760 BTU/hr
BTU/hr =
BTU/hr =
BTU/hr =
COMBUSTION and VENTILATION AIR
W
H
FP2439
combustion air
Room Divider
Fireplace
Figure 3 -
Example of a Large Room with a Room
Divider
FP439
W
ARNING
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/NFPA54, Air for
Combustion and Ventilation or applicable
local codes.