Specifications
6
NBST27 Unvented Gas Log Set
This heater shall not be installed in a confined space or unusually tight construction unless provi-
sions are provided for adequate combustion and ventilation air.
, 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. An unconfined space is defined 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.
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
2
) 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 penetra-
tions for plumbing, electrical, and gas lines, and at
other openings.
L
2
L
1
W
H
FP2360
space
Inside Wall
Fireplace
Figure 1 -
Example of a Large Room
with a See-thru Unit as 1/2
Wall Divider
The following formula can be used to determine the maximum heater rating per the definition of
unconfined space:
BTU
/
Hr
=
(L1 + L2) Ft x (W) Ft x (H) Ft.
x 1000
BTU
/
Hr
50
Consider two connecting rooms with an open area between, with the following dimensions:
L
1
= 15Z\x Ft., L
2
= 12 Ft., W = 12 Ft., H = 8 Ft.
BTU
/
Hr
=
(15Z\x + 12) x (12) x (8)
x 1000 = 52800
BTU
/
Hr
50