5
76683
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 one perm
(6 X 10.
11
kg per pa-sec-m
2
) 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-ceiling joints, between wall panels, at
penetrations for plumbing, electrical and gas lines and at
other openings.
If your home meets all of the three criteria above, you must
provide additional fresh air.
You may provide two permanent openings: one within 12" of
the ceiling and one within 12" of the floor. Connect these items
directly to the outdoors or spaces open to the outdoors. These
spaces include attics and 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.
IMPORTANT: Do not provide openings for inlet or outlet air into
attic if attic has a thermostat-controlled power vent. Heated air
entering the attic will activate the power vent.
L
W
D
Flue Damper Closed for Unvented
Operation and Maximum Heat
Output
Flue Damper Locked Open
to a Minimum Free (Vent)
Opening of 15 sq. in., (for
areas where unvented
products are not permitted)
NOTE: For round flue opening,
minimum flue diameter (d) = 5”. For
square or rectangular opening,
length x width (L x W) must equal 15
sq. in.
T104
Fig. 1 Minimum flue diameter and flue damper positions.
Option 1 -
Vents to
Adjoining
Room
Option 2 -
Remove
Door to
Adjoining
Room
Option 3 -
Vents to
Adjoining
Room
12”
12”
VO370-2
Fig. 2 Ventilation options for confined space.
WARNING: Air openings that
provide fresh air from an adjoin-
ing unconfined space shall not be
blocked or obstructed in any way.
Installation of unit should allow a
minimum of 2" clearance from any
part of the heater to any of the
ventilation openings.