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.
PROVISIONS FOR ADEQUATE COMBUSTION AND VENTILATION AIR
5
Figure
Figure 2
Ventilation Air from Inside
WARNING: Air openings that provide fresh air from an adjoining
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.
