16
7. Intake Venting
(Continued...)
c.)
Boiler located in a room under negative pressure:
If the boiler is to be installed within a home where the operation of exhaust fans,
attic fans, kitchen ventilation systems, clothes dryers or fireplaces may create
severe negative vent pressures causing unsatisfactory combustion and venting,
special provisions should be made for additional make-up air to supply the other
air requirements. If building is of tight construction, combustion air requirements
may not be met and combustion air ducts from outside may be necessary. Please
refer to NFPA No. 31.
Tight Construction (as defined by ANSI Z223.1):
1. Walls and ceilings exposed to the outside atmosphere have a continuous water
vapor retarder with a rating of 1 perm or less with openings sealed with gaskets,
etc..
2. Weather-stripping has been added on open able windows and doors, and
caulking or sealants are applied to areas such as: joints around windows and
door frames, between sole plates and floors, between wall ceiling joints, between
wall panels, at penetrations for plumbing, electrical, and gas lines, and in other
openings.
If the building is of tight construction, air openings must be provided from the
outside, with appropriate sizing depending on amount of BTU/HR as shown in
Figure A. The boiler room must never be under a negative pressure, even if the
appliance is installed as direct vent. Always provide air openings sized not only to
the dimensions required for the firing rate of all appliances, but also to handle the
air movement rate of the exhaust fans or air movers using air from the building or
boiler room.
4,000
Figure A.
