QHT B3-B9 installation instructions Figure a

6. Intake Venting Cont.

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/H as shown in pictures. 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.

Figure A.

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