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Heat & Glo • ST-42TVFL-IPI • 455-902 Rev. C • 12/07
Step 3
Negative
Pressure
Make-up Air
Negative Pressure warning: When negative pressure
is present, an atmospherically vented fireplace (with a
draft hood) may not function properly and it may down
draft. In the case of a gas appliance, spillage of the
combustion gases may occur. This may create a
dangerous carbon monoxide situation in the house.
The causes of negative pressure to a house can include
the following:
• Stack effect in the building.
• Exhaust only appliances (mechanically and
atmospherically vented).
• Inadequate make-up air (which is increasingly
more prevalent in new construction).
NOTE: This fireplace will operate correctly only if
adequate ventilation is provided to allow proper draft to
the fireplace system. Heat & Glo assumes no
responsibility for the improper performance of the
fireplace system caused by inadequate draft due to
environmental conditions, down drafts, tight sealing
construction of the structure, or mechanical exhausting
devices which create a negative air pressure within the
structure where the fireplace is located.
It is recommended that all natural venting non-air tight
gas fireplaces have outside air connected to them. It
is also recommended that the building be
mechanically or passively balanced to allow
atmospherically vented appliances, such as top
vented gas fireplaces with draft hoods, to draft
properly. If the home experiences negative pressure
or is likely to experience negative pressure,
connection to an outside air source is mandatory.
Installing Optional Outside Make-up Air: This unit
is equipped to accept outside air. By using outside
make-up air, the amount of room air used for
combustion will be reduced. It is recommended that
an AK-TV air kit be used with this appliance.
WARNING: IN A NEGATIVE PRESSURE
CONDITION (LIKELY TO OCCUR IN NEW
HOMES THAT DO NOT HAVE ADEQUATE
MAKE-UP AIR) THE OUTSIDE AIR KIT
MUST BE INSTALLED TO OBTAIN
PROPER PERFORMANCE AND TO HELP
PREVENT SPILLAGE OF COMBUSTION
GASES.
A 4-inch damper assembly (found in AK-TV Kit) must be
installed to the fireplace. See Figure 5. Attach the
damper assembly to the outer wrap of the fireplace using
sheetmetal screws
!