Direct-vent systems are sold
as complete listed and approved
packages. Mixing and matching
components and/or do-it-yourself
engineering is not approved and
creates hazardous conditions.
With both chimney venting and
power venting, each joint of the flue
pipe must be fastened with at least
three screws. Since direct vent sys-tems
are under positive pressure,
there should not be any screws into
the flue pipe. Typical manufacturer's
instructions say, “Do not install
screws into or otherwise penetrate
any part of the vent pipe under any
circumstances.”
National Oilheat Research Alliance 31
8. Check the barometric draft control to
insure the gate swings freely.
9. Check the safety system devices—start the
heating system, and then disconnect the pres-sure
sensing tube from the pressure switch—
this should stop the burner. Reconnecting the
tube should restart the burner.
10. Correct all deficiencies found and adjust
the appliance to the manufacturer’s specifica-tions.
Direct Venting
Direct-vent Oilheat systems use the power of
the burner fan to push products of combustion
through the appliance to the venting system
and out of the building (Figure 9). They require
high static pressure burners and outside air is
used for combustion.
Unlike chimney venting and power vent-ing,
the appliance exhaust is under positive
pressure. If there is a leak in the exhaust pipe,
products of combustion will leak into the build-ing.
The intake is under negative pressure and
must be sealed according to manufacturer’s
instructions to prevent chamber pressure imbal-ances
that lead to nuisance lock-outs. Because
of this, it is critically important that the system
be completely sealed according to the manu-facturer’s
instructions.
It is always important to follow manufac-turer’s
instructions but special mention is
made here because the instructions may be
significantly different from those with which an
installer is familiar.
For example, consider this statement:
“PB Heat, LLC requires that the vent slopes
down 1/4" per foot towards the vent terminal.
This takes precedence over the requirements
shown in the Z-Flex manual.”
If the installer followed the flue manufac-turer’s
instructions, rather than the appliance
manufacturer’s, the appliance may not operate
properly and/or may present a safety hazard.
Installation Considerations
The installation criteria for a direct vent
system are similar to those for power vent
systems, with a few differences:
• All joints on the venting system must be
sealed with a high temperature sealant.
Figure 9