Chapter 3
Alternative Venting Systems
Figure 2
Figure 1
Conduction
Advantages
National Oilheat Research Alliance 25
With chimney venting, the flue gases travel
through the heating appliance and up the vent-ing
system because hot gases naturally rise.
Today’s high-efficiency appliances absorb
more heat and produce lower temperature flue
gases that do not rise as quickly, or as reliably,
as they do with older, less efficient systems.
As discussed in Chapter 2, these lower flue gas
temperatures often require chimney liners to
be installed when high efficiency appliances
are installed. One alternative to chimney lining
is to install an alternative venting system that
does not rely on high temperature flue gases.
This chapter will explain two types of al-ternative
venting systems for non-condensing
Oilheat appliances.
Power-venting: a fan, attached to the flue
pipe where it exits the building, pulls the flue
gases out of the heating unit. According to
NFPA-31, power venting is “The application of
a mechanical means of removing combustion
products to the outside atmosphere.”
See Figure 1.
Direct-venting: the
static pressure created
by the burner pushes the
combustion gases through
the heat exchanger and
out of the building.
Figure 2.
Both of these types of
venting are often referred
to as sidewall venting.
Direct venting requires
that the oil burner primary control has valve-on
delay and burner-motor-off delay features.
Power venting requires that the oil burner
primary control has valve-on delay and burner-motor-
off delay features and/or the vent must
have pre-purge and post-purge cycles.
Figure 1
The advantages of alternative
venting systems include:
• Better draft control
• No cold chimney problems
• Lower initial cost than a chimney
• Less floor and wall space used
• Elimination of back drafts
• Reduction in standby losses