outside exposed chimneys can cause drafting
problems. Figure 12 above.
When that happens, a draft inducer (aka a
“draft fan”), in conjunction with a control kit,
can be installed to provide the necessary draft.
A draft fan should be installed as close to the
chimney as practical and must be electrically
interlocked with the appliance, utilizing a prov-ing
circuit before combustion takes place.
How Draft Inducers Work
Figure 13, on preceding page, illustrates
how draft inducers, installed with a control kit,
provide necessary draft when needed.
18 National Oilheat Research Alliance
Flue Pipe (Chimney Connector)
Flue pipe sizing is determined by the appli-ance
manufacturer. Figure 14.
There are a number of regulations in NFPA
31 regarding the connection between the appli-ance
and the chimney. Technicians should refer
to the current edition of the standard and the
local authority having jurisdiction for the most
up-to-date requirements. The 2011 version of
NFPA 31 requires the following for natural
draft appliances (Figure 15):
1. The flue pipe must be at least 18" from a
combustible wall or ceiling.
2. The flue pipe must maintain a pitch or
rise of at least ¼ in./ft. of horizontal length of
pipe from the appliance to the
chimney.
3. The horizontal length of
a flue pipe must not exceed
10' unless a draft fan is used.
Figure 12
Figure 14
Draft Inducer