Figure 20
This view, looking up a masonry chimney, shows
cracks and flaking of the liner due to condensation.
National Oilheat Research Alliance 21
Figure 19: Blocked vent switch installation diagram.
the heat loss of the building and allow smaller
Oilheat appliances to be installed.
Boilers and furnaces are much more efficient
than those that were available 40 years ago.
Common gross flue gas temperatures before
the energy crisis were in the 650–700 degree
range and typical firing rates ranged from
1.25–1.50 gallons per hour (gph).
Today’s high efficiency Oilfired heating sys-tems
have gross stack temperatures that typi-cally
range from 300–500 degrees with average
firing rates of .75–.85 gph.
All of these improvements have led to prob-lems
with chimneys that had functioned prop-erly
with older, less efficient Oilheat equip-ment.
Exhaust temperatures decrease as ef-ficiency
increases and chimney draft decreases
as the flue gas temperature drops. In addition,
flue gas temperature at the top of the chimney
decreases as the gross stack temperature drops.
Installing higher efficiency heating equipment
in larger and/or older chimneys increases the
probability of flue-gas condensation and related
chimney concerns. Figure 20.
Signs that a Chimney Needs
Repair/Relining
NORA recommends that Service Techni-cians
begin troubleshooting before they enter a
customer’s home or business. As the technician
approaches the building, he or she should look