Figure 6
National Oilheat Research Alliance 27
For example:
We measure out a zone to
be a total of 80 feet, including
all the elements and the
supply and return piping to
the boiler.
Head = 80 X 1.5 x .04 =
4.8 foot of head.
A circulator that can provide
a total of 2.7 gallons
per minute and overcome
4.8 feet of head is therefore
required. This information
and calculation is often
shown in circulator performance
curves. Figure 6.
Looking at these performance
curves, the figures
along the bottom of the chart indicate flow in
gallons per minute (gpm), and along the left
side of the chart is the head produced in feet.
The curves represent what a circulator can produce.
Using the information that was calculated
for the zone, 2.7 gpm with 4.8 foot of head, we
plot that point on the curve.
Now look for what circulator
to choose based upon
the need of the system. If
circulator #1 was chosen for
the project, it would not heat
the home adequately when it
got colder outside.
The ideal circulator for this
job is #3.
Three-speed
Circulators
Three-speed circulators
are specifically designed for
the wide range of flow and
head requirements of today’s
heating systems. Their threespeed
switching capability
provides fine tuning control to match a wide
combination of system requirements. They are
an ideal replacement circulator type to use in
any emergency no-heat call. Figure 7.
When using a 3-speed circulator, use the
same calculations as before to choose the
proper speed setting the circulator will use. In
this case, the setting should be Low Speed.
Figure 7