ability to flow through the lines, pass through
the filter and be fully atomized in the nozzle.
As the fuel becomes even colder it begins to
gel, leading to what is commonly called “frozen”
fuel lines.
Free water trapped in fuel lines can also
freeze and clog the fuel line. Outdoor ASTs
with fuel lines that are run from the bottom of
the tank are most susceptible to icing problems.
It is much easier to prevent frozen lines
than to treat them. There are several additives
available commonly referred to as ‘cold-flow
improvers,” that lower the temperature at
which the fuel in the tanks and lines “freezes.”
Most of these products do a very good job
of preventing waxing and gelling problems
but are far less effective when added to a tank
that already has a problem. Two good ways
to dispense these products is to have them
automatically dispensed with each delivery
or to manually add the proper dose to each
tank before delivery. Typically, pouring a dose
into an already frozen tank does not solve the
problem.
Another method of dealing with cold flow
problems is to use kerosene either instead of, or
blended with the fuel. Kerosene dissolves wax
and flows better in very cold temperatures.
As more and more USTs have been replaced
with outdoor ASTs, cold flow problems have
become more common. Too many tanks
have been installed outside without sufficient
thought being given to potential service
problems. Outside tanks should be encased in
enclosures and exposed fuel lines should be
48 National Oilheat Research Alliance
insulated to protect them from the elements.
When an outside tank does “freeze” it’s the
service technician’s job to get the system up
and running so the rest of the house doesn’t also
freeze. Once the technician has determined that
the lines are frozen the following procedures are
recommended:
• Check the tank connection. If the fuel line
is pulled off the bottom of the tank,
reroute the line to pull through a tapping
at the top and set the line at least 6" off the
bottom. Be sure to fully close and plug the
valve at the tank bottom. Never assume
that the valve is closed. There have been
instances of tanks thawing and draining
through a “closed” tank valve when temperatures
increased
• Use a manual push-pull pump to be sure
the line is clear all the way to the burner
• Insulate the line from the tank to the
location where it enters the building
• Advise the customer about the advantages
of a tank enclosure and encourage them to
add one
• In addition to frozen lines, cold fuel causes
other problems. Cold fuel doesn’t atomize
well and as its viscosity increases, more
fuel flows through the nozzle. In areas
where outside tanks are exposed to cold
temperatures, it’s advisable to consider:
• Installing a fuel de-aerator to warm the fuel
before it reaches the nozzle
• Installing a fuel line heater to improve
combustion
• Inform the customer on the advantages
of an inside tank