Model 7100 has "Firetubes". Fire, Flames, or hot gasses enter the
inside of the pipes or heat exchanger tubes. Room air flows across
the outside of the pipes.
Model 2100 & 4100 has "Airtubes" similiar to "Watertubes". Room air
flows inside the tubes. Fire, flames or hot gasses flow outside the
How important are clean tubes? Note the statement below that soot has
many times the insulating characteristics of insulation material. Be
grateful for airtubes rather than watertubes. How would one clean
mineral deposits off the tubes of a water boiler?
Are You Keeping Customers' Boiler Tubes Clean?
00/05/0000 by Steve Spielmann
There are two types of tubular boilers: firetube and watertube. In
the watertube boiler, water is carried in the tubes and heated until
it becomes high pressure steam. In most areas, watertube boiler
plants must have licensed stationary engineers on hand at all times,
and maintenance is usually performed by in-house personnel.
In the firetube boiler, water surrounds the tubes and hot gasses
travel through them. This results in soot and scale deposits
accumulating within the tubes. No matter what fuel is used, the tubes
need to be cleaned regularly. If they aren't, boiler efficiency is
sacrificed and fuel wasted. Soot actually has five times the
insulating capacity of asbestos.
For example, a 18-in. coating of soot can accumulate in a firetube
boiler in just two weeks, resulting in a heat loss of 47% and an
increase in fuel consumption of 812%. As the layer of soot builds up,
the stack temperature rises. For every 40F rise in stack temperature,
boiler efficiency is reduced by 1%. That's a pretty good argument for
regular tube cleaning.
Some Firetube Cleaning History
Over the years, several methods have been developed for cleaning
boiler firetubes. Twenty-plus years ago, one popular method was the
use of soot blowers: steel tubes fitted with blowing nozzles that
were mounted on the tube sheet of the boiler. They were mounted in a
way that allowed nozzles to be maneuvered to blow steam or air
through each tube.
Soot was simply blown out through the smoke stack and into the
atmosphere a practice that is frowned upon today. Today, soot
blowers are used mainly in large power utility boilers where the
smoke stacks are equipped with scrubbers and other environmental
Another tube cleaning method practiced by some boiler technicians was
washing out the tubes using a fire hose. One can imagine the mess
this left behind. Yes, the tubes were cleaned, but the boiler room
was left with a layer of black mud on the floor. It took longer to
clean the floor than the tubes.
In most cases, tube cleaning was strictly a manual operation
requiring a great deal of time, labor, mess, and inconvenience.
Brushes fastened to long, heavy metal rods were manually pushed and
pulled through the soot laden boiler tubes, resulting in clouds of
soot filling the air and settling on every surface in the room.
The backbreaking effort went on for hours, followed by the immense
task of individually vacuuming each tube and cleaning up the boiler
Now for Watertubes
Most watertube boilers have tubes in a more or less vertical
position. Though some have straight tubes, which can be cleaned as
described above, most watertube boiler tubes have bends in them,
making them more difficult to clean.
In addition, where firetube boilers commonly have only soot and ash
to be removed, watertubes commonly have scale deposits that adhere
stubbornly to the tubes.
The amount and nature of the scale are determined by the water
quality and the effectiveness of water treatment. Scale is formed
when water is heated and suspended solids in the water precipitate
out onto the heating surfaces. A well-managed water treatment program
is essential to minimizing scale deposits.
Early watertube cleaning devices used cylindrical air motors fitted
with complicated cutter heads fastened to the end of a heavy
compressed air hose. The entire motor/cutter assembly was then fed
manually through the tubes and cleaning was performed dry, followed
by a flushing with a water hose. Each air motor was good for only a
narrow range of tube sizes, so if the user had many tube sizes to
clean, he had to have multiple air motors, which drove up the cost.
Good News: There are Better Ways
Over the years, great strides have been made in tube-cleaning
technology. Equipment is now available that enables one operator to
perform two tasks at once in a fraction of the time.
For firetubes with soot deposits, there are machines that
mechanically drive brushes or scrapers through the tubes, requiring
almost no human effort. These machines are, in turn, connected to
powerful vacuums that draw the loosened soot from the tubes
simultaneously, leaving the tubes, boiler room, and operator
Some firetube boilers develop scale deposits. This is particularly
true with waste heat boilers and boilers fired on lesser quality
fuels. Some of the worst waste heat boilers are found at hospitals
where medical waste is burned in incinerators and a boiler is used to
capture the subsequent heat generated. In many cases, a straight
brushing action isn't sufficient, and rotary equipment must be used.
Manually fed rotary systems are available that incorporate
simultaneous vacuuming as well. Many of these systems were based on
designs originally intended for condenser and chiller tube cleaning,
and they work extremely well on scaled boiler tubes.
There is also equipment now available with more powerful air motors
that drive flexible shafts fitted with a wide variety of cleaning
tools. The flexible shaft is sheathed in a water-tight casing that
transports water right to the cleaning tool. This allows tubes to be
cleaned and flushed in a single operation.
About Chemical Cleaning
Chemical cleaning has been used on boilers for many years and is
still periodically needed to clean the waterside of firetube boilers.
Chemicals effectively remove calcium carbonate and other scales that
adhere to heating surfaces. However, this method should only be
performed when deemed necessary by technicians trained and equipped
to do the work safely. Chemical cleaning presents the following
Cost - chemicals are expensive
Safety - chemicals present potential danger to personnel and
Environmental concerns - what if there is a spill?
Time - chemical cleaning can add up to a week to an outage.
Considering these challenges, it's important to know when a boiler
needs chemical cleaning. It's worse to chemically clean a boiler that
doesn't need it than to not clean one that does. Improving water
chemistry and start-up practices can extend the time between
Every boiler maintenance program should include regular efficiency
testing because such tests reveal trends that indicate it's time to
clean the boiler. For example, an increase in stack temperature
frequently signals soot or scale build up. An electronic combustion
efficiency tester should be considered standard for the maintenance
program. They are absolutely essential for tuning the burner
properly. Many models of testers are available today with
capabilities to measure and/or calculate net stack temperature,
oxygen, carbon monoxide, carbon dioxide, nitrous oxide, excess air,
and other values.
Regular boiler maintenance that includes thorough cleaning of the
boiler tubes will result in lower operating costs and fuel
consumption, greater efficiency and longer heating system life.
Steve Spielmann is the customer service and technical manager at
Goodway Technologies Corp., Stamford, CT. He has been in the HVAC
maintenance business for more than 27 years. He can be reached via e-
mail at: sspielmann@...