Heating System Oddities

Written on: June 19, 2013 by George Carey

Following are examples of jobsites I have seen over the past heating season.
Each one was exhibiting some type of problem
due to someone either ignoring the standard installation practices or thinking
the job was located in an area where the “laws of physics” did not apply.
A large apartment complex in the downtown Boston
area was experiencing some very severe overheating
with their steam system. The Management Company
had recently purchased a weather-responsive control
from our company. This control was suppose to measure
the indoor temperature, the outdoor temperature
and then make a decision on how long the burner/boiler
should run to satisfy the building’s heating needs.
I met with the service technicians who were trying to
figure out the problem. We started by going through
the operation of the control. Within a few minutes,
we found one of the problems. One of the components
of these weather-responsive controls is a sensor that
is located near the end of a steam supply main. It is
wired back to the control and its purpose is to sense
when there is temperature in the system. This tells
the control that steam has been distributed throughout
the building. The control will let the boiler run for so
many minutes, then keep it off for so many minutes,
based upon the heating cycle. However, none of this
can happen until the “steam-established” sensor measures
temperature in the system.
In this system, someone installed the sensor on a
return line that had long been disconnected from the
system. That’s why the building was overheating. The
sensor never “sensed” any temperature, so the control
kept telling the boiler to run and run! The boiler was
cycling off its pressure control. The solution was to relocate
the sensor to one of the steam mains.
As we walked through the building, I noticed the
basement apartments, which were on the same grade
as the boiler room, had two-pipe radiators with
s t e a m t r a p s .
The steam system had no condensate return
p u m p s , o n l y gravity returns. Logically, these
radiators should be filled with water all the time
because they are below the water line of the boiler.
Nevertheless, I was told they were working fine.
I asked the maintenance man if he knew anything
about these radiators and he started to smile, then
said, “Follow me.” He took us outside to the courtyard
and pointed to all the holes in the building where pipes
were draining water. Every basement radiator was
piped to the outside where its condensate was dumped!
No wonder they were “working.” Of course, the makeup
water was eating the cast-iron sections for lunch
and the fuel usage had to be excessive, but at least the
basement apartments were warm!

Here’s a good one—and it’s true! A local service
manager contacted me to look at a heating system
his installation department had installed
two years ago. The system consisted of five
zones of baseboard and one indirect water heater. They
installed a good air separator with a diaphragm expansion
tank and pressure-reducing valve on the supply.
They also installed all the circulators on the supply,
“pumping away” from the expansion tank. That is why
he had me at the job. It turns out the homeowner was
threatening to sue the Oil Company because the circulators
were on the supply-side of the system. Huh???
Recently, the homeowner had a family party and a
relative, who happens to be a plumber, looked at the
heating system and proudly exclaimed, “This system
will never work! These circulators have to be installed
on the return so they can pull the water back from the
He explained that these circulators would never be
able to lift the water out of the boiler, which is why
the system will never heat! Mind you, the system has
gone through one heating season and is now entering
its second one. Of course, the house has heated wonderfully.
Nevertheless, the “plumbing relative” convinced
the homeowner that his heating will not work and that
is why he is suing the Oil Company. So here is a little
warning to all you who believe in locating your circulators
on the supply. We all know it is the better way to
install circulators. The system operates more quietly,
with no gurgling or sloshing noises. But, make sure you
tell your customers to keep their relatives away from
their new heating systems!

This last job was interesting…the steam system
had both its main vents and radiator vents on
the first floor spitting water. Naturally, in addition
to the spitting, there was a fair amount
of water hammer. I met one of the service technicians
at the job and he walked me around the building.
The system was a one-pipe steam system with a gravity wet-return.
One of the things I noticed was, at the end of each main
and at the base of each riser, a float and
thermostatic trap was installed. The outlet of each trap then
drained into the wet-return that ran on the floor
around the basement and into the Hartford Loop. We
walked over to the boiler and checked out the settings
on the pressuretrol. It was set for five pounds and the
differential was set for two pounds. This meant the
system’s pressure operated between three and five psi.
I was starting to see the cause of the problem. We then
measured the distance between the outlets of the traps
and the water line of the boiler. There was only three
feet of vertical distance between them. When you have
steam traps in a system, remember that one of the
functions of the trap is to prevent the steam from getting
past the trap and into the return lines. The traps
on this job were working fine. Unfortunately, in this
situation, it was the cause of the problem. This was a
one-pipe system with gravity returns. There were no
condensate or boiler feed pumps, so there was no need
for the traps. Why someone bothered to install them is
another story.
Without any steam pressure in the return, the only
help the returning condensate had to overcome the
pressure in the boiler was its static pressure. For every
pound of pressure in the boiler, the water would have
to stack up 30″. In this system, the boiler was running
between three and five pounds. Therefore, the water
would have to stack up 90″ to 150″ (7′ to 12′) to enter
the boiler.
This explains why the vents were spitting water. As
the boiler was firing and building steam pressure, the
condensate returning from the system was “stacking”
in the returns, trying to develop enough pressure to
overcome the pressure in the boiler. Eventually, the
condensate backed up high enough to reach the first
floor radiator vents. This situation also explained why
the boiler was flooding. Initially, they thought it was
a defective water feeder, so they replaced it. However,
when the problem persisted, they asked for help. We
concluded that while the condensate was backing up
in the system, trying to overcome the boiler pressure
and was not able to return to the boiler. This obviously
affected the water level, causing the automatic feeder
to add make-up water into the boiler. Once the system
satisfied and shut the boiler off, the leftover steam
condensed in the boiler, allowing all the water out in
the system to drain back. This raised the water level
to the point of flooding the boiler.
The quick solution to this system’s problem was to
replace the pressuretrol with a vaporstat. The vaporstat
allowed us to set the maximum pressure at 14
ounces. By keeping the pressure low in the boiler, the
condensate would not have to stack any higher than
28-30″, which was still below the F&T traps. We also
added extra main vents near the end of each main to
improve the venting capacity. This helped prevent the
burner from short cycling due to the lower pressure

If you have any questions or comments, e-mail me at
gcarey@fiainc.com or call me at FIA. 1-800-423-7187 or
follow me on Twitter at @Ask_Gcarey