If you try to solve a heating problem by raising the steam pressure,
you’ll overheat the rooms and consume more fuel in the process.
and change it into steam. A thermometer
can’t sense this energy,
although it is very real. In fact, in
a low pressure system (0-15psig),
the amount of latent heat is usually
five times as much as the sensible
heat per pound of steam. Steam can
hold a tremendous amount of energy
while requiring no assistance to
travel throughout the system.
When steam is manufactured in
the boiler, it races out of the boiler
into the piping system and towards
the radiators. As it does, it encounters
the cold pipes that cause the
steam to condense back into water.
During this condensing process, the
steam gives back the latent heat it
received in the boiler. In a steam
heating system, this is what heats
the rooms. It is not high pressure
that heats the house, so there is no
sense in turning up the pressuretrol.
In fact, the lower the pressure, the
greater the quantity of latent heat
per pound of steam.
The problem arises when the
boiler can’t produce enough steam to
offset the system’s ability to condense
it. The steam condenses in the
near-boiler piping, supply mains and
maybe in some of the closer radiators.
The thermostat never lets the
burner shut off. No matter how high
you turn the pressure up, you can’t
produce enough steam. One symptom
I have consistently noticed is
that the pressure gauge never registers
any pressure when the boiler is
undersized or underfired. The boiler
can’t build any pressure because as
soon as any steam is produced, the
system condenses it.
When you install a replacement
steam boiler, it is important that it
be sized to the connected load. Once
you have picked the correct size
and have installed it according to
the manufacturer’s specifications,
make sure you also fire the burner
to the connected load. If you don’t,
the results can be the same as an
undersized boiler.
You have to realize that just because
the boiler manufacturer says
it’s a steam boiler and supplies all
the necessary trim, it doesn’t make
steam by magic. You have to input
enough energy so that the boiler can
offset the connected load’s condensing
ability. That means when the
boiler is rated to a certain gallons
per hour (GPH), you have to use that
firing rate. If you don’t the boiler
won’t be able to produce enough
steam. The steam won’t be able to
reach the furthest radiators because
it’s condensing in the pipes. ICM
If you have any questions or comments,
e-mail me at gcarey@fiainc.
com, call me at (800) 423-7187 or follow
me on Twitter at @Ask_Gcarey.
ICM/September/October 2017 17