# Steam Heating

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```					Steam Heating

Calculating the “A”
Dimension
Water seeks its own level
(most of the time)

In this example, the weight of the
atmosphere is pressing down on
both sides of the “U” tube equally.
Thus, the water level remains the
same on both sides
Water Level
Water seeks its own level
(most of the time)
weight to one side of the
tube. For every pound (per
square inch) we add to one
side, the water will rise 28
inches in the other.

This number shows up a lot
in heating!
Water seeks its own level
(most of the time)
Water seeks its own level
(most of the time)
Here we’re pumping air OUT of
the right side. That lowers the
pressure and causes the right
side to rise.

It’s important to note that it’s not
the vacuum pulling the water UP,
it’s the greater weight of the
atmosphere on the left side
pushing down that causes the
right side to rise.
The All Important “A” Dimension

Think of the piping
from the end of the
supply main back to
the boiler as the
previously shown “U”
tube. The waterline
will remain equal
across the system,
when the boiler is
not firing.
The All Important “A” Dimension
• Typically, residential steam piping is sized for a
two ounce pressure drop. ½ psi is used for
larger systems (>100,000Btuh)
• This means that if you start out with 1psi in the
boiler, you wind up with about 7/8 psi at the end
of the system. (1/2 psi in larger systems)
• With this in mind, the water inside the boiler will
always be higher pressure than the condensate
attempting to come back!
The All Important “A” Dimension
• Because of this, we need to ‘stack’ the
condensate up vertically, to overcome this
pressure differential.
• The stacked-up condensate must NOT be
allowed into any pipe containing live
steam, or massive problems will occur!
The All Important “A” Dimension
(Systems > 100,000Btuh)
The All Important “A” Dimension
(Systems > 100,000Btuh)
Steam pressure drop across the system
(1/2psi)……………………………………14”
Condensate pressure drop…………….......4”
Storage space for the extra condensate
That occurs at start-up……………………...8”
Extra safety margin (future pressure drops
due to dirty returns, etc)……………….…2”
Total “A” dimension………………………..28”
The All Important “A” Dimension
(Systems < 100,000Btuh)
The All Important “A” Dimension
(Systems < 100,000Btuh)
Steam pressure drop across the system
(2 ounces/1/8 psi)..……………………..…3.5”
Condensate pressure drop……………....3.5”
Storage space for the extra condensate
That occurs at start-up……………………...7”
Total “A” dimension………………………..14”
What can go wrong?
How do I fix that???
The Hartford Loop

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 views: 3 posted: 10/13/2012 language: English pages: 15