Well........... being technically correct. With natural gas there are three
types of gas used in old cities, primarily because of the presence of cast
iron pipes that are sealed with oakum and lead the same way that cast iron
drain pipes are sealed. Most areas with steel or plastic pipes are supplied
with dry gas, any water in it will be accidental such as in new piping or
where the line is punctured letting water in. Old areas are supplied with
"humidified" gas where they add some steam to keep the oakum moist, or they
add oil vapour to do the same job. In older cities you will see small iron
fittings in the street or sidewalk that say "drip". These are not a comment
on the local people but a low point in the underground piping where water or
oil accumulates from condensing of the injected steam or oil. At regular
intervals, the gas utility will access these drips to pump out excess water
or oil.


"RP" wrote in message
...


EXT wrote:

You are wrong, natural gas and propane do NOT contain water or the pipes
would have ice blocking the pipes where the water accumulates in cold
weather. However both are hydrocarbons, they contain hydrogen and
carbon.
When burned with oxygen they form carbon dioxide and water (hydrogen
oxide).

While you are technically correct, I just wanted to note that as I read
it he implied exactly that, i.e. when he referred first to combustion
byproducts. The statement "gas contains moisture" is subject to
interpretation Take everything in context. One might call this
*latent moisture*. OTOH, there is some actual trace moisture present in
the gas mixture even before combustion, so let's go ahead and dot some
more i's while where at it. BTW, I have encountered frozen gas lines,
FWIW. Not many, but a few.

Richard Perry

It is this water vapour that you see condensing outside the furnace
chimney
or vent. This is the same process that forms condensation at your car's
exhaust pipe or water dripping from the exhaust pipe and the con-trails
that
leave white streaks behind jet airplanes.

"Edwin Pawlowski" wrote in message
m...

wrote in message
...

Greetings. I live outside of detroit, mi. I notice that my neighbors
natural gas water heaters that are vented with b-vent seem to give a
fair sized cloud of "steam" if you will, on a cold morning. My 220,000
btu boiler that is venting into a clay flue 8x8 chimney does not cause
any steam to be visible at all. It should be noted that my natural gas
water heater vents into the same chimney. People with the 90+%
furnaces have a huge cloud of steam coming from their furnace vents.
My question is: what causes some people to have steam and others not?


I'm glad you put "steam" in parenthesis, because, as you already surmise

it

is not steam. To be picky, steam is invisible. It is a vapor and cannot

be

seen at all. What you are seeing is condensation that is now visible in

the

cold air.

When fuel is burned, there are products of combustion that are given of

into

the air. The type of products depends on the fuel. Could be ash, soot,
smoke (that contains many compounds) and water. Propane and natural gas
both contains some water. the water, of course will not burn but will
be
vaporized and later condensed (made visible) and that is what you are
seeing. For the products of combustion to pass up that big cold clay
chimney, some of the condensation will drop back down and dry up. some

will

exit and not be seen. High efficiency units are sending the water vapor

out

a shorter length of PVC and you see more of it.