bill wrote:
most of the time you see the vapor cloud above the metal chimneys but
this one had a stream of water. nothing like it on the other similar
houses. maybe he's got a real humid envirnoment inside?


Did he happen to upgrade his gas furnace recently to a high energy
efficiency model? If so, google "orphaned chimney". (here's a link:
http://www.askthebuilder.com/B205_Ho..._Venting.shtml )

In this setting, typically what happens is that a home owner used to
have both his old gas furnace and water heater both vent out of the
chimney. But one day they upgrade the furnace to a newer high
efficiency model, that vents out of the the side of the house with PVC
pipes since the flue gases coming out of a high efficiency furnace are
too cool to vent out of a chimney properly. So now the only thing left
venting out of the chimney is just your water heater, which depending
on the chimney flue size, may not be able to vent all of its combustion
gases properly (CO2 and H20) in cold weather, causing the water vapors
to condense and freeze up inside the chimney, only to melt when it gets
hotter outside.

The solution for this is to get your chimney lined with a smaller metal
liner (often 3" or 4" diameter) so that your water tank can properly
vent out of your chimney. Or, change your hot water tank from a
chimney venting model, to a model that vents out of the side of the
house (power vented or direct vented), and cap your chimney since
you'll no longer be using it (unless you have a fireplace).