chimney-condensation


whats the cause? just noticed my neighbor's roof. water is running from the base of the chimney. outside temp is 30, its a hot air gas fired furnace, in Maryland. i didnt notice this on other roofs. ideas?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
bill wrote:

Rain or snow there recently? Perhaps there's a hollow spot someplace trapping moisture that's now melting.
Sounds like something worth mentioning and investigating as could be indicative of a chimney problem that might affect draft and hence perhaps lead to high CO inside at worse end or roof or other structural damage at the lesser....then again, it just might be from designed-in weeps doing their job for external drainage if it's a masonry chimney.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

When gas burns, it does give of water vapor. At the right temperature, it can condense in the chimney and drain down.
From http://www.naturalgas.org/overview/combust.asp
Combustion of NG is: CHI[g] + 2 O2[g] -> CO2[g] + 2 H2O[l] + 891 kJ That is, one molecule of methane (the [g] referred to above means it is gaseous form) combined with two oxygen atoms, react to form a carbon dioxide molecule, two water molecules (the [l] above means that the water molecules are in liquid form, although it is usually evaporated during the reaction to give off steam) and 891 kilajoules (kJ) of energy.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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?
wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
bill wrote:

where others aren't and so is condensing more external moisture than others.
Also, relative efficiency of the furnaces could have an effect -- a low-efficiency furnace would use more fuel in a comparable house...is there a cap, perhaps that is a condensation point? If it's flue-moisture, it should just be vented as steam--the water (if from combustion or internal humidity) has to have some surface on which it either condensed or collected to run from.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
bill wrote:

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_Hot_Water_Heater_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).
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.