February 22nd, 2017 2:43 PM by Dan Howard
It sometimes takes “Television Show Like” Crime Scene Investigation (CSI) work to get to the source of the water vapor, to then get to the source of the excess moisture that creates the mold conducive conditions.
This is what a flue liner looks like after the defective liner was removed from the chimney. The original installer was required by code to install a metal liner in the clay liner for the chimney.
The low temperature exhaust of high efficiency furnaces and hot water tanks is the reason we need liners in the first place. Picture I take you up to a two-man balloon at a state fair. If I give you a hair dryer to warm the balloon enough to get off the ground, you will laugh at me. We all know that it takes a big propane heater to get the big balloon into the air. When we make furnaces more efficient, we do so by keeping MORE of the heat from combustion in the home and less going up the chimney. That is like changing from the big propane heater to the hair dryer.
Now picture the toy balloon with a miniature basket and little toy men. The hair dryer would be able to get the toy to go up into the air.
The liner reduces the size of the chimney, so that the lower heat will make its way up the chimney and out of the house…..just like the toy balloon lifts with less heat. We want that exhaust to happen because the chimney gets rid of water vapor as well as combustion gases.
When there is a hole in the liner, like the picture above, the moist exhaust air goes into the chimney cavity instead of leaving the house. This results in moisture from combustion soaking the wall inside the home and outside brick of the chimney.
Wet walls result in mold growth. If the wet wall problem is not resolved, mold can come back after even the very best mold treatment.
I can tell you that over the years, I have seen many homeowners and roofers struggle trying to find a chimney or roof leak as the cause of wet walls when the actual cause is a hole in a liner such as one pictured in the section of pipe above….or the failure to install ANY liner when a high efficiency gas venting appliance is installed
Bottom line: If it appears that there is a leak and mold growing on walls near a chimney, check the flue liner that was damaged or may have not been installed. Both of these conditions result in condensation collecting at the dew point in the house somewhere between the gas appliance and the top of the chimney.