Wet Basement Wall
Q: I had a new gas heating system installed over three years ago. I have found a wet area in the foundation and it goes to the floor where there is a white powder-like substance. The cement on the floor is breaking down, it seems. Do I need a liner installed due to the evaporation of the gas heat, or is it due to the small crack I have outside at the base of the chimney?
A: Several different conditions could affect the answer, including the following:
- The efficiency of the new heater. The higher the efficiency of the heater, the cooler the exhaust gas temperature. Condensation is more likely at cooler exhaust gas temperatures.
- Size and type of the chimney. New high efficiency gas heaters are built to use small diameter PVC piping to carry the exhaust gases out of your house and use a fan to push the gases. Older heating units needed the "chimney effect" of a hot chimney to carry the exhaust away and relied on a much larger diameter chimney. Newer furnaces don't put out enough heat to raise the temperature of the masonry mass of an old style chimney. Thus water in the exhaust more easily condenses on the walls of the chimney when the moist exhaust contacts the cold chimney walls.
- You didn't mention where you live. Obviously, the colder the climate, the more condensation can be produced.
- Spalling (the white powder) is the result of the masonry breaking down and the minerals being carried away by water. When the water lands somewhere and evaporates, the minerals are left behind. Acids are what break down masonry. Acids as weak as vinegar will "eat up" masonry. The exhaust from high efficiency gas furnaces is mildly acidic and if it condenses and runs back down the chimney, the masonry will deteriorate.
Having said all that, I would advise the following:
First, fix the crack.
Second, determine how the manufacturer recommends venting the exhaust gases. You can find that information in the owners manual that the contractor left with the furnace. If the exhaust wasn't handled in the recommended manner, have it changed. The contractor should have followed the manufacturer's instructions during the installation. This is a situation where you can't mix old technology with new technology. High efficiency heaters rely on new technologies in every phase of operation.
To locate a mason to fix that crack, visit Home Advisor, search for "Find A Tuck Pointing Service" (to repair and replace mortar) and submit a service request.
To locate a reliable heating specialist to determine the most appropriate venting system, please search for Repair A Gas Heating System and submit a service request to be matched with the ideal service professional in your area.
This information is brought to you by Don Powell of Powell Building Corporation in Mt. Laurel, NJ.
-- Tips courtesy of HomeAdvisor.com