Excessive moisture in home caused by buried air ducts

Posted1/30/2022 6:00 AM

Q: I bought my house over three years ago and have had seasonal problems with wet ceilings since. After replacing the roof and rain gutters, I learned the problem was moisture condensation into the heating ducts below the slab floor. Shouldn't my home inspector have known this would be a problem, and shouldn't the seller have disclosed the issue of ceiling moisture?

A: In homes that were built during the 1950s and 60s, forced air heating ducts were sometimes installed beneath concrete slab floors. This practice was abandoned when moisture-related problems became apparent.


Experienced home inspectors know forced air ducts under a slab are exposed to ground moisture, water intrusion and rust damage. Home inspectors cannot determine conditions that exist within a duct system, but disclosure of potential problems is advisable.

Aside from moisture intrusion, buried ducts can incur severe rust damage, and there is also the potential for mold infection on the interior surfaces of the ducts. In such cases, airborne mold spores can be conveyed into the dwelling when air is blown through the ducts. Replacement of your air duct system is recommended, and a mold survey of your home is advised.

Q: Why does the water in our upstairs toilet bowl slosh back and forth, even when the toilet has not being used? Our home is only three years old, and the toilet has been doing this since the place was new. Is something wrong with our plumbing?

A: The various drains in your home may be vented through a single vent pipe. If this is the case, water that drains from a sink, shower or laundry can create a vacuum in the system, and this can cause water movement at some toilets.

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Correcting this condition can be costly, depending on the accessibility of the vent piping, but the adverse effects of the existing condition are typically minor in nature, and repairs are usually not necessary.

Q: I have some questions regarding the temperature pressure relief (TPR) valve on my water heater. How can I tell if it has been activated? Does it reset by itself? Can I reset it manually? And should it be tested?

A: TPR valves are installed on a water heater to prevent the tank from exploding if the fixture should overheat. The valve is held in the closed position by means of a spring. When the pressure or temperature in the tank causes the valve to open, hot water is released from the system into a discharge pipe that should terminate outside the building. If the valve is working properly, it will reseal by itself when the temperature or pressure returns to normal. Most TPR valves, however, never fully reseal because of corrosion or mineral deposits. That is when the valve needs to be replaced.

You can determine if the valve is leaking by checking for wetness at the end of the discharge pipe.

Testing TPR valves is not recommended because they often tend to leak after being tested.

• To write to Barry Stone, visit him on the web at www.housedetective.com, or write AMG, 1776 Jami Lee Court, Suite 218, San Luis Obispo, CA 94301.

© 2022, Action Coast Publishing

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