Loose connection a likely culprit for water condensation on pipe

q the heavy-duty exhaust pipe from my two-year-old water heater continues to collect and drip water, which condenses on the pipe's surface. A gas company technician cleaned out all scale, which had lodged on the heat element, and suggested that I wrap the exposed section of exhaust pipe in insulation. I followed this advice, but the condensation persists. What should I try next?

- W.S.C., Carlisle, Pa.

A As the outer surface of a glass of ice water set in a warm room will start to "sweat" - condensation forms due to a significant difference in temperatures - so will water vapor appear on a exhaust pipe that is not properly installed, says a technician at Rheem Water Heaters in Montgomery, Ala.

Even thick insulation will not be able to compensate for condensation if a PVC air-exhaust pipe was not properly connected to a water-heater tank. Furthermore, if the main combustion products - fuel, heat, and oxygen - are cooled too rapidly in the tank before air is released into the exhaust pipe, condensation is likely to occur.

The fact that condensation and dripping continue even after scale has been removed and insulation was added points to a problem of too much vent restriction, which takes place when the vent pipe has been installed incorrectly.

There should not be a technical problem with a water heater that is only two years old. The solution probably lies in a careful reading of the installation manuel and checking the connection of the PVC air-exhaust pipe and the water heater.

It's best to consult with a technician who works for the manufacturer of the water heater. Make sure that the exhaust pipe is properly installed before focusing on lack of insulation, scale, or other less-likely explanations for the water.

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