Sweating Cold Water Pipes []


We have two cold water supply pipes in our duplex. One pipe is getting unbelievable condensation on it, and the other is perfectly dry. How can it be, that one pipe is wet and the other not, since they both are cold water, immediately following the indoor split in the same room? Second, what can be done to take care of the problem?


Your cold water pipes are a classic, summer humidity occurrence. Fear not, a minor issue when corrected! The cold pipes are sweating, or condensing the moisture out of the very “wet” air in the basement. This is just like a glass of ice water sweating on a humid summer day.

The dew point in the basement must become lower, which is to say the basement air must become drier and/or the water pipe warmer. Your solution choices are to lower the humidity in the basement with a dehumidifier, warm up the water pipes (unlikely), or totally insulate the sweating pipes so that the humid basement air does not touch the cold metal of the pipes (difficult).

I suggest you procure and continuously run a dehumidifier(s) to lower the relative humidity in your basement. The dehumidifier will dry your basement air and remove the moisture in a controlled way, much like your water pipes are doing now in an un-controlled way. You may need a simple box fan to circulate the air in the basement so that all the wet air in the basement circulates past the dehumidifier and becomes drier. This high humidity is very important to lower. This is the cause of mold, musty odors, and unhealthy air. Lower the basement humidity to protect your health and all the things in your basement.

The two cold water pipes, with one sweating and the other not, is likely indicating water flow. The sweating pipe is carrying all the new, cold, water flow from the relatively cold ground outside, and the dry pipe is carrying little or no water flow. If no water is demanded by fixtures to make water flow through the pipes – then the water will remain warm at room temperature, and not sweat. No water flow, no cold pipe. The non-sweating pipe may be to a hose faucet that is not turned on much. When the pipe starts carrying water from the cold ground outside the home … it will sweat substantially. The sweating pipe is carrying the cold water flow to the house. With a constant supply of cold water from the ground outside, with the pipe buried 30” deep, the water pipe is like running it through a cave. The ground temperature remains well below 70 degrees throughout the summer at a 30” depth where the water pipe is buried.

I suggest you purchase a digital humidity gauge from the hardware store and keep it in your basement. Maintain your basement humidity no higher than 55%. Above 55% the dust-mites, spiders and bugs begin to thrive and take over the basement. Lower the humidity, circulate the air, improve your health, and stop the pipe condensation.