When Pipes Sweat: Causes and Cures for Sweating Pipes

Updated on April 9, 2019
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I am currently a licensed contractor performing remodeling services for residential and commercial customers in Wisconsin.

The PEX tubing and brass ball valve were sweating substantially in a basement that the building owner wanted to finish but couldn't until this issue was corrected.
The PEX tubing and brass ball valve were sweating substantially in a basement that the building owner wanted to finish but couldn't until this issue was corrected. | Source

In hot summer months, it is not uncommon to find the pipes sweating in basement and crawlspace areas. This issue, while common, is typically not addressed because it is considered fairly normal. The issue that does arise, however, is that over the years, the moisture breaks down the integrity of the plumbing, connections, and valves. Furthermore, if the space is finished, there is enough moisture to promote mold growth and that can greatly affect the air quality of the building. There are some simple fixes to prevent excess moisture, but it also depends on the cause of the moisture.

Moisture Causes on Plumbing Pipes

Sweating pipes often occur in the summertime. In this case, the PEX tubing is made primarily of a plastic material while the manifold or main supply line that the pipe connects to is made of copper. The cold water coming out of the pipe causes the pipe to conduct the cold energy from the water to the walls of the pipe. The warmer air temperature and excess humidity in the air meet with the cold walls of the pipe through the process of convection and condensation begins to form, sometimes in large enough amounts to leave puddles on the floor or, in this case, a water trail (see picture below).

In the wintertime, pipes can sweat for the same reason, except that it is typically the hot water pipes rather than the cold water pipes. While this is less common, it does happen and is typical in crawlspaces where the pipes are close to the perimeter of the building. This is a good indication of a poorly insulated and air sealed basement or crawlspace but could also be an indication that the water heater temperature is higher than is typical causing a larger temperature differential between the air and the pipes.

Trail of water from sweating plumbing pipes.
Trail of water from sweating plumbing pipes. | Source

Curing Sweating Pipes

Curing sweating pipes is fairly simple as all you are really doing is preventing the convection process from occurring on the surface of the pipe. This can be accomplished by installing a pipe insulation material. There are a few different types of pipe insulation material available on the market.

Polyurethane Foam Pipe Insulation

This type of insulation is typically black and comes 4-6 foot lengths. The center of the pipe wrap is slit to allow to easy installation over the pipes and can easily be cut in order to fit varying lengths. This insulation material equates to roughly and R-4 and is usually sufficient enough to prevent pipes from sweating.

Fiberglass Pipe Wrap

Fiberglass pipe wrap is spun fiberglass wool that comes in a flat roll with a polyethylene vapor barrier attached to the back of it. The wrap is laid on top of the pipes that you want to insulate and is wrapped and tapped so that the insulation encapsulates the pipe. Plastic elbows can be purchased also to continue the insulation along the pipes, creating a complete pipe insulation system. Another variety of this insulation system is a fiberglass encapsulation with a more rigid polyurethane-based exterior vapor barrier giving the pipe insulation more rigidity and cleaned joint connections. The R-value ranges from R-4 to R-12 depending on the size and style of pipe wrap.

Polyurethane Spray Foam Pipe Wrap

While this is strictly a commercial type of system, it can be used for residential use also. A plastic shell is installed over the pipes that is a clear material. The polyurethane foam is either poured or sprayed into the shell expanding and completely encapsulation the pipe. This system is very effective and is also the most costly. The typical R-value of these systems is R-7 to R-14, but can be customized into higher R-value applications for commercial use.

Sweating pipes are a typical issue in buildings around the world. Do not panic when you see this, as a few hundred dollars is usually more than enough to fix the issue. If you are not sure if the pipes are sweating or leaking, dry the pipes with a cloth and monitor the area(s) in question. If water droplets are forming on the edges of the pipe joints, you may have a leak. Otherwise, it is most likely just sweating pipes, and some pipe insulation will rectify the problem.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2011 Energy Guild


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    • profile image


      2 years ago

      best way to picture it is the soda can theory what happens on a hot summer day when you pull a cold drink out of the fridge... condensation it's the same thing with anything if it's cold on the inside and has warm air or vice versa there will be condensation it happens a lot with duct work with poor insulation or not correct r value for the area it's in

    • profile image


      2 years ago

      Just went through something like this. Heard a water drop but could'nt figure from where. Checked the shower head, under the bathrom sink and nothing. Then early morning on my way to the restroom I hear it again. Look up at the hallway ceiling and BAM! There it is. It was the condensation pipe leaking. Rgh!

    • profile image

      Ron Jeremy 

      2 years ago

      I'd be happy to help with your education, email me.

    • Simone Smith profile image

      Simone Haruko Smith 

      8 years ago from San Francisco

      I had never heard of sweaty pipes before, but then again, I am not familiar with pipes in the least! Thanks for sharing some solutions to the problem and going over the major insulation materials. Great Hub!


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