Should PEX Plumbing Pipes Be Insulated?

Should PEX Pipes Be Insulated?

It’d Be A Lot Cooler If You Did

PEX piping is used in nearly all new home construction and plumbing re-pipes done today. PEX has become the go-to plumbing supply pipe for plumbers because the installation is much easier and it’s inexpensive. PEX is light weight and it’s ability to bend reduces the number of connection joints needed. Beyond it’s ease of installation, PEX has the ability to expand up to 20% which greatly decreases the chance of failure. I get the warm and fuzzies just looking at PEX, especially when it’s insulated. The need for insulating PEX has been a debated topic for some time, leaving some of us feeling dazed and confused.

Coincidentally, PEX insulation was mentioned multiple times by actor Matthew McConaughey in the 1993 film Dazed and Confused. I’ve included a few of these famous quotes for reference.

“Say, man, you got insulated PEX?”
“No, not me, man.”
“It’d be a lot cooler if you did”

Does PEX Need To Be Insulated?

While PEX is far more resilient than the more rigid copper, PVC, or CPVC pipes, it can still freeze in the extreme cold. Generally, you don’t need to insulate the PEX piping that is located within interior walls or insulated exterior walls. However, any PEX located outdoors or within uninsulated areas such as attics or crawlspaces should be insulated, especially when temperatures fall below 20 degrees. Limiting the exposure risks and insulating PEX piping reduces water pipes’ chances of bursting or leaking and causing tiresome and frustrating outcomes, which may be costly to repair, not to mention the potential necessity for piping replacement. 

Insulating PEX piping also important for energy efficiency. Pipe insulation significantly reduces heat loss and helps to ensure that hot water gets to the fixtures sooner. Pipe insulation keeps the water hotter by reducing the temperature drop from the source of hot water to the shower outlet. This saves significant energy by making it possible to reduce the set point for the storage temperature at the hot water heater. On the other hand, during the cool-down phase, pipe insulation increases the time it takes for the temperature of the water to cool down, roughly doubling the cool-down time.

Insulation for hot water pipe with a minimum thermal resistance (R-value) of R-3 shall is recommended for the following:

  1. Piping larger than 3
    /4 inch nominal diameter.
  2. Piping serving more than one dwelling unit.
  3. Piping from the water heater to kitchen outlets.
  4. Piping located outside the conditioned space.
  5. In occupancies with three or more bedrooms, piping from the water heater or recirculation system piping to the
    outlet for any shower or tub/shower combination.
  6. Piping from the water heater to a distribution manifold.
  7. Piping located under a floor slab.
  8. Buried piping.
  9. Supply and return piping in recirculation systems other than demand recirculation systems.

Source of energy requirements. Note: Licensed home inspectors are not energy raters and local building codes may vary by local building officials.

“That’s what I love about these insulated PEX pipes, man. I get older, they stay the same age.”

PEX Pipe Insulation Requirements

PEX piping can be insulated with the same foam insulation sized for copper, commonly found in home improvement stores. The standard IPS sizing can be applied to PEX piping and effective for insulation, but the fit would not be as snug due to inaccurate size.

That being said, trapped air space commonly plays a role in various insulation techniques. Such an approach would be efficient enough and may even add additional insulation based on this principle. So, it’s important to select piping insulation that is properly sized for a proper fit.

  1. Type of Material for Insulation of PEX Piping

Foam is usually the recommended type of insulation for PEX piping, as it meets the flexibility levels that such material demands. Since PEX is commonly used with curved positioning instead of connection joints, the insulation material needs to be flexible. Fiberglass insulation is far more rigid and would not be able to accommodate such tractability. 

  1. Type of Fit for Insulation of PEX Piping

Once the correct insulation material has been identified, the appropriate type of insulation will need to be chosen. Persons can select between a continuous length and polytype, both of which have various features and benefits for users. While the continuous length type can be useful for PEX pipe, which spans over a long area, polytypes are generally better suited to PEX flexibility and are easier to apply post-construction. 

Continuous Length Type: This type of insulation can be described as a full-length tube with no openings of necessitated closures, which offers thorough and even insulation across the entire length of the PEX pipe. While this would certainly be beneficial, this is more commonly used during the building’s construction phase, as it can be slipped over the PEX piping before it has been installed within the building.

Utilizing a continuous length type of insulation will not be practical post-construction unless the PEX pipe is removed and disconnected completely or if the insulation is cut, which may defeat the purpose of selecting the continuous type. 

Poly Type: This type of insulation is far more practical and simpler to apply since it is flexible and can be used in awkward spaces or angles, common with PEX piping, which is used in corners with bent positioning as opposed to the use of elbows for corners. 

For installing insulation post-construction, insulation with an opening on one side is the most practical, particularly for odd spaces, tight corners, and event tees. It’s crucial to ensure that the PEX piping is thoroughly cleaned with a wet cloth before installing and insulating, as it is commonly laden with dirt, grime, or debris which may build up over time, promote corrosion, and may not accommodate adhesive as well as a smooth and clean surface would. 

The PEX piping should be covered by the insulation and fitted snuggly by pushing down the insulation until the pipe pops into place. After the insulation has been fitted, the opening would be sealed off by pulling off the protective strip to reveal the adhesive. The seams would then be pushed together to seal the insulation completely. Many professionals also make use of contact cement for joining the ends of insulation lengths for further durability.

Let me tell you this, the older you do get the more rules they’re gonna try to get you to follow. You just gotta keep insulatin’ man, I-N-S-U-L-A-T-I-N.


How to Insulate PEX Piping

Plan Where PEX Pipes Are Run

Insulating a new home involves proper planning. It’s a good idea to route PEX pipes through interior walls rather than exterior walls where possible. The heat from your home’s heating system can prevent PEX pipes from freezing.

When outside temperatures are 2o degrees or lower, keep your interior temperature at 55 degrees or higher. This will keep your interior pipes from freezing.

Insulate PEX Piping Exposed Outside

Sometimes, having PEX pipes outside can’t be avoided. Pipes must be run for exterior spigots (hose bibs) or other uses such as tankless water heaters. Any PEX piping exposed outside needs a minimum of R3 (3/8″ thick) piping insulation. Some colder climates require an R4 (5/8″ thick) or higher pipe insulation.

Insulate all exposed PEX pipe and secure the pipe inspection in place with tape along seams and bends where pipe insulation is loose.

Open an Interior Faucet During Freezing Temperatures

When a hard freeze occurs, generally 25 degrees or lower, it’s a good idea to open the cold water tap on an interior faucet to allow the water to dribble out a small stream of water. Flowing water won’t freeze as easily or as quickly. This also reduces water pressure on the walls of the piping.

Winterize the PEX Pipes in Vacation Homes

If you have a secondary vacation home that you don’t visit in the winter, you should consider winterizing the plumbing. Winterizing the plumbing includes draining the entire plumbing system, including the water heater and toilets. The cold won’t hurt the plumbing system when water is not present. Also, insulate the plumbing P traps under sinks and inside crawl spaces or basements.

PEX Piping in Basements and Crawl Spaces

Crawl spaces and unfinished basements are particularly vulnerable spaces for PEX piping during the winter months. These spaces are not heated or insulated like the inside walls, which can cause the pipes to freeze if it gets cold enough.

Your hot and cold water supply lines (as well as your PVC drain traps) need to be insulated in unfinished spaces. Often, these pipes and freeze and crack along connection joints. PEX will expand about 1 inch to 2.5 inches per 100 feet for every 10-degree temperature change. This can help prevent some damages from occurring. However, in short spans of PEX pipe, freezing and cracking can and likely will still occur.

Insulating the hot side will assist in delivering hot water to fixtures quicker and the water inside the pipe cools at a slower rate. The cold water side may condensate in the summer months contributing to damp crawl space conditions.

PEX Piping in Attics

When installing insulation for PEX piping in an attic, the most challenging part is the tight spaces, sharp corners, hangers, joists, and tees running across the area. The use of PEX and foam insulation will provide enough flexibility to cope with such factors, coupled with open insulation on one side.

This allows users to have varying approaches for applying the insulation, such as trimming it and running it from the opposite end for tees, mitering the insulation at elbow curves, and securing the ends with cable ties for extra hold and support for the adhesive.

PEX piping in the attic is susceptible to fluctuations in climate and temperature as they are more exposed to outdoor conditions. Both the hot and cold lines should be insulated effectively, as insulation of the hot side will assist in delivering hot water to the load faster. In contrast, the cold line’s insulation will lower the risk of condensation forming in summer, which may cause seepage through the ceiling. 

The Best Way To Insulate Pex Pipes

Any insulation that you can add to your home, in the walls, wrapping pipes, windows, cracks in doors, etc. will help to prevent your water pipes from bursting and creating an expensive mess.

Our tips on the best way to insulate your pex pipes is…

  • It is important to choose the right insulation material. Because PEX piping is flexible, it is often used in angles, loops, or other non-linear shapes, which makes it imperative to have equally flexible insulation material. Foam is used most commonly, and generally works well.
  • The surface of PEX piping can become grimy over time, so before insulating you should take just a few minutes to clean it off. A wet rag should easily wipe away any visible dirt or debris.
  • The piping should then be completely sealed within the insulation; this is the best way to promote efficient energy use. Tape the end seams of each insulation length with insulating tape.

As long as you have the materials on hand – insulating your PEX pipes should be an easy task. Properly traversing attics takes years of practice to learn to safely avoid damage and injury. Call a qualified handyman or plumber if you’re not able to safely maneuver through tight areas such as attics or crawlspaces.

In our experience, we find that foam is a very good insulation product for PEX pipes. It’s flexibile (like a PEX pipe is) and it does the job like any other insulating materials.


Current building standards advise for pipe insulation on hot water supply piping and non-insulated spaces of homes such as attics and crawlspaces. Pipe insulation is relatively inexpensive so if you can see it, why not insulate it? Taking the time to properly insulate your PEX piping will protect your home during freezing temperatures and increase energy efficiency.

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