Is PEX or copper better for water heaters?

Quick Answers

Both PEX and copper have advantages and disadvantages for use with water heaters. Here are some quick answers:

• PEX is cheaper and easier to install but more prone to damage from UV light, some chemicals, rodents.
• Copper is more expensive but very durable and resistant to damage.
• PEX can expand when heated to prevent bursts but copper cannot.
• Copper is better for very hot water but PEX can handle normal residential water heater temps.
• PEX requires fewer joints/connections which reduces potential leaks.
• Copper allows better water flow due to smooth interior walls.

Overall, for most residential water heater applications, PEX offers a good combination of price, performance, and ease of installation. Copper may be preferable for high-end or commercial applications needing the most durable piping.

Cost Differences

One of the biggest differences between PEX and copper is the material cost. PEX tubing is made from flexible plastic (cross-linked polyethylene) which is far less expensive than copper. Here are some typical costs for materials:

Pipe Material	Cost per Linear Foot
PEX	$0.30 – $0.50
Copper	$1 – $3

Copper pipes are around 3-5 times more expensive than PEX for the raw tubing. In addition, PEX is faster for DIY and professional installers to work with, resulting in lower labor costs too. So PEX can often save 50% or more on a total installed cost compared to copper.

Installation and Bends

The flexibility of PEX tubing makes the installation process much easier than using rigid copper pipes. PEX can make tight 90 degree bends without additional fittings, while copper cannot bend at all without specialized bending tools.

With copper, you need elbow joints every time you change direction. But PEX can snake around obstacles and make multiple bends in a single continuous length. This flexibility results in a faster installation with fewer connections or joints.

Joint Integrity

Since PEX doesn’t require as many joints as copper, it ends up being more leak-proof overall. Each push-fit PEX connection or crimp is a potential leak point down the line when pipes age or shift. Copper systems with soldered elbows and T-joints have many more opportunities for joints to fail and start leaking.

PEX has up to 75% fewer connections compared to copper. And when PEX joints do leak, they will often only leak a drop at a time. Copper joint leaks can fail catastrophically and result in significant water damage if not repaired quickly.

Freezing and Bursts

One big advantage PEX has over copper is its ability to resist freezing and bursting during cold weather. Copper pipes become completely rigid in freezing temperatures. If water inside happens to freeze and expand, the pipe material cannot flex at all, usually resulting in a burst section.

PEX tubing is more flexible by design. If water freezes inside, PEX can expand slightly to accommodate the increase in volume of the ice without rupturing. This makes it very resistant to wintertime pipe bursts, a common problem with copper and other rigid pipe materials.

Heat Tolerance

Copper is considered one of the best pipe choices for hot water applications. It can safely contain water heated up to 200°F like may be present with tankless water heaters or commercial boilers.

PEX tubing is heat rated for temperatures up to 180°F continuous exposure. This makes it fine for standard household water heaters storing 120°F or less. But for systems with sustained very hot water, PEX could potentially weaken or fail before copper.

Inside Surface and Water Flow

Copper pipes have an extremely smooth interior surface that allows for excellent water flow and pressure due to low friction loss. PEX tubing has a slightly corrugated texture on the inside walls which can create more turbulence and reduce flow rates.

In most residential plumbing applications, the difference in flow between PEX and copper is not very noticeable. But over very long runs or commercial systems, copper may be able to deliver measurably higher water volume.

Chemical Resistance

Copper has excellent chemical resistance and can safely contain just about any residential water chemistry. The only exception is highly acidic water below pH 6.5 which can corrode copper over time.

PEX tubing should not be used with petroleum products, powerful solvents, or highly concentrated acids/bases. It also degrades over time when exposed to chlorine or chloramines above normal drinking water concentrations. So copper may be a safer choice for homes with well water chemical treatment systems installed.

UV Light Resistance

An issue with PEX tubing is that exposure to UV light can cause it to become brittle and damaged over time. This is why PEX should not be used for exposed outdoor plumbing applications unless it is specially UV-shielded or coated.

Copper has complete UV resistance and will not degrade in any way when exposed to sunlight. It can withstand permanent outdoor use without protection.

Rodent Resistance

Rodents like mice, rats, and squirrels can sometimes bite through PEX tubing with their sharp teeth. Copper is much more resistant to gnawing damage from critters. Areas with known rodent problems may benefit from copper pipes instead of PEX to prevent plumbing leaks.

Noise Transmission

The plastic composition of PEX dampens sound better than rigid copper pipes. This can make PEX the quieter choice when running water lines through living spaces like bedroom walls. Copper transmits more noise and water hammer echoes through the house.

Ease of Repair

Fixing a damaged section of PEX pipe is a simple cut and replace task. Just cut out the bad segment and splice in a new piece using couplers. Sweat soldering repairs on copper is slower, more difficult, and requires draining all the water out of the pipe first.

However, PEX has a shorter lifespan than copper, so it will likely need full replacements sooner. Copper can last 50+ years in a house with no repairs needed in many cases.

Recycling and Environmental Impact

Copper is one of the most highly recycled materials on the planet. Old copper pipes can be remelted and manufactured into new products. Recycling rates for copper exceed 70%.

PEX cannot be recycled nearly as effectively. It is more likely to end up in landfills after use. However, PEX is quite abundant and made from common natural gas and petroleum compounds. So it may have a lower net environmental impact compared to mining and smelting copper ore.

Resale Value

Homes with copper plumbing may have a slightly higher resale value over PEX. The material is more prestigious and associated with quality. However, PEX has gained widespread acceptance in the real estate market, so any value difference is likely minimal in most cases.

Conclusion

For typical residential water heater applications, PEX offers an excellent combination of affordability, ease of installation, and reliability. The flexibility, freeze resistance, and leak protection make it our recommended choice for most homes and DIY installs.

Copper may be preferred for high-end custom homes, commercial applications, or systems with specialized plumbing needs. It all comes down to budget and performance requirements. Either material can provide many years of quality service life.

As always, be sure to consult local building codes for any restrictions on PEX or copper for your area and application. A professional plumber can also help assess the best pipe material based on your specific water quality and plumbing layout.