How to Connect PEX to Plumbing Under a Kitchen Sink

If you’ve ever stared at the maze of pipes under your kitchen sink wondering how to connect PEX tubing without causing a flood, you’re not alone. Many homeowners tackle this task to replace old copper lines, install a new faucet, or upgrade to more flexible, durable PEX piping. In this guide, we’ll walk you through how to connect PEX to plumbing under a kitchen sink—safely, efficiently, and with confidence—even if you’ve never held a crimp tool before.

Why Use PEX Under a Kitchen Sink?

Before diving into the “how,” it helps to understand the “why.” PEX (cross-linked polyethylene) has become the go-to choice for modern plumbing thanks to its flexibility, freeze resistance, and ease of installation.

According to the Plumbing-Heating-Cooling Contractors Association (PHCC), over 60% of new residential plumbing installations in the U.S. now use PEX instead of traditional copper or CPVC. Why? Because it’s:

• Resistant to scale and chlorine
• Quieter than metal pipes (no “water hammer” noise)
• Faster to install—no soldering required
• Cost-effective (up to 30% cheaper than copper)

For under-sink applications—where space is tight and connections are frequent—PEX’s bendability is a game-changer.

💡 Fun fact: PEX was first used in Europe in the 1970s for radiant floor heating. It gained U.S. approval for potable water in the 1980s and is now codified in all major plumbing codes, including the IPC and UPC.

What Tools & Materials Do You Need?

Connecting PEX isn’t hard—but you’ll need the right gear. Here’s a checklist:

🔗 For more on PEX standards and safety, see the Wikipedia entry on PEX.

Step-by-Step: How to Connect PEX to Plumbing Under a Kitchen Sink

Follow these steps carefully. Even small mistakes can lead to leaks or reduced water pressure.

Step 1: Turn Off the Water Supply

Locate the main shutoff valve or the individual valves under the sink. Turn them clockwise until tight. Open the faucet to drain residual water.

Step 2: Remove Old Supply Lines

Use an adjustable wrench to disconnect the existing supply lines from the faucet tailpieces and shutoff valves. Keep a towel handy—some water may drip out.

Step 3: Measure and Cut PEX Tubing

Measure the distance from the shutoff valve to the faucet inlet. Add 1–2 inches for maneuverability. Use a PEX-specific pipe cutter to ensure a clean, square cut—critical for leak-free connections.

⚠️ Never use regular scissors or hacksaws—they create uneven edges that compromise seals.

Step 4: Deburr and Insert Fitting

Run a deburring tool around the inside and outside of the cut end. Slide a crimp ring onto the PEX tube, then insert the PEX-to-compression adapter fully into the tube until it bottoms out.

Step 5: Crimp the Connection

Position the crimp ring ¼ inch from the end of the tube. Use your crimping tool to compress the ring evenly around the fitting. For extra assurance, use a go/no-go gauge to verify proper compression.

✅ Pro Tip: If you’re using stainless steel clamp rings (like those from SharkBite), you’ll need a cinch tool instead—but the process is nearly identical.

Step 6: Connect to Faucet and Valve

Attach the compression end of the adapter to the faucet tailpiece and hand-tighten. Then connect the other end to the shutoff valve. Use a wrench for a final ¼-turn snug—but don’t overtighten, or you’ll crack the valve.

Step 7: Test for Leaks

Slowly turn the water back on. Check every connection for drips. If you see moisture, turn off the water immediately and re-crimp or replace the fitting.

PEX Connection Methods Compared

Not all PEX connections are created equal. Here’s a quick comparison of common methods for under-sink use:

For most homeowners, crimp or clamp systems offer the best balance of cost, reliability, and ease.

Common Mistakes to Avoid

Even experienced DIYers slip up. Watch out for these pitfalls:

• Skipping the deburring step → leads to turbulence and fitting failure
• Using non-PEX-rated fittings → violates code and risks contamination
• Over-bending PEX → kinks restrict flow; use gentle curves or elbows
• Ignoring local codes → some municipalities restrict PEX near water heaters

Always check your local plumbing regulations before starting.

FAQ Section

Q1: Can I connect PEX directly to a kitchen faucet?

A: Not usually. Most faucets use 3/8″ compression or 1/2″ NPT threads. You’ll need a PEX-to-compression adapter to bridge the gap. Direct PEX-to-faucet connections aren’t standard and could void warranties.

Q2: Do I need special PEX for hot water lines?

A: Yes—but most PEX-A, PEX-B, and PEX-C are rated for both hot and cold water (up to 200°F). Just ensure your tubing is labeled “NSF/ANSI 61” for potable water safety.

Q3: How long do PEX connections last under a sink?

A: When installed correctly, PEX systems can last 40–50 years. The weak point is usually the metal fittings—not the tubing itself. Use brass or stainless steel fittings for longevity.

Q4: Can I reuse old shutoff valves with PEX?

A: Only if they’re in excellent condition and have compression or sweat outlets compatible with adapters. If they’re corroded or older than 10 years, replace them with quarter-turn ball valves—they’re more reliable and easier to operate.

Q5: Is PEX safe for drinking water?

A: Absolutely. All PEX sold in the U.S. for potable water must meet NSF/ANSI Standard 61. Independent studies (including by the EPA) confirm no harmful leaching when properly installed.

Q6: What if I don’t own a crimping tool?

A: Consider push-fit connectors like SharkBite for temporary fixes—but they cost 3–5x more per connection. Alternatively, many hardware stores (Home Depot, Lowe’s) rent crimping tools for under $20/day.

Conclusion

Now you know exactly how to connect PEX to plumbing under a kitchen sink—without stress, guesswork, or costly plumber fees. With the right tools, a little patience, and this guide, you’ll create leak-free, code-compliant connections that last for decades.

✅ Benefits recap:

• Saves money vs. hiring a pro
• Reduces risk of leaks with modern materials
• Gives you full control over your home’s plumbing

If this guide helped you, share it on Pinterest, Facebook, or Reddit to help fellow DIYers! Got questions? Drop them in the comments—we’re here to help you succeed.

Remember: Great plumbing starts with one smart connection. 🛠️💧