The Complete Guide to Choosing PEX Pipe Fittings

PEX (crosslinked polyethylene) piping has become popular for plumbing systems thanks to its durability, flexibility, and low cost. However, to assemble a PEX plumbing system, installers must select from a wide range of PEX pipe fittings and connection types to join pipes, change directions and adapt to various interfaces. With so many options available, choosing the right PEX pipe fittings for an application can become complicated.

This comprehensive guide provides a systematic approach to selecting PEX pipe fittings. We will analyze the types of PEX fittings, their purposes, and their pros/cons. We explore the differences between crimp, compression, and expansion PEX connections. We compare materials like brass, copper, and plastic. We provide sizing charts to properly match PEX tubing and fittings. We also offer tips for PEX plumbing designs to minimize fitting usage. Our goal is to simplify the PEX pipe fitting selection process for DIYers and professionals alike to achieve high-quality plumbing systems.

 

Types of PEX Pipe Fittings

The first step in fitting selection is understanding the different types available:

- Elbows: Allow piping to change directions at 90 or 45-degree angles. Used where PEX pipe cannot easily bend.

- Tees: Splits a single source pipe into two separate branches. Accommodates pipe size changes.

- Couplings: Join two pieces of PEX pipe together end to end. Used to extend pipe to the required length.

- Caps: Seal the end of an open pipe for plugging or testing. Should be removable.

- Adapters: Transition between pipes of different sizes or between PEX and other pipe types. Allows interface with non-PEX plumbing components.

- Manifolds: Provides multiple ports for connecting pipe branches to a central trunk line. Simplifies plumbing layouts.

- Valves: Control water flow direction, rate, or shutoff. Types include ball valves, stop valves, drain valves, and control valves for thermostatic devices.

These fitting categories ensure installers have the right components to execute any residential or commercial plumbing design using PEX. Choosing between the options comes down to the precise dimensions, performance, and interface requirements of each application.

Connection Types: Choosing Crimp vs. Compression vs. Expansion

The next key choice is determining the best way to connect PEX pipes and fittings: crimp, compression, or expansion. Each has unique pros and cons:

Crimp: Crimp rings or bands seal over the junction of pipe and fitting. A hand or hydraulic crimping tool is used to squeeze the ring tightly and create a weather-tight seal. Pros include speed, low cost, and durability. However, special tools are required and connections cannot be undone. Crimping also reduces internal pipe diameter slightly.

Compression: Part of the fitting protrudes into the pipe, creating a seal when tightened with a nut and washer. Pros include reusability and no special tools needed. However, compression fittings tend to be more expensive and time-consuming to install than crimps. They also protrude into the pipe, slightly reducing flow.

Expansion: The PEX pipe end gets expanded before inserting into a fitting. When released, the pipe attempts to return to size, creating a tight seal. Pros include speed and weather-tight seals. However, special expansion tools are required. This method works best on PEX-a (chlorination) pipe which has the ability to forcibly return to size.

Selecting between these connection types depends on priorities for cost versus reusability, available tools, effect on flow, installation timeline, and PEX piping type. There is no one right choice for all applications. Thinking through options based on situational factors will lead to the ideal connection method for each PEX fitting.

 

Brass vs. Copper vs. Plastic PEX Fittings: Comparing Materials

PEX pipe fittings are available in several materials:

- Brass: Durable, corrosion-resistant, and inexpensive. Works with all PEX types. Potential leaching risks for potable water mean brass PEX fittings must meet plumbing standards.

- Copper: Nearly as durable as brass but more expensive. Will not leach chemicals. Works best for hot and cold water PEX plumbing systems. Prone to corrosion in acidic or alkaline environments.

- Plastic (ABS, PVC, CPVC): Lightweight, non-corrosive and affordable. ABS and PVC fittings work for drainage and vent applications but not pressurized plumbing. CPVC is rated for potable water but can become brittle over time. More prone to cracking compared to metal.

- Stainless Steel: Highly durable and corrosion-resistant but the most expensive option. Works for all PEX applications including high-pressure or marine plumbing. Can scratch the PEX pipe if not properly interlinked.

- Polypropylene: Lightweight, non-corrosive plastic fitting resistant to solvents and chemicals. Inexpensive but have lower pressure ratings than metal fittings. Used for gravity flow drainage, venting, and some low-pressure plumbing where codes permit.

For most standard PEX plumbing, brass, copper, or stainless steel fittings are good durable choices. Plastic options may suit some limited applications but need to be properly pressure-rated and certified to safety standards for potable water systems. Comparing pros, cons, and costs will determine the optimal fitting material for your PEX project needs.

 

PEX Fitting and Pipe Sizing

When it comes to PEX plumbing, sizing fittings properly is as important as choosing their types and connection methodology. Understanding sizing conventions and accurately matching PEX tubing diameters with fitting dimensions avoids inefficient flow rates, leaks or pipe burst risks.

PEX tubing uses nominal pipe sizing (NPS) to indicate internal pipe diameter. So 1/2” PEX nominally means around 1/2” inner diameter. PEX tubing sizes range from 1/4” up to 2” for most residential and commercial plumbing applications. As pipe diameter increases, so do maximum flow rates and water volume contained.

Meanwhile, PEX pipe fitting sizing refers to the outer diameter of piping it can join. A 1/2” PEX elbow fitting will work with a nominal 1/2” PEX pipe, and a 3/4” compression PEX coupling will fit 3/4” tubing. Matching these sizing levels ensures fittings join properly without leaks, though the specific inner/outer sizing may vary slightly between PEX and fitting.

Most importantly, achieve optimal flow rates by selecting tubing and fitting sizes that keep water velocity between 2 to 5 feet per second. This provides enough volume and pressure for fixture needs without excessive noise or energy losses. Consult plumbing sizing tables to choose dimensions satisfying flow rate requirements for each section of PEX pipe in the system.

Good drainage pipe slopes also contribute to sizing for flow. Pitch horizontal PEX drainage pipe at least 1/4 inch per foot for sections up to 75 feet in length. Increase slope for longer pipe runs. A sloped pipe helps wastewater and fluids move freely at the required rates.

 

Minimizing Fittings in A PEX Plumbing System Design

While fittings serve a vital purpose, optimizing a PEX plumbing system design using as few fittings as possible maximizes flow efficiency and minimizes both costs and potential leak locations:

- Consolidate multiple small bath fixtures onto looped home run manifolds to avoid excess joints.

- Use PEX pipe minimum bend radius to your advantage to curve pipe around corners or obstacles rather than cutting and fitting to change directions.

- For long supply lines to sinks or tubs on any floor, run a direct vertical length of PEX from below to above instead of cutting in horizontal fittings.

- Where installs require adapting pipe sizes, do so at the point closest to the demand source rather than at the manifold supply origin. This is especially useful for laundries or other high-demand terminations.

- For radiant floor heating, use manifolds to adapt in line and change loop directions instead of cutting pipe. This keeps loops independent and uninterrupted for balanced pressure.

- When estimating materials, add around 15% additional PEX tubing to account for trimming to length. This avoids coming up short, which requires additional joining to extend. More pipe is less costly than more fittings.

Plumbing and piping may not be design arts, but applying creativity and thinking one step ahead about reducing connections and maximizing direct runs results in a clean, uncluttered PEX configuration. Solve more with pipe vs. fittings where feasible for high-quality installations that afford both form and function.

 

Selecting PEX pipe fittings requires weighing multiple trade-offs around cost, flow, compatibility, and reliability for each application. But by approaching fitting choice systematically – analyzing types, connection methods, materials, and sizing – installers can navigate options efficiently and make informed decisions for premium results. With the right plumbing layout and a minimalist mindset minimizing extra connections, DIYers and professionals alike can produce sleek, high-performance PEX systems that will endure for lifetimes using as few fittings as possible and maximizing hydraulics. Choosing wisely and designing thoughtfully allow this affordable plumbing material to achieve upscale ambitions. PEX's reputation depends on attention to detail at every joint explored in this fitting guide to channeling the waters of tomorrow.