PEX fittings buying guide

Polyethylene (PE) pipe was first used to carry water in large scale water systems about 50 years ago and it wasn't long before this material was adapted for use in domestic plumbing systems. The result of this adaptation is PEX or cross-linked polyethylene pipe.

Highly versatile and very easy to install, PEX pipe or tubing has slowly been replacing copper pipe – or even lead pipe in very old systems – over the years. PEX is very resistant to both high temperatures and pressure meaning it can be used for sanitaryware and heating systems. What's more, it does not require soldering to install as long as the right types of fittings are used.

A plumbing system is made up of a series of pipes and pipe fittings. It's important to pick the right type of fitting for the system (i.e. hot or cold water) to ensure that it is watertight and productive. A productive system means one with as little flow or pressure loss as possible.

The most important factors to consider when choosing PEX fittings are as follows:

• connection type: compression, expansion or crimp;

• fitting type: straight coupler, elbow, tee, etc. ;

• male or female;

• size: PEX pipe tends to measure 10 to 25 mm (rarely more for domestic installations).

1. Connection type

PEX compression fittings

PEX compression fittings can be used to secure PEX piping or to connect PEX pipe to other types of pipe like copper. These fittings are compressed by tightening a compression nut or ring around a compression insert using an open ended spanner or adjustable spanner. They are quick to fit and do not need to be soldered. These fittings can be used for cold or hot water systems and tend to be the most straightforward of all PEX fittings to install.

PEX expansion fittings

PEX expansion fittings are used to connect pipe to fixtures. They are easy and quick to assemble provided you have a special tool to briefly stretch the pipe. These fittings feature a male connection which is inserted into the expanded PEX pipe. The connection is secured by sliding a clamp ring over the male connection to trap the pipe between the two components. Much more reliable than compression fittings, the only downside of expansion fittings is that they cannot be disconnected once in place.

PEX crimp fittings

PEX crimp fittings can be used to connect PEX pipe to any type of installation. Crimp fittings are the only type of PEX fitting that can be installed in a wall or behind a partition wall. The connection is made by compressing a crimp ring over the PEX pipe using a special PEX crimping tool. Like expansion fittings, these fittings are absolutely watertight but are permanent meaning they cannot be removed once fitted.

2. Fitting type

A domestic hot or cold water system usually requires several types of fitting depending on its layout.

Here are some of the most common:

• straight couplers: to connect PEX tubing to another element in the system;

• elbows: to change direction (usually to 90°);

• tees: to create a junction or diversion;

• valves: to open or close the system;

• wall plates: unions, elbows, tees or valves with a wall-mounted fixing plate;

• end stops: to close off a circuit.

3. Male / female

PEX fittings can be male or female.

The gender of the fitting, i.e. if it features male or female threads, determines the type of connection that can be made when the fitting is in place.

It's worth noting that the type of fitting where PEX pipe is connected is always male.

4. Size

In a domestic hot or cold water system, the size of the fitting must match the size of the PEX pipe. The most common sizes are 12, 15, 22 and 28mm. In larger shared buildings, sizes can occasionally be larger though the piping in this case will usually be made of polyethylene (PE) instead of PEX.