A Complete Guide to Using Plumbing Fittings for Joining PEX Pipe, PVC and Copper
A DIY Guide to Plumbing
Basic plumbing isn't rocket science. If you are reasonably adept at DIY, understand the basics, and take care when putting it all together, it's not too difficult. This is a comprehensive and easy-to-understand guide to pipe types, plumbing fittings, thread sizes, with instructions for how to use fittings to connect copper, PVC, and PEX pipes.
What's Covered in this Guide
- Pipe and tube types and thread sizes
- Compression fittings
- Threaded fittings
- Push fittings
- Soldered capillary fittings
- How to cut tube and pipe
What Material and Type of Plumbing Pipe Is Right for the Job?
Plumbing pipe is made from various materials, including copper, galvanized steel and iron, polyvinylchloride (PVC), chlorinated polyvinylchloride (CPVC), cross-linked high-density polyethylene (PEX), and polybutylene. Fittings are made from brass, plastic, copper, or malleable iron.
- Copper. Copper is widely used and can withstand very high temperatures. It is always used for the final connections made to central heating boilers/furnaces where temperatures may exceed 100°C (212°F). The disadvantage of copper pipe (or "tube," as it is known in the plumbing industry) is that it is rigid and either must be bent by using special tools or by using separate lengths of pipe and 45° or 90° joints.
- Stainless Steel. In the 70s during a copper shortage, stainless steel plumbing was popular. It is even more rigid than copper, however, so any bending can be difficult. Stainless steel is supposed to be more corrosion-resistant than copper and is sometimes used for aesthetic reasons where plumbing must be exposed.
- PVC and CPVC. Piping made from these plastic polymers has several advantages over copper. Plastic pipe is ductile and can be easily bent, reducing the number of bend fittings required. If a really tight bend is required, 90° elbow joints can be used. It can also be easily routed through floor and wall spaces. Plastic is a better insulator than metal, so heat loss is reduced. Usually, plastic piping has more "give" and will stretch more than copper when water freezes and expands inside the pipe, reducing the danger of bursting in sub-zero temperatures. PVC or polyvinyl chloride is the most basic type of plastic pipe used for both drinking water and waste pipe plumbing. Chlorinated PVC or CPVC has the same characteristics as standard PVC but has better corrosion resistance at higher water temperatures and is also significantly more bendable.
- PEX. Plumbing tubing is also made from cross-linked high-density polyethylene (PEX). This is a tough, ductile material which can survive temperatures as low as -20°C (-4°F) without bursting. PEX is also less than half the price of copper and doesn't corrode when used in places where the water is acidic. Just like PVC, PEX is flexible and can be bent over a tight radius and easily routed to fittings. It does expand more than copper so it shouldn't be stretched to reach fittings and should be allowed to drop slightly between fixings to allow for contraction. On long runs, a loop of tubing can be included in a line to allow for a lot of contraction. When running tubing through holes in walls, make the holes sufficiently large so that the tube can slide freely as it expands and contracts. PEX is susceptible to UV, and if used outdoors, it needs to be shielded (with insulation or otherwise) to prevent degradation.
- Ductile (Malleable) Iron. Used for water, gas, compressed air, and as a rigid metal conduit (RMC) for housing cables in industrial and commercial applications, ductile iron is much stronger than copper or plastic pipe but not so common in domestic installations. Ductile iron or cast iron was often used for larger-diameter water mains before the invention of plastic.
- Lead. No longer used for plumbing because of its toxicity, lead piping was phased out after WWII when copper became popular.
A note about plastic piping: Care needs to be taken when working near plastic piping or fittings to avoid heat damage from blow torches or other heat-producing tools. Piping should also be routed during installation so that it isn't subjected to high temperatures from heat sources such as flues.
Domestic copper and plastic plumbing are technically referred to as tubing. Steel and heavier gauge plastic plumbing is referred to as piping.
What Material and Type of Plumbing Fitting Is Right for the Job?
Fittings are made from various materials, including plastic, brass, copper, and iron. There is a huge variety of types with different functions, including 90° and 45° elbows, offsets, T-joints, Y-joints, cross joints, gate valves, ball valves, non-return (check valves), reduction fittings, couplers, and flange (bulkhead) fittings for making a connection to oil or water tanks.
- Brass Threaded and Compression Fittings have two or more ports or entry points for connection to pipes or fixtures. They may be compression-only, compression-and-screwed, or screwed-only. The compression port is used for connecting a pipe, and the screwed port (if included) connects to a fixture or device such as a radiator, WC, furnace, spigot, pressure gauge, or water tank. The screwed section of the fitting may have male or female threads. Fittings with compression ports only are used to join two or more pipes together and are simple to use by the average DIYer once pipes are prepared correctly, and the fitting is assembled properly. Brass threaded and compression fittings make use of a copper or brass olive ring (also known as a "ferrule" or compression ring) which is slid onto the end of the pipe before insertion. This is then bent and squeezed tightly against the tapered surface of the fitting as a nut on the pipe is tightened. This seals the fitting and prevents water from leaking out.
- Compression fittings can be used for connecting plastic or copper pipe and, although easy to use, are relatively bulky and more expensive than other joining methods. Another disadvantage is that a pipe can possibly turn within the fitting (e.g., a coiled copper pipe behind an ice-making refrigerator can turn as the fridge is pushed in and out repeatedly), and over time, this can cause leaks. Compression fittings can be easily disassembled. Plumbers often use PTFE tape or jointing compound (which is like soft putty) on compression fittings to be totally sure they don't leak. However, manufacturers don't recommend this because they reckon it can prevent the olive from sealing properly. Brass fittings are not recommended for use underground.
- Capillary Fittings are made from copper and require a soldered joint to connect pipes together. The pipes-to-be-joined are inserted into the fitting, which is heated. Solder fills the small gap between pipe and fitting, sealing and making a strong joint which is resistant to pulling and rotation of the pipes. This type of fitting either comes with a ring of solder included (Yorkshire fitting) or solder wire must be melted and fed into the joint as it is heated. Capillary fittings are slim and neat, inexpensive, and form a strong joint between pipes. However, they are more difficult to use, and since the fitting must be heated using a blowtorch, there is always the danger of fire. Also, preparation of pipes and fitting is essential, and these must be cleaned with wire wool so that solder flows and coats all the surfaces being joined.
- Ductile (Malleable) Iron Screwed Fittings can be used with water and compressed air and are relatively inexpensive. These fittings are often encountered on the inlet/outlets of central heating boilers/furnaces, on pumps, and on-air compressors. Because iron is less expensive and stronger than brass, iron fittings are advantageous, especially when large sizes are required.
Galvanized versions of these fittings are available which are resistant to external corrosion.
- Plastic and Copper Alloy Push (Stab-In) Fittings are available for joining plastic and copper pipe. To use them, you just have to square-cut the end of a pipe and push it into the fitting; an internal O-ring compresses tightly against the pipe when inserted. These fittings also incorporate some form of collet/toothed ring arrangement which digs into the pipe and prevents it from being pulled out again. These type of fittings are very easy and convenient to use, especially in tight spaces, enabling pipes to be jointed quickly. They can also usually be disassembled by hand or by using a special key. In either case, the teeth retract, allowing the pipe to be removed. Fittings which can be disassembled by hand, without a key, sometimes have a twist-lock feature. This locks the collet, preventing the inadvertent release of a pipe from a fitting if something accidentally pushes against the collet. Sharkbite and Speedfit are two well-known brands of this type of fitting.
Push fittings can be used with copper, CPVC, and PEX tube, but aren't suitable for PVC. See Connecting PEX to PVC for more details.
For large projects, the cost of push or compression fittings on PEX can mount up. A cheaper alternative is crimp fittings, which are slimmer but must be installed using special tools. See How to Install PEX Tubing—Making a Crimp Connection.
Examples of Plumbing Fittings
What Is a Union Fitting and How Do I Use It?
A union fitting enables two parts of the fitting to be attached to each other without having to turn the whole fitting or attached pipes.
- These are often encountered on the plumbing to radiators or on the end of gas or water hoses.
- A nut on one part of the fitting is tightened, pulling the two halves of the fitting together.
- A curved or cone-shaped profile on one part presses into a similar-shaped socket on the other half to make a watertight seal.
- The two halves are easily separated by undoing the nut, e.g., when removing a hose from an outside tap or replacing a radiator.
Standard Sizes of Fittings, Pipe Sizes, and Threads in the US, UK, and Ireland
- U.S.A. Fittings follow the National Pipe Thread Taper (NPT) standard defined in ANSI/ASME B1.20.1. Commonly used sizes are 3/8, 1/2, 3/4, and 1 inch. This dimension refers not to the diameter of the threads, but to the internal diameter of the iron pipe used with the fittings (specifically, schedule 40 pipe). Copper and plastic tubing follow the Copper Tube Size (CTS) standard with the outside diameter being 1/8 inch greater than the Nominal Pipe Size (NPS). For example, a 1/2 inch tube has an OD of 1/2 + 1/8 = 5/8 inch. Fittings can also have a parallel thread (also abbreviated NPS). Whereas NPT fittings may not need a sealant in order to be air- or water-tight, NPS fittings must be sealed with PTFE tape or dope. National Pipe Thread Tapered Fuel (NPTF) fittings are used for applications that cannot use PTFE tape or other sealant due to high temperatures or pressure or because of the nature of the fluid transported by the pipe (e.g. gasoline or hydraulic oil). The difference standard NT and NPTF is in the smaller and bigger diameters of the threads and their roots and crests, a joint relying on the taper of the thread to form a seal as male and female components are forced into each other on tightening.
- U.K. The thread used for fittings is BSP (which stands for British Standard Pipe Thread, defined in BS EN 10226-1 and BS EN ISO 0228-1). The most common sizes encountered in the home are 3/8, 1/2, 3/4, and 1 inch. These sizes originally referred to the inner diameter of a steel pipe for which the fitting was intended. Copper and plastic tube used with these fittings has been metric since 1971. The most common sizes are 10, 15, 22, and 28 mm for domestic applications. The size refers to the outside diameter of the tube.
- Ireland. Threads on fittings are BSP. Tube sizes are imperial and normally quoted by referring to the BSP thread size of the corresponding fitting, e.g., 1/2, 3/4, or 1 inch. The outside diameter of plumbing tube is slightly less than the corresponding British versions, which can lead to issues with leaks if fittings and tube are mixed-and-matched (see table below).
FIP and MIP (female iron pipe and male iron pipe) are terms sometimes used to refer to the shape of the threads on a fitting. For more info and sizes, see
NPT Pipe, Thread and Tube Sizes
Pipe Sizes and Standards Can Be Somewhat Confusing
For example, if you measure a 1/2 inch pipe or 1/2 inch fitting, neither the internal or external diameter of the pipe nor the diameter of the thread are necessarily 1/2 inch. It is only called 1/2 inch for historical reasons. This dimension originally referred to the internal diameter of a pipe used with the 1/2 inch fitting, which in the early days of manufacture would have been thick-walled.
BSP Pipe, Thread and Tube Sizes
How to Cut Copper or Plastic Pipe
Copper or plastic tube can be cut with a hacksaw. However, if you use a pipe-cutting tool it gives a cleaner, squarer cut without burrs. The tool in the video below can be used to cut copper tube. It can cut plastic tube also with a little bit of effort, however, plastic pipe-cutting shears do a better job. Tighten it gradually after each couple of turns. If you tighten it too quickly, it can deform the end of the tube. If you use a hacksaw on copper pipe, file off any burrs afterwards.
How to Bend Copper Pipe
You can't just grasp the two ends and bend because the pipe will kink in the middle. There are several techniques for bending copper pipe:
- Use Sand to Prevent Kinking. This is an old technique. The pipe is tightly packed with fine, dry sand and tightly plugged at the end with a kitchen towel or a rag. The pipe is then bent to the desired shape.
- Use a Bending Spring. This method is only suitable for bending reasonably long lengths of pipe so that the length of the pipe can be used for leverage during the process. The spring is slid into the pipe so that it extends beyond the bend point. If necessary, a string can be tied to its end so that it can be retrieved. The pipe is then bent over the knee (just under your kneecap).
- Use a Pipe Bender. This tool has long levers to aid bending and enables one or more bends to be made in pipe. It also has several dies or guides to allow various diameters of pipe to be bent.
How to Use a Compression Fitting
- Measure the tubing to be cut and mark with a felt-tipped marker. If a fitting needs to be inserted into existing tubing (e.g., a T-joint for a branch off), a section of tubing must be removed. Sometimes, marks are provided on the outside of the fitting that indicate the location of the shoulder inside the fitting which the tubing butts up against when inserted. This aids in working out how much of the tubing needs to be removed. This needs to be reasonably accurate if copper tubing is being used as it can be difficult to pull the two ends of the tubing apart to insert the fitting if a too-short section is removed, or difficult to pull the two sections of tubing together again if too much tubing is cut out. Temporarily remove any clips holding the tubing so that the sections can be moved apart easier
- Cut the tubing to be joined to the correct length. Ideally, use a pipe cutter which gives a square, smooth edge. Alternatively, use a junior hacksaw. Try to cut the tubing square and file the cut edges smooth
- Slide the compression nut over the end of the tubing followed by the olive ring
- If plastic pipe is being used, push an insert into the end of the pipe. This prevents the pipe from being crushed by the olive as the compression nut is tightened
- Push the tubing as far as it will go into the fitting
- Tighten the compression nut by hand
- Mark the nut with a felt-tipped marker, so you know how much you've turned it while tightening with a tool
- You need two tools: one to hold the fitting and the other to tighten the compression nut. You can use open-ended wrenches, vice grips, or water-pump pliers. Make sure the tools are properly sized and grip tightly so that they don't slip off while tightening. In general compression, nuts should be tightened one half to one whole turn after you've tightened by hand. If possible, you can tighten by half a turn, then turn on the water supply and wait for a few minutes see if the joint "weeps." If this is the case, try tightening further. It's important to not over tighten as this can deform the olive, preventing it from sealing properly and causing a leak. Knowing how much to tighten a nut is learned by experience, and as a rule of thumb, once the nut suddenly becomes difficult to turn, it is tight enough.
How to Use Push Fittings
These vary somewhat, but in general, this is the procedure
- Measure, mark and cut the pipe. In general, you should avoid using a hacksaw as a square cut on the end of the pipe is more critical. Use a proper pipe cutter suitable for copper or plastic pipe. File off any burrs on the end of copper pipe.
- If using plastic pipe, push an insert fully into the end of the pipe
- Slide the pipe into the fitting until it will go no further. Pull back to ensure the teeth on the collet insert in the fitting have gripped the pipe and it is secure.
- Some fittings have a twist lock feature which prevents inadvertent release of the pipe if the collet is accidentally pushed back against the fitting. If this is the case, twist the screw cap on the fitting about half a turn. This further compresses the O-ring in the fitting and locks the teeth.
- Fittings can be disassembled when new by turning the twist lock counter-clockwise, pushing the collet back against the fitting body and pulling on the pipe. This retracts the collet teeth so that the pipe can be removed. Some fittings require the use of a key to retract the collet.
The video below shows how to use Speedfit twist lock fittings. These are very convenient to use for connecting both copper and plastic pipe.
How to Use a Speedfit Standard Twist-and-Lock Fitting
How to Use a Capillary Fitting With Copper Pipe
Capillary fittings require some skill in order to be assembled properly; however, they are the cheapest, neatest and strongest solution for joining copper pipe.
Copper pipe and capillary fittings are "sweated" together. This involves heating the pipe and fitting so that solder melts and holds the joint together.
- Mark and cut the pipe using a hacksaw or pipe cutter. Remove any burrs with a file.
- Clean the inside of the fitting and outside of the pipe with wire wool until both are shiny.
- Apply flux to the inside of the fitting and outside of the pipe.
- Insert the first pipe into the fitting until it goes no further. Insert remaining pipes into the fitting. (All pipes should be soldered together rather than one at a time).
- If a Yorkshire fitting is being used (which has an integral ring of solder in each port), heat all around the fitting until a shiny ring of solder appears at the edge of the entry port on the fitting. Solder-free fittings should be heated, and solder wire applied to the edge of the entry port so that it flows into the gap between the fitting and pipe. (make sure it is lead-free solder if the water is for potable (drinking) use). Avoid overheating. If the flux starts to char, you're over doing it!
- Wipe off excess flux after completing the joint. Some fluxes are acidic and can eventually eat through copper.
Be careful when using a blowtorch and take suitable precautions to avoid starting a fire. Adjacent plastic plumbing and wiring can easily be melted. Fireproof mats are available for placing behind fittings during heating. A ceramic tile can also give some protection, but avoid directing the flame directly on it, as it can shatter.
How to Use Screwed Plumbing Fittings
Steel pipe with a screwed end, normally has a tapered male thread which mates with a female thread on the other fitting. PTFE plumbing tape or other proprietary thread sealing cord wrapped around the threads increases lubrication and enables the male thread to be screwed in tighter to produce a watertight seal. The secondary benefit of the tape is to fill the gap between the female and male thread, helping to seal the joint.
You can also smear pipe dope (jointing compound) over the tape on the joint to improve sealing in case the tape catches on the threads and rolls around as the fitting is being screwed into place. Traditionally hemp and jointing compound (Boss White, Plumbers Mait) were used for sealing joints. For some applications, if temperature is excessive, PTFE tape may be unsuitable, and jointing compound can be used.
Sometimes both male and female threads are parallel in which case they are supposed to be sealed using a fiber washer or O-ring which is compressed by a flange on the fitting. This is often the case with a spigot (outside tap) or a hot water tank. A tapered fitting would possibly result in the fitting tightening suddenly with the spigot at the wrong angle. A washer however allows more leeway as regards tightening the fitting to the correct angle
- Hold the fitting or pipe and starting at the inner end of the threads, wrap PTFE tape tightly and evenly clockwise and upwards in a helical fashion until all but the last thread is covered. Leaving the first thread bare makes it easier to get the thread started during assembling of joints.
- Continue to wind the thread clockwise and downwards to where you started.
- Wind a third layer onto the fitting
- Screw the male thread into the female fitting
There is a certain degree of trial and error when winding tape onto fittings. If they are made to a tight tolerance, only a few layers of tape may be needed. Sometimes if fittings are a loose fit, extra tape may be needed (4, 5 or 6 turns).
Wrapping Thread Seal Tape
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
Can Pex or PVC pipe be chased into a wall? I'm guessing maybe something like pipe insulation might be prudent to allow for expansion and contraction as well as protecting the pipe itself from the mortar?
I don't see why not as long as it's well insulated. PEX is also resistant to bursting even if it freezes. Metallic tape is supposed to be wrapped around the plastic pipe so that a metal detector can be used to locate it if any fixings need to be inserted in the wall in the future. It'd also be prudent not to have any joints in walls just in case they leak. I'm not a plumber, so maybe try posting on this forum to double check (or an alternative forum if you're in the US or other country that may have different regulations):Helpful 2
I am attaching a brass fitting to the threads of black pipe in a natural gas application in order to get to the flex line to the appliance. Or is it better to use the stainless steel, or whatever material it is that comes with the gas connection kits? This is an outdoor application, so I thought brass would hold up longer, but I'm not sure about the dissimilar metals factor?
There could be an issue with dissimilar metals and Galvanic corrosion. Indoors since water isn't going to get into threads in a gas connection, it's not an issue, but outdoors it may be a different story.
I'm not a qualified gas plumber/fitter, so I'm not going to advise you.
You could post on one of the several plumbers forums and they might be able to advise you, but will probably refer you to a professional.Helpful 2
Can I connect a 1/2 T pipe to the main 3/4 water copper pipe, one end of the T goes to the washer, the other end goes to bath faucet?
Possibly, you'll need either a T if it's available with a 3/4" outlet port and 1/2" ports on the two ends of the T. Alternatively a 3/4" T could be used with inserts in the other two 3/4" ports to drop them to 1/2" (this is for brass fittings). The inserts are just brass rings that reduce the inlet to 1/2". I'm not a plumber so I'm not going to give advice and there may possibly be regulations about how this is done and other complications. Maybe post the question on a plumbers forum.Helpful 1
I recently had our kitchen faucet changed and now we get a terrible chemical taste only from that faucet, could there be something wrong with the faucet?
Have you spoken to the manufacturer/retailer? Sometimes plastic (which would be used in seals) has a smell or produces a taste from residues left over from the manufacturing process (e.g. the distinctive smell of PVC or taste from water left for a period in a plastic bottle). Try running the faucet for several minutes and see if it improves the situation.Helpful 1
What is used to connect a 5/16 inch rubber tube through a hole on a one-inch copper pipe? The system I have that the rubber tube is inserted with a piece of one-inch PVC tube half way and the PVC tube is then inserted into the copper pipe through the hole. The one that came loose can be easily pulled out. I do not see anything on the PVC tube, glue or cement. Other fittings cannot be pulled out easily. Can you tell me how this is done so that the plumbing will not leak?
If the system isn't under pressure, possibly some form of grommet arrangement could be used to suit the hole in the copper and then the rubber tube would feed through the grommet. This system is sometimes used for fuel lines exiting tanks on e.g. string trimmers.
© 2015 Eugene Brennan