The K-Zone: Speed up your plumbing with push-fit plastic fittings

So there I was, crouching in the boiler cupboard, 15 solder joints done and one more to make, blowtorch in one hand, solder in the other; a quick dab of the solder on the last joint... aaargh! it hasn't taken! Solder's all lumpy... more heat, more solder, solder running down the pipe now... still hasn't taken! More heat... now the next joint's melted... there's a puddle of solder on the floor... Oh, I give up. Have you been here?

What this article is about

I am writing this article to introduce amateur plumbers -- or would-be amateur plumbers -- to the pleasures of push-fit plastic plumbing. I had been plumbing the old-fashioned way (copper fittings, solder, blowtorch, wire wool, etc) for a year before I realized that I'd had enough. If I had come across an article like this myself when I began my home improvement, I would never have experienced the scenario above, and my life would have been all the better for it.

[Update 11/05 -- I recently had a telephone call from a gentlemen who found that mice had nibbled through his plastic pipework, and made something of a mess. I think it's entirely possible that mice, if they are sufficiently determined, probably can knaw through plastic pipework eventually. I've certainly known them to chew a hole in a plastic oil can. However, apart from this one report, I've never known mice to damage plastic plumbing. If you know differently, please contact me].

Types of plumbing

In the UK most plumbing is done with copper pipe and fittings. It is available in two standard diameters: 15mm amd 22mm, and there are a range of adapters, couplings, tap connectors and valves. Copper pipes are joined in one of three ways: compression joints, solder ring, and end-feed soldering. Of the three, compression joints are the least reliable and the most expensive, but need no particular skill to assemble. When I moved into my house all the central heating pipework was joined using compression joints, and they all leaked, every single one. Solder-ring fittings have a ring of solder built into the joint. When the joint is assembled, it is heated using a torch or an electrical gadget, and (you hope) the solder melts and seals the joint. End-feed soldering requires the greatest skill, and is the cheapest.
      None of these methods is very satisfactory. Solder-ring and end-feed joints require the pipe ends to be exceptionally clean -- gleaming -- with not so much as a speck of grot in sight. Getting the joints this way is time-consuming and fiddly, expecially if the pipework is already in place, and you're working in a confined space. Compression joints are expensive and unreliable. In addition, copper pipe is supplied in straight lengths, and it it has to be bent or jointed wherever there is a change in direction.
      The last few years have seen an increase in the acceptability of plastic solder-free plumbing materials. In the UK there are two major brands: Speedfit, which is a push-fit system, and Hepworth which is a screw-assembly system [It's been pointed out to me that, despite the screw-cap arrangement on the Hepworth parts, that system is also push-fit, not compression. The screw-cap arrangement is, presumably, for extra stability]. Both use similar plastic pipe, but with different fittings. The Hepworth system is somewhat more fiddly to assemble, as it requires the fitting of metal collars and olives, and the tightening of a screw cap. Some plumbers favour one system and some the other; personally I use the Speedfit push-fit system as it takes only about five seconds to make a joint, and doesn't appear to be any less reliable. In both systems the joints can be broken down and reassembled.
      If your only experience of plastic plumbing is with push-fit waste pipes, be reassured that the plumbing systems I am describing here are nothing like that. Plastic mains plumbing fittings are as reliable as soldered joints.

Advantages of push-fit plastic plumbing

1. Unlike copper joints, push-fit joints need no particular preparation. The ends to be joined need to be moderately clean and moderately square, but that's all. They don't have to be surgically clean with perfectly square ends.
2. Push-fit joints can be dismantled and reassembled at will. If it turns out you've cut a length of tube too short to reach between two couplings, don't worry: just dismantle it and cut a longer piece.
3. Speedfit couplings and accessories can also be used with copper pipe, if necessary.
4. Plastic pipe does not burst if it freezes, so it can be used safely in cold areas like cellars and attics.
5. Plastic pipe is flexible, and can be run in a non-straight line without jointing or explicit bending. Different pipe brands have different levels of flexibility.
6. Because it is flexible, plastic pipe can be pushed through holes in joists rather than laid in notches. This is not usually practical with copper piping because it is difficult to get the holes exactly in line. Drilling holes has less impact on the structural strength of a joist than notching. Having said that, most professionals still uses notches because it's quicker.
7. Plastic couplings can be assembled even when there is water running trickling along the pipes. This sometimes happens when a stopcock or isolator does not close fully. Soldering pipe in these conditions is a nightmare.

Disadvantages of push-fit plastic plumbing

1. Plastic pipe can't be used in contact with very hot metalwork. The most important such location is the connection to a boiler. The tubing may melt if it is connected directly to a boiler, so manufacturers recommend that the first few feet of pipework from the boiler is cooper. This is no problem because push-fit couplings can join copper and plastic pipe.
2. Plastic pipe does expand under heating quite a bit more than copper. Because the pipe is flexible this does not usually present a hazard, but it does look a bit odd if the pipe is allowed to bow.
3. Because it is flexible, plastic pipe assemblies will not support their own weight. This is not a hazard -- the joints don't require support -- but it can be awkward to poke a bent pipe up through a hole in the floorboards.
4. The pressure rating of plastic pipe decreases with temperature. Usually it is rated at 10 bar at 25 degrees celcius, but perhaps only 4 bar at 85 degrees. This means that there is an outside chance that a pressurized hot-water system operating at maximum pressure and temperature may exceed the rating of the pipe. Some push-fit accessories will only stand 65 degrees celcius, so check before you use them on a heating system if it runs at a higher temperature than this.
5. Push-fit joints are larger and uglier than soldered joints, so they may not be appropriate where the joints are to be visible.
6. Plastic pipe and fittings can't be used for carrying gas, and are not supposed to be used with liquids other than water.
7. Plastic pipe and fitting are more expensive than copper, as discussed below.

Relative pricing

15 mm plastic piping currently sells for about Ł1 per metre, while copper tube is about 70p per meter. So the pipework prices are not that different. However, push-fit fittings are very much more expensive. For example, a 15 mm straight coupling will cost about 80p (purchased in bulk), while an end-feed soldered straight coupling is only 5p! Of course you will need to add the cost of solder and wire wool to the latter, but it's clear that the soldered coupling is still much cheaper than a push-fit coupling.
However, the cost differential is not as great as it first appears, for three reasons. First, you will never need to throw a push-fit coupling away. If you have to dismantle a soldered joint, the coupling is likely to be unsuitable for re-use. Second, you will need far fewer joints, as the plastic pipe is flexible. Third, if you use plastic fittings exclusively you will not need to buy a blowtorch, gas refills, a bending spring, wire wool, asbestos matting or a pipe cleaning brush.
In any event, time is money, and it only takes a few seconds to assemble a push-fit joint.

Accessory availability

Plastic pipe is available in 15 mm and 22 mm diameter, and can be used with both plastic push-fit joints and metal compression joints. The following accessories are widely available.

Straight, right-angle and T-couplings, to fit 15mm and 22mm tube, or a combination of the two sizes. These can be used to join copper to plastic pipe, if required.
Washing-machine taps. These take a 15 mm pipe at one end, and a washing-machine or dishwasher hose screws into the other end. There is a tap to isolate the appliance for maintanance.
Tap connectors. These take a 15 mm pipe at one end, and the other end screws onto the bottom of a sink or bath tap. These are available with isolating valves if required (very useful if you ever want to shut of the supply to the tap to change a washer).
In-line stopcocks and isolators.
One-way valves (these are a legal requirement in the UK where water might be drawn into the main by back-syphonage. This usually applies to hosepipe fittings and shower hoses, among others).
Stop-ends. These push-fit onto an open tube to seal it off -- very useful if you are assembling a system in stages.
Tank connectors. These are used for connecting pipework to a water tank or cistern.

To the best of my knowledge, the following fittings, which are available in copper, are not available in Speedfit. But don't forget that plastic pipe and couplings can be used with copper and brass fittings as well.

Pre-formed crossovers, used to route one pipe over another neatly. These wil not usually be necessary, however, as the plastic pipe is flexible.
Hosepipe taps.
Draincocks (for radiators).
Air vents.
Er... that's it.

Suppliers

Most plumbers' merchants now stock Speedfit plumbing, as do some DIY retailers. The cheapest mail order supplier I know of is Screwfix Ltd. (www.screwfix.com; phone 0500 414141 and ask for a catalogue).

Hints

Speedfit couplings have lines scored on their bodies to indicate where the pipe ends will come to when the coupling is assesmbled. You can use this to work out how much to add to the length of the pipe when cutting it to size. OK, so it's obvious, but it took me a year to figure this out.
Because of the expansion of the pipe at high temperatures, ideally a hot-water pipe should just stretch the required distance. Because it is flexible, it is tempting to cut the pipe a little too long because it is easier to assemble that way. However, this will lead to the pipe bowing as it warms up.
When push-fit joints are assembled, they click together with a noticeable `clunk' (rather like a car seatbelt). When assembled, it should not be possible to pull the joint apart by hand, except by operating the release collar.
Push-fit joints will rotate when assembled, even when full of water. This does not indicate an incorrect assembly, and can be used to your advantage.
Most push-fit systems require the insertion of a strengthening collar in the ends of pipes that are to be fitted into a coupling. This stops the coupling crushing the pipe end. If you put the collar into the pipe as soon as you have cut it, you avoid the risk of assembling it without the collar.
Even if you don't use plastic plumbing normally, it's worth having a length of pipe and a pair of straight couplings around the place in case a copper pipe bursts in winter. You will be able to mend a burst pipe in about 2 minutes with push-fit plumbing, and the repair will be permanent.
You can use a metal compression fitting on plastic pipe, provided that a strengthening insert is fitted. There are places you will have to do this. For example, if you are using plastic pipe to connect a radiator, you will have to compression-fit the pipe to the radiator valve. Alternatively you can fit a short length of copper pipe to the valve, and use a coupling to attach the copper to the plastic pipe. If you can do this under the floorboard it won't look too bad. Although I feel a bit uncomfortable about using a metal compression fitting on a plastic pipe, it does seem to work in practice.