Using copper pipes in plumbing

Copper tubing can serve many purposes in the home plumbing system. It can be employed in underground water systems, both those which bring water into the home and those which remove it from the home. Since copper tubing resists corrosion, it provides an excellent means of conveying hot water.

Copper tubing finds supplementary work in heating systems, especially in those using forced or gravity hot-water systems. It can also be used in drainage systems. However, the corrosive action of ammonia on copper limits its effectiveness as a conveyor of waste.

Underground systems

Three traits of copper tubing make it a good means of connecting the piping system of the house to the source of water supply:

  1. its wall thickness gives copper tubing the ability to withstand all normal backfilling pressures, i.e., those pressures caused by the material used to fill the trench in which the pipe is laid
  2. copper tubing resists corrosion brought about by external causes
  3. its flexibility enables soft, annealed copper tubing to conform with uneven ground contours.

In addition to the common underground installations, sprinkling systems, extensions to other buildings, water service lines and the like can be laid with copper tubing. It also minimizes the dangers of extremely cold weather. Iron or lead pipe is apt to burst on the first freezing. Copper tubing, on the other hand, can withstand the effects of six or seven freezings. If it is placed below the normal frost level, there is no reason why copper tubing should ever burst from freezing.

Cinder fill

Cinder fill is the greatest danger to copper tubing laid underground. Especially if the area is frequently wet, the sulphur compounds in the cinders will corrode the outside of the tubing. This, of course, is true of any pipe. One way to remedy such a situation is to wrap the pipe with canvas and asphaltum, thus preventing contact of pipe and cinders.

It is also possible to surround the pipe with clean sand or impervious clay before putting in the cinder fill. Some companies manufacture prepared compounds that will protect pipes laid in cinders. The best method, obviously, is to avoid cinder fill whenever possible. Care in this matter will reduce replacement costs.

House water piping

Ease of installation, elimination of fittings, and low cost of maintenance recommend copper tubing for plumbing within the house. Since it can conform to irregular contours and can be dropped easily from one floor to the next, copper tubing can be used in replacing old pipe or putting in new plumbing. It enables the home plumber to do the job with a minimum of damage to his house. The flexibility of copper tubing also permits the elimination of many fittings. As a result, frictional resistance caused by fittings is not so great when copper tubing is used as when other piping is installed.

Copper does not accumulate rust. For this reason, smaller sizes of copper tubing can be used to do the same job as larger sizes of other piping. Copper tubing reduces heat losses in hot-water systems, which also profit from accelerated circulation. Finally, the hot-water system can utilize a one-pipe system in place of the two-part, supply-and-return system when other pipe is used.

Drainage systems

The smooth interior surface of copper tubing does much to eliminate clogging in drainage systems. Because it retains heat well, it prevents grease in waste water from solidifying and impeding the flow. Vent pipe systems can utilize lighter weight copper tubing economically. However, ammonia from urine will attack copper soil pipe. Ammonia removes the oxide which protects the pipe itself from further corrosion and leaves it open to fresh attack.


Three characteristics which make copper tubing a worthwhile form of piping are its adaptability during installation, its non-corrodibility, and economy over long time periods.

Installation of copper pipes

Soft copper tubing is adaptable during installation because, unlike other pipes, which come in short sections, copper comes coiled in lengths of 20, 30, 45, 60, and 100 feet. This means that long sections of pipe can be installed without the use of connecting fittings, which tend to decrease the efficiency of the piping system.

The temper of copper tubing can be soft or hard. Bending soft copper tubing to conform with structural variations is relatively easy. Bending eliminates extra labour and additional fittings, and cuts down the amount of friction between water and pipe.

Other types of pipe must be thicker because they have to be threaded for fittings. Threading, by reducing the thickness of the metal, makes the connections with fittings the weakest points in the system. Copper tubing, when joined or fitted, remains as strong at the juncture as elsewhere. This results from the kinds of fitting used, usually either soldered fittings or flared tube fittings. Both are relatively easy to make and install, to remove and replace.

Frequently, adequate plumbing repairs go by the board because the householder feels that a good job would require too much tearing-up of floors, ceilings, and walls. Copper tubing can actually be installed in existing structures without too much trouble. The tube can be "fed" through a small opening, and repair jobs completed without a room being permanently marred.


Copper, except under unusual conditions, is non-corrodible. As was mentioned previously, ammonia will cause it to deteriorate rapidly, and the sulphur from cinder fill will eat away underground piping. The atmosphere of cities, because it usually contains a comparatively large amount of carbonic acid and sulphurous or sulphuric acid, can cause copper roofs to corrode in the rain. This danger, however, does not apply to copper tubing.

Rustable pipe material is subject to constant deterioration, either because the pipe becomes rusty and contaminates the water supply or because the pipe becomes clogged and the flow is reduced or cut off. These eventualities usually necessitate replacement of the pipe, always at considerable expense and inconvenience.

Although materially dearer, copper tubing does away with replacement costs due to erosion. Such tubing works as efficiently after years of use as it did when first installed. In many cases, its life expectancy has proved equal to that of the building in which it was placed.

There are indications that the over-all cost of maintaining a system using rustable pipe may begin to exceed that of a system using copper tubing after four and one-half years. In twenty years, the cost of ripping out and replacing rust-able pipe may vastly exceed the initially greater cost of copper tubing.


Copper tubing is a little more expensive than the same size and length of corrodible pipe. However, in several ways this first expense is offset by its durability. Savings in installation and replacement expenses have already been described. Besides these there are further savings in fuel and water.

Copper tubing can be one size smaller than the size that would be used in a similar system using corrodible pipe. This tends to equalize costs to a certain extent. The smaller pipe effects day-to-day savings in fuel and water that cannot be ignored. The reduction in the loss of draw-off-water — water in the pipe which must be drawn off before heated water reaches the faucet—represents a considerable saving. This loss can be eliminated by a return or circulation line.

In water systems using rustable pipe, it is customary to use a pipe slightly larger than necessary to compensate for diameter loss due to rust accumulation. The larger pipe, since it holds more water, increases the draw-off proportionately. Hot water in copper tubing retains its heat for a longer period of time, and the amount of heated water allowed to cool off in the pipe is kept to a minimum by the smaller pipe.

The pressure drop refers to the allowable loss of pressure in the run of pipe. For instance, if you have a pressure of 30 lbs. at the start and need 10 lbs. pressure at the end to provide a suitable flow of water, you have a maximum pressure drop in the run of 20 lbs. If the drop is less, the pressure and delivery at the end will be greater.

Expansion and contraction

In the design and installation of copper tubing systems, provision must be made for expansion and contraction caused by changes in temperature. Copper expands and contracts greatly-50% more than iron at the same temperature. If ruptures are to be avoided, a double allowance must be made.

Since annealed copper is easily bent, allowances for the effects of heat and cold can be made by putting an expansion loop or bend in longrunning sections of pipe, especially between rigidly fixed branch connections. The best rule is this: Allow 1 1/4" for expansion in every 100 feet of tubing.

Water hammer

When water is suddenly checked in its flow—as when a faucet is turned off—alternating waves of high and low pressure are exerted on the interior surface of the pipe. A knocking in the pipes sometimes results. It is called water hammer. On occasion pipes have been known to burst under the pressure of water hammer, but copper tubing has proved quite resistant.

Oddly enough, smaller sizes of tubing are stronger than larger sizes. Whereas a 3 1/2" to 4" pipe would burst under 1,000 to 2,000 pounds pressure, 3/8" pipe will withstand up to 7,000 pounds pressure. The smaller sizes are used to carry water to faucets. This is fortunate, since the strain caused by a faucet's being turned off quickly is great.

For instance, a pipe leading to a faucet and carrying water at a normal pressure of 60 pounds at a rate of 10 feet per second may be subjected to a sudden pressure of almost 700 pounds when the water is turned off. Copper tubing is quite capable of bearing this sudden strain, to which it may be subjected many times each day.

However, water hammer can do great damage and should be corrected right away. Piping may withstand this pressure at first but cannot do so over a long period. Apparatus either to reduce the pressure or to alleviate the hammer should be installed.


Contrary to what one might expect, the flow of water is not even. Pressure actually alternates rapidly and, unless piping is properly supported and cushioned, visible and audible vibration will occur. The flexibility of copper tubing makes it easy to support, even along varying structural designs. The type of fitting used is stronger than the screw-type rigid fitting and is not easily broken by vibration.


Hard-drawn copper tubing will burst as readily as iron pipe when it freezes. Soft, annealed tubing, however, is much more hardy. Smaller sizes can freeze half a dozen times before they are so weakened that they burst. The sizes over one inch may withstand a dozen freezings without mishap. Soft annealed copper, therefore, gives excellent protection against the hazards of cold.

Ground settlement

Copper tubing laid underground seldom springs a leak because of the strain consequent on settlement. Since it can be laid in a continuous line, there are not many fittings which can be pulled apart. It stretches easily without appreciable damage, and can sag with the earth settlement without being torn apart.

Resistance to crushing

Tests of copper tubing's resistance to crushing indicate that it will withstand all normal pressures. It took 700 pounds of pressure at a single point of hard copper tubing to reduce the tubing to 75% of its original size, and 500 pounds of pressure to crush 1" annealed copper tubing to the same extent. This strength is sufficient for all normal usages.

However, underground tubing should always be shielded from the direct pressure of rocks and stones. Always fill in trenches with soft dirt until the tubing is covered by at least four inches. Then, if you put in rocks so that they cannot press the tubing y single point, there will be little danger of crushing. This is important as crushed pipe reduces flow, and requires costly repairs.

Types of copper tubing

The three major types of copper tubing are designated Type K, Type L, and Type M. Manufacturers mark the tubing clearly. If you are installing more than one of the types of copper tubing, try to get a brand that states the type at frequent intervals along the pipe. This guarantees that you can use odd pieces of tubing with the certainty that you have the right type.
The three types differ in purpose, although Type K is a safe bet for just about any job. All of the types come in hard temper; K and L are also available in soft temper.

Type K

This type comes in sizes from 3/8" to 12". It can be used in underground installations and for almost all general heating and plumbing purposes.

Type K has approximately the same wall thickness as usable thicknesses of iron pipe after it has been threaded. It finds employment in all sorts of buildings, from the largest to the smallest, but particularly in areas where the water is highly corrosive. Its bursting pressure is high: 3/4" Type K copper tubing has a bursting pressure of more than 5,000 lbs. per sq. inch.

Type L

Coming in the same sizes as K, Type L copper tubing is used chiefly for medium-pressure interior plumbing, and for steam and hot-water heating systems. It should not be used outdoors in underground connections. The wall thickness of Type L is about half way between the wall thicknesses of Types K and M. In 3/4" size, its bursting pressure is about 4,000 pounds per square inch.

Type M

Available in sizes from 2 1/2" to 12", Type M is used where water conditions are normal for low-pressure plumbing. It is also used in low-pressure steam and hot-water heating systems. Its bursting pressure is 3,000 pounds per square inch in the 3/4" size.

As a general rule, use Type K whenever possible, Type L only when necessary, and Type M rarely. Type M might be used, for example, in a place where piping will not be subjected to considerable pressure and a lighter tubing is necessary.

Hard and soft tubes

Hard tubes of Types K, L, and M are usually furnished in straight lengths of 20 feet. Types K and L soft tubes come in 20-foot lengths in the larger sizes and in coils of 30, 45, 60, and 100 feet in the sizes up to and including 1".

Hard-drawn copper tubes retain their shape better than soft-drawn tubes. Consequently, they should be used wherever a specific pitch is required to aid drainage; otherwise water will lie in the pipes instead of draining properly. Hot-water circulating lines near heaters, since the sag in soft annealed tubing might impede flow, should be of hard-drawn tubing. The same thing is true of piping hung from ceilings. It is usually best to use hard-drawn tubing for any exposed piping.

For lines bedded in the ground or laid in floors where the support is practically uniform, soft tubes may be used to advantage. They are also excellent for remodelling and replacement work in existing buildings. It is possible to work the lines down through finished walls and partitions without cutting into the building construction and without excessive damage to the appearance of the room. Table 4 shows the dimensions and weight of each size of copper tubing.


The fittings used with copper tubing are one of its major advantages. The threads used in making ordinary connections weaken pipe. Threadless fittings which join lengths of copper tubing are, if anything, stronger than the pipe itself. Fittings for copper tubing may be made of copper, brass, or bronze, cast or wrought. They are obtainable in all the standard varieties of fitting and are able to meet almost any need.

Joints in copper tubing can be made in one of two ways: the flared compression joint, which utilizes the compression of metal to metal, and the soldered joint, in which the capillary action of a thin film of solder seals the tube to the fitting. The second forms the stronger union. In one test, 7,500 pounds of stress caused the surrounding pipe to break, yet the joint remained intact.


The tools needed for joining tubing and fittings are not expensive. Making the joints, though not especially difficult, requires careful and patient workmanship. To make a flared joint, you will need in addition to the usual pipefitting tools: flanging tools for flaring the ends of soft pipe to fit flared fittings; a bending rig or tool with which to make smooth, kink-free bends; a sawing vise and a jig to insure square cuts; a hacksaw; reamers and files to get burrs out of the tube.

Soldered joints will require the following: steel drift plugs to straighten out and round off ends of soft tubing; a saw and vise as above; a blow torch, or some other source of heat; soldering equipment, including iron; an abrasive; and a solder and flux recommended for this type of work.

Most plumbers prefer a soft solder that will harden rapidly. You can buy a commercial copper flux, but a 20% zinc chloride solution, obtainable from any drug store, will do the job. Another good flux is muriatic acid neutralized with zinc.

Select the right solder for the job. A solder with a low melting point will be weakened by the heat from the water in hot-water supply lines.

Flared fitting

After cutting the tubing to the desired length, slip a sleeve nut-the size of nut corresponds to the size of tubing-onto the section of copper tubing. De-burr the tubing with your reamer and, if necessary, file it slightly.

Burrs must be extracted if the flow of water is to be unimpeded. Next, the tube held firm in a vise, preferably with friction clamps, flare out the end with a flaring tool.
The flaring tool should be of the proper size for your tube. Apply a few drops of oil to the tool. Then insert it into the end of the tube and centre it carefully.

Strike the tool with your hammer until the end of the tubing is flared to the outside diameter of the flaring tool. Now place the flared end of the tube over the fitting. Run the sleeve nut up into position and tighten it with a wrench. This method is used with all sizes of copper tubing.

Soldered fitting

A soldered fitting slips over the end of the sections of tubing which are to be connected. Before placing the fitting, de-burr the tubes and clean the ends, both inside and out, with steel wool or emery cloth until they are clean and shiny. This enables the solder to take hold. After polishing, apply to both tube and fitting one of the non-corrosive soldering fluxes already suggested. The flux frees the pieces from oxide and promotes their union.

Slip the fitting onto the tubing and give it a few turns to distribute the flux evenly over all portions of the metal. Now you are ready to solder. Some fittings have side holes through which solder is fed. If there are no side holes, apply the solder around the edges of the fitting. In either case, the procedure is much the same.

Apply your blow torch to the fittings until the flux boils out from the edge of the fitting. ( Shield nearby woodwork with asbestos board.) The fitting should now be sufficiently hot to melt the solder. Test this by dropping a bit of solder on the fitting. Remove the flame and place the solder on the edge of the fitting where it comes into contact with the tubing. Use enough solder to make a strong seal. The amount of solder should equal the size of tube, i. e., 1/2" of solder for 1/2" tubing, 1 1/4" of solder for 1 1/4" tubing, etc.

Feed the melting solder onto the fitting until no more is drawn up into the seam. When the seal is complete, a ring will appear around the fitting. Wipe this excess solder off with a rag or a stiff brush. After the solder has cooled, remove any discoloration on the fitting or pipe with steel wool. If there is a second connection-and there often is-wrap wet rags around the pint already soldered.

The wet rags will keep the finished joint from melting when the pipe is heated in preparation for the new joint. Be careful not to move the connection while it is still hot, since this might crack the joint.

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