Plumbing and Frost Precautions

Under normal atmospheric pressure water freezes and turns into ice at 0°C. As it freezes it expands, increasing its volume by between 9 and 10%. These two facts explain the importance of adequate frost protection in plumbing installation.

Great Britain usually enjoys relatively mild winters. Even so, there are few years in which air temperatures do not fall below 0 C on at least some occasions. It does not require a very long memory to recall winters during which sub-zero temperatures and bitter north-easterly winds were maintained for days or weeks at a time.

Because a really hard winter is something of a rarity installers and householders tend to regard frost protection rather casually. Thus, when a prolonged freezing spell does occur, thousands of homes are without water and the thaw brings flooding from a thousand burst pipes. To many people frost protection simply means efficient lagging. Yet intelligent design and installation can do far more to prevent freeze-ups and burst pipes than any amount of lagging.

Frost rarely penetrates deeper than about 2ft into the soil in this country. The service pipe bringing water supply into the house from the main should therefore be at least 0.82m underground throughout its length. The last three words are stressed because it is by no means unknown for an enthusiastic landscape gardener to reduce the effective depth of the service pipe to 1ft 6in or less by constructing a sunken garden or sunken lawn above it.

If the service pipe rises into the house via an open sub-floor exposed to draughts from air-bricks, it should be threaded through the centre of a 6in length of drainpipe packed with vermiculite chips. The service pipe or rising main should preferably rise up into the roof space via an internal wall. Where this cannot, or has not, been arranged this pipe should be thoroughly protected from the cold external wall.

Interposing a Viin wooden slat between the pipe and the external wall would probably be sufficient protection so far as frost precautions alone are concerned but problems would then arise from the condensation of moisture from the warm, damp air of the kitchen onto this pipe. It is therefore better to protect the pipe both from frost and condensation by thorough lagging. Use an inorganic lagging material and make sure that it extends behind the pipe so as to protect it from the cold wall. Foam plastic pipe lagging units, such as Armstrong ‘Armaflex’, are suitable for this purpose. New pipework can be threaded through these units as it is installed. Armaflex can also be used to protect existing pipework by slitting it and snapping it over the pipes.

It is best if the rising main can enter the roof space as far as possible from the eaves. If it rises against an outside wall it will enter the roof space in the immediate vicinity of the eaves where it will be exposed to draughts and inaccessible for thorough lagging and, if necessary, for thawing out.

The roof space is a particularly vulnerable area so far as frost damage is concerned and plumbing installations in this area in a modern home with a conscientious and intelligent occupier may be at even greater risk than those in an older house with an occupier of a different kind.

In a modern home the bedroom ceilings will be insulated against heat loss by means of a fibreglass quilt or loose fill insulating material. The rooms below will be warmer but the roof space will be that much colder. There will be no escape of warmth from the rooms below to give the plumbing installation that little extra measure of protection during icy weather.

The roof space therefore demands special attention. The lengths of service pipe and distributing pipes within this area should be kept as short as possible and should be particularly thoroughly lagged. The bodies of ball-valves, gate valves and any other control valves should not be overlooked. These too should be thoroughly lagged so that only the handles or heads protrude from the lagging. Do not omit to lag the vent pipe of the hot water system. It will be filled with water to the same level as that of the water in the storage cistern.

The means of protecting the cold water storage cistern from both frost and contamination have been discussed in a preceding post. If the house has a solid fuel boiler for a hot water or central heating system the storage cistern is best situated against the flue serving this boiler. Ideally, the boiler, hot water storage cylinder and cold water storage cistern should be arranged in a vertical column so that there will be a continuous flow of warm air upwards towards the vulnerable cistern. Prevent cold draughts from entering the roof space via the overflow or warning pipe by turning the internal end over, as suggested in a preceding post, so that it dips an inch or so below water level when the cistern is full.

In a modern, effectively heated and thermally insulated home, no special precautions need to be taken for the protection of water distribution pipes below the level of the roof space. They should be kept away from external walls or, where this unavoidable, thoroughly lagged.

It is largely as a frost protection measure that the Building Regulations require waste and soil pipes to be contained within the fabric of the building. Where a house has external waste and soil pipes the important point to remember is that an empty pipe cannot freeze. Every householder’s routine autumn frost precautions should include the renewal of the washers of any taps showing a tendency to drip. A waste pipe, dripping all night into an exposed hopper head, can produce a hopper head and down-pipe choked solid with ice on the morning following a night of severe frost.

Lagging, however thorough and efficient, cannot add heat to the plumbing system. It can only reduce the rate of heat loss. Careful positioning of the storage cistern above the hot water cylinder can actually add heat to the system. This too can be done in other ways. Lagging units incorporating a low power electric heating cable can be bound round vulnerable pipes and switched on when severe frost threatens. It may be possible to protect the flushing cistern of an external w.c. by thoroughly draught proofing the compartment and then, by means of an extension lead plugged into the electric light socket, suspending a 60 watt electric light bulb outside the cistern a few inches below the ball valve inlet.

Under more or less draught free conditions the heat generated by a bulb of this kind will be sufficient to afford protection from quite a severe degree of frost.

The fact that lagging does no more than reduce the rate of heat loss must be borne in mind when a house is unoccupied for more than a few days during severe winter weather. Continued occupation of a dwelling and continued use of its plumbing system are, in themselves, important safeguards against frost damage. The interior of the house is maintained at temperatures well above freezing point and this warmth is transmitted to the water pipes contained within it. Water enters the house from the main at a temperature a few degrees above freezing point. In the roof space it may begin to cool down but, before it can reach danger level, it is drawn off through the taps or flushing cisterns and replaced by marginally warmer water from the main.

The fabric of an empty, unheated house quickly chills off. Water stagnates in the supply and distributing pipes and in the storage cisterns. During a prolonged spell of freezing weather-no matter how thoroughly the pipes are lagged-an ice plug will eventually form and spread through the system. Unless you protect the plumbing system before departing on, say, a winter ski-ing holiday, you may well return to find it frozen and in a thoroughly dangerous condition.

The steps to be taken depend largely upon the nature of the domestic hot water and space heating system, but in every case it is wise to turn off the main stop-cock and to drain the rising main and the cold water storage cistern from the kitchen and bathroom taps. This, of course, will not empty the hot water storage cylinder, the boiler and flow and return pipes, or any central heating system that may be installed.

If you have a ‘direct’ cylinder hot water system, drain the system completely. Let out the boiler and turn off the immersion heater. Then connect one end of a length of garden hose to the draincock beside the boiler or, if your cylinder is heated by an immersion heater only, at the base of the cold supply pipe to the cylinder. Take the other end to an outside gully, open up the drain-cocks and leave to drain. After draining leave a large and conspicuous notice on the boiler and beside the immersion heater switch to remind you that the system has been drained and that the boiler should on no account be lit or the heater switched on before it has been refilled with water.

Refilling after drainage can produce troubles from air-locks. Leave all taps open until water starts to flow through them. It is often helpful to refill by connecting one end of your garden hose to the cold tap over the kitchen sink and the other end to the boiler draincock. Open up the tap and draincock, and the system will fill upwards, driving air in front of the rising water.

Central heating systems and the primary circuits of indirect hot water systems should not be drained. Particularly in central heating systems, water drying on the internal surfaces of radiators, valves and the circulating pump could result in serious damage from corrosion. With a modern gas central heating system the best course is to leave it switched on under the control of a ‘frost stat’. This is a thermostatic device that will bring the system into operation when air temperature falls to a predetermined level.

Systems that do not lend themselves to this degree of control may be protected by the introduction of a suitable antifreeze solution into the feed and expansion tank. Automobile antifreeze should not be used. The manufacturers of Fernox corrosion-proofing products manufacture suitable antifreeze solutions and will be pleased to advise. Don’t leave the introduction of antifreeze solution until the last moment before you leave. It must have time to circulate through the system.

Do not omit to flush the w.c. cistern or cisterns before leaving the house. Water in w.c. traps and other traps must not, of course, be drained off. Throwing a handful of salt into the water in the traps will generally afford adequate protection. A more positive means of protection for the vulnerable w.c. trap is to fix a stopper into the end of a length of rubber tubing and pass the stoppered end into and round the w.c. trap. If the water in the trap freezes and expands the expansion will then be accommodated by the rubber tubing.

If a freeze-up occurs

The first indication that water has frozen in the plumbing system of an occupied house will be the failure of water to flow from one or more of the taps or into the w.c. flushing cistern.

At first the ice plug will be a small one, easily dealt with. Action should be taken quickly to prevent stagnation of cold water in the pipe affected and the inevitable growth of the plug.

Identify, as accurately as possible, the point at which the blockage has taken place. If, for instance, water is flowing freely from the cold tap over the kitchen sink but is not flowing into the cold water storage cistern, the ice plug will be in the rising main, probably within the roof space.

Strip off the lagging and apply cloths, wrung out in hot water, or a hot water bottle, to this pipe. Modern copper tubing is a good conductor of heat and application of heat in the way suggested will thaw a small ice plug several feet from the point of application. An electric hair dryer, or even a vacuum cleaner operating in reverse, can prove useful in directing a stream of warm air to an otherwise inaccessible pipe.

Dealing with a burst pipe

The idea persists that pipes burst with the thaw. This is, of course, incorrect. Pipes burst when they freeze, but the burst only becomes evident when the ice thaws and water can flow again.

The first indication of a burst is usually water dripping from a ceiling or into an airing cupboard. Rapid and intelligent action by the householder immediately this occurs can limit the damage and save furniture and furnishings from being spoiled.

Immediately the householder should turn off the main stop-cock and open up all the taps in the house. This will cut off the water supply to the house and drain the storage cistern. There is no need to put out the boiler fire though it might be wise to keep it as low as possible. The hot water storage cylinder will still be full of water. Only after taking this action should the householder seek out the point at which the burst has occurred and consider the remedy.

If the house has copper plumbing joined with compression or soldered capillary joints, the chances are that the ‘burst’ will merely be the result of one of these joints having pulled apart. Copper tubing may sometimes split under internal pressure from expanding ice. A burst in a lead pipe will almost certainly take the form of a split. It must be mentioned that householders are sometimes led into a state of false security by the fact that a lead pipe may have frozen on a number of occasions and has never burst. Each time the pipe has frozen the ice plug, on expanding, will have increased the bore of the pipe-and reduced the thickness of the pipe walls. Since lead lacks elasticity the pipe will not resume its former dimensions on thawing out. This process may be repeated several times before internal pressure finally splits the pipe wall.

The remedy in the case of a split pipe is to cut out the damaged section of the pipe and replace it with a new length. If the pipe is of lead the new length will be connected to the old by means of two wiped soldered joints. Professional help should be obtained.

However a temporary repair can be made with the use of one of the epoxy resin fillers such as Isopon or Plastic Padding. The edges of the split should be knocked together and the area thoroughly dried and cleaned with abrasive paper. The filler is then made up according to the manufacturer’s instructions and buttered round the area of the split. Before setting a length of fibreglass bandage is bound round the area affected and a further layer of filler applied to the fibreglass bandage.

Boiler explosion and cylinder collapse

Any period of prolonged severe weather produces at least one report in the national press of fatalities from a boiler explosion. This creates a great deal of anxiety among householders, particularly the elderly who will sometimes take the ‘precaution’ of letting the boiler fire out during frosty weather —the worst possible course of action under the circumstances. Boiler explosions are, happily, extremely rare. It is, after all, ‘the exception that makes the news’, as any journalist will confirm. When they do occur their results can be catastrophic.

An understanding of their cause should do a great deal to allay totally unnecessary anxiety.

A cylinder storage hot water system, whether direct or indirect, resembles a U tube, with two open ends-a larger version of the kind of U tube found in every school physics or chemistry laboratory. The two ends, open to the atmosphere, are the vent pipe and the cold water storage cistern. Provided either one of these ends remains open and unobstructed, no boiler explosion can take place. A spring loaded safety valve, situated close to the boiler in most hot water and central heating systems, provides a final line of defence.

Typically, boiler explosions take place when a family has been absent from home during a prolonged cold spell, without taking the precautions suggested earlier in this post. Ice plugs have formed in the flow and return pipes between boiler and cylinder or in the upper part of the vent pipe and the upper part of the cold water supply pipe to the cylinder . The boiler fire is lit but, of course, the water in the boiler can neither circulate nor expand upon heating.

Boiling depends upon temperature and pressure. The temperature of the water in the boiler rises to above 100°C but the water cannot, because it is confined within the boiler, turn to steam. Pressure increases until, ultimately, something gives. In an instant the superheated water in the boiler is converted to steam, occupying thousands of times more space than the equivalent volume of water. The system explodes like a bomb with catastrophic results.

Cylinder implosion or collapse is rather more common. It can occur where pipework in the roof space is inadequately lagged and where the householder, perhaps through fear of a boiler explosion, has let the boiler fire out at night during icy weather. A small ice plug forms in the vent pipe and in the upper part of the cold supply pipe to the hot water cylinder. Meanwhile the water stored in the cylinder, originally hot, cools-and contracts.

Copper hot water cylinders are constructed to withstand considerable internal pressure but very little external pressure. As the cooling water contracts a partial vacuum is created within the cylinder and it collapses like a paper bag under the weight of the atmosphere. Typically, cylinder implosion occurs first thing in the morning when the householder turns on the hot tap to draw off some water. The additional loss of water proves to be the final straw that breaks the camel’s back.

The best safeguards against boiler explosion, cylinder collapse and, indeed, all troubles arising from frost, are intelligent lagging, particularly in the roof space, keeping the boiler fire alight and the house warm during frosty weather and taking the precautions suggested earlier in this post if the house is left unoccupied for more than a few days during a period when icy weather might reasonably be expected.

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