The Hot Water System
As with cold water systems, there are two basic types of hot water system. In one, the water is heated and stored ready for use, while in the other it is heated as it is required.
Storage systems Cold water is supplied (usually from the loft storage tank) to a copper cylinder, where it is heated and is then piped on to feed the hot taps around the house. The heating may be by means of an electric immersion heater set in the top of the cylinder, or else by a separate boiler. On older direct systems, water flows from the cylinder to the oil boiler service and back again, usually relying on gravity for its circulation (warm water is lighter than cold water and so rises and drives the water round the system).
The cold supply pipe and the feed to the boiler are connected near the base of the cylinder, and the boiler return pipe is connected near the top. The hot water take-off is from the domed top of the cylinder, and a vent or warning pipe runs up to the loft where it discharges over the cold water tank in the event of the system overheating. This system is not used nowadays because the constant intake of fresh water causes serious scale build-up within the boiler and cylinder.
On indirect systems, there is a copper coil inside the cylinder through which circulates water heated by the boiler. The water in the cylinder is heated indirectly by the hot water in the coil; the two never mix so scale build-up in the boiler and coil is minimal. It still occurs on the outside of the coil, but this is less of a problem except in areas with extremely hard water.
Such a system has an additional cold tank in the loft — the feed-and-expansion tank mentioned earlier. Where the boiler also supplies the central heating system, the circuit to the cylinder may rely on gravity for circulation, but on newer systems it is usually pumped.
Instantaneous systems Where it is not feasible to have a cold water storage tank or hot cylinder (typically in flats), some form of instantaneous water heating is usually provided. This may be a gas-fired multi-point water heater (supplying hot water only) or a combination boiler which also supplies the central heating.
Mention has already been made of boilers supplying central heating as well as hot water, and the vast majority of homes with central heating have this type of system. The circulation from boiler to radiators is driven by a pump, and on more sophisticated systems, motorized valves control the distribution of hot water to the hot cylinder or the radiators as directed by the system controls.
Waste Water Systems
Getting rid of all the waste water a house produces is generally much simpler than supplying it in the first place since you can rely on gravity to do the job for you.
Two-pipe waste system These are generally found in older homes. Here the
WC waste runs to a large-diameter soil pipe which runs down the outside wall of the house and which is connected directly to the underground drains at a manhole or inspection chamber. The soil pipe also runs up to roof level, where it is vented to the open air.
Waste water from other upstairs appliances runs to a hopper mounted on the outside of the house wall. It then goes via a downpipe to a gully at ground level and on to the drains via a separate underground pipe. Waste water from downstairs goes direct to an open gully and then via another branch to the drains. Rain-water downpipes often also discharge into the same drains.
Single-stack waste system These are found in newer homes. Here a single soil pipe collects waste from all the water-using appliances in the house and takes it direct to the underground drains. This soil pipe is again usually vented to the open air at roof level, but may be capped inside the house with a special pressure relief valve in certain circumstances. There may also be gullies at ground level to take waste from appliances remote from the soil stack, but the waste pipes discharge into them below the level of a gully grid instead of over it. Rain-water down-pipes are no longer connected to the foul-water drains, but run either to separate surface-water drains or to soak-aways.
The twin advantages of this single-stack system are that all the pipework can be concealed within the house, and that it does away with open discharges at gullies and hoppers which lead to smells and blockages. However, they must be designed carefully if they are to work properly, and there are strict rules about where connections can be made into them.
The most important feature of any waste water system is that it must not allow drain smells to enter the house through the waste pipes. All waste systems do this by having water-filled traps connected to every water-using appliance for built in in the case of WC pans), and these are designed so that they retain the water seal as the appliance is emptied. On modern single-stack systems the trap should always be the deep-seal type, with a water depth of 75mm (3in).
The soil pipe and any branch pipes from gullies run underground from the house and link up at a manhole. This will
be a brick-built chamber on older properties, or a smaller plastic one on newer ones. From there a single drain carries the combined wastes to the main sewer, which generally runs beneath the road next to the property. Additional manholes are provided wherever the drain run changes direction, and on older properties the final manhole may contain a trap and a capped-off rodding eye — this is known as an interceptor trap, and is designed to prevent sewer gases and rats from entering the system. Such a trap is not needed on modern drainage systems.
A few rural properties remote from mains drainage may have a cesspool or septic tank to dispose of waste water. A cesspool is just a watertight underground chamber which retains sewage and waste water until it can be pumped out and disposed of by a special tanker — a job that has to be carried out regularly. A septic tank is in effect a miniature sewage works, encouraging the decomposition of stored sewage through the action of anaerobic bacteria so that harmless effluent can then be discharged safely into a stream, ditch or land drain.