Direct & Indirect plumbing systems: what’s the difference?

There are many different types of plumbing system to be found in UK households. Each system comes with its own set of advantages and disadvantages. In this article, we’ll discuss the difference between direct and indirect plumbing systems, and what those differences mean.

Direct & Indirect plumbing systems explained

The fundamental difference difference between direct and indirect plumbing systems relates to how cold water is distributed throughout the home.

In an indirect system, the mains enters the property and branches off to supply the cold kitchen tap. It then rises up to the loft to feed the cold water storage cistern. The cold cistern supplies cold water to everywhere else in the household, such as the cold bathroom taps, and the hot water cylinder.

In a direct system, all of the cold outlets are supplied by the mains. The cold water storage cistern supplies only the hot water cylinder. Alternatively, there may not even be a cold water storage cistern, if the property has a combi boiler or an unvented hot water cylinder. Both of these appliances are also fed directly from the mains.

Advantages and disadvantages

As one would expect, each of these systems comes with its own set of advantages and disadvantages. The main advantage of an indirect system is that even in the event of an interruption to the mains, the household will still have a reserve of water. Residents will still be able to flush the toilet for a limited period of time, for example. Indirect systems also operate at a lower pressure than mains water. Consequently, they are much quieter, and less susceptible to water hammer and wear and tear.

The main disadvantage of indirect systems is the risk of stagnation and contamination that comes with keeping a large quantity of water open to the atmosphere. While current water regulations require cisterns to be fitted with a set of components to ensure the water remains potable, i.e. drinkable, the concept of brushing one’s teeth in water which has come from a tank in the loft may not be very appealing.

This rings particularly true in the past, when the approach to the quality of water in the cistern was much more relaxed, and it was not uncommon to find drowned insects, rodents, and even birds at the bottom of a cistern. Indirect systems are ultimately why people in British homes are usually advised not to drink from the bathroom taps. On the other hand, a household with a direct system will offer drinking water from every cold tap in the property.

The other main advantage of direct systems is that their higher pressure means much greater flow rates

The other disadvantage of indirect systems is that they require space in the loft for a bulky water tank. Long, narrow “coffin” tanks can be fitted, but in the case of a loft conversion, a change of plumbing system may be needed.

Hot water cylinders

So there you have it – the difference between direct and indirect plumbing systems explained. Note that direct and indirect may also refer to types of hot water cylinder. In this context, direct and indirect refers not to how the cylinder is supplied, but how the water is heated. For more information, check the hot water cylinder page.

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