What is a dip tube?

Small pieces of plastic in showers can indicate a degraded dip tube.

A dip tube is the cold water inlet tube into a water heater. A dip tube is specifically made to be long enough to introduce cold water into a water heater near the bottom of the vessel and near the heat source. Tube length is critical to maintaining the correct convection cycle within the heater. If the tube shortens due to breakage, the heater may no longer produce an acceptable amount of hot water or provide only lukewarm water. These tubes are also made exclusively of non-metallic materials, such as heat-resistant plastics, so they will not interfere with or damage the heater’s sacrificial anode.

Water heaters rely on the principles of convection to efficiently produce an acceptable leaving water temperature and volume. An efficient convection cycle in a water heater causes incoming cold water to concentrate around the heat source at the bottom of the tank. As the water heats up, it moves towards the top of the tank, where it exits through the hot water outlet when one of the hot water faucets is turned on. The heater thermostat is usually located at the bottom of the tank in the cooler water area, and as the water heats towards the bottom of the tank, it reduces the heat or cuts off the heating elements completely.

This positional relationship between cold and hot water is essential for the efficient operation of the heater and depends on the cold water being introduced to the bottom of the tank. If cold water were, for example, introduced near the top of the tank, the convection cycle would be nullified. This would have several negative effects, the most immediately noticeable being lukewarm water or a brief flow of hot water from the faucets. Heating bills would also increase because cold water ingress would simply destroy the entire functioning of the heater, causing it to have to run longer to keep the water hot.

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All these factors mean that a dip tube of the correct length is essential for an efficient water heater system. Any signs of the aforementioned symptoms could indicate a damaged or broken dip tube. Small pieces of plastic in appliance filters, faucet aerators and shower heads can also indicate a degraded dip tube. Fortunately, replacing a dip tube is not a big expense and is, for the most part, a fairly straightforward exercise for the do-it-yourself brigade. Many dip tube variants have a flared top end, which means a new tube can simply be placed in the heater fitting and the inlet spout clipped to it.

Immersion tubes are made of heat resistant plastic to prevent damage to the heater’s sacrificial anode and should always be replaced with tubes of similar construction. The sacrificial anode is a metal rod inserted into the tank that serves as a preferential target for corrosion, thus sparing the tank from excessive rust. The use of metal, particularly copper, in the dip tube can damage the anode or nullify its effectiveness, thus causing eventual rust-related leaks in the tank.

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