|Water heaters for hot drinks (tea, coffee etc) need to raise the temperature to nearly 100oC and a range of specially designed products is available for this purpose, ranging from simple manual fill catering urns to sophisticated wall-mounted and countertop autofill autofill water heaters. Domestic hot water from taps in bathrooms and kitchens is normally around 60oC. Water heaters for producing domestic hot water come in two main types: instantaneous water heaters (where cold water is heated on demand) and storage water heaters (where water is pre-heated and subsequently drawn off as required). Further details available by browsing the relevant product categories. |
C) and special products are designed for this purpose. The choice essentially comes down to traditional manual catering urns or automatic units. Automatic boiling water heaters are connectly directly to the water supply and perform very well but are significantly more expensive. These may be either wall mounted above a sink or mounted on a counter top and are plumbed in to the cold water mains supply. In 'boiling tap' models a dispensing tap is mounted on the work surface with the storage unit being located out of sight beneath the work surface. Most units are 3kW or less which enables simple electrical installation. Close
Water heaters for hot drinks operate at or close to boiling point (100
C). Where three phase electricity is available (normally only in commercial premises) instantaneous water heaters are available with power ratings of up to 27kW which can provide flow rates of up to 12L/min. Close
are small electrically powered units that heat water 'instantly' as it flows through the product. Instantaneous water heaters are compact, will not run out of hot water and have no stand-by energy losses but have to be wired to the electric consumer unit. The principal draw-back of instantaneous electric water heaters is that the flow rate of hot water is limited by the electrical power rating; single phase units have power ratings of up to 12kW and can provide maximum flow rates up to 6L/min (assuming a temperature increase from the incoming cold supply of 30
If you just need enough hot water for occasional handwashing at a single sink, an instant water heater is a good place to start. These are small electrically powered units that heat water 'instantly' as it flows through the product. Instant water heaters have the advantages of being compact, relatively cheap to buy and easy to install above a sink but they can only serve one sink and they can normally only heat water relatively slowly as hot water flow rates are limited by the electrical power rating. This means that you might have to accept quite a slow flow rate when the incoming water is very cold, for example in winter. If your typical application is dish washing at a single sink, you will need larger quantities of hot water at a time than an instant water heater can easily supply. In this case a storage water heater is likely to be the best option. These pre-heat a quantity of water in a tank for later draw-off. Over-sink storage water heaters are economical and easiest to install. These are mounted over a sink and are supplied complete with a valve and a spout. However you are usually limited to locating them above a sink and you can also only serve one sink at a time. Note that a small unvented undersink storage water heaters is normally considered more appropriate in domestic situations (see the next product category for further details).
Unvented 'mains pressure' units below 50L capacity are electrically heated and operate at the same mains pressure as the incoming cold water supply (typically 3 bar or so) and therefore provide excellent hot water flow rates. They may be used to supply more than one outlet using conventional taps but might require additional accessories (typically an expansion vessel and check valve) to be fitted to the cold water supply pipe depending on the installation. Unvented storage heaters with more than 15L of hot water storage capacity are supplied with these accessories as standard as required by Building Regulations. Vented water heaters do not store hot water at mains pressure, but operate instead by using vented (non-standard) taps to control the flow of cold water into the unit which displaces hot water out of the unit through the tap. These units can only supply a single outlet, and expansion of hot water can result in dripping from the hot tap when water is heated. Vented taps are not generally supplied with the heater and can represent a significant additional expense unless already available (for example where a water heater is purchased as a like-for-like replacement). Combination units have an integral cold header tank and do not need any special valves. All that is required is to connect to the water supply and to power. They are thus ideal when speed and simplicity of installation is the key but they provide poor pressure for showers and have to be wall mounted as high as possible.
Unvented hot water cylinders are now the most popular option for new hot water systems and operate at the same mains pressure as the incoming cold water supply (typically 3 bar or so) and therefore provide excellent water flow rates without requiring an header tank in the loft space or additional pumps. The more traditional 'vented' hot water cylinder operates with a header tank and generates lower water pressure than an unvented cylinder. In 'Direct' units the water is heated by one or more electric immersion heaters. In 'Indirect' units the heat source is an external boiler that circulates hot water through a coil heat exchanger within the cylinder. Indirect cylinders are generally more expensive to purchase and install but usually result in faster reheat times. Direct (all-electric) units come into their own when a gas/oil boiler is either not available or too expensive to install, or in situations where the requirement for annual gas safety checks of appliances, flues and pipework is considered onerous, for example at rental properties. Combination units have an integral cold header tank and do not need any special valves. All that is required is to connect to the water supply and to power. They are thus ideal when speed and simplicity of installation is the key but they provide poor pressure for showers and have to be wall mounted as high as possible.