Tank shape
The shape of the water heater.
The traditional options are
cylindrical and
rectangular, but nowadays there are more specific options —
flat cases,
slim cylindrical devices. Here are the features of each of these options:
— Cylindrical. This form is traditional for storage water heaters. It is because with the same total volume, less material is needed for a cylindrical tank than for a rectangular one; and in production, such tanks are simple and cheap, which allows them to be used in water heaters of any price category. The disadvantages of this form include, first of all, some bulkiness in comparison with other options.
— Rectangular. The case is rectangular in shape, with pronounced front and side faces; the corners can be both sharply defined and rounded. It is the traditional form for instant water heaters, primarily gas, but it can be found in a fairly large number of storage models. Accordingly, the features of a rectangular case will be different — depending on the type of heater. So, in instant water heaters, the “rectangle” is simply one of the most convenient options in terms of the overall layout. But in storage water heaters, this shape differs from the flat one (see below) only with a slightly greater thickness and, in some cases, pronounced angles.
— Flat. A variant found mainly in s
...torage electric heaters. Such devices look as if the classic cylindrical body was flattened at the back and front, reducing its thickness by increasing the width (and sometimes height). Thus, such a boiler does not protrude as much in front of the wall as a cylindrical one; in some cases, this point may be fundamental — for example, when installed in a bathroom, where a cylindrical device would hang over the toilet bowl, creating discomfort.
— Slim. A variety of cylindrical cases are characterized by a reduced diameter. In other words, boilers from this category are also round, but with the same volume, they have a noticeably smaller width and thickness than traditional cylindrical ones. In cramped conditions, this can be very useful. However, it must be borne in mind that the price for reducing the diameter is an increase in height.Power consumption
Electrical power consumed by the heater during operation.
This parameter is of key importance for electric models (see "Energy source"). In them, the power consumption corresponds to the power of the heating element and, accordingly, the heat output of the entire device. The overall efficiency and flow rate of the water heater directly depend on the useful power. Accordingly, high-flow rate models inevitably have high consumption. At the same time, we note that the heating power is selected by the designers in such a way as to guarantee the necessary flow rate and water temperature. So when choosing a device according to flow rate, you need to look primarily at flow rate and temperature. Power must be taken into account when connecting: for example, if a 220 V model (see "Power source") consumes more than 3.5 kW, it, as a rule, cannot be plugged into a regular outlet — connection is required according to special rules. And the most productive and high-powered models — 10 kW or more — are connected only to three-phase mains.
The power consumption has a similar value for combined boilers — adjusted for the fact that in them the electric heater is an additional source of heat. For gas and indirect models, this parameter describes the power consumption of control circuits and other auxiliary structural elements; this power consumption is usually very small — on the order of several tens of watts, less often up to 1.5 kW.
Heating modes
The number of heating modes provided in the device.
This parameter is specified only for models with
several heating modes. We emphasize that you should not confuse such functionality with temperature control (see "Features"). The heating mode is the general format of the device; these formats differ primarily in such parameters as the actual heating power, the number (and in combined models, and types) of the heating elements involved, etc. The thermostat, if it is in the design, allows you to change the temperature within a specific mode.
In general, the presence of several heating modes expands the functionality of the water heater but affects its cost. Of course, the specific features of these modes do not hurt to clarify in advance before buying.
Max. water temperature
The highest water temperature provided by the device. The standard temperature of hot water in the water supply is 60 °C, and this value is actually the minimum for modern water heaters: models with more modest rates (usually from 40 °C) are extremely rare. But higher values can be found much more often: for example,
water heaters of 75 °C and
80 °C are very popular, and in the most powerful models in this regard, the temperature can reach
95 °C and even higher.
On the one hand, strong heating requires appropriate power (which is especially noticeable in the case of instant electric heaters). On the other hand, the higher the temperature of hot water, the less it is needed for a comfortable outlet temperature, after mixing with cold water; this reduces the consumption of heated water, which is especially important for storage boilers. In addition, many models have thermostats (see "Features").
Also, note that heating to operating values may involve different ΔT (degree of temperature change) — depending on the initial temperature of the cold water. The actual performance of the heater directly depends on ΔT; this moment is described in more detail below, in the paragraphs devoted to performance at different ΔT.
Heating time
Time to heat the storage tank (see "Type"), filled with cold water, to operating temperature.
It is worth remembering that this characteristic is not 100% accurate. Manufacturers usually indicate the heating time for certain conditions: a filled tank, maximum heating intensity, and temperature rise (∆T) by a certain number of degrees. In practice, the heating time may differ, both one way and the other. For example, if the heating time for the device is 20 minutes at ∆T = 50 °C, then when the water is heated from 15 °C to 60 °C, the time will be shorter (∆T = 45 °C). Nevertheless, this indicator allows us to evaluate the overall flow rate of the boiler, and with equal ∆T and volumes, different models can be compared in terms of heating time.
Heating elements
The number of heating elements provided in the design of the water heater. In this case, it is the total number of elements that are taken into account, regardless of whether they belong to the same type or different ones: for example, 2 heat exchangers and 1 heating element are considered as 3 elements.
All gas models (see "Energy source") have only one heating element — this is quite enough for efficient operation. In
combined devices (see ibid.), on the contrary, there are several heating elements by definition (at least two — a heat exchanger and an electric one). In electric and indirect water heaters, the options may be different.
The meaning of several heaters of the same type is primarily to increase the heating efficiency. For example, in an instant (see "Type") electrical water heater, in this way, it is possible to increase the working length — the distance that water passes inside the device from inlet to outlet; by increasing the working length, the water is heated longer. In storage electric models, several heaters provide more uniform heating of the water, and in indirect ones, they allow more heat to be taken away. In addition, in indirect devices, heat exchangers can differ in the source of heating: for example, one can work from a heating boiler, the second from a solar collector.
Also, note that duplication of heating elements can also be used as protection against failures: if one of them
...fails, the heating efficiency decreases, but the device remains operational. However, this possibility is not available in all models with several heaters, its presence should be clarified separately.Controls layout
Location of heater controls. It is worth choosing by this parameter, taking into account where it is planned to install the device and from which side access to it will be most convenient. For example, when installed in cramped conditions, the water heater can only be opened from the side or the bottom; for such cases, it is worth looking for a model with the appropriate location of the controls.
Weight
The weight of the device, excluding the water collected (passing) into it.
