Comparison Thermex Surf 3500 vs Thermex City 3500

The regular way to install a water heater.

The choice for this parameter depends primarily on how much free space is available for installing the device and what shape this space has. Therefore, when there is a lot of space (for example, the user has an entire wall in the boiler room of a private house at his disposal), this parameter can be ignored. But in cramped conditions, each installation method will have its nuances.

— Vertical. Vertical arrangement devices, elongated in height. This option is well suited for narrow cramped spaces — for example, a bathroom in a small city apartment.

— Horizontal. The horizontal layout is less suitable for tight spaces than the vertical one but in some conditions, it may be optimal — for example, if the place under the device looks like a low horizontal niche. Also, note that many instant water heaters are produced in this design (see "Type") — they do not take up much space, and horizontal orientation is considered optimal for such devices for several reasons.

— Floor. Floorstanding models (as opposed to all of the wall mount options described above). The main advantage of such an installation is simplicity: there is no need to drill walls and prepare other special fasteners; it is enough to have free space on the floor. In addition, weight restrictions are not so critical for floor water h...eaters, and this method can be used even for the most powerful, capacious and, accordingly, large models. On the other hand, free space on the floor is not always available, and this installation method is not suitable for cramped conditions.

— Universal (wall mounted). Devices that can be placed in any position — both horizontal and vertical (see above for details). The advantage of this option is obvious: the user can choose the installation method of his choice, depending on the situation.

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.

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.

— Open coil. The open coil is made from a high-resistance electrical wire enclosed in a thin insulating sheath. The main advantages of such an element are the heating rate, high efficiency and precise temperature control; in addition, scale is almost not formed on the spiral. And of the shortcomings — a low service life.

— Wet heating element. Wet heater is a metal tube with a heating thread laid in the centre; the space between the tube and the thread is filled with an insulating material with good thermal conductivity. Heating elements heat up more slowly than open coils, have lower efficiency and are prone to the formation of scale on them; on the other hand, their service life is much longer, and in instant heaters, heating elements are not so sensitive to air pockets.

— Dry heating element. A kind of heating element with an improved design: the heater tube is enclosed in an additional shell (most often made of metal with an enamel coating on the outside) and does not come into contact with water, hence the name. Thanks to this, the likelihood of scale formation is reduced, which is especially important when working with hard water. Also, the replacement of such elements is significantly easier than conventional ones. Among their shortcomings can be called a rather high cost.

— Infrared heating element. Tu...bular electric heater of a special design: in the form of a transparent glass tube, in which the incandescent spiral is enclosed. The principle of operation of such an element is somewhat different from a conventional heating element: a significant part of the heating is provided by infrared radiation, which heats not so much the water as the walls of the tank — and heat is already transferred from them to the water. Thus, the water is heated not only at the point of contact with the heating element but also at the point of contact with the walls — which means that the heating is faster and more uniform. Also, note that the IR heater itself is usually "dry"; see above for the advantages of this design. The main disadvantages of such heaters are high cost and relatively short service life.

— Heat exchanger. It is used in gas and indirect heaters (see Water heater type). It is a metal structure heated by burning gas (in gas heaters) or passing inside a heated coolant (in indirect heaters). Usually has a ribbed shape. It is done to ensure the maximum area of contact with the heated water with relatively small dimensions — the larger this area, the more heat is transferred to the water per unit of time and the more efficient the heater is.

The safety of water heaters can be carried out by such functions as overheat protection frost protection, dry heating protection, surge protection, electrical protection (RCD), anti-legionella, gas control and draft sensor. More about them:

— Overheat protection. Water heater safety system that automatically turns off the power supply or gas supply (depending on the type) when the heating element reaches a critical temperature. It avoids overheating and the troubles associated with it, ranging from heater failure to fire.

— Frost protection. Function to prevent freezing of water in the circuits, tank and/or heat exchanger of the water heater. It will be useful when the device is installed in a room with a low temperature and works with long breaks. Frozen water expands, which can damage the device; to avoid this, the frost protection monitors the temperature of the water in the device and turns on the heating when this temperature drops to a critical level.

— Dry heating protection. A safety system that prevents the heater from being switched on without the presence of water in it. Since the heating element does not transfer heat to the water when turned on, it heats up very q...uickly and, in a short time, reaches a high temperature that can lead to damage to the heater and even to a fire. The presence of protection against switching on without water allows you to avoid such unpleasant consequences.

— Voltage surge protection. System for protecting the heater from power surges. Electronically controlled models are usually equipped with such protection (see Control) since it is the control electronics that are most sensitive to problems with the power supply. Note that the capabilities of such systems are noticeably more modest than those of specialized stabilizers or protective systems: the “hardware” of a water heater can smooth out relatively weak power surges, but in case of serious failures, it will most likely simply turn off the device to avoid damage. However, this feature will be useful; except that in very unstable electrical grids, prone to frequent fluctuations, such a heater may require an external stabilizer.

— Electrical protection (RCD). Built directly into the heater, the RCD is a residual current device. Such a device is primarily intended to protect people from electric shock — for example, if the insulation is damaged and electricity leaks into the case or water. When a person comes into contact with this electricity, a so-called leakage current occurs. The RCD reacts to it and almost instantly turns off the power to the boiler, preventing electric shock.
Note that such safety devices are standardly installed directly in switchboards. However, the presence of an RCD in the water heater provides additional security. Naturally, such equipment is found mainly in electric models.

— Safety valve. A safety system that prevents a critical increase in water pressure in the heater. Usually, this protection is based on a safety valve that opens when a certain pressure level is reached and drains excess water, avoiding damage to the heater.

— Gas control. Gas heater safety system that automatically shuts off the gas supply in the event of a burner flame failure. It avoids filling the room with gas and possible unpleasant, and even tragic consequences. Resuming the gas supply after the protection is triggered must be done manually.

— Draft sensor. A sensor that monitors the presence of draft in the flue of a gas water heater. This function is especially important for models with open combustion chambers: in the absence of a draft, combustion products will fill the room where the heater is located. And this, in turn, can lead to a deterioration in people's well-being, health problems and even deaths. To avoid such consequences, this sensor, when detecting problems with the draft, turns off the gas supply and issues a warning about the problem. However, such equipment can also be found in models with closed combustion chambers. In them, the draft sensor performs mainly a diagnostic function, allowing you to determine what interferes with the normal operation of the burner.

— Anti-legionella. A function that prevents the growth of pathogenic bacteria in the tank and water heater circuits. Some types of such bacteria can live and multiply in fairly hot water — up to 60 °C. To avoid this, the anti-legionella system monitors the temperature of the water in the tank and periodically raises it to a level of about 65 °C. The specific methods of operation of such systems can be different: for example, some work strictly according to a set schedule (for example, once every two weeks), others turn on additional heating only if for some period (for example, a month) the water has not been heated to sufficiently high temperatures.

- Mechanical. Manual control using rotary knobs and mechanical buttons. Models with mechanical controls are inexpensive, but the control capabilities themselves are quite limited and, as a rule, include only basic functions.

- Electronic. This control is carried out using an electronic unit. Electronically controlled heaters, as a rule, have a wider range of functions than their “mechanical” counterparts; they can be programmed and equipped with a display to indicate various parameters. On the other hand, with all other characteristics being equal, such heaters are much more expensive.

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.

The direction from which pipes are connected to the heater. The choice for this parameter depends primarily on the characteristics of the place where the device is planned to be placed. Note that in universal models (see "Installation"), the place of connection of pipes depends on the method of installation, while specific options in different models may be different, this should be specified separately.

The presence of its own tap in the design of the water heater. In such models, the nozzle is attached to the body. This feature is typical mainly for instant heaters (see above); it allows you to do without buying a separate tap for hot water.