Tank volume
The volume of the tank installed in the storage water heater (see "Type"). It is one of the key parameters for such devices. On the one hand, a large tank allows you to keep a large supply of water and reduces the risk that it will run out at the most inopportune moment; this is especially important when water consumption is high, such as in a large family. On the other hand, a volumetric tank correspondingly increases the size, weight and cost of the entire device, requires reliable fastenings (when installed on a wall), and more energy is spent on heating and maintaining the temperature of the water in it. Accordingly, when choosing, it is worth not chasing the maximum volume but proceeding from the actual water consumption and this point of view determining the optimal capacity of the tank.
Some special tables and formulas allow you to calculate the optimal volume of the tank depending on the format of use (washbasin, shower, kitchen sink ...), the temperature of the water used and other parameters. These data can be found in special sources. Here we note that the smallest storage water heaters can hold only 5 litres; such devices are designed for washing, washing dishes for 1 – 2 people and other tasks that do not require a lot of water. The average value is considered to be a volume of 80 – 100 litres, such a tank is quite enough for an apartment in which 3 – 4 people live. In the largest models, the volume is already calculated in cubic metres; such water he...aters are designed, for example, for hotel buildings, showers in sports complexes and swimming pools, and other similar places where a lot of hot water is required.
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.
Heat loss
Heat losses arising in the storage water heater due to imperfect thermal insulation of the tank.
No insulating material, even the highest quality, can completely prevent heat from escaping to the outside. This paragraph just indicates the amount of heat that “leaks” through the thermal insulation of the boiler per day; to maintain the temperature, this leakage must be compensated by additional heating, even if no water is consumed. So from a practical point of view, heat loss is the amount of energy that the heater spends solely on maintaining the temperature of the water inside. Accordingly, the lower this indicator, the more effective the thermal insulation and the more economical the device is in terms of energy consumption. On the other hand, a decrease in heat loss inevitably affects at least the cost, and often also the size and weight of the heater.
Note that this parameter is indicated for standard conditions: a filled tank, heated to operating temperature, zero water flow and a certain outdoor temperature (usually about 20 °C). Under other conditions, the actual level of heat loss may differ from the claimed one in one direction or another. Nevertheless, according to this characteristic, it is quite possible to compare different models directly: lower heat losses claimed by the manufacturer will mean more economical energy consumption.
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.
Tank manufacturer's warranty
The warranty period declared by the manufacturer for the storage water heater tank (see “Type”).
This parameter is important for the reasons of maintenance terms. The tank is the most complex element: other parts of the water heater are relatively easy to repair and change, and if there is a problem with the tank, it is often easier to replace the entire boiler. In the most advanced models, the warranty on the tank can be 10 years or more.
Weight
The weight of the device, excluding the water collected (passing) into it.
