Domestic hot water storage tank - how to choose the right one for your installation needs?

Hot water storage tank - what it is and what its function is?

Domestic hot water storage tank (c.w.u.), also known as a heater or boiler, is a device used to store and heat water for sanitary and household purposes. With a storage tank, users can use hot water at any time - without having to wait for it to be heated by a heating device.

The reservoirs come in a wide range of capacities - from small models, having about 80-120 liters, designed for small apartments or single-family houses, up to large tanks with a capacity of up to several thousand liters, used in industrial buildings, hotels or sports facilities.

How the c.w.u. connects to the installation?

A typical c.w.u. is mounted in a technical room (e.g., in a boiler room) and connected to:

• water system (supplying cold domestic water and discharging heated water to consumption points such as showers, sinks, bathtubs or sinks);

• heating system (to a boiler, heat pump, solar thermal system or other heat source that provides energy to heat water).

Connecting the tray is relatively simple. The tank has plumbing connections - usually spigots or threads, to which the installer connects cold water pipes (inlet), hot water pipes (outlet), and possibly spigots connecting to the heat source. In the case of c.w.u. with built-in coil - internal heat exchanger - heat energy from the heating system is transferred to the domestic water through this particular coil. Domestic water in the tank does not mix with heating water.

Storage tanks with and without a coil - differences:

C.w.u. are available in essentially two design variants:

What you will find later in the article?

We go on to discuss in detail how to correctly select the capacity of a c storage tank.w.u., taking into account both the number of users, the type of installation, the specifics of the heat source, as well as other important technical aspects.

Factors affecting the selection of storage tank capacity

When choosing a tank size c.w.u. there are several key factors to consider that determine hot water demand:

• Number of users and water consumption - The more people using the system, the greater the daily hot water demand. It is assumed that one adult consumes on average from approx. 30 to 60 liters hot water per day. Some sources even report approx. 80 liters per person for comfortable use. Of course, lifestyle matters - for example, long showers or frequent baths increase this consumption.

• Number and type of consumption points - Home furnishings are also important: whether there is one or more bathrooms, whether there is tub (which requires more water at one time than a shower), additional showers, as well as other points of use (such as a dishwasher, a washing machine that draws hot water from the system, etc.), and other water sources.). More points operating at the same time means more instantaneous water demand and often requires a larger storage tank or a unit with a higher continuous capacity.

• Heat source characteristics - The type of heating device providing heat for water heating is of great importance. Gas boilers tend to have a lot of power and can quickly heat up the water in the tank, so even at medium capacity they are able to cope with instantaneous consumption. Heat pumps on the other hand, they operate more efficiently with longer cycles and lower power, so larger storage tanks are often recommended for them so they can accumulate more water and switch on less often. In addition, heat pumps require a sufficiently large heat exchanger (coil) area in the tank - for every 1 kW of pump power, there should be about 0.20-0.25 m² of coil area. For example, for a 9 kW pump, a storage tank with a ~2 m² coil is recommended to efficiently transfer heat. Fireplaces with water jacket(wood-fired boilers), because of their erratic operation and high instantaneous power output when burning, usually work with larger heat storage tanks or buffers - so that excess energy is stored when the fire is burning and can be used later.

• Simultaneous intake and peak demand - Evaluate whether, in typical use, there are situations where several people use hot water at the same time (e.g., simultaneous showers in two bathrooms in the morning). The greater the simultaneity of intake, the greater the capacity or output required to maintain comfort (hot water without overcooling). Circulation c is often used in residential buildings.w.u., to have hot water immediately at the tap - this also affects heat loss and capacity (larger circulating systems use larger tanks).

• Economic and spatial aspects - A large storage tank means a higher purchase cost and the need to set aside adequate space in the boiler room (note the dimensions and floor/ceiling resistance to water weight). A small storage tank is cheaper and takes up less space, heats up faster, but can cause discomfort with high water intake. It is necessary to find compromise between comfort and efficiency - select a tank as small as possible, but large enough to meet needs under typical consumption conditions. It's also worth thinking ahead about future needs (e.g., family enlargement) - sometimes it is better to anticipate spare capacity.

Storage capacity vs. number of users - indicative recommendations

The simplest starting point for capacity selection is the number of people using hot water. There are general recommendations for storage tank capacity for typical households:

• 1-2 people - tray ~100-150 liters. This capacity is usually enough for a single or a couple, providing comfortable use of the shower and basic facilities. For example, a ~120 L boiler is considered optimal for two household members, giving a certain supply of hot water.

• 3-4 people - tray ~150-200 liters (sometimes up to 200-300 liters are given for higher consumption). A medium-sized family should consider a tank of approx. 200 liters, especially if the house has tub or two bathrooms. Such a storage tank will allow you to take a bath and several showers a day without the risk of running out of hot water, and at the same time it will not overburden your energy budget.

• More than 4 people - tank 200-300 liters or more, depending on the intensity of use. For a larger family (5 or more people), tanks are often used 300 liters, even 400-500 liters with a very large house and high comfort. It is worth taking into account that in such a situation often two-three points of consumption (e.g., two bathrooms + kitchen) can work simultaneously, which requires both a considerable capacity and adequate power of the heat source for rapid heating. Tanks above 300 liters are already quite large in size - often floor standing models that must have space in the boiler room.

Remember: the above values are approximate and apply to average conditions. Every home is different - if household members like long baths, have a Jacuzzi or use a high-flow rain shower, consider a larger tank than the sheer number of people indicates. On the other hand, when water consumption is low (e.g., frugal living) or the heat source is very powerful and can heat water quickly, then you can afford a slightly smaller storage tank. It is always best to analyze daily water consumption profiles at home - when and how much water is drawn - to select a capacity that ensures a continuous supply at an acceptable cost.

Examples of capacity selection in typical domestic installations

Small detached house (1 bathroom, shower) - In a house inhabited by 1-2 people, without a bathtub, the following is usually sufficient tank ~100-120 liters. This capacity allows for comfortable showering, washing dishes or basic kitchen needs, with relatively quick heating of water. A small storage tank means that the boiler will turn on more often, but the water will not linger for long - this reduces heat loss. For example, a couple living in a small house often chooses a boiler about. 80-120 L and it is completely sufficient for them, as long as they do not anticipate the simultaneous use of two showers. Space is also important for such a house - smaller storage tanks can be hung on the wall or fit in a small boiler room. In addition, if the house has a dual-function (gas-fired flow-through) boiler, it may not require a separate storage tank at all - but the comfort of hot water is then sometimes lower with two points of consumption at once.

Larger house with bath (3-4 people) - If a typical family of 3-4 people lives in the house and there is a tub, it is recommended storage tank at least 150 liters, and preferably ~200 liters. A bath can consume 100-150 liters of hot water at a time, so a ~200-liter tank will ensure that once the tub is full, there will still be a supply left over for other needs or another shower. In houses with two bathrooms (e.g., one with a bathtub, the other with a shower) and a family of four, bare minimum is about 200 l. In practice, it is common to use 250 l tanks, especially when household members can use the bathrooms at similar times (e.g., in the morning while getting ready for work and school). A ~20-25 kW boiler is able to reheat such a storage tank quite quickly, so interruptions in hot water supply will be short. To improve comfort, you can also arrange circulation c.w.u., so that hot water comes right out of the tap - but then remember that maintaining a circulation loop increases heat loss and effectively reduces the useful capacity(some heat goes into heating the pipes).

House with several bathrooms (5+ users) - In a large house, where there is, for example. 3 bathrooms and many people live (multi-generational family or frequent visits by guests), it is recommended to hoppers 300 liters and larger. Such a tank will make it possible to serve, for example, two people taking a shower at the same time and a third using the kitchen - without a drastic drop in water temperature. In practice, for 5-6 residents of a house with a high standard (a bathtub, a few showers, maybe a swimming pool or a large Jacuzzi), even a boiler 400-500 liters. However, it should be remembered that with such large capacities, standstill losses and heating time increase - the heat source must be strong enough. It is also common for large houses to install two storage tanks connected in series or parallel (e.g., two of 300 liters each instead of one of 600 liters), which makes transportation and installation easier and also provides some redundancy. Alternatively, systems are used sandwich tanks or buffers with coil, which give up heat faster on consumption - but these are more advanced solutions designed individually. It is important that, with multiple points of consumption, the system designer should provide for appropriate pipe diameters and, possibly, circulating pumps, so that a large storage tank really translates into comfort (with a bad installation, even 500 liters will not help when hot water takes a long time to flow to distant points).

Heat pump installation - When heating water with a heat pump, the recommendations for tank capacity are usually higher than for a boiler. For 3-4 people, a tray is recommended minimum 200 liters, better ~250-300 litersâ. This is due to the fact that the heat pump heats water more slowly (it has less heating power than a typical gas boiler) and works most efficiently at the lower temperatures in the tank. The larger capacity allows to accumulate a supply of water at a moderate temperature, which the pump can heat gradually, operating at the optimal range. In addition, a large storage tank means longer pump cycles - less frequent turning on and off of the compressor extends its life span. An important parameter when selecting a storage tank for a heat pump is coil surface: it should be large enough to transfer all the power of the pump to the water. Manufacturers often offer special tanks dedicated to heat pumps - They are characterized by a larger coil (e.g., double coil) or even two coils and better insulation. In practice, for a domestic heat pump of, say, 8 kW, a ~300 l tank with a >2 m² coil is typical. If the pump is of the monobloc type integrated with a tank, such a tank is often with a stainless steel (to minimize the need for service - it is difficult to replace the anode in a built-in unit). In general, investing in a slightly larger storage tank with a heat pump improves comfort, because even with increased one-time consumption, there will be no need to run the electric heater (which in the pump assists with heating at peak). It is worth mentioning that in the case of heat pumps c.w.u. is usually set at a lower temperature (e.g., 45-50°C instead of 60°C as with a boiler) to increase the COP - which also argues for more capacity (because lower temperature means less energy in the same volume of water, so you need more to cover your needs).

Installation with fireplace with water jacket - A mantle fireplace (or solid-fuel boiler) transfers heat to the water mainly during combustion, so for a continuous supply of hot water, you'll need a substantial supply. Most often such an arrangement works with 300 l or more storage tank, often also acting as a heat buffer for heating. In practice, one encounters solutions where it is buffer (e.g., 500 l) with built-in coil for c.w.u. or double-walled exchanger - thanks to this, when we fire in the fireplace intensively, the accumulated energy heats a significant amount of water. Such water then can be consumed during the day, even when the fire goes out. A well-chosen large storage tank allows the morning fire to provide a warm bath in the evening. Of course, a lot depends on the power of the fireplace and habits - if the fire burns every day, you can have a smaller tray, but most users opt for a more stock for safety (For example, when we do not fire one day, a large 500-liter boiler supported by an electric heater or gas boiler will provide hot water). In an installation with a fireplace, it is also important to protect against overheating - in the case of very large tanks, an additional protection may be a cooling coil or a thermal valve, so as not to boil the water in the tank in the absence of heat extraction. Bottom line: for a fireplace with a mantle it is better to oversize the storage tank than to risk the excess energy having nowhere to go or running out of hot water when the fire goes out.

Capacity selection in commercial and industrial installations

In larger commercial facilities - such as hotels, restaurants and public buildings - the demand for hot water is much higher than in single-family homes. The selection of a storage tank (or battery of tanks) should take into account peak loads and the required comfort of hot water supply. Here are some examples:

• Hotel/Pension - A hotel with a dozen or more rooms requires a very high capacity c.w.u. Guests usually consume water in waves (morning and evening peak bathing). For a small guesthouse (e.g., 5-10 rooms), a storage tank of the order of 300-500 liters supported by a high-efficiency boiler or several flow heaters. Larger hotels (50+ rooms) are already using the entire c preparation stations.w.u. - e.g. several tanks of 500-1000 liters each connected in a system, powered by a cascade of boilers or high power heat pumps. It is also important to circulate hot water through the risers so that guests do not have to wait for hot water - this further increases heat loss and must be factored into the balance of capacity. It is often assumed indicatively, for example. 50-60 liters of hot water per day per accommodation unit in a mid-range hotel, but due to simultaneous intake, the actual storage capacity required may be greater. For example, a 30-room hotel might have two tanks of 500 liters each, providing some buffer to handle the morning peak (a dozen showers per hour). Premium facilities with in-room baths or spas use even larger storage tanks and often also heat recovery systems (e.g., from gray water) to help heat such large volumes of water.

• Catering (restaurant, canteen) - In catering establishments, hot water is needed mainly for sanitary purposes in the kitchen (washing dishes, cleaning) and in guest toilets. Consumption is sometimes erratic - for example, a large intake occurs during cleanup after the property closes or before peak lunchtime. For a restaurant with several people working in the kitchen, it is often enough to tank 100-200 liters supported by flow heaters in dishwashers. However, in larger catering facilities (school canteens, company canteens, hotel restaurants), storage tanks are installed 300-500 l, to ensure that a large amount of hot water can be drawn in a short period of time (e.g., several sinks per hour). It is important to maintain a high level of hygiene - the temperature in the tank should periodically reach 60 ° C (thermal disinfection), and the tank itself should be approved for contact with drinking water (in the kitchen this is especially important). In catering, electric instantaneous water heaters are also often used directly at the sinks as a supplement - this allows to slightly reduce the required capacity of the main storage tank, because at points of highest demand water is reheated on the fly.

• Schools and educational institutions - In schools, hot water consumption is mainly associated with sinks (hand washing) and showers at gymnasiums. If the school has showers for students (e.g., after PE classes or for athletes after training), then demand tends to be concentrated after these activities. For example, for a set of school locker rooms with 4-6 showers that can be used by a dozen people at a time, a tank will be useful 500 l or more, to dispense this water in a matter of minutes or so. In smaller schools, where showers are not used intensively and hot water is needed mainly for washing hands or cleaning, a storage tank may suffice 150-300 l (common to the entire building). An important factor here is health safety - water cannot stagnate in too large tanks with minimal consumption, because the risk of bacterial growth (e.g. Legionella) increases. Therefore, in schools without much need, it is better to give a smaller tank and possibly reheat the water more often than to maintain a huge tank that few people use. In large schools or boarding houses (dormitories), the problem is similar to that of a hotel - you need to provide for larger water storage systems with circulation.

• Sports halls and fitness facilities - In sports facilities (e.g., swimming pools, sports arenas, gyms), the demand for hot water is very high at certain times - usually after training or sporting events, when many people go into the shower at once. Such a hall with more than a dozen showers may need as much as several thousand liters of hot water per hour. A combination is often used here: a large storage tank (or several, such as 2-3 × 1,000 l) plus efficient flow heaters/boilers that start up at peak. The storage tank itself acts as a buffer that provides an immediate large outflow of water, but the heat source must be able to replenish this energy on an ongoing basis. Modern swimming pools, for example, use stratified heater systems, where water is heated and stored in layers of different temperatures, allowing a large amount of heat to be expended quickly. A typical school sports hall (e.g., 4 showers on the men's side and 4 on the women's side) can use a ~300-400 l storage tank backed by a powerful 50 kW boiler, which is enough for a short intensive intake of. On the other hand, large public facilities (municipal swimming pool, large gym with dozens of showers) will already have installations counted individually by designers - usually tank batteries of several thousand liters plus redundant heat sources (gas boilers, heat pumps, solar panels) to provide hot water regeneration.

Summary for Commercial Facilities: understanding is key wear profile - Whether it is continuous and even, or abrupt and tied to specific times of the day. On this basis, both storage capacity, as well as heat source output. Advanced systems are often used, such as coupling several storage tanks or combining a buffer with a flow heat exchanger to ensure high efficiency. In each case, however, the same rules apply as at home: too small a storage tank - risk of no hot water at peak; too large - unnecessary off-peak heat loss. A well-designed system will be balanced, and the tanks will be equipped with adequate insulation and controls (such as priority heating c.w.u. during demand, water heating schedule, etc.).

Materials and workmanship of c trays.w.u.

Hot water storage tanks made of different materials and with different internal coatings are available on the market. The choice of material determines the tank's durability, corrosion resistance, maintenance requirements and price. The most popular types are:

• Enameled steel (carbon steel enameled) - Most domestic storage tanks are steel tanks with an inner layer of ceramic enamel. Enamel protects metal from contact with water, preventing corrosion and at the same time is inert to water (meets hygienic requirements). The quality of workmanship is key - the enamel coating must cover the entire inner surface of the tank (including the coil, if any) without cracks or cavities Reputable manufacturers take care of the continuity of the enamel; in cheaper units there are sometimes microcracks or uncovered areas at welds, which can result in corrosion after some time. Since even the best enamel does not give absolute protection (e.g., it can undergo microcracking due to the heat work of the tank), w enamelled tanks always install a magnesium anode as additional corrosion protection. A magnesium anode is a rod of material that is "sacrificed" - it corrodes instead of the walls of the tank, protecting the steel. The disadvantage is the need for regular inspection and replacement of the anode - usually every 2-5 years (depending on water quality and intensity of use). Nevertheless, enamel storage tanks are very popular because they provide good water protection (they are certified for drinking water) and are relatively inexpensive. Typical guaranteed lifespan is about 5-8 years, although with anode replacement and mild water they can last several years.

• Stainless steel (acid resistant) - Storage tanks made of high quality stainless steel (e.g., 316L grade) provide a more durable, maintenance-free alternative to enameled. Stainless steel is resistant to corrosion, so the does not require enamelling or protective anode - the tank can operate for many years without special maintenance. Such a solution is particularly appreciated in installations where it would be difficult to service the tank (e.g., compact heat pumps with built-in storage, located in tight spaces). Stainless steel also stands up well to higher temperatures and sudden temperature changes (for example, in systems with a solid-fuel boiler), as there is no risk of enamel cracking. The disadvantage is the price - Acid-resistant steel heaters are usually much more expensive (up to 2-3x) than comparable enameled ones. Nevertheless, many investors are opting for stainless steel because of the maintenance-free and long life. It is worth making sure that the manufacturer has the required hygienic approvals - stainless steel is generally safe for drinking water, but the PZH approval confirms that the material does not adversely affect water quality.

• Galvanized steel - Slightly less common are trays with hot-dip galvanized steel (inside and sometimes outside). Layer zinc on the inner walls acts as an anti-corrosion coating - like enamel, it insulates the steel from water, in addition to having a protective effect (zinc, as a less noble metal than iron, protects the steel from rust). Galvanized tanks were popular decades ago; today they are still used mainly in larger capacities (e.g., 300-1000 l) or where water is chemically aggressive to enamel. Galvanized tank does not require magnesium anode, because zinc itself plays a protective role - it forms the so-called cathodic protection of steel (instead of steel, zinc gradually dissolves). However, it is important that the galvanizing layer is continuous and thick enough. Zinc can slowly degrade (dissolve) in usable water - therefore, manufacturers must be certified by the PZH to confirm that the amount of zinc ions, if any, penetrating into the water is safe for health. The advantage of galvanized trays is their durability in conditions where enamel could crack (zinc is metallic, so it "works" together with steel). Often galvanized tanks are used in industrial or agricultural installations where water quality is variable. For example, Polish manufacturer Thermo offers storage tanks made of carbon steel, hot-dip galvanized on both sides (e.g. model 1000 L) - which means that the sheets are galvanized both inside and outside, giving full corrosion protection. In practice, the galvanized storage tank also stands up well to higher temperatures. The downside may be a slightly heavier weight (the zinc layer adds weight) and a potential post-zinc "contamination" of water in the first period of use (leaching of excess zinc - that's why usually after installation of such a tank it should be rinsed several times).

• Other materials - Occasionally, plastic (e.g., polypropylene) or copper trays are found. Plastics are resistant to corrosion, but are more difficult to use at higher temperatures and pressures, so steel structures dominate. Copper tanks have great thermal conductivity and natural antibacterial properties, but copper is expensive and in large capacities not cost-effective - copper is more often used in coils than for the entire tank. Regardless of the material, each domestic water storage tank should be certified by the National Institute of Hygiene (Polish Institute of Hygiene) or equivalent certificate confirming suitability for contact with drinking water. This provides assurance that the materials (enamel, gaskets, anodes, etc.) do not adversely affect water quality and are safe for health.

Thermal insulation vs. standstill losses

A very important element of any c.w.u. is thermal insulation. The storage tank stores hot water, so in order to reduce energy loss, its walls must be well insulated with a material with low thermal conductivity. Most modern heaters are equipped with insulation from the polyurethane foam or polystyrene (styrofoam), with a thickness usually from 50 to even 100 mm. For smaller capacities (80-150 l), the insulation is sometimes permanently integrated - the foam is the filling of the space between the tank and the outer shell and cannot be removed. In larger storage tanks (e.g., 300+ l), the insulation is often removable or applied separately during installation - this makes transportation easier (the bare tank itself is narrower, and the thick lagging is applied only on site). Increasingly, foams with added graphite or special nano-space materials (aerogel, vacuum panels) are used - they allow to reduce heat transfer not only by conduction, but also by radiation, so the insulation can be thinner while maintaining the effectiveness of the.

Standstill losses is the loss of thermal energy from the heated storage tank to the environment per unit time. Manufacturers often quote them in kWh/24h (e.g., 1.5 kWh/24h). The better the insulation, the lower the losses. For modern storage tanks with a capacity of. up to 300 l these losses are usually 1-2 kWh per day (at temp. waters ok. 60°C and ambient ~20°C). For example, a well-insulated 300-liter storage tank can lose only ~1.5 kWh/24h, which corresponds to a continuous loss of power of ~60 watts - about as much as a light bulb. On a monthly basis, this translates into approx. a dozen or so zlotys in cost (if you heat with gas). For larger tanks (500 liters and above), losses are slightly higher, but are also typically in the range of 1.2-2.5 kWh/day due to thick layers of insulation. In practice, this means a drop in water temperature of only a few degrees per day in the absence of consumption. Of course, older boilers or appliances without proper lagging can lose much more heat.

To minimize heat loss, worth noting energy efficiency class storage tank (according to EU regulations there are classes from A to F for water heaters). The class is determined by m.in. on the basis of standstill losses - nowadays most good storage tanks are class B or C, the best ones (e.g., with vacuum insulation) - class A. Additionally, proper installation affects losses: it is essential to insulate all pipes feeding and draining water from the boiler (especially the sections right next to the tank), because through the bare metal pipes heat escapes very quickly. If the storage tank is equipped with circulating c.w.u., it is good to control its operation (e.g., circulation pump on a timer) - continuous circulation can even double the standstill losses, because it cools the water circulating in the system.

To summarize: a good storage tank should have effective thermal insulation - is a feature as important as the material of construction. When investing in a tank with a larger capacity, choose a model with thicker insulation to avoid unnecessary energy loss while storing water.

Corrosion protection and hygienic approvals

As mentioned earlier, corrosion protection is critical to the life of the c.w.u., which is constantly filled with water. Manufacturers use different corrosion protection: enameling, galvanizing, use of stainless steel, and protective anodes. Below is a brief summary of these safeguards and the importance of PZH attestation:

• Magnesium anode - standard on most enamel heaters. It is a rod (usually screwed into the tank from above), made of easily corrodible magnesium alloy. In an aqueous environment, magnesium oxidizes instead of iron - thus protecting exposed areas of steel. The anode wears out over time and it should be replaced periodically. Neglecting to replace the anode can result in faster corrosion of the tank from the inside (especially if the enamel layer is damaged). Therefore, it is important for the user to remember about inspections - often boiler services also offer to check the condition of the anode at the annual visit. The cost of the anode itself is not large, but its replacement can sometimes be cumbersome in built-in installations, and in large tanks the anodes can be difficult to access. The life of the anode depends on the quality of the water - in soft water (few minerals) the anode "disappears" faster.

• Titanium anode (electronic) - is an upgraded solution found in more expensive trays. The titanium anode does not dissolve, but acts as an electrode to protect the tank using electricity from a small power supply. Such an anode is maintenance-free - it does not need to be replaced every few years, but only to check whether the power module is working (it has a status LED). Titanium anodes are used especially in large tanks and where access to the anode is difficult (such as solar storage tanks with very long anodes). The disadvantage is a higher price - retrofitting the tank with an electronic anode is a cost of several hundred zlotys, but in return you get peace of mind for many years. If the titanium anode fails, it is simply replaced (this happens rarely).

• Cathodic protection by material - hoppers with stainless steel provide protection themselves - they don't need anode or coatings, as their material is rust-resistant. Similarly galvanized steel protects itself thanks to the presence of zinc. In these cases, only care should be taken to ensure that any possible repairs or welding were professionally performed (e.g., after welding stainless steel, it may be necessary to passivate again, and after welding a galvanized tank - to replenish zinc).

• PZH approval - Any tank designed for hot water should be hygienically certified (in Poland it is most often an attestation of PZH - the National Institute of Hygiene). Such a certificate confirms that materials in contact with drinking water (internal coatings, gaskets, anode) do not release harmful substances into the water in above-normal quantities. For the home user, PZH certification is a guarantee that tap water will maintain its quality. When buying a tray, it is worth checking whether the product has the appropriate document. In practice reputable brands always have approvals - problem may arise with cheap imported devices of unknown origin. Then the lack of certification raises the risk that, for example, the enamel contains admixtures of heavy metals, or that the galvanizing emits too much zinc/nickel into the water. To summarize: do not buy domestic water storage tanks without certification - users' health comes first.

Storage tank selection vs. type of heat source

Different heat sources place slightly different requirements on the c storage tank.w.u., both in terms of capacity and the design of the heat exchanger inside the. Here's how the specific issues are presented for the most popular sources:

• Gas boiler - Gas boilers (single-function boilers that work together with a boiler) usually have a lot of power and are able to quickly heat the water in the storage tank. This means that you can afford to smaller tank compared, for example, with a heat pump, because the boiler will reheat the water in a dozen minutes if necessary. With a gas boiler, the key is to match the coil in the tank to the power of the boiler - most standard storage tanks have coils sufficient for 25-30 kW, which covers typical domestic boiler capacities. However, if the boiler has a very large capacity (e.g., 35-40 kW, found in larger homes), it is worth choosing a storage tank with a larger coil to take full advantage of the boiler's power (otherwise the boiler will clock out). Importantly, the gas boiler can heat water to a high temperature (up to 70-80°C), so the storage tank should be able to withstand this - practically all brand boilers are designed for 95°C, so there is no problem here. The capacity selection itself at a gas boiler depends mainly on the number of users (according to the principles discussed above). Worth mentioning dual-function boilers: they do not use a separate storage tank, but heat water by flow at the time of consumption. They provide unlimited hot water for an unlimited period of time, but with more outlets their efficiency decreases (it's hard to use two showers at once, for example). The solution is dual-function boilers with small stratified storage tank (~20-50 liters built into the boiler) - increase comfort at temporary higher consumption, although it is still not the same as a large external storage tank. To sum up: for a gas boiler choose a tank mainly in terms of comfort (number of people, bathrooms), and not technical limitations - as long as it has an appropriate coil and insulation, the boiler will "take care" of the rest with its power.

• Heat pump - As previously described, the heat pump generally needs a larger storage tank and a special design of the exchanger. When selecting a storage tank for a heat pump, we pay attention to manufacturer's markings - Often dedicated boilers have, for example, "Heat Pump", "HP" in their name or are described as "with enlarged coil". A standard coil in a 200-liter storage tank may be ~0.8 m² in size, while an 8 kW heat pump requires ~2 m² - hence the need for dedicated solutions. Some manufacturers use instead of one large coil two coils connected in parallel or coils with a smaller diameter but longer length (multi-coil spiral) - all to increase the heat transfer surface area. If the storage tank has too small a coil for the pump, it will manifest itself in the fact that the pump will have to reheat the water with an electric heater or will operate with lower efficiency (longer heating time, higher operating temperature - lower COP). Another issue: temperature altitude - Heat pumps operate efficiently up to approx. 50-55°C, above that the heater often turns on. Therefore, the storage tank should be large enough so that water at a temperature of, say, 50°C is enough for the needs of the household. Solutions such as bivalent tank - For example, combined with a solar system to reheat water in the summer without charging the pump. Finally, the water in the heat pump tank should be periodically superheated (e.g., with a heater to 60°C once a week) for disinfection - the tank must provide for this. To summarize: for heat pump choose a tank with a larger capacity (by approx. 30-50% larger than for a boiler with the same number of people) and with a large heat exchange surface area. It is best to use the offer of dedicated tanks - for example, many companies offer ready-made heat pump kits with 200-300 l tanks optimally adapted to them.

• Fireplace with water jacket / solid fuel boiler - Here, the tray often acts as both heat buffer. Burning in a fireplace or boiler is cyclic - so a well-chosen tank should store all the energy from one cycle of burning to give it back gradually afterwards. If the fireplace has, for example, 15 kW of water power and we burn for 2 hours, it will generate ~30 kWh of energy - which will approximately heat 500 liters of water by 50-60°C. Hence the frequent use of trays of the order of 400-500 l or larger. Often these are the so-called. bunded storage tanks or water jacketed tanks, where the entire structure acts as an exchanger (larger heat transfer area than a single coil). With a fireplace, it is important to protect against corrosion, because the exhaust gas can cause acidic reaction of water (especially if there is an open system). Therefore, sometimes the following are recommended for fireplaces stainless steel hoppers or enamelled with reinforced protection. Another aspect - if the fireplace is also to be used in the summer only for heating water, a large storage tank may not be very economical (you have to light a fire only for water). That's why some people install an electric heater in the top of such a tank in the summer to reheat only, say, 100 liters for current use, not the entire 500-liter buffer. Such combinations go beyond the topic of purely capacity selection, but show that the in solid fuel systems, usually excess capacity is more beneficial than undercapacity - because it increases safety (stores peak energy, prevents overheating) and gives flexibility in operation. Of course, if the fireplace is a booster (in addition to a gas boiler, for example), the storage tank is selected based on total demand anyway - but it's worth considering a larger one to make the most of the heat from the wood when it's available.

Summary

Choosing the right hot water storage tank capacity is a decision that will affect the daily comfort of homeowners and the operating costs of heating. It should be undertaken based on a sound needs analysis - number of users, style of water use, sanitary facilities in the house - and taking into account the specifics of the heat source and installation. A well-chosen storage tank is one that is neither too small (so that there is no shortage of hot water) nor unnecessarily too large (so as not to waste energy on heating unnecessary volume). In addition to capacity, quality aspects are also important: solid thermal insulation, suitable material and corrosion protection (enamel, galvanized, stainless steel), possession of a PZH certificate, and availability of service (e.g. anode replacement).

If you are unsure about your choice, it is worth consulting an experienced plumber or plumbing designer. A professional will help estimate the peak hot water consumption of our home or facility and advise whether a 200-liter or 300-liter tank is better, whether two coils are needed, etc. Let's remember that dHW tank is an investment for years - it is better to invest in a device of slightly better quality, which will serve for a long time and without failure. With proper operation (maintaining water quality, periodic anode service, cleaning from scale, if necessary), a good storage tank will repay you with trouble-free operation and constant access to hot water at the right temperature. As a result, both the home user and the installer can rest assured - the installation of c.w.u. will operate efficiently, economically and without unpleasant surprises.

Ultimately, the selection of storage capacity c.w.u. it comes down to finding the golden mean between comfort and efficiency - so that every tap you turn on surprises you with pleasantly warm water, and keeps your water heating bills under control. If you need help selecting a hot water storage tank - contact us - wkm@wkm.store.en.