Installation of a solar storage tank: procedure, placement and installation requirements

Installation of a solar storage tank: a complete technical guide to installation

The solar storage tank is the heart of every thermal solar system. You can have the highest quality collectors on the roof, powerful pump units and a well-designed control system – but if the tank is poorly placed, incorrectly connected or installed without respecting basic technical requirements, the entire system will operate inefficiently, unreliably or will break down prematurely. I have seen many such mistakes in practice: a tank in an unventilated room where the temperature exceeds 50 °C in summer, unsuitable loose connections without expansion, an anode never replaced, a pump unit connected upside down. This article is therefore written for those who want to understand the installation of the tank in depth – whether you are planning the installation with a contractor or want to know what to check after the work is completed.

We will cover everything: from the selection of the room and the static assessment of the floor, through handling the tank, hydraulic connection, ventilation and insulation, to the first filling and pressure test. Where relevant, we also refer to other topics in the Knowledge Center – for example, the article Dimensions and connections of solar storage tanks: what to check before purchase or Connecting a solar storage tank to a boiler and circuit distributor, where you will find more detailed information on specific connection schemes.

Why correct installation of the tank is critical

A tank heated by solar can reach temperatures of 80–95 °C in the solar circuit and 60–80 °C in the tank water. The difference compared to a standard hot water heater is significant – the material, pressure and temperature requirements are much higher. Stainless steel tanks, enamelled tanks with a magnesium anode, tanks with two heat exchangers or with an embedded TÚV tank – each type has slightly different installation requirements.

From the point of view of warranty and safety, there is another important point: most manufacturers condition the validity of the warranty on professional installation, which in practice means a person with the appropriate professional qualification (gas fitter, heating engineer, or installer with authorization for pressure equipment according to Decree 508/2009 Coll. and NV 1/2016 Coll.). A tank with a volume of more than 10 liters under pressure is a pressure equipment and is subject to safety requirements.

Choosing a room and placing the tank

In most family homes, a solar storage tank is located in the boiler room, technical room or in the basement. Unlike a boiler, where you primarily care about access to the burner, for a tank other factors are key: the static load capacity of the floor, the height of the room, the distance from the collectors and from the hot water draw-off point.

Static load and floor strength

A 300-liter tank filled with water and insulation typically weighs 350–380 kg. A 400-liter tank can exceed 470–490 kg when full. A concrete floor in a standard boiler room can easily handle these loads, but a wooden floor on joists or a thin cement screed without a steel mesh can be problematic. If you have any doubts, have a structural assessment done – in practice, this mainly concerns older houses with a wooden ceiling structure.

We recommend placing the tank on a concrete base or a steel grid, not directly on ceramic tiles without a base. Ceramic tiles themselves are not load-bearing – they crack under point loads from the tank's feet. If the tank has no feet, we create an intermediate link from thick rubber pads or a steel plate.

Room height and handling

Larger tanks (300, 400 liters) have a height including insulation of typically 1 850–2 100 mm. If you add space for connections and a safety valve above the tank, you need a minimum room height of 2 300 mm. Tanks with a flat bottom and flat ceiling can sometimes be "tilted" during transport, but with stainless steel tanks with thin-walled heat exchangers you need to proceed carefully – a tilt of more than 45° can damage internal components or the anode.

The entrance to the room must be at least 700–750 mm (for a 200 l tank) to 900 mm (for a 400 l tank) wide, because the tank with insulation has a diameter of typically 650–750 mm. I have often seen situations where the tank physically did not fit into the boiler room and it was necessary to remove the door and part of the frame. It is better to measure before ordering than after delivery.

Distance from collectors and from the withdrawal point

Solar collectors are usually on the roof, while the tank is in the basement or utility room. Every meter of pipe in the solar circuit means heat loss and a larger volume of filling medium. For single-family homes, an approximate rule applies: the length of the solar circuit (the sum of the supply and return branches) should not exceed 50 meters with standard pump units with a power of up to 65 W. If the route is longer, the pump and piping must be dimensioned accordingly.

The tank should be as close as possible to the hot water withdrawal points – bathroom, kitchen – to minimize the length of the TWH distribution and thus the volume of cold water in the pipe at each tap opening. In a single-family home, the ideal distance from the tank to the nearest withdrawal point is up to 10 meters.

Installation requirements and standards

The installation of a solar tank in Slovakia is governed by several regulations and standards that must be known:

• STN EN 12977 – Thermal solar systems and components, custom equipment
• STN EN 806 – Requirements for potable water supply systems
• Decree of the Ministry of Transport, Construction and Regional Development No. 508/2009 Coll. – safety of pressure equipment
• NV SR No. 1/2016 Coll. – equipment and protective systems in potentially explosive atmospheres (relevant when combined with a gas boiler)
• STN EN 1717 – Protection against backflow of potable water

For the installation of a tank on potable water (TWH side), EN 806 and EN 1717 are particularly important – the tank must be protected against back pressure and contamination. Therefore, a safety valve is always installed on the cold water inlet, typically set to 6–8 bar, a non-plastic check valve, and a pressure reducing valve (if the network pressure is higher than 3.5 bar).

Step-by-step installation procedure

The following procedure assumes a tank with two heat exchangers, intended for a combined system of solar collectors + boiler/heat pump. If you install a solar tank with two heat exchangers including insulation, the insulation is delivered directly with the vessel, which simplifies the procedure – there is no need to solve additional wrapping.

Step 1: Preparation of the room and base

Before transporting the tank into the room, check the floor – it is not cracked, is flat, dry and clean. If it is necessary to make penetrations for pipes through walls or the floor, do it now – it will be much more difficult later. Prepare the drainage – during the installation of the tank, you will need to drain water from the safety valve and the emergency drain, which must lead to the sewer via a visible drain pipe (not hidden).

Step 2: Transportation and Installation of the Tank

Larger tanks (300, 400 liters) are delivered on a pallet and wrapped in cardboard with PE film. When removing from the pallet, do not use forklift tines directly on the tank shell – only on the pallet. When carrying up the stairs, you will need at least 3 people for a 300 l tank and 4 people for a 400 l tank.

The tank is placed in the designated location in an upright position. Check that it is evenly supported and not standing on one foot more than the others – long-term unevenness may cause deformation of the bottom. Most tanks have adjustable feet that compensate for slight floor irregularities.

After installation, leave the tank so that you have free access to all connections from all sides. The minimum distance from the wall for a 300 l tank is 200 mm on each side for convenient work with the wrench and later for anode replacement.

Step 3: Hydraulic Connection

This is the technically most demanding part. The tank typically has the following connections to be connected:

• Cold water inlet (SV) – usually a lower connection, G6/4" or G1" internal thread. This place is for: a ball valve, pressure reducing valve (RVT) set to 2.5–3.5 bar, check valve, safety valve (set to 6 bar for tanks up to 200 l, 8 bar for larger ones) with a visible discharge pipe to the sewer.
• Hot water outlet (TÚV) – upper connection, ball valve, possibly a circulation pipe.
• Lower heat exchanger connections (solar circuit) – inlet and outlet for the solar medium (a mixture of water and glycol), typically G1" or G6/4". You connect the pump group of the solar circuit here.
• Upper heat exchanger connections (boiler/TČ circuit) – inlet and outlet for the secondary heat source.
• Immersion temperature sensor – direct contact of the sensor with the tank water, usually an immersion well (thermowell) G1/2".
• Drain cock – at the lowest point of the tank, for draining.
• Anode – on the side or top flange, accessible for regular inspection.

All threaded connections should be sealed with Teflon tape or hemp rope with paste (LOCTITE 55, Fermit). Do not use dry hemp rope without paste – at temperatures of 60–80 °C and with pipe movements, the seal may dissolve. Stainless steel tank connections are sensitive to over-tightening – do not over-tighten with a wrench, approx. 2–3 turns by hand and then 1 additional turn with a wrench is sufficient.

When connecting the solar circuit, pay attention to the correct position of the pump group – the supply (from the collectors) usually goes to the lower inlet of the heat exchanger. In winter months without collector operation, there is still solar medium under pressure (ca 1.5–2 bar) in this circuit, so every connection must be precisely sealed.

We recommend using industrial manifolds and collectors for the tank circuit distribution – for example, an industrial stainless steel manifold/collector with ball valves 6/4"x1"; 2-way, which allows clean and clear branching of the circuits at the tank.

Step 4: Pipe Insulation and Electrical Connection

Every pipe at the tank that carries hot water or solar medium must be insulated. For temperatures up to 80 °C, standard rubber tube insulation (Armaflex, Tubolit) with a thickness of 13–19 mm is sufficient. The solar circuit with temperatures potentially exceeding 120 °C (during stagnation) requires heat-resistant insulation – rubber HT or mineral wool. An uninsulated meter of DN22 pipe with TÚV at 60 °C loses up to 15 W of heat – on 10 meters it is 150 W, which represents significant annual costs.

The electrical connection includes: connecting the pump group of the solar circuit, electric heating element (if the tank is equipped with it), temperature sensor for solar regulation, and possibly a thermostat or thermostatic valve for legionella heating (reheating to 60 °C once a week). These works are performed by an electrician with the appropriate authorization according to Ordinance 508/2009 Z.z.

Step 5: Filling, Air Venting and Pressure Test

The tank (TÚV) side is filled with potable water through the cold water inlet. Before filling, open the drain valve and let the water run to release air. Also open the TÚV connection – water flows up and pushes out the air. The tank is full when water flows continuously from the TÚV outlet. Then close the drain valve and gradually bring the pressure to the operating value (2.5–3.5 bar).

Visually check all threaded connections with a dry paper towel – even a small leak is immediately visible on a wet connection. Leave the system under pressure for 24 hours without heating and check again.

The solar circuit is filled with solar medium (usually a mixture of water with propylene glycol up to 40 % for protection down to -26 °C) using a solar medium pumping station. Filling is done from the bottom through the drain/filling cock, air venting at the highest point of the circuit (usually at the collector or at the top of the pipe). Operating pressure of the solar circuit at cold installation: typically 1.5–2 bar. The expansion tank must be pre-charged to a pressure 0.2 bar lower than the cold system operating pressure.

Ventilation and Room Temperature Requirements

The room with the tank must have sufficient ventilation – not because of the tank itself, but due to possible leakage of the solar medium (propylene glycol is practically non-toxic, but at high temperatures it creates vapors that can irritate mucous membranes). If the tank is in the same room as a gas boiler, the requirements for air supply for combustion apply (800 cm² air inlet for a boiler up to 35 kW according to STN EN 12828).

The room temperature should not exceed 35 °C in summer – this is a problem mainly in poorly ventilated attic spaces. At ambient temperatures of 40–50 °C, the tank insulation performance decreases, heat losses increase, and regulation loses accuracy. The tank should never stand in direct sunlight or near a heat source without a shield.

Connecting the storage tank to solar collectors and secondary source

For proper system operation, hydraulic balance is key – the solar medium must flow through the lower heat exchanger at an optimal rate (for most systems 0.4–0.6 l/min per 1 m² of collector area). The pump set must be dimensioned for this flow rate at the actual hydraulic resistance of the circuit.

When connecting a boiler or heat pump to the upper heat exchanger of the storage tank, an important rule applies: the upper heat exchanger must never be permanently closed without the possibility of heat dissipation. In combination with automatic control (e.g., a three-way valve), the boiler switches between heating the storage tank and space heating. More detailed connection diagrams can be found in the article Connecting a solar storage tank to a boiler and circuit distributor in the Knowledge Center.

Storage tanks with larger volumes – for example, 300-liter tank or 400-liter tank – are suitable for larger households or for combination with a larger collector area (10–20 m²). With proper tank and collector sizing, you can cover 60–75% of your annual TÚV demand with solar energy. The question of volume is discussed in more detail in a separate article What solar storage tank volume do I need for my home.

Special installation requirements for tanks with two heat exchangers

A tank with two heat exchangers has one key advantage – you can combine two independent heat sources (solar + boiler, solar + heat pump, or solar + electric booster). But it also has a significant installation requirement: the position of the heat exchangers in the tank is not random. The lower heat exchanger (solar) uses the principle of stratification – it heats water in the lower, cooler part of the tank, from which the temperature gradually rises upwards. The upper heat exchanger (boiler) reheats the water in the upper part, where the TÚV withdrawal is also located.

If you were to connect the tank in the opposite way – for example, the boiler to the lower and solar to the upper heat exchanger – you would lose the efficiency of both systems. The boiler would unnecessarily heat the entire tank volume before the heat reaches the upper, withdrawal zone. And the solar circuit would try to heat water that the boiler is just reheating – by inactivity, you would lose both stratification and the system's economy.

The temperature at the inlet to the lower heat exchanger (solar) must be higher than the temperature of the water in the tank at this heat exchanger – otherwise, the control will stop the pump. This is the basic function of differential control: measuring the temperature difference between the collector and the lower zone of the tank. Typical settings: the pump starts at ΔT ≥ 5–8 °C, stops at ΔT ≤ 2–4 °C.

Ventilation and expansion tank of the storage tank

On the TÚV side of the tank (drinking water), there is no standard expansion tank – the drinking water system is open via a safety valve. However, if a check valve is installed before the tank (which must be!), the system becomes closed and the water expands when heated. Without an expansion tank, the safety valve would repeatedly drip, which is undesirable. Therefore, a small expansion tank (5–8 liters for a tank up to 200 l, 8–18 liters for larger tanks) is always installed on the inlet pipe of the cold water.

The pre-charge of the drinking water expansion tank is set to 0.2 bar less than the operating pressure (e.g., at 3 bar operating pressure: pre-charge 2.8 bar). Check this setting every 2 years – the membrane ages and the pre-charge decreases.

Installation of tank insulation

Most solar storage tanks are sold without insulation or with optional insulation. Some models, such as a solar storage tank with two heat exchangers including insulation, have insulation as part of the delivery, which is a more practical solution – the insulation is shaped to fit, saving time on the construction site.

If you install insulation additionally, the tank shell must be clean and dry. Insulation made of rigid polyurethane foam (PUR) with a PVC shell has a thickness of 80–100 mm and is shaped as a shell with a longitudinal zipper or dry zipper. Connections are cut directly in the insulation – make sure the cutouts fit tightly around the connections, as gaps cause heat loss and possible condensation.

In practice, I have seen tanks without insulation in a glass boiler room – in winter, the boiler room served as a "heated space" due to the tank's loss of 100–150 W. While this is amusing, in reality, it means the tank loses 876–1,314 kWh of heat per year, which at an electricity price of 0.18 €/kWh represents 158–236 € in unnecessary annual costs. Insulation is therefore always worth it.

Most common installation errors with tanks in practice

After years of working with customers and service cases, I repeatedly encounter the same mistakes. Here are the most serious ones:

• Tank without an expansion tank on the drinking water side – the safety valve regularly drips, limescale deposits, the valve stops sealing.
• Heat exchangers connected in reverse – boiler at the bottom, solar at the top – loss of stratification and efficiency.
• Missing or unconnected temperature sensor in the lower zone – incorrect regulation, collectors overheat, risk of stagnation.
• Safety valve without drainage to the sewer – when opened, water spills on the floor.
• Tank in a too warm room without ventilation – increased heat loss, regulation problems.
• Connections tightened too forcefully – cracked stainless steel flanged ends.
• Solar medium without antifreeze additive or with poor concentration – freezing in winter or degradation of inhibitors in summer.
• Forgotten anode check during the first service – the anode flattens within 2–3 years with aggressive water and the tank starts to corrode. More about this issue can be found in the article Maintenance of a solar storage tank: cleaning, anode check, and heat exchanger.

Installation requirements according to tank type

Not every tank is installed the same way. The differences are mainly in these areas:

To choose the correct type of tank, I recommend reading the article Single or double heat exchanger tank: which is more suitable and Solar tank with internal DHW tank: how it works and when it is worth it in the Knowledge Center.

System commissioning and first service protocol

After the physical installation is completed, the commissioning follows. This includes:

• First filling and purging of the solar circuit at cold (with shaded collectors)
• Setting the regulation: differential temperature for pump start and stop, maximum tank temperature (usually 80–85 °C), frost protection, thermostatic disinfection (legionella heating)
• Checking the flow direction in all circuits (flow meters, flow meters on the manifold)
• Testing the safety valves – manually opening them to check functionality
• Setting the expansion tank to the correct pre-pressure
• Preparing the installation protocol with values: medium volume, medium type, glycol concentration, cold pressure, installation date, regulation settings

The installation protocol is important not only for the warranty, but also for future service. In two years, when the service technician comes to check the anode and top up the medium, they need to know these basic values. Without the protocol, they start from scratch.

Most frequently asked questions (FAQ)

Must the tank always stand vertically, or can it be installed horizontally?

Most solar tanks are designed exclusively for vertical position. Heat exchangers, venting, anode and stratification are designed for a vertical axis. Horizontal installation is possible only for specially designed tanks marked by the manufacturer as "suitable for horizontal installation" – and even then, the connections must be in the correct position. Never try to tilt a standard vertical tank sideways – you will disrupt the stratification and anode function.

What is the difference between a pressurized tank and an open tank?

A pressurized tank is a hermetically sealed pressure vessel connected directly to the drinking water network (typical for Slovakia, pressure 2.5–6 bar). An open tank (unpressurized) is supplied by gravity from a raised well or cistern – it is simpler and cheaper, but requires a different system layout. In family homes in Central Europe, pressurized tanks are almost exclusively used for solar systems.

Can I install the tank myself, or is it a job for a professional?

Physically moving and placing the tank can be helped by a layperson, but the hydraulic connection, pressure test and commissioning must be performed by a person with professional qualifications for pressure equipment (heater, boiler, installer). For the potable water side, it is necessary to have the right to install plumbing according to current STN standards. Electrical work is carried out exclusively by an electrician with the appropriate qualification. In addition to the warranty, insurance of the property also plays a role – insurance does not cover damages from improperly installed systems.

Where should the tank be in relation to the boiler – above the boiler, next to it, below it?

The tank and boiler are usually installed next to each other in the same boiler room in family homes, with the tank possibly standing 2–5 meters from the boiler. The height of the tank in relation to the boiler is not critical from a hydraulic point of view with forced circulation (pump). More important is that the tank's heat exchanger is connected to the boiler's hydraulic circuit correctly (in series or with a diverting valve) and that the regulation correctly switches between DHW heating and heating. More on hydraulic connections can be found in the article Connecting a solar tank with a boiler and circuit manifold.

How long does the tank installation and connection take?

For an experienced installer: a 200–300 liter tank in a boiler room with a prepared location and piped in – 4 to 6 hours of pure installation. If new pipe runs need to be cut and welded, expect 1–2 days. Filling and commissioning including

Do you have a question about this topic?

Not sure or dealing with a specific situation in your household? Write to us – we are happy to help.