Tank with or without a coil? What type of tank and what capacity for a given gas boiler? Investors ask themselves such questions before purchasing a new or replacing an old gas boiler. We explain what you need to take into account when choosing the right tank and which models will best fulfill their function.
Types of gas boilers
For the correct selection of the tank, the type of gas boiler we will use is crucial. There are two basic types of gas boilers available on the market - single-function and dual-function.
Single-function boilers
These are devices that primarily power the heating installation in the building (e.g. radiators or underfloor heating ). They can heat domestic water only after connecting a separate water heater to them. Heating takes place via a spiral coil built into the tank, to which the gas boiler is connected. Single-function gas boilers for this type of boilers - domestic hot water exchangers - are available in two versions - hanging and standing. Hanging tanks can have capacities from 80 to 140 l, while standing tanks can have capacities up to 3,000 l.
The efficiency of hot water preparation is closely related to the tank capacity - the larger the capacity, the higher the efficiency. A larger tank also improves the comfort of using the heating system.
Combination boilers
They also heat water in the building's central heating circuit, while utility water is prepared in a flow manner, i.e. it is heated immediately at the time of consumption. For this purpose, the boiler is equipped with an additional plate exchanger. This allows you to separate two heating functions: central heating and domestic hot water. In dual-function boilers, the domestic hot water capacity depends on the boiler power. Typically, to maintain comfort in an apartment or house, it is necessary to use a boiler with a power of 20–24 kW. The efficiency of such a hot water installation can be increased by using layered hot water tanks - their capacity usually does not exceed 100 l.
The tank connected to the boiler then serves as a domestic hot water tank. The water heated in the gas boiler is collected in the upper part of the tank and from there it is taken to the domestic hot water installation. This solution guarantees almost immediate consumption of hot water, even at several consumption points, and almost no heat loss. The estimated total heating time of a full water tank with Δt=45°C, in cooperation with a 24 kW boiler, is only 20 minutes. The water tank is equipped with a 3-stage charging pump with adjustable capacity, forcing cold water to flow through the gas boiler and starting it. The charging pump is mounted on the cold water inlet (taken from the bottom of the tank) to the gas boiler, which causes the boiler to run at maximum power.
Check out SGW(S) Rondo tanks at the Onninen wholesaler
Advantages and disadvantages of systems with gas boilers
Each of the described heating systems powered by gas boilers gives users many benefits, but also has its drawbacks. The cost of purchasing a set consisting of a single-function boiler and an exchanger with a spiral coil will certainly be lower than the price of a set of a dual-function boiler with a stratified tank. However, it should be taken into account that such a system takes a little longer to prepare hot water (up to several minutes). The system with a dual-function boiler and a stratified tank, although slightly more expensive, is more efficient and allows for quick preparation of hot water (practically from the moment the boiler is turned on), and is also subject to slower wear thanks to the limited number of times the gas boiler is turned on.
Advantages of SGW(S) Rondo Premium tanks: 
- Energy class A
- Dedicated to single-function boilers
- Optimal capacity 120 or 140 liters.
- Convenient installation and service - all outlets in the upper bottom
- Gas savings - faster water heating thanks to a spiral coil with a very large surface
- Works with any type of boiler: gas, coal, oil, etc.
- Possibility to install a GE electrical kit
- Top quality EXTRA GLASS® ceramic enamel
- Additional protection with a magnesium anode
- Thermometer as standard
The best tanks for gas boilers
The best results of cooperation with single-function gas boilers are provided by GALMET tanks type SGW(S) Rondo Premium - A class (capacity 120 and 140 l). They can also work with all other types of central heating boilers. A spiral coil enlarged by over 25% with an area of up to 1.2 m2 ensures quick water heating, and the high energy class A guarantees economical operation of the system and gas savings. Standstill losses are only 38 W. Rondo Premium tanks are insulated with polyurethane foam and secured with a metal casing. Inside, the tank is covered with EXTRA GLASS® ceramic enamel, applied using the wet method, guaranteeing the longest service life.
SG(S) Fusion tanks (100 l capacity) are intended for gas combi boilers. These are layered tanks used to store hot water. Thanks to the layering of heated water in the tank, small water consumption does not activate the boiler too often, which extends its life and effectively saves gas. SG(S) Fusion are also insulated with polyurethane foam and secured with a metal casing. Inside, the tank is covered with EXTRA GLASS® ceramic enamel, applied using the wet method, guaranteeing the longest service life. The stratified tank, only 90 cm high, can be easily installed under a gas boiler. All connections in the Fusion tank are located in the top cover, which greatly simplifies installation and increases the comfort of using the tank.
Advantages of SG(S) Fusion tanks: 
- Dedicated to dual-function boilers
- Reduced water heating time
- Economical operation of the system - no water losses.
- Optimum capacity 100 l.
- Maximum use of water layering
- Reducing gas consumption with small water consumption
- Three-stage circulation pump with adjustable capacity (built in the tank)
- Possibility to install a GE electrical kit
- Top quality EXTRA GLASS® ceramic enamel
- Additional protection with a magnesium anode
- Thermometer as standard
Check out SG(S) Fusion tanks at the Onninen wholesaler
Help and advice – free of charge
Additional information and advice on tanks for gas boilers can be obtained from experts of the National Heating Technology Advisory Center. They also help in the selection, configuration and adjustment of heating devices to a specific building, selected system and existing infrastructure. GALMET experts are available by phone: 77 403 45 60 or by e-mail: [email protected]