Finding the right DHW cylinder

Topics at a glance

DHW heating
Selection criteria
Material
Consultation
Product range

Whether for a morning shower or a relaxing bath at the weekend: for most people, constant availability of domestic hot water is fundamental to home comfort. It can be generated and stored in different ways. A basic distinction is made between centralised and decentralised DHW heating. Viessmann Vitocell DHW cylinders store centrally prepared DHW over a longer period of time and make it available when required.

To the product range

Centralised and decentralised DHW heating: a comparison

An existing boiler is indispensable for central DHW heating. It provides heat not only for room heating, but also for heating the required DHW. To ensure that DHW flows out of the tap as required at all times, heating systems of this kind are equipped with a DHW cylinder.

Boiler-independent DHW heating

Unlike centralised DHW heating, the decentralised version does not need to be connected to a boiler. In an instantaneous water heater, the DHW is only heated to the required temperature at the moment of demand. Small storage water heaters or undersink storage water heaters, on the other hand, store the DHW. Both generally run on electricity, allowing very flexible installation.

Another option for decentralised DHW heating is the hot water storage heater. This is a cylinder with little or no thermal insulation that both heats and stores the DHW. However, due to the poor or in some cases non-existent thermal insulation, the water cools down quickly. This means that the water heater has to heat the water again and again. Water heaters of this type are rarely available, as the technology is considered obsolete.

Buying the right DHW cylinder

Vitoladens 300-C with a Viessmann DHW cylinder

Before you buy a Viessmann DHW cylinder, it is as well to find out about the different versions. This is because, in addition to the cylinder size, other factors also play a role, depending on the characteristics of the building and the DHW demand. DHW cylinders also require space. To cater for differences in available space, Viessmann offers horizontal DHW cylinders and cylinders installed adjacent to or below the boiler. In addition, you can choose between different materials such as stainless steel or steel with Ceraprotect enamel coating. In the following sections you will learn more about important criteria to consider when buying a DHW cylinder.

Determining the right size of DHW cylinder

Dimensioning is a crucial factor when it comes to finding the appropriate cylinder. Choosing the precise size depends not just on the number of residents, their individual consumption habits and the actual DHW demand. In addition to the general heating output of the system, a further important factor is whether just heating water alone is to be provided or domestic hot water as well. If the general heating capacity is rather low, it is advisable to buy a somewhat larger cylinder. Always consult a Viessmann partner for advice in this regard. Our partners are familiar with the wide range of different DHW cylinders. The Vitocell product range is available with capacities from 130 to 1000 litres. This means that these products are a worthwhile purchase for use not only in detached houses, but also in apartment buildings or other buildings where the DHW demand is high. This also includes commercial or municipal buildings.

The right solution for every available space

To avoid unnecessarily long pipe runs, DHW cylinders are installed in the direct vicinity of the boiler. The various options, as already mentioned above, are as follows: horizontal, adjacent to the boiler and below the boiler. The DHW cylinder must be selected to match the available space as well as DHW demands and individual requirements. For example, the Vitocell 100-W offers the perfect solution for a comparatively low DHW demand with a small footprint, because this model can be installed under a wall mounted boiler (for example, under a Vitodens 300-W gas condensing boiler) to save space and can store up to 150 litres of water. The all-round thermal insulation ensures convenient and economical DHW heating throughout a detached house.

The adjacent DHW cylinder models are Vitocell 100-L, Vitocell 100-V and Vitocell 300-V. As the name suggests, they are located directly next to the boiler. They are cylindrical, floorstanding DHW cylinders equipped with an indirect coil. This extends right down to the cylinder floor, which enables the entire water content to be heated.

The Viessmann product range also includes horizontal DHW cylinders: Vitocell 100-H and Vitocell 300-H. These are built to be particularly sturdy so that the appropriate boiler can be placed on top of them. They offer plenty of space above, for example for a gas condensing or oil boiler.

Should you buy a mono or dual mode DHW cylinder?

Depending on your heating system, you can buy a DHW cylinder that suits your individual circumstances. There are basically two types: mono and dual mode DHW cylinders. The former are equipped with one indirect coil, whereas dual mode models have two coils. This enables quick and easy integration of a solar thermal system for DHW heating. The solar collectors heat the DHW cylinder via the lower indirect coil. If the solar energy available is not sufficient to cover the demand for DHW, the upper indirect coil provides additional heating. The heating water, heated previously by an additional boiler, flows through this coil. The dual mode solution is particularly economical and environmentally responsible, because most of the DHW is produced using free solar energy.

Indirect or direct DHW heating

In Viessmann DHW cylinders, the DHW is heated indirectly via an indirect coil. There are also small storage water heaters or instantaneous water heaters that heat the water directly. If you would like to purchase a small storage water heater of this type, Viessmann offers a Vitotherm electric hot water storage heater that heats the water using electricity. You heat only as much DHW as required –– directly where you currently need it. Purchasing a small storage water heater is particularly worthwhile where a central supply of DHW is not possible or not necessary due to low demand.

Universally applicable and available as a cylinder loading system

If there is a particularly high demand for DHW, the floorstanding Vitocell 100-V DHW cylinder is the ideal solution. The enamelled Viessmann DHW cylinder is available in a choice of two colours and with a capacity of 160 to 950 litres. Several DHW cylinders can also be combined to form a cylinder bank, if required. Depending on the model, the Vitocell 100-V is especially suitable for DHW heating in conjunction with heat pumps or condensing boilers. This makes it almost universally applicable.

Viessmann hot water storage heaters for heating systems can also be extended to include a separate heat exchanger set (Vitotrans 222). In this combination, they form a cylinder loading system for heating domestic hot water. This is particularly useful during peak output, for example when high draw off rates (how often water is drawn off) and different reheat times have to be covered temporarily. Cylinder loading systems are also preferred for operating heating systems that require low return temperatures, such as condensing boilers. The Vitocell 100-L from Viessmann is the right DHW cylinder for these and other applications. It performs impressively, with accurate cylinder heating to the right degree even with modulating flow temperature, as well as easy installation thanks to removable thermal insulation (500 litres and over).

Opt for the highest water quality and the best corrosion protection

The picture shows a Vitocal 200-G brine/water heat pump next to a DHW cylinder.

Viessmann Vitocal 200-G brine/water heat pump and DHW cylinder

Especially when storing DHW, it is important that hygiene standards are maintained. Viessmann DHW cylinders are manufactured accordingly, using enamelled steel or stainless steel to EN 12897. When it comes to enamelled DHW cylinders, those with Ceraprotect enamelling provide the best performance. The Vitocell 300-H and Vitocell 300-V offer the added benefit of stainless steel and meet the highest demands. They require no coating and guarantee years of protection against corrosion thanks to their chemical properties. These cylinders are available as adjacent and horizontal types. When you purchase these stainless steel DHW cylinders, you receive a ten year guarantee against leaks caused by corrosion.

Purchasing advice

For long term, convenient, safe and economical operation, the heating system and DHW cylinder must be perfectly matched right from the start. Whether you wish to combine a heat pump, solid fuel boiler, oil or gas heating system with a DHW cylinder or are looking for another dual mode solution, consultation with a Viessmann partner is indispensable. Our partners not only help with the choice of appliances, but also take care of the sizing, connection and, as an option, the maintenance of the DHW cylinder. With our local trade partner search, you can find the right contact person in your area, in just a few steps.