Hot water cylinders: storing water, the efficient way.
How a hot water cylinder works
The science behind hot water cylinders.
Hot water cylinders do more than just heat your drinking and domestic water - they store it, so you always have warm water ready when you need it. At the heart of the cylinder lies an ingenious spiral-shaped coil, also known as a heat exchanger. Heated water from your heating system flows through this coil, transferring its warmth to the surrounding drinking water stored within the cylinder. This ensures even and consistent heating throughout. The drinking water never directly contacts the heated water in the coil. When warm water is drawn, cold water automatically flows in and is heated through the same exchange process. The result? A reliable supply of warm water, any time.
A well-insulated cylinder reduces heat loss, keeping your water warmer for longer periods and improving overall energy efficiency. For hygiene and safety, the water temperature should remain at a steady minimum of 60°C to prevent harmful bacteria, such as Legionella. Vaillant systems are designed for maximum efficiency, relying on advanced coil-based solutions like the uniSTOR exclusive. Unlike less effective double-jacket systems, which transfer heat through the walls of an internal tank, our high-performance systems ensure precise temperature layering, consistent results, reliable operation for years to come, and a constant supply of hot water.
Advantages of hot water cylinders
Big cylinder, big benefits.
- Simple integration for any heating system.
Hot water cylinders connect effortlessly to existing heating systems. They are the perfect retrofit or modernisation solution, bringing convenience and adaptability to your home without major changes.
- Consistently reliable hot water supply.
Even with several taps running simultaneously, your hot water cylinder ensures a dependable supply of warm water. It provides comfort and reliability, no matter how high your household's demand may be.
- Designed for renewable energy systems.
Hot water cylinders pair seamlessly with renewable energy solutions like heat pumps, offering a sustainable and efficient way to manage your household’s energy while reducing your carbon footprint and saving on costs.
- Maximum efficiency for large households.
The more people in your household, the more effectively hot water cylinders handle high water demand. They're an efficient, cost-effective choice for busy homes, ensuring everyone has warm water when they need it.
Two options of hot water preparation
The difference between direct and indirect heating.
When it comes to hot water cylinders, there are two options to consider: indirect and direct heating.
Indirectly heated cylinders use your heating system to warm water through a heat exchanger. They’re efficient, hygienic, and work seamlessly with renewable energy sources. When located near your boiler, they also minimise heat loss. That’s why they’re the recommended choice for most homes today.
Directly heated cylinders, often referred to as boilers, warm water directly using electricity or gas, operating independently from the heating system. However, they consume more energy and incur higher running costs. Because of this, they’re now mainly used in specific scenarios, such as individual apartments or smaller commercial units. For most households, indirectly heated cylinders are the better option.
Types of indirect hot water cylinders
From monovalent to bivalent: a cylinder for every need.
- Monovalent cylinder
- Bivalent cylinder
- Shift-load cylinder
Monovalent cylinders are the classic choice for heating systems with a single energy source, such as a gas or oil boiler. They are straightforward in design and perfect for households that don’t use additional energy sources like solar thermal systems. A great example is the Vaillant uniSTOR plus, which stands out for its high efficiency and dependable hot water supply.
Flexible heating solutions for modern homes
The right hot water cylinder for every need.
- 1/2Domestic hot water cylinderuniSTOR exclusiveHot water cylinder for single-family houses and smaller apartment buildings.Get more details
![[This image is AI generated] uniSTOR exclusive VIH R/6 M](/_next/image/?url=https%3A%2F%2Fvaillantprod-media.e-spirit.cloud%2F108250ea-00ea-48fd-b0a1-ab37982ed2f9%2Fimportedmedia%2Funistor-plus-vih-r-m-scenic_IMAGE_4_3.jpg&w=3840&q=75)
This image is AI generatedHot water cylinder for single-family houses and smaller apartment buildings.
- Suitable for wall-mounted heaters and gas or oil boilers
- High hot water comfort due to short heating times and high output
- Lowest energy consumption due to patented vacuum heat insulation
- Cylinder is made of hygienic steel enamelling
- Compact design with low space requirement
The round space-saving hot water cylinder uniSTOR exclusive VIH R/6 M offers a high level of hot water comfort for detached houses and apartment buildings. It is available in 120L, 150L and 200L capacities. The thermal insulation using a patented combination of vacuum panels and hard foam offers a high level of heat insulation performance which leads to reduced energy costs. For additional anti-corrosion protection, the vessel is equipped with a magnesium protection anode. With its high quality materials, you can rely on a safe operation for a long time.
- 2/2Domestic hot water cylinderuniSTOR plusHot water cylinder for different requirements.Get more details
Hot water cylinder for different requirements.
- Flexible: The right choice for many applications
- Can be combined with heat pumps, boilers and solar
- Efficient hot water comfort
- Hot water volumes for families of 3 to 10 people
- Reliable and durable cylinder made in Germany
It doesn't matter whether you're talking about detached houses, apartment buildings or commercial premises: The uniSTOR plus VIH domestic hot water cylinder with a capacity of 200 to 500 litres is the solution you're looking for. It fits perfectly with various heat sources such as heat pumps, gas condensing boilers and solar thermal systems. Hot water production is efficient because the cylinder's heat exchanger is matched to the characteristics of the connected heat generator, thus maximising its performance. In addition, the cylinder insulation is firmly connected to the cylinder, reducing heat loss. And last but not least, the high-quality materials ensure safe operation over a long period of time.
The right clyinder size
Size matters - the higher demand, the larger the cylinder.
Choosing the right cylinder size is key to ensuring a reliable and energy-efficient hot water supply. Too small, and there’s not enough hot water during high demand. Too large, and you risk unnecessary heat loss - especially when using renewable energy like solar thermal or heat pumps. The ideal size depends on household size and individual hot water usage. Here’s a general guideline:
- Compact electric cylinders: Ranging from 50 to 120 litres, these are perfect for smaller households, apartments, or rooms with minimal demand like guest WCs or hobby spaces.
- Hot water cylinders and instantaneous water heaters: Best suited for single-family homes or larger households with multiple bathrooms.
- Solar cylinders: Designed for homes that harness solar energy, ideal when paired with a solar system or a heat pump.
- Domestic hot water heat pumps: Combine renewable energy with hot water heating. Easily integrated into existing systems and optionally powered by photovoltaic electricity.
For the perfect fit, we recommend consulting a local expert. They’ll ensure your hot water cylinder is tailored to your home’s layout and heating system.
