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Unvented Hot Water Cylinders Explained: Direct vs. Indirect & Key Benefits
For quite some time, an unvented cylinder has been a popular choice for installing a hot water system in homes and businesses. This is due to their ability to deliver high water pressure alongside a consistent performance.
This guide explores how unvented cylinders work, and the differences between direct and indirect models. Whether you’re considering a direct unvented cylinder or an unvented indirect cylinder, this guide will help you make an informed decision.
What is an Unvented Cylinder?
How does an unvented cylinder work?
- Delivers water from mains supply
- Does not require a separate cold water tank
- Allows for stronger water pressure and quicker heating times
As part of a hot water system, an unvented cylinder heats water under pressure directly from the mains supply. While vented hot water systems would rely on a cold water storage tank, unvented do not require this. Instead, its design allows for stronger water pressure, faster heating times, and a streamlined installation.
For water to be heated up in an unvented hot water system, an immersion heater or an indirect heat source such as solar thermal, renewable energy, or gas/oil boiler is required.
Benefits of Unvented Cylinders
There are several benefits as to why you would want an unvented cylinder in your home or business.
- High Water Pressure – As water is directly supplied from the mains, unvented cylinders can deliver strong flow rates to multiple outlets simultaneously.
- Faster Heating Times – Whether using a direct immersion heater or an indirect heat source like a boiler or heat pump, unvented cylinders heat water more quickly.
- No Cold Water Storage Required and Saves Space – Unlike vented systems, unvented cylinders don’t need a separate cold water tank. This makes installation less disruptive and ideal for properties with limited loft space.
- Compatible with a Range of Heat Sources – From gas and oil boilers to renewable options such as solar thermal systems and heat pumps, unvented cylinders are highly adaptable.
- Improved System Hygiene – Because of the pressurised and sealed design, the water provided will be cleaner and more efficient.
Types of Unvented Cylinders – Direct and Indirect
Direct Unvented Cylinder
An unvented direct cylinder implements heat sources located within the cylinder itself. This heat source is often an immersion heater.
Additionally, a second immersion heater can enable home and business owners to take advantage of off-peak energy tariffs.
Indirect Unvented Cylinder
Unlike direct unvented cylinders, indirect tanks rely on an external energy source to heat up water. These can come in the form of primary or renewable and alternative heat sources.
Primary heat sources consist of gas, oil, and electric boilers. Whereas heat pumps, solar thermal systems, and biomass boilers are recognised as renewable and alternative sources for indirect unvented cylinders.
Newark Cylinders only manufacture indirect unvented cylinders.
Unvented vs Vented Cylinders – What is the Difference?
| Feature | Unvented Cylinder | Vented Cylinders |
|---|---|---|
| Water Source | Mains water supply (pressurised) | Cold water storage tank (gravity fed) |
| Water Pressure | Higher, consistent pressure from mains | Dependent on tank height (lower pressure) |
| Space Requirements | No cold water tank needed; more compact | Requires elevated space for cold water tank |
| Installation Cost | Potentially higher due to specialist components | Lower cost due to simpler installation |
| Heating Method | Direct via immersion heater, or indirect from external source (heat pump, solar, boiler) | Indirect heating via external boiler |
| System Efficiency | More efficient; works well with renewables | Less efficient due to heat loss from tank |
| Suitability | Modern homes with high water demand | Older properties / Properties with loft space |
The main difference between vented and unvented cylinders is how cold water is supplied to the cylinder.
For vented cylinders, the system is reliant on being gravity-fed. This means the cold feed tank (header or feed & expansion) installed in an elevated position (like a loft) supplies cold water via a vent pipe into the cylinder to be heated up.
The height of the feed tank determines the water pressure. For example, the higher the tank, the greater the pressure.
Learn about vented cylinders here.
How do I know if I need a direct or indirect model?
If your system relies on a gas or oil boiler, an indirect cylinder is advisable. Alternatively, heat pumps, solar thermal systems, and biomass boilers can be used as heat sources in indirect systems.
If your property relies on an electric source for hot water and doesn’t depend on a boiler or external heating source, a direct cylinder is suitable. However, the running costs mean direct cylinders can be expensive to maintain.
In addition to the type of heating system you have (or want), it is worth considering energy-saving aims, the amount of hot water usage, and the size of your home. Further details on unvented cylinder sizing can be found here.
Conclusion
Unvented cylinders have proven to be efficient, reliable, and suitable for modern homes and businesses. Furthermore, Indirect unvented models are capable of utilising primary and renewable heat sources.
Newark Cylinders specialise in manufacturing highly efficient, bespoke unvented (and vented) hot water cylinders tailored to your needs. Whether you require a custom size, multiple connections, or have unique performance requirements, our sales team can make it happen.