Indirect unvented cylinders – Unvented indirect hot water cylinders

Indirect unvented cylinders or indirect unvented hot water cylinders, take their supply water directly from the mains water for the domestic hot water requirements. Because they can supply hot water at mains water pressure, indirect unvented hot water cylinders are great for properties with multiple bathrooms, as they have the flow capacity to run multiple showers, baths or taps.

Mains pressure has many benefits, the most important being is a better flow rate compared to gravity feed system hot water cylinder heating products.

These cylinders are also known as an indirect pressurised hot water cylinder, unvented indirect hot water cylinder or an unvented indirect cylinder.

Indirect unvented hot water cylinders require an external source of heating, normally a gas boiler, heat pump or an oil boiler,as a heat source for example. This warm water then circulates via a stainless steel heat exchanger coil in the water cylinder, heating the surrounding domestic water without mixing with it. Thus, the term an “indirect” water heating system.

A direct unvented hot water cylinder on the other hand, uses electric immersion heaters as a heat source, which are installed into water tank / cylinder to heat the hot water directly, again at mains water supply pressure. Whereby an indirect cylinder has a heating coil within the tank which is powered by a boiler or other heating source.

Thus, the term mains pressure ” direct unvented cylinders” or “direct unvented cylinder”

We do an extensive range of this type of direct unvented cylinders on this dedicated webpage – direct unvented cylinder

Indirect unvented hot water cylinders

So, what are the benefits of unvented hot water cylinders?

In one line – it’s a mains pressure domestic water hot water system, with all the benefits of higher pressure and flow for your hot water heating

The advantage of utilizing an unvented cylinder is that a cold-water feed tank in the property is not necessary,

As the water is fed directly which means that properties with limited space will not have to give up valuable storage space in the attic, which you require with gravity-fed systems. The eradication of this cold-water feed tank also eliminates the possibility of it freezing during prolonged cold spells.

In an unvented system, the pressure of the warm water flowing out of taps and showers is higher

This is due to the fact that water is supplied from the cold-water mains supply rather than a water tank . Higher pressure is especially significant when there are many bathrooms that may be running warm water from multiple showers or taps at the same time.

Unvented hot water cylinders can benefit homeowners by reducing noise

This is due to the feed tank not being filled with cold water, as none is required in an unvented system.

Because an unvented system is a closed water supply system

It benefits from reduced danger of contamination, with fewer opportunities for foreign contaminants to enter the hot water cylinder and consequently cause harm or damage to the domestic water heating system. This is a real possibility with vented cylinders in a property.

Unvented cylinders

Unvented hot water cylinders require an internal air bubble or expansion vessel to be installed to work correctly, as any stored water in the hot water cylinder expands when it heats up. This heated water volume expands and needs to be absorbed, so that the pressure does not get excessive, and a vessel or air bubble takes this expansion.

Expansion vessels are installed external to the unvented cylinder, whilst an internal air bubble is obviously internal to the unvented cylinder, as the name suggests, these systems are used by the heatrae sadia megaflo or sadia megaflo eco units.

Our innovating and unique solution to this problem is a self-sustaining air gap system for our unvented cylinders.

Details on how the system works on our unvented cylinders

The mixing of liquid with air or, more precisely, the induction of air bubbles into the liquid, is what distinguishes the patented self-sustaining system technology, with the system now capable of maintaining the internal air gap when hot water is drawn off farther upstream during hot water demand i.e., when taking a shower, bath or using the hot taps in the kitchen or sinks.

There is no requirement for expansion vessel refilling or regular servicing since it continually replaces the internal expansion mechanism in this high quality cylinder.

Because there are no internal moving components in the cylinder, and once the venturi valve is installed, no more parts are required, this automated replenishment of the air gap saves time and money. This pinnacle of fit and forget technology will provide landlords, developers, self-builders and heating installers confidence that they do not have to inspect for wear and tear or be called out to repair problems on a regular basis.

This means no external expansion vessel, thus less space is required great for limited space or access locations

Because there is no external expansion vessel, the cylinder may be installed in more compact locations, providing builders and heating installers considerably more freedom in where to install the unvnted cylinder, whether for a new build or restoration project.

 

Download the installation details here for the self-sustaining unvented system

Flexiheat UK Installation 3S Air Gap Device information for unvented hot water cylinders

Heat pump indirect cylinders

If you require an indirect hot water cylinder for use with a heat pump, then you require a larger heating coil than these standard units – we have a range of heat pump cylinders, which are listed on this webpage- hot water cylinders for heat pumps

Cylinder product accessories and valves

Each cylinder is factory fitted with temperature and pressure relief valves. These valves are pre-calibrated to open at 7 bar or 90°C.

Prior to the hot water tank, the supplied combined cold water valve can be installed anywhere on the cold water mains. If it is more convenient, it can be positioned near where the water mains supply enters the property.

Water Pressure and Flow Rates

The minimal criteria for satisfactory operation of our cylinder are 1.5 bar pressure and a flow rate of 20 litres per minute. The unvented hot water cylinder will continue to function below this level, but two or more hot water outlets will not be able to be used at the same time.

Cylinder hot water supply

Any type of boilers can feed these unvented indirect cylinders, be it gas boilers, oil boilers, electric boilers but not suitable for solid fuel boilers or wood fired boilers.

Sizing an indirect cylinder- How many litres do I need?

Here’s what product manager recommends with the Hot Water Association of the United Kingdom provides a solid rule of thumb that might help you determine the size of your water cylinder.

In a typical home, 30 to 50 litres of warm water per person per day is required

A low-consumption household will require 20 to 30 litres of warm water per person per day.

In a high-consumption residence, 50 to 70 litres of warm water per person per day is recommended.

Please bearing in mind the following –

A standard UK bath requires 60 litres at 60 C with the other 40 litres being cold – to get the mixed water temperature of 40C

A standard UK shower head is around 8 litres of water per minute – will use around 5 litres of 60C water- a drench type shower can use an awful lot more!

However, it should be emphasised that personal behaviours have a significant role in overall warm water usage. Two identically sized families can consume drastically different quantities of warm water, with one needing twice as much as the other, as people usage patterns can differ drastically.

Should your require larger commerical units – then please look at our webpage Commercial hot water cylinders

Unvented indirect hot water cylinders range

All of our indirect unvented hot water cylinder products have a 22mm diameter stainless steel high performance coil & outlet with 1 x 3kw immersion heater, as a back-up direct unit, should you lose your external source of heat indirectly feeding the water cylinder / store.

Our unvented hot water cylinder range is manufactured from duplex stainless steel, which for your information is the best available – information product warranty is 25 years for our unvented cylinders when used in a domestic property, and 5 years when used as commercial indirect unvented cylinder i.e., non-domestic hot water heating applications.

Product ErP information / ErP information product / library ErP information – The 80 to 130 capacity litres cylinders are “A” rated , the 150 to 280 capacity litres cylinders are “A” minus or “B” plus , and the 305 to 500 litre unvented indirect cylinders are better than “C” rated for this hot water unvented cylinder range of products.

All unvented cylinders in this range have a maximum working pressure of 5.5 bar, and are tested to 10 bar pressure for the hot water cylinder.

We have dedicated

The 170 litre indirect unvented cylinder to 500 litre indirect unvented cylinder are fitted with a DHW return connection to the unvented hot water tank, for large hot water heating systems.

We can also supply “Hi-Flow” models with larger a 28mm inlet/outlet and a 28mm Venturi valve for high flow rates, these units are available from our 255 Litre to 500 Litre indirect unvented cylinder models.

Dimensions

 

Hot water heating times, recovery rates and coil output ratings based of a flow temperature of 85C to the heat exchanger coil.

If you require large kW outputs than out standard coil units, then we do a range of rapid recovery cylinders with larger kW coil ratings, these are detailed here – high recovery cylinders

Download the Hot water cylinders indirect and direct unvented cylinder brochure from Flexiheat UK

Installation manual is here –

Flexiheat manual for direct & indirect hot water cylinders

We have dedicated webpages for our most popular indirect unvented cylinders –

150 Litre Indirect Unvented Cylinder

210 Litre Indirect Unvented Cylinder

250 Litre Indirect Unvented Cylinder

300 Litre Indirect Unvented Cylinder

400 Litre Indirect Unvented Cylinder

and the largest in this range 

500 Litre Indirect Unvented Cylinder

We supply larger indirect cylinders above 500 Litres – the please look at this webpage – Commercial hot water cylinders

Immersion heaters

Our immersion heater is manufactured in Incoloy 825 – which offers great resistance to hard water.

We can also do pre plumbed units as well from 175 Litres to 300 Litres

Unvented indirect hot water cylinder installation

Unvented water cylinders require the installation and maintenance by suitably qualified plumbers / heating engineers since they run at a greater pressure than a vented system and have numerous additional safety precautions incorporated into the hot water unvented cylinders. All heating engineers / plumbers installing the cylinder must be qualified in “G3” unvented cylinder system installs.

Contact us

Should you require any more information or discount prices on the best indirect unvented cylinder / unvented indirect hot water cylinders on the UK market with a warranty of 25 years (hi-flow commercial units are 5 years) as they are duplex stainless steel construction, then give our sales team a call on 01202 822221 or use our contact us page, as you can direct shop with us. Follow us on Facebook or Twitter online for our latest offers .