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“Megaflo cylinders are the choice of architects and plumbers – the system most of them would choose for their own home”

Megaflo is the market-leading brand name of Heatrae Sadia‘s unvented hot water cylinders. Consequently, the Megaflo name has become synonymous with unvented cylinders and is often used to refer to unvented cylinders in general!

Whilst Megaflo is priced at the upper end of the UK market, there are now over 20 other manufacturers offering similar products. Like Megaflo, they are also made from high-quality duplex stainless steel and typically come with 25+ years warranty (on the cylinder). 

The cylinders are heated by a gas boiler, electric immersion heater or a renewable heat source, such as solar thermal or heat pumps.

Above all, unvented systems are available for all budgets to suit individual and specific requirements. 


Megaflo Unvented cylinders store hot water under pressure and are supplied directly from the mains. Consequently, the hot water is forced through by the incoming cold water. This obviously removes the requirement for a cold water storage cistern and vent pipe.

Without getting too technical, an unvented cylinder operates on the incoming water pressure and flow rates. There are no moving parts and when correctly installed, provides a reliable and efficient hot water system. The use of several safety devices is essential to ensure safe operation.

Vented Systems

In the UK, traditional domestic hot water systems consist of a hot water cylinder fed by a storage cistern within the loft. This is vented to the atmosphere, hence the name Vented Hot Water. The water pressure is created by the height of the storage cistern relative to the outlet.

A typical house or bungalow with a storage cistern in the loft will have a vertical distance of 1 meter from the storage cistern to the showerhead. This equates to 0.1 bar pressure.

Unvented Systems typically deliver at least 10 times that pressure for both hot and cold water!

Unvented Systems

Today, most new homes have Unvented hot water storage systems installed as standard. These are usually connected directly to the cold water mains and therefore do not rely on a storage cistern in the loft. Megaflo is most commonly associated with unvented hot water systems, but other brands are becoming more common.

Unvented cylinders are sealed to the atmosphere and provide a highly efficient means of storing and distributing hot water throughout your home. Operating at pressures of around 3 bar, they must be installed correctly by a G3 qualified engineer.

So Vented or Unvented?

Generally, Megaflo Unvented systems perform better than traditional gravity systems. To emphasize, they provide mains pressure hot and cold water to all outlets. Without a doubt, they are suitable for anything from a small studio flat to a large multi-bathroom mansion. It just needs to be specified and installed correctly.

We have only seen a handful of cases where we would not recommend a Megaflo Unvented system. This may be due to the existing plumbing layout, lack of space or some other overriding factor.


A Megaflo or Unvented system is almost always better than a traditional gravity system. However, it is extremely important to use a company that fully understands the requirements and available options to ensure optimum performance.

If you are in the Guildford, (Surrey) or surrounding areas, contact Apex Plumbing and Heating for a written quote or just some honest and professional advice!

Why Choose Us

At Megaflo Unvented, we do what we say we’ll do. Our integrity and competence values demand this. We are accountable for our words and actions, and that we deliver a service that meets or exceeds all expectations of quality and timeliness.

Customer service is our highest priority and to reinforce this, we adhere to the following guidelines:

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