Unvented Hot Water Cylinders





Prices start from around £1300 supplied and fitted (Main & Ariston) (Worcester & Megaflo £1500) and can go up to and

around £3500, its dependant on the size of Cylinder required, and the location of where it will be installed.


The UK has seen the popularity of high efficiency unvented hot water systems grow significantly in recent years. But what exactly is an unvented hot water system?


Unvented hot water systems have a high efficiency pressurised cylinder which is fed directly from the cold water mains supply. They are very efficient at delivering high pressure fast running hot water to all taps and showers throughout the property.


Unvented hot water systems exceed the Energy Efficiency Partnerships ‘Best Practice’ for recovery times and insulation levels. This means the system heats up quicker and is more efficient at retaining the water temperature.


There are other benefits too, an unvented hot water system does not require water tanks in the loft, so the existing tanks can be disposed of. This makes an unvented hot water system more hygienic and space saving.


The unvented hot water system cylinder can also be placed anywhere in the property. It does not need to be located in the airing cupboard. The system cylinder could be installed somewhere less central, such as the garage.


What are the benefits of unvented hot water systems?


* Powerful showers and fast running taps.

* No need for booster or shower pumps.

* Elimination of water storage tanks freeing up loft space.

* Quicker and more energy efficient at heating water.

* Retain water temperatures for longer.

* Duplex stainless steel construction.

* Very reliable and require very little maintenance.

* 25 year manufacturer’s guarantee.

* Can be located anywhere in the property, often the garage.


Megaflow unvented hot water cylinders


Megaflow are renowned for quality unvented hot water cylinders and are manufactured by a company called Heatrae Sadia. Heatrae Sadia are the UK's leading manufacturer of hot water systems with their flagship brand ‘Megaflow‘ leading the way in unvented hot water cylinders.


Megaflow HE cylinders




    * Internal air-gap with patented floating baffle

    * Strong, Duplex stainless steel construction

    * High performance 'coil-in-coil' heat exchanger

    * No sacrificial anode (eliminates need for annual inspection)

    * Appliance-like plastic-coated outer case

    * Patented cold water inlet diffuser minimises mixing of cold and hot water

    * Water inlet controls increase flow rates by up to 35%

    * Improved performance even at 1 bar

    * Every unit tested to 15 bar (217psi)

    * 25-year transferable cylinder guarantee

    * ½" temperature and pressure relief valve


The above features describe MegaFlow's new range of HE cylinders which use a ‘coil in coil’ heat exchanger to deliver more hot water quicker than previous models. Please also note that older models may differ in specification, always consult your manual.


Benefits of Megaflow HE system


    * Higher flow rates for efficient hot water delivery (Up to 72 l/min)

    * High performance showering –throughout the home

    * Fast-filling baths

    * Quieter mains pressure system (no noisy cistern in the loft)

    * Balanced water pressure - no surprises

    * Fast recover rates (eg. 15 minutes for CL125HE)

    * Exceeds CHeSS Best Practice for heat recovery and insulation

    * CFC free insulation for maximum heat retention

    * No anode to check or replace

    * Mains feed hygienic hot water

    * Appliance quality, easy-clean finish

    * Long-life Duplex stainless steel interior

    * 25-year transferable cylinder guarantee

    * Patented internal expansion system

    * No external expansion vessel

    * Complete with mains water isolating valve

    * All units are fully factory tested to ensure reliability

    * Neater and quicker installation.


Building Regulations


The installation of an unvented hot water system must comply with both the Water Regulations and the Building Regulations. You must also notify your local Building Control Office, who will want to ascertain who will be installing the system. The system must be installed by a competent person, in other words someone who is qualified for the installation of unvented hot water cylinders.



In the UK this means training and assessment by a recognised training body with cards being issued by organisations such as the Institute of Plumbing (IoP) or the Construction Industry Training Board (CITB). This qualification is not part of Gas Safe and so please make sure that if someone is installing an unvented system they hold the relevant qualification - we hold a CITB card and so are qualified to install, service and maintain your unvented hot water system.

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