Best Unvented Cylinders 2020

Unvented cylinders are widely recommended by professional installers over traditional vented systems, but which brands come out on top?

An unvented cylinder offers several advantages over traditional vented cylinders. They take their water supply directly from the mains so there is no need for a cold water tank in the attic, they can be installed almost anywhere in your home and they generally provide a much stronger flow of water. Also, because there is no tank of water needed, the system is completely sealed which prevents contamination.

The most well known brand of hot water cylinder is the Megaflo by Heatrae Sadia and for a long time the Megaflo dominated the market, but today there are several other options available to you.

Which are the Best Unvented Cylinders?

We’ve done some research around the most popular brands of unvented cylinders to help you make the right choice for your home. Each cylinder is comparable in terms of volume capacity and suitable for the average 3 bedroom home with up to 2 bathrooms. All the cylinders compared here are to be heated indirectly i.e. by a gas or oil boiler (or solar panels if compatible).

Find out everything you need to know about solar in our handy solar guides.

Directly heated cylinders are heated solely by an immersion heater within them and are an option for homes without a boiler. Some indirect cylinders may include an immersion heater as a back up in case of boiler failure.

Brand Model / Size Re-heat Time from cold ErP Efficiency Rating Guarantee Approximate Price range (cylinder only)
Heatrae Sadia Megaflo Eco Plus 170l 22min B Lifetime £800 – £900
Telford Tempest Stainless Steel 170l 36min C Lifetime Components: 2 years £450 – £550
Gledhill StainlessLite Plus 180l 30min B 25 years £470 – £570
Worcester Bosch Greenstore 180l 27min B 25 years £900 – £1000
Santon PremierPlus 170l Yes Unknown 30-year transferable cylinder guarantee

(5-years on cold water control valve & expansion vessel, 2 years on all other components)

£800 – £900
OSO Delta 210l 24min A Tank 25 years, parts 2 years Unknown
Viessmann Vitocell 200-V 180l 30min B 25 years against corrosion Unknown

All of these unvented cylinders are fully compatible with solar.

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Megaflo by Heatrae Sadia

The Megaflo by Heatrae Sadia is one of the biggest names in heating cylinders and has a reputation for both reliability and excellent performance. The Megaflo Eco’s floating baffle expansion vessel is contained within the unit so there are no extra sections to accommodate. Key features include:

  • Pre-plumbed and pre-wired SystemFit and SystemReady options for use with heat only or system boilers
  • 60mm CFC / HCFC-free injected foam delivers both heat retention and energy efficiency
  • Includes high performance ‘coil-in-coil’ heat exchanger for faster recovery times
  • Unique ‘L’ shaped immersion heater maximises the volume of hot water available when heated electrically.

Heatrae Sadia have been manufacturing heating products for over 95 years and, while the company originated in Norwich, today it is owned by Baxi UK, part of the international BDR Thermea group.

Tempest by Telford Copper & Stainless Cylinders Ltd

Telford Copper & Stainless Cylinders Ltd is a family business that has been trading since 1989 are particularly proud of the quality of the Duplex 2304 Stainless Steel used in their cylinders which they claim to be up to 40% thicker than some competitors. They offer a lifetime guarantee on the cylinder itself and 2 years on the components within.

  • High density insulation
  • Full unvented kit supplied, including remote expansion vessel
    WRAS approved
  • Treated to protect against corrosion

Variations include:

  • Heat Pump and solar
  • Gravity coils
  • Triple Coils
  • Quad Coils (where available)
  • Slim Lines (up to 250litre)
  • Extra toppings/Larger Tappings

Stainless Lite Plus by Gledhill

Gledhill was established in 1926 in Blackpool by the Gledhill brothers and today manufactures a range of both vented and unvented cylinders. As of 2015 Gledhill is now owned by the international Groupe Atlantic.

The Stainless Lite Plus cylinder is the lightest on the market. It includes a high efficiency corrugated tube coil delivering much faster recovery times than plain tube coils. It includes a temperature and pressure relief valve which is factory set at 6 bar and 95 degrees celsius. In addition to a 25 year guarantee the key features include:

  • Compatible with gas or oil boilers (sealed system or open vented)
  • High efficiency corrugated coil maximises heat transfer
  • Corrugated coil provides faster reheat times compared to plain coil
  • 3kW incoloy immersion heater for emergency back-up
  • 90° elbow, flexihose and drain valve included
  • Standard and slimline models also available.

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Greenstore by Worcester Bosch

Worcester Bosch are synonymous with heating appliances in the UK. It began as a Worcester based company 1962 but was acquired by the Bosch Group in 1996. The brand is widely acknowledged as one of the highest quality of the market and is regularly awarded ‘Best Buy’ awards for their products. They also boast the Royal Warrant for supplying boilers to the Royal Estate of Sandringham.

Their unvented cylinder is the Greenstore and is available as both a standard model and a solar compatible model. It sits at the pricier end of the market but there are package deals including a Worcester Bosch boiler with a cylinder.

  • Optimised controls (maximised flow rates)
  • 60mm insulation
  • Quality stainless steel construction
  • Installer-based design
  • Exceeds Business Regulations 2010 Part L
  • Multiple sensor/thermostat pockets
  • Wide range of cylinder sizes
  • G3 accessories included
  • UK support and manufacture assistance from Worcester Bosch Group.

PremierPlus by Santon

The Santon brand is actually owned by Heatrae Sadia, who are in turn owned by the BDR Thermea group, and has over 70 years of industry expertise behind it. They offer one of the longest cylinder warranties of 30 years.

The cylinders are designed and manufactured in the UK and are built to the highest standards from Duplex stainless steel. They offer exceptional corrosion resistance and long-life expectancy. Advanced primary coil and cold water controls design gives rapid reheat and good flow rate performance. 50mm of CFC/HCFC-free (ODP zero) foam insulation prevents heat loss.

  • High performance showers and balanced mixers
  • High flow rates – fast filling baths
  • Fast recovery rates
  • Safe, economical performance
  • No anode to check or maintain
  • No loft pipes to freeze up
  • 30 year on-site parts and labour cylinder guarantee (5-year on-site parts and labour expansion vessel guarantee and 2 year on-site parts and labour guarantee on element and all other controls).

Delta by OSO Hotwater

OSO have been producing unvented, stainless steel cylinders for UK homes for over 20 years while the company has been leading water heating technology in Norway for over 70 years. In fact, the company were the first in the world to mass-produce stainless steel water heaters and in the 1950’s OSO cylinders were twice as efficient per litre than any other brand.

OSO Hotwater offer the Super series of cylinders which are produced using Duplex steel to deliver low weight and high strength with corrosion resistance. Their range includes the A rated OSO Delta, the OSO Super S and the OSO Super Express SXDIQ. OSO Hotwater claim their water cylinders can last up to 30 years. Unique OSO ECO Foam insulation reduces heat loss of all standard water heaters by 30%.

  • Extremely Low Weight
  • Extremely Low Heat Loss
  • High Efficiency
  • High Corrosion Resistance
  • Made with Recycled Materials
  • Safety Tested

Vitocell 200-V by Viessmann

The Viessmann brand turned 100 years old in 2017 celebrating a long history of innovation in the heating, energy and cooling industry. The company manufactures and distributes high quality products internationally including a well established presence in the UK.

Viessmann produce the Vitocell 200-V hot water cylinder to work alongside their range of Vitodens system boilers. However it can be installed alongside non-Viessmann system boilers or traditional S or Y heating systems if purchased with an additional safety kit.

The cylinder is manufactured with high quality stainless steel to resist corrosion and has 50mm layer of insulation to prevent heat loss. In addition, this cylinder has the added benefit of a backup immersion heater in case of boiler failure.

  • 50mm polyurethane foam insulation exceeds CHESS Best Practice with energy loss as low as 1.4 kW/24 hr
  • Heating coil recovers in less than 19 minutes delivering a 30 minute water reheat time from cold
  • A back up 3kW immersion heater is included
  • No anode required which makes maintenance much simpler
  • 25 year warranty against corrosion is included as standard
  • The Vitocell 200-B is also available which is compatible with solar panels
  • Lightweight design for easy transport and installation.

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How to Choose the Best Cylinder for Your Home


Direct or Indirect?
This refers to the method used to heat the water in the cylinder and will have an impact on your ongoing running costs.

Cylinders that use an indirect system rely on an external boiler as the heat source for the water. The boiler is usually fueled by gas or solar energy. Directly heated cylinders use an internal immersion heater, which is powered by electricity, to heat the water. Electricity is more expensive to run but for some homes without access to gas it is the only option.

Indirect systems are usually the preferred option but there is a risk that if the boiler should fail you will lose access to hot water completely. To prevent this many homes opt for an indirectly heated cylinder with an immersion heater included as a back up.

What size of cylinder do you need?
There’s a balance between finding a cylinder that has enough capacity to supply your home with all the hot water you need but also ensuring it’s not so big it uses unnecessary energy heating water you never use. A professional installer will be able to advise you as to the right capacity for your home, but the below figures are used by industry professionals as a guideline:

Bedrooms Showers / Bathrooms Indirect (litres) Direct(litres)
1 1 75/120 120/150
2 1 150 180
3 2 180 210
4 2 210 250/300
 Larger properties 300+ 300+

The better the insulation of your cylinder the longer it will be able to store your hot water. Some cylinders have insulation included such as foamed polyurethane but you can also purchase jackets and foam tubing to maximise heat retention.

Expansion Unit
As the water is heated in the cylinder it increases in volume. In traditional vented cylinders this water would expand into the vent pipe to prevent a buildup of pressure. In unvented cylinders, as the name suggests, the vent pipe is not there. Some unvented cylinders deal with the excess pressure by including an external expansion unit and some use an internal air bubble that is created at installation.

Note: Legally unvented cylinders can only be installed by engineers with a G3 Unvented Hot Water qualification. This is in addition to being Gas Safe registered.

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