Unvented Hot Water Cylinders – Mains Pressure Hot Water

Do you mean ‘unvented cylinder’ or ‘Megaflo’ ?

Firstly, Megaflo is a trade or brand name for an unvented hot water cylinder. The actual manufacturer of Megaflo is Heatre Sadia Limited, not a name familiar with the public. In the same way that people generally say they will hoover a room rather vacuum it, Heatre Sadia’s marketing department deserve top marks for making sure there hot water cylinder is the No.1 brand known both to the trade and the public.

Are they good? Yes in our opinion they are the Rolls Royce brand. However there are cheaper options that do the same job ie Ariston.

Today, Londoners like no time before live more demanding lives, studies show that more people now prefer a shower to a bath. This means that London’s Victorian water mains are now at straining point, this is a separate issue, however Thames Water have huge project replacing London’s old lead, galvanised and even asbestos (yes you read it correctly) water mains.

Firstly lets understand what an ‘unvented hot water cylinder is’ and what are the benefits of having a hot water cylinder.

The UK traditional Hot Water model or system has been to have a cold water tank (proper name cistern) in the loft which then supplies a hot water cylinder, this has limited capacity and tanks a long time to recover or reheat the hot water once it has been used making it very inefficient.

The European model or system is to not have a cold water system, and instead feed all the hot water, cold water appliances directly from the water mains. The benefit is high pressure and flow rates* throughout the property and more importantly a highly efficient means of heating hot water. A traditional hot water cylinder supplied via a cold water tank in the loft takes 30 – 40 minutes to recover or reheat hot water, mains supplied ‘unvented hot water cylinder’ will take to recover or reheat the hot water nearly 40% faster thus saving on your gas or electricity supply, depending on how you heat up your hot water .

Will an unvented cylinder work in any London Property?

This depends on the following critical information, bearing in mind that the objective of an unvented cylinder irrespective of brand is to have consistent hot water pressure and flow throughout the property allowing simultaneous showers; you must have a min cold water pressure and flow rate entering the unvented cylinder, there is no magic unvented cylinder that increases the water pressure and flow rate.

Heatre Sadia Limited & Ariston Thermo Limited recommends a min water pressure of 1.5bar and a min flow rate of 20 litres per minute. The flow rate, this is the amount of main water that flows out of the kitchen* tap within 1 minute, it is the most important measurement. *please note some sink taps restrict the flow of cold water so it also worth checking the water flow at an outside water tap or you may have an inaccurate flow reading.

All unvented hot water cylinders heat up hot water which then expands in volume, a ‘Megaflo’ has an inbuilt expansion vessel which operates like a ‘lung’ expanding and contracting as the water heats up and then cools down. All other manufactures of unvented cylinders have an external expansion vessel; the only advantage of a Megaflo over another brand is space.

The Solar Unvented Hot Water Cylinder – Perfect even of you don’t have Solar

If you are connecting your new unvented hot water to a gas central heating boiler, it may be worth considering a Solar Unvented Cylinder as this has 2 coils inside it rather than one. You can then connect your boiler ‘primary’ flow and return to both coils, this means that you will heat up your hot water even faster, thus improving your efficiency and reducing your gas bill.


Solar Unvented Hot Water Cylinder with twin* coils

*No Solar at home? Just connect both coils to your boiler for improved hot water recovery and lower gas consumption