Megaflo unvented hot water systems

We are seeing more and more people install Megaflo heating systems in their home, but what are they and why are they becoming so popular? Well a Megaflo is essentially a brand of hot water tank – but the major difference is how they are plumbed in.

Older, traditional heat only systems have cold water expansion tanks up in the roof, and it is the height of this cold water tank above the hot water cylinder that generates the pressure that delivers the hot water to the taps. For taps on the lower floors this tends to work perfectly, but for bathrooms upstairs the pressure is often not great and so you get issues like weak showers or baths that take an age to fill up. In many cases this is sorted by installing a pump that drives the water from the hot water tank to the required faucet, but installing a Megaflo does away with all these issues!

Megaflo – an unvented hot water cylinder

Megaflo cylinders form what is known as a unvented systems – these are pressurised to mains water pressure, ensuring a strong flow of hot water when you turn a tap on in the home regardless of where it is located in the home. The actual pressure in this type of hot water cylinder is normally about 3 bar – which is equivalent to a cold water tank being 30m above the tap for a heat only system. The cold water is fed into the bottom of the tank at mains pressure – this forces the hot water out at the top and this then travels to the tap.

This means that you have great pressure all the time so gone are the days of the dreaded dripping shower!

Since the volume of water increases as it gets heated, all unvented systems require some sort of expansion vessel to absorb this increased volume. The nice thing about the Megaflo models is that they contain an enclosed air bubble within the tank itself, which acts as the expansion vessel so you don’t require an external one – its worth mentioning though that over time the air bubble can be absorbed into the water but this can be recharged as part of the annual boiler service.

Like other heating systems, the hot water within the Megaflo can be produced by immersion units (so heated with electricity), boilers or even solar thermal. If you buy a twin coil unit, you can feed the tank with two sources of hot water so a boiler plus solar thermal for example.

Although there are lots of hot water tanks suitable for use within unvented systems, the Megaflo is the market leader here in the UK. This is partly because the brand, but the performance of these cylinders really is very good. They are tested to withstand 15 bar of pressure, so you can be sure they are up to the job of operating at these higher pressures (compared to conventional heat-only systems).

Megaflo cylinders have lots of safety features?

Megaflo cylinders also have great safety features incorporated into them. This includes thermostatic controls that prevent the water in the cylinder ever being heated above 100 degrees centigrade, as well as expansion release valves that allow expansion to take place if the cylinder doesn’t perform correctly. There is also a temperature and pressure release valve situated on top of the tank, which vents water if it hits unsafe temperature levels.

The Megaflo cylinders also include a 60mm-thick layer of polyurethane foam to insulate them. This ensures that once the hot water is created within the tank it stays warm for longer, minimising the need to reheat the water.

So having looked at the advantages of the Megaflo cylinders, what are the issues with them? Well, performance-wise not many, however they are significantly more expensive than other unvented cylinders.

Unvented systems are also generally more expensive to install compared to heat-only boilers. They must be installed by a competent and qualified G3 engineer; this is a legal requirement in the UK and all installations must be certified and registered with the local council. This means that your average plumber/heating engineer is not actually going to be allowed to install one in your home.

The other issue – and this is not just Megaflo, but all unvented systems – is the high pressures involved. Obviously if everything is working correctly then the performance will be great, but all pipework needs to be able to withstand the higher pressures!

The performance of the Megaflo cylinders though does make them extremely popular – the hot water is delivered to every tap at mains pressure and the tanks themselves are well insulated ensuring they operate very efficiently – but be prepared to pay more if you do look to install one of these in your home!

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