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Witten by Bernard Morgan (Engineer).
First Published: January 25, 2024. Updated: January 26, 2024

What is a Megaflow System? Overview & Costs

A Megaflow system, also known as a Megaflo unvented system, is a high-capacity water storage cylinder. It is not a boiler. It is designed to meet large hot water demands in homes.

It comes in direct and indirect types, with the former using built-in heaters and the latter relying on an external boiler for heating water.

What is a Megaflow system?

The Megaflow system, produced by Heatrae Sadia, is an unvented stainless steel cylinder that forms part of a central heating system. It stores hot water for domestic use at mains water pressure.

It is not a boiler but a storage unit for heated water, available in direct and indirect models.

Direct vs. indirect Megaflow systems:

  • Direct Megaflow systems have built-in immersion heaters and directly receive water from the main supply, heating it internally.
  • Indirect Megaflow systems are more common. They store hot water supplied by an external boiler. They sometimes also feature an immersion coil for emergency heating if the boiler fails.

When to Consider a Megaflow system:

  • Ideal for properties with high hot water demand, needing to run multiple showers or baths simultaneously.
  • Suitable for larger properties with space for a water tank and where the main water pressure and flow rate are sufficiently high.

Cost considerations:

  • The price of a Megaflow system varies based on cylinder size, brand, and model.
  • Factors like property size and hot water requirements play a crucial role in determining the appropriate cylinder size.
  • Megaflow systems can cost anywhere from £600 to £2,300. Installation will cost you between £400 and £1,500.

Pros & Cons

  • Can be used with solar panels to heat water.
  • Can be installed anywhere with access to a few pipes.
  • Can be used if the boiler fails if it has an immersion heater.
  • Pressure remains equal no matter how many taps or showers are running.
  • Won’t be good if you have bad cold water pressure.
  • Can be noisy.
  • Can take an hour to refill if all the hot water is used.
  • It is an additional cost to the boiler used for heating your home.


A Megaflow system is an efficient solution for homes with significant hot water needs. They offer high pressure and capacity.

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