Curious about what a Megaflow system actually is – and whether your home needs one? This no-nonsense guide covers everything you need to know, from how it works to when it’s worth installing.
- What is A Megaflow System?
- How Does a Megaflow System Work?
- When You Need A Megaflow System
- When a Boiler Might Be a Better Choice
- Cost Of A Megaflow System
- Cost Of Installing A Megaflow System
- Other Factors That Affect The Cost Of A Megaflow System
- Pros And Cons Of A Megaflow System
- Megaflow Warranty Period
A Megaflow system (or Megaflo, depending on spelling) is a type of unvented hot water cylinder that stores heated water and supplies it at high pressure - straight from the mains.
But let’s clear something up right away: a Megaflow isn’t a boiler. It’s a water storage tank, and despite the confusion with Baxi’s “Megaflo” system boiler range, the two are not the same thing.
In this guide, we’ll explain how Megaflow systems work, when they make sense, how much they cost - and why, for many UK homes, a good boiler might be a smarter, cheaper, and more space-efficient solution.
Key Points:
A Megaflow is an unvented hot water cylinder that delivers mains-pressure hot water without needing a cold water tank.
Ideal for large homes with multiple bathrooms and strong mains pressure.
Not suitable for homes with low water pressure or limited space.
Boilers - especially combi boilers - may be a better fit for smaller households or those wanting a simpler, more affordable heating setup.
What is A Megaflow System?
The Megaflow is manufactured by Heatrae Sadia, a renowned brand in manufacturing hot water cylinders and storage water heaters.
A Megaflow system comprises a stainless steel unvented cylinder. It can form part of the central heating system and store hot water for domestic use.
A Megaflow system is not a boiler replacement but just a cylinder that stores heated water, which can be used when required.
The cylinder can either work directly with an in-built heating system or indirectly alongside system boilers or regular boilers.
Let’s delve more into the working of direct and indirect Megaflow systems.
The image below shows an immersion system element:
How Does a Megaflow System Work?
Direct Megaflow System
This type has an immersion heater built in, which uses electricity to heat the water. The cylinder fills with mains water, heats it via the immersion element, and stores it until needed. It’s a self-contained unit - no boiler required.
Indirect Megaflow System
This version is connected to a boiler (typically a system boiler). The boiler heats the water, which is then stored in the Megaflow. It also includes an emergency immersion heater for backup if the boiler fails.
⚠️ Tip: Never run the immersion heater and boiler at the same time - it’s inefficient and can risk overheating the system.
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When You Need A Megaflow System
Here are some criteria that make Megaflow systems suitable for a property, in case you're debating whether you need one or not:
Need to run 2 to 3 showers or baths at the same time
High demand for hot water and high-pressure
Large property for storing the water tank
High main water pressure (at least 1 bar)
High flow rate from main water supply (at least 16 litres per minute)
When a Boiler Might Be a Better Choice
Despite the benefits, Megaflow systems aren’t for everyone. Here’s when you might be better off with a boiler - especially a combi:
Small households: A Megaflow is overkill if you only need hot water for one or two people.
Limited space: Megaflow cylinders are bulky and need installation space. Combi boilers, on the other hand, are compact and don’t need separate tanks.
Budget-conscious installations: Megaflow systems are more expensive to install and maintain. Combi boilers offer an all-in-one solution with lower upfront costs.
Low mains water pressure: If your home doesn’t have strong pressure, a Megaflow system won’t perform properly - making a combi boiler the more reliable option.
Cost Of A Megaflow System
The cost of unvented cylinders depends on three aspects: the size of the cylinder, the brand, and the model.
Size
Refer to the following size chart to determine the size of the cylinder suitable for your property.
Property size | Number of bathrooms | Cylinder size (in litres) |
3 bedrooms | 2 | 180-210 |
4 bedrooms | 2-3 | 210-300 |
5 bedrooms or more | 2-3.5 | 300 and more |
The size will also depend on how many members there are in the household, as the need for water rises with the number of members.
A single person needs between 35 and 45 litres of water per day, on average. Hence, with more members, your water requirement increases too.
A qualified heating engineer can undertake an in-depth evaluation of your property, your hot water usage, and other factors to help you select the most optimum size suitable for your needs.
Brand And Model
The brand and model will affect the price of the cylinder as well. Typically, the cost ranges from £300 to £2,000 or more.
Here's a look at the price range of unvented cylinders from different brands:
Brand | Cylinder capacity (in litres) | Price range (in £) |
Heatrae Sadia | 70-500 | 550-2,250 |
Telford | 90-400 | 320-1,230 |
Gledhill | 90-400 | 290-1,200 |
Worcester Bosch | 90-300 | 630-1040 |
The model you select will also affect the cost. Due to the availability of various features and designs, there is a vast price difference even between 2 models of the same brand.
PS You may find our guide on the UK's most popular home heating system combi boilers of interest and our new boiler cost guide.
Cost Of Installing A Megaflow System
Installation costs for high-pressure systems like Megaflow are quite high because they require a qualified boiler specialist.
Additionally, when the system is not installed by a professional, many companies nullify warranties.
As a result, when you don't hire a qualified person, you are more at risk and may have to pay higher costs in the long run.
Installing a Megaflow system involves the following procedures:
Cylinder installation
Cylinder thermostat
Safety features
Connections to the system
So, when installing a new Megaflow system, expect to pay anywhere between £500 and £2000.
However, if you are just replacing an old Megaflow system with a new one, the cost will be cheaper, somewhere between £300 to £450.
Other Factors That Affect The Cost Of A Megaflow System
Installing a new Megaflow system can include many other repair and installation works.
These expenses will add to the final cost. Some requirements that you need to think about are:
Your Water Main's Pressure
A Megaflow system requires water at high pressure. If the pressure is lower than the minimum threshold, a Megaflow system is not worth installing.
However, including accumulator tanks, laying a new pipe supply, and pumps can help rectify the poor pressure and flow. These solutions are costly and can be disruptive as well.
Age Of Your Radiators
If you are working with an old heating system, there are chances that the high pressure of the unvented cylinder will be too much for the radiators and pipes to handle. So, you will have to get them fixed as well.
Megaflow Is Not A Standalone System
If you are installing a new heating system, you cannot just install a Megaflow system.
It is just a hot water cylinder, and you will need to install a system boiler to heat the cold water in the tank.
Pros And Cons Of A Megaflow System
If you are about to install a Megaflow system, look at its advantages and disadvantages before making the final call.
Pros
As a Megaflow system eliminates the need for a cold water tank, it is less space-consuming
You can have high-pressure showers as the system uses the main water supply. The water pressure is not affected even when you run two baths or showers at the same time
Solar panels can be used to heat water. This is good for the environment and cost-effective
The system is completely sealed, so you do not have to worry about water contamination
You can install the system anywhere in the house
The system has many safety features. When the system reaches the desired temperature, the cylinder thermostat shuts down the boiler. The system also has a Temperature/Pressure Relief Valve (TPRV) which throws water into the drain when the temperature is too high
Cons
As the system uses water directly from the main supply, the main pressure will also define the water pressure in your taps and baths. So, you need to take a flow rate test, which will determine if your main water pressure is suitable for a Megaflow system
The main water supply powers the system. So, although the hot water is stored in the cylinder, it still requires a push from the main water supply to deliver the hot water
A Megaflow system works on high pressure. So, you will need to check your pipework for strength and if it can handle the high pressure. If not, you will have to replace the entire pipework
The water rushing through the pipes is at a very high velocity, so expect a lot of noise.
Wondering how much a new boiler may cost? Use our boiler installation cost calculator and if you're wondering how two of the biggest boiler brands compared, check out Worcester Bosch vs Baxi.
Megaflow Warranty Period
Different brands offer different warranty periods.
While Heatrae Sadia offers a 25-year warranty, brands like Viessmann or Worcester Bosch offer up to 10 years of warranty.
However, this warranty only covers the stainless steel cylinder vessel.
Other components like controls, immersion heater and valves have a much shorter warranty. Depending on the brand, they may have a 1 or 2-year warranty.
However, two components - the hot water expansion vessel and cold water combination valve - have a warranty of up to 5 years depending on the brand.
Safety Precautions To Take
Unvented water cylinders are high-pressure systems that carry a high-risk factor. When installing one in your home, keep the following safety precautions in mind:
The cylinder is default set at 60-65 °C, which is the ideal temperature range. When the temperature falls below this range, the probability of the growth of dangerous bacteria and the risk of diseases like Legionnaires disease greatly increases
If and when the temperature of the cylinder increases above 85 °C, the cylinder thermostat cuts the boiler off
One important property of water is that it expands on heating. This leads to an increase in pressure in the cylinder. If it reaches a point where it becomes dangerous and even explosive, the Temperature/Pressure Release Valve (TPRV) opens. This releases the excess pressure and reduces the water temperature
It is important that a Gas Safe Engineer install any central heating system, including the cylinder. The professional must hold an unvented hot water qualification (also known as G3 Qualifications) to be eligible to carry out the procedure
Megaflow System Conclusion
Megaflow systems are merely unvented hot water cylinders, not boilers. They can meet high water demands and can be installed alone (direct system) or alongside boilers (indirect system).
A Megaflow system can cost anywhere from £300 to £2,000, depending on the size, brand, and model.
Also, these charges do not include installation, so be prepared to spend an additional £500 to £2000 for new installation and £300 to £450 for replacement installations.
