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Which type of boiler do I need?

November 2, 2018
hiber Energy

So the time has come - the creaky old heater from another era in your cupboard has finally given up, and you need to replace it with something new. Or perhaps you’d like to upgrade to the latest, most efficient model. Whatever the reason for replacing your boiler, you’re probably thinking about important factors such as price, reliability and running costs. But the first thing to consider is the type of boiler that’s best for your property.

Here, we outline the three main types of gas boiler on the market - Combi, System and Regular. (If you've got a non-gas boiler, such as oil or electric boilers, you’ll need a company that specialises in these - feel free to give hiber a call and we can make a recommendation).

Combi boilers

Probably the most well-known variety of boiler, and also the most common. Short for ‘combination’, these boilers both heat tap water and provide central heating for your pipes and radiators, all in a single unit, and 'on demand.'

Combi boiler benefits:

  • Ideal for small homes, with 1-2 bath/shower rooms and anything up to 15 radiators
  • The water to your taps is heated directly as it flows through from the mains supply - you don’t have to wait for hot water before you have a shower
  • No tanks or cylinders are needed, so you’ll save on space in the loft (where the cold water tank would sit) and in your airing cupboard where the hot water cylinder would normally be
  • Because hot water flows from the mains, it uses mains pressure, so you can have a powerful shower anywhere in the house
  • You won’t need any pipework in your loft, which makes it less likely that your water pipes will freeze in cold weather
  • The cost of a like-for-like can be attractive due to the simpler setup and gas pipe arrangement, as well as fewer parts

Things to watch out for:

  • Combi boilers are not the best option for houses with very low mains pressure, as it doesn't change this pressure.
  • If multiple people use hot water at once, you may need a high power combi, if your water pressure supports it. If your water pressure isn't sufficient for two showers at once, and you often require it, a system or regular boiler is the best choice.

Combi boilers are the best option for around three-quarters of the UK’s households. However, for larger properties with 2 or more bathrooms or lots of rooms to heat, you might need a boiler with a hot water tank (System or Regular) - especially if there are multiple people in the house who want to shower or use hot water at the same time.

System and Regular boilers

Both System and Regular boilers follow the more recognisable central heating design of a boiler plus hot water cylinder, usually in the airing cupboard. The cylinder ensures there’s a good store of hot water available, so lots of people can run showers and baths at once, all with great pressure.

In a nutshell, the main difference between Regular and System boilers is that System boilers have key parts like the water pump and expansion vessel integrated into the boiler itself, while Regular boilers have these components as separate parts of your central heating system. This means System boilers are a little more expensive compared to Regular boilers, but make things a little more compact and are easier to install.

Otherwise, they're quite similar in terms of design.

System and regular boiler benefits:

  • A big home may need higher flow to get hot water flowing throughout the house efficiently. This can place excessive demand on a combi boiler, while a separate hot water tank lets water flow on demand, at the same pressure, letting multiple people use hot water at once without issue.

Things to be aware of:

  • As the system heats up a hot water cylinder, you can run out of hot water if you're using a large volume of hot water (for example, running a bath, followed by multiple showers)
  • Taps upstairs likely will have lower pressure than downstairs, as pressure is determined by gravity

Other other choice: Vented vs. Unvented systems

For Regular and System Boilers, there is one other choice that has a big impact on the performance of your central heating system - your cylinder. There are two types of cylinders to choose from - open-vented (relying on gravity for water pressure) and unvented (a sealed system with better hot water pressure). This is determined by the type of hot water cylinder you have - you can upgrade from a vented to unvented system for better performance.


Open-vented central heating systems are the most common - they have a cold water tank in the loft, and rely on gravity to push water around the house. This is better for older systems that may be vulnerable to high system pressure, avoiding leaks in older radiators. Open vented systems tend to be less expensive.

Open-vented system benefits:

  • Less expensive to install & maintain
  • Suitable for older piping and radiators to avoid risk of leaks


Unvented central heating systems are a closed system not open to the air, and therefore maintain the mains water pressure. The advantage is no cold water tank in the loft, and improved pressure in the system. This means better shower and hot water pressure compared to vented systems (where pressure is based on gravity). If you don't have one of these already, you'll need a new unvented tank like a Megaflo to turn your system into an unvented one.

Unvented system benefits:

  • Better performance in terms of good water pressure to all outlets
  • You don’t need a cold water tank in your loft

So...which boiler should I choose?

When it comes down to it, there are three main choices:

1) Combi boiler (suitable for most UK homes, such as a 3 bed, 1 bathroom home, and many homes with 2 bathrooms)
2) Regular boiler with a Vented Cylinder (suitable for larger homes with 2 or more bathrooms, such as a 5 bed, 2 bathroom home)
3) System or Regular boiler with an Unvented Cylinder (best performance for larger homes)

We find small to medium houses typically are best off with a combi, while larger homes are best with a System or Regular Boiler, particularly if there are more bathrooms.

Replacing your boiler with a like-for-like swap is usually the most economical in terms of installation - for example, replacing your combi, or using your existing Vented cylinder and just replacing the regular boiler. If you have a regular system, for the best performance, consider switching to a combi or unvented set-up, depending on your needs.

The guidelines above should help, but for medium sized properties (such as a 4 bed 2 bathroom home) it becomes a little more of an art than a science. The best choice will be influenced by the short and long term cost, the age of your existing system components and your mains water pressure, for example. Speak to a good installer who understands the mix of factors that determine the best type of boiler for your home, and be sure to explore your options before you decide.

We're happy to provide no-obligation advice on the best options for your home - just get in touch below or drop us a line on 0808 169 6484.

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