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A combination boiler, or combi boiler for short, is one of the most popular boiler types in homes all over the United Kingdom. In fact, over 50% of all new boilers installed in UK homes every year are combi boilers. Choosing the right type of boiler is very important. You need it to be a practical and efficient fit for your home.

With so many types of boilers available, it can be confusing to choose the right one. Combi boilers are popular because they are compact and can fit into a standard kitchen cabinet. This means they don’t take up too much space, especially in homes with little or no loft area to install a system. They are also very energy efficient, which means they use less energy to heat water. Let’s see how these works, and what makes them so popular.

Combi Boiler – Compact & Efficient Solution

A combi or combination boiler is a type of boiler that functions as both a central heating boiler and a water heater. Combi boilers typically have high efficiency and, usually are more than 90% efficient. That means the higher the efficiency, the lower the running cost.

Combi boilers are usually sleek and compact units that can fit inside a standard kitchen cabinet. These boilers save space and are efficient. Combi boilers heat water directly from the mains and supply it on demand. This will eliminate the need for having a hot water cylinder or a storage tank.

Combi boilers are also one of the most energy-efficient kinds of boilers in the market. They heat water instantly instead of heating and storing it in a hot water cylinder. You also get high water pressure because it comes directly from your mains. This eliminates the need for a separate pump to maintain water pressure.

How Does a Combi Boiler Work?

There are three common types of boilers:

  • Regular
  • System
  • Combi

Regular boilers require a large feed of water from a water storage tank. Regular boiler and system boilers also need a hot water cylinder to store the water they heat. On the other hand, combi boilers heat water on demand directly from the mains.

Combi boilers function as an instant water heater as well as a central heating boiler. A combi boiler takes water from the mains, heats it, and supplies it to your hot water shower, tap and central heating system.

Most modern combi boilers in the United Kingdom come with a condensate pipe. A condensate pipe is part of the Flue Gas Heat Recovery System. Older boilers waste flue gases and heat. But a condensing combi boiler captures the heat from flue gases and uses it to preheat new cold-water flowing in. This is why combi boilers are so efficient. Using their Flue Gas Heat Recovery System, they waste less energy on heating and drain away condensed vapour.

What Are the Best Combi Boilers?

There are several boiler companies in the United Kingdom manufacturing excellent combi boilers. Many manufacturers have combi boilers falling in different price ranges. However, the best combi boilers are those that are the most energy-efficient, powerful, and compact. The following boilers fit all three of these criteria:

Worcester Bosch Greenstar I: The Greenstar I is one of the most popular combi boilers in the United Kingdom. It is an extremely sleek and compact model, measuring only 710x400x330 millimeters. The combi boiler comes in the 25kW and 30kW variants. It has one of the highest efficiency ratings in the market, at 94%.

Valiant EcoTEC Plus: The EcoTEC Plus comes in three different sizes, 25kW, 32kW, 35kW and 38kW. The boiler is fairly compact, measuring just 720x440x340 millimeters and just has a 92% efficiency rating.

Ideal Logic+: The Logic+ is one of the most compact boilers on this list, measuring just 700x395x278 millimeters. However, it comes in 25kW, 30kW and 35kW variants. The Logic+ has a 94% efficiency rating, making it a popular choice across Britain.

Glow-Worm Energy: The Glow-Worm Energy combi boiler measures 700x390x280 millimeters and comes in three sizes. You can opt for the 25kW, 30kW or 35kW variant. The boiler has a slightly lower efficiency rate, standing at 93%.

Baxi EcoBlue: The EcoBlue comes in 4 sizes, 24kW, 28kW, 33kW and 40kW. It is slightly bulkier than the other boilers above, measuring 763x395x345 millimeters. However, it can still fit into most standard kitchen cabinets. The Baxi EcoBlue has the least efficiency out of all these boilers at 92%.

The combi boilers listed above rank A for efficiency according to EU standards. They are all also compact enough to fit into your kitchen cabinet and not take up precious space. Most accredited installers recommend all of the above brands and their combi boilers.

Different Types of Combi Boilers

The combi boilers we just discussed above are gas burning. But there are several other types of combi boilers which include:

Gas Combi Boiler: Gas combi boilers are by far the most common type of combi boilers installed in the United Kingdom. Gas combi boilers burn natural gas to heat your water, which they get directly from the gas network. If you live in a home with a connection to the gas network, a gas combi boiler is your best option. Natural gas is a cheaper fuel source than oil, LPG or electricity. This is why a gas combi boiler can help you keep your energy costs comparatively low.

Oil Combi Boilers: Oil combi boilers are usually found in homes not connected to the gas network. An oil-burning combi oil will require a steady supply of fuel. This means you will need to keep a tanker of oil outside your home. You will also need to arrange with an oil supplier to periodically top up the oil tanker.

Electric Combi Boiler: Electric combi boilers are another popular choice in households that are not connected to the gas network. It does not burn fuel to heat water, which makes it a much eco-friendlier option than other combi boilers. Such boilers pass the water over an electric element to heat it. However, electricity is quite expensive, which makes electric combi boilers a poor choice for larger homes.

LPG Combi Boiler: Some combi boilers use liquefied petroleum gas or LPG to heat your water. LPG is a type of hydrocarbon fossil fuel. LPG combi boilers will require a fuel tank outside your home to keep supplying it with fuel. You may also need an arrangement with an LPG supplier for refueling.

The Pros of Choosing a Combi Boiler

Combi boilers are popular for several reasons, which is why they are the most commonly found type of boilers in the United Kingdom. Choosing a combi boiler has numerous advantages, which include the following:

Energy Efficiency: Most well-known combi boilers, as we saw above, have a higher energy efficiency rating than other types of boilers. Boiler regulations in the United Kingdom require all combi boilers to be at least 92% efficient. A 92% efficiency means only 8% of the fuel used in heating water is wasted. The other 92% is used efficiently in heating. Combi boilers make for lower energy bills and a reduced carbon footprint.

Energy Bills Savings: Since combi boilers are 92% efficient, only 8p out of every £1 you spend on heating goes to waste. This is significant savings because combi boilers require less energy to heat your water and home. Older boilers only had efficiency ratings of around 55%.

Quick & Easy Installation: Combi boilers are relatively easier to install, especially when compared to other types of boilers. Combi boilers have no additional pieces or elements other than the boiler itself. Since they are easier and quicker to install, this automatically makes them cheaper to install as well. You can fit a combi boiler anywhere in your home without taking up too much space.

Compact and Convenient: Most popular manufacturers advertise their combi boilers as being small enough to fit inside a kitchen cupboard. Combi boilers also do not require a hot water cylinder or a cold-water storage tank. This makes it very convenient to install them where they will not be an annoyance. Because they are compact, combi boilers are very popular in small homes and flats.

Good Water Pressure: The water mains supply the combi boiler with water to heat. It does not rely on an elevated water tank and gravity to supply hot water throughout your home. This means you usually get stronger water pressure in your shower or hot water tap.

The Cons of Choosing a Combi Boiler

There are a number of disadvantages to combi boilers. This means they are not always the perfect choice. Some of these disadvantages include the following:

Water Flow Depends on Mains Pressure: A combi boiler gets its water supply directly from the mains. This means there needs to be an adequate supply and pressure of water in the mains for you to get it in your home. If your home has a weak mains pressure, then your taps and showers will have an inconsistent or weak flow of hot water. You can get a separate pump installed to solve this, but it will add to the cost. Combi boilers are generally not suitable for homes with weak mains pressure.

Weaker Flow in Larger Homes: If you live in a larger home or have several bathrooms in your home, you may want to reconsider buying a combi boiler. A combi boiler heats water on demand by taking it directly from the water mains. There is no place to store the hot water, which means there is a weaker flow if there are multiple outlets.

Pipework Compatibility: Combi boilers are not always compatible with older pipework. If you originally had an older heating system, the pipework is designed for weaker water flow. This means your pipework may not be able to handle higher water pressure from a combi boiler. In certain cases, installing a combi boiler may require you to replace the older pipework as well.

What Combi Boiler Should I Get for My Home?

When getting a combi boiler for your home, you should pay careful consideration to the output of the boiler. You also need to consider the number of bedrooms and bathrooms in your home. More bedrooms mean more radiators in your home the combi boiler needs to supply water to. More bathrooms mean the combi boiler has to handle more water outlets, which will affect the water pressure you get.

  • If you have up to 2 bedrooms and 1 bathroom in your home, you should get a combi boiler with an output of around 24-27kW.
  • If your home has up to 3 bedrooms and 3 bathrooms, you should consider getting a combi boiler with a 28-34kW output.
  • If there are 4 or more bedrooms in your home or more than 3 bathrooms, consider a combi boiler with an output between 35 to 42kW.

Combi boilers are the most common type of boilers found in British homes because they function as both a central heating boiler and a water heater. Moreover, these boilers are extremely energy efficient, with the lowest acceptable energy-efficiency at 92%. Combi boilers help you save on gas bills because they waste only 8% of the energy they use to heat water. This type of boiler is also very compact and can fit easily into a standard kitchen cupboard. Combi boilers do not require a separate water storage tank or a hot water cylinder. They take their water supply directly from the mains and give you a stronger flow of water in your shower or hot water tap.

However, combi boilers do have a number of disadvantages. They are usually not suitable for larger homes. They also don’t work well in homes with weaker mains pressure. If you are replacing your old boiler with a combi boiler, you may need to replace the pipework as well. Your older pipework may only be able to handle weaker pressure flows, not the mains pressure your combi boiler gives. Despite this, combi boilers remain extremely popular solely because of their compact size and energy efficiency. 

What Is a Combi Boiler How Does Combi Boiler Work