Condensing Boiler vs Combi Boiler

When you’re buying a new boiler, there are many factors to consider before you buy. Take time to assess your hot water and heating usage before you buy. This will mean you’ll end up with a boiler that’s the right size, meets your household water needs and has reasonable running costs.

The two most compared options are combi and condensing boilers. Many people get these two mixed up, thinking they’re the same, but in fact, they describe different aspects of boilers.

A combi boiler is a type of condensing boiler, but it doesn’t need a water tank, whereas a system or regular condensing boiler needs a separate hot water cylinder.

In this guide, we’ll go through the differences between the two, the suitability and pros and cons of each system, so you can look at the combi boiler vs condensing boiler before you replace or upgrade your water and heating system.

Let’s get started…

What is a Condensing Boiler?

All boilers sold in the UK are condensing boilers. This has been a legal requirement since 2005 and applies to combination boilers. They work by using gas to heat water, which is also supplied to radiators to warm the home.

During this process, water vapour is produced in the form of steam, which is hot. Before condensing boilers, this hot water vapour was lost through the flue and escaped back outside. This meant around 30% of the heat produced by a boiler wasn’t used, although you were paying for it.

Condensing boilers capture the water vapour and pass it through a heat exchanger, which recycles it and keeps the heat, which is then fed back into the home. It means less waste and a more efficient way of providing heat and hot water.

Unlike combi boilers, you do have to wait for the water in the cylinder to heat up, but you won’t lose water pressure if more than one person is using the water.

What is a Combi Boiler?

Combi boilers don’t need a separate water tank because they take water directly from the mains. This makes combi boilers ideal for flats or smaller homes.

The combi boiler still uses a condensing system to be more efficient, but you get hot water straight away. However, if more than one person is using water, the pressure will drop and the water temperature will fall.

The Key Differences

All boilers, including combi boilers, use condensing technology to work more efficiently. When you’re buying, you can compare three types:

• A condensing combi boiler
• A condensing system boiler
• A condensing regular boiler

Combi boilers are compact units that provide heating and hot water without a feed or storage tank.

Regular boilers have a boiler unit, a cylinder and a feed tank, which is usually in the loft. The water from the mains goes into the feed tank, which is then heated by the boiler and sent to the radiators. The boiler only provides heat, and the hot water cylinder and cold-water tank supply water.

System boilers have a main boiler and a hot water storage cylinder. They don’t need a cold-water tank. The water comes directly from the mains, where it is heated up and stored. A smaller household with one bathroom may be better with a space-saving combi boiler.

If you have a larger household with more than one bathroom and room for a tank and cylinder, then a regular or system boiler may be better for you.

Cost Comparison – Condensing Boiler vs Combi

A combi boiler is cheaper to buy and install. The average cost of a combi boiler is between £500 and £3,000, depending on the manufacturer, model and output rating.

Installation costs will depend on whether you’re replacing an old combi boiler with a new one, or fitting a combi boiler and removing an old regular or system boiler, where the cylinder and feed tanks will need to be removed. Expect to pay between £1,500 and £3,600.

A regular or system boiler will cost between £1,500 and £5,550, with an average of £3,600 to install.

A new condensing boiler, whatever type, will save you up to 30% more energy than an old non-condensing boiler. Both a combi and a regular or system condensing boiler will cost the same to run.

For example, let’s take the average medium annual running costs of a 3-bedroom home according to Ofgem. Medium energy use of gas is around 11,500 kWh per year, and electricity is 2,700 kWh per year. If you use 11,500 kWh of gas per year with a gas price of 6.30 per kWh, then your running costs will be £724.50 per year, not including standing charges.

2,700 kWh of electricity per year with electricity prices at 26.35 means the running costs will be £711.45 excluding standing charges.

Combi vs Condensing Boiler

Efficiency and Performance – Condenser Boiler vs Combi

Combi boilers are more efficient than a regular or system boiler. A new gas combi boiler has an efficiency rating of at least 92% and new electric combi boilers can rate at 99% to 100% efficiency.

A Combi boiler is perfect for a small or medium home with one bathroom. Heating and hot water on demand.

Regular and system boilers are at least 92% efficient, but can be improved with energy-saving controls like timers and thermostats. They are less efficient than combi boilers because they have a separate hot water cylinder, which means some heat is lost.

Large households with more than one bathroom will benefit from regular or system boilers. They are also good for properties with underfloor heating, as they work well at the lower temperatures that underfloor heating uses. Water and heating can be supplied at the same time, and if two people are showering at the same time, it won’t affect the water pressure.

Suitability

You don’t have to choose to have a condensing boiler; all new boilers are now condensing. You have to choose between a combi boiler and a regular/system boiler. If you live in a flat or a small property with no loft, then a combi boiler will suit your household if you have low to medium hot water demand.

Large homes with more than one bathroom and space for a tank and cylinder will benefit from a system boiler, which can cope with a larger household that might want to bath or shower at the same time.

Pros and Cons

Pros & Cons of a Combi Boiler

Pros of a combi boiler

• ✔ Saves space as there are no other tanks, ideal for smaller properties
• ✔ Instant hot water and heating when you need it
• ✔ High efficiency
• ✔ Low maintenance
• ✔ Easy installation

Cons of a combi boiler

• ✖ Water pressure will drop if two people shower at the same time
• ✖ Not suitable for homes with low water pressure or poor flow rates
• ✖ Don’t work with solar water heating systems

Pros & Cons of a Regular Boiler

Pros of a regular boiler

• ✔ Suitable for larger homes with higher hot water demand
• ✔ Works with solar water systems
• ✔ Mains pressure doesn’t drop when two people shower at the same time

Cons of a regular boiler

• ✖ Hot water isn’t instant; you normally have to wait for it to heat up
• ✖ You need space for the cylinder and the tank
• ✖ Some heat is lost through the cylinder, so they are not as efficient as combi boilers.
• ✖ Don’t work with all new heating systems

Pros & Cons of a System Boiler

Pros of a system boiler

• ✔ Ideal for large households
• ✔ No need for a loft as there is no cold-water tank
• ✔ Works with underfloor heating

Cons of a System Boiler

• ✖ Not instant heat. Once the hot water has been used up, you’ll need to wait for a fresh supply
• ✖ space needed to put the hot water cylinder
• ✖ Water flow rate is dependent on your mains pressure.

So, as you can see, all boilers are now condensing boilers. The choice you have to make is whether to have a regular, system or combi boiler for your home. While combi boilers will give you heat and hot water on demand, they may not be the right choice for larger households.

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