What are the Benefits of High Efficiency Condensing Boilers?

Modern boilers are significantly more efficient because they are condensing boilers. A condensing boiler has a much larger heat exchanger designed to extract over 90% of the heat from the fuel it burns, which would normally be lost to the atmosphere through the flue, and recycle it back into the heating system.

This means that much cooler gases are eventually sent up the flue. Sometimes the flue gases become so cool that water vapour in the gas condenses out, hence the name, condensing boiler! When this happens, even more energy is recovered from the condensing vapour, and the heating system's efficiency rises even further.

Read our full guide to gas boilers here

Why are Condensing Boilers More Efficient?

In older generations of boilers, water circulated continuously through a central heating system or the system that heats tap water. Water would pass over the flame through a series of pipes, reach its desired temperature, and then be sent around the circuit.

One critical flaw made this highly inefficient: the water would only pass over the flame once, but the flame was delivering much more heat energy than the water could absorb in such a short time. Most of the heat and some noxious gases were therefore vented straight into the atmosphere.

How the Condensing Process Works

With a condensing boiler, the return pipework from the central heating system doesn’t head straight for the burner. Remember, it has circulated through the system and warmed your radiators and your home, so by the time it re-enters the boiler, it has lost a lot of its heat.

At Ideal Heating, we utilise this lost energy through innovative engineering. The water enters the boiler and is piped through the secondary condenser just before it vents hot air to the atmosphere. That heat that would once have been wasted to the air now gets a chance to start warming the cool water as it re-enters the boiler.

As the circulated water gets closer to the burner, it continues passing through hotter and hotter air, and therefore warms up. By the time it reaches the burner itself, it has already been considerably preheated, so the burner only has to give it a bit of a boost to help it reach the 50–60°C typical of a central heating system. Because the water doesn’t need to be heated as much, you don’t need to use as much fuel on the burner.

The Physics of Efficiency

As the water gets warmer and warmer as it approaches the burner, the gases from the flame lose more and more of their heat to the water in the pipes. That’s why the water vapour can actually condense. Reducing the temperature of water vapour from the burner flame to well below the boiling point of water (usually around 50°C) in a few seconds is remarkable and shows just how efficient condensing boilers are.

Learn more about how to make your boiler more energy efficient

Efficiency Standards and the Law

To meet efficiency standards for environmental reasons, the law was changed so that as of 1 April 2005, any new gas boiler being installed had to be a condenser type and have an SEDBUK (Seasonal Efficiency of a Domestic Boiler in the UK) efficiency rating of A or B. Oil-burning boilers followed suit on 1 April 2007.

Since boilers have a lifespan of around 15–20 years, it’s likely that by now, the majority of the UK’s boilers will already be condenser type. Note that they only became compulsory on that date; thousands had already been installed by 2005. However, it could already be time to upgrade your boiler, and below we’ll look at why.

Is it Time to Replace Your Old Boiler?

If your boiler is more than 10 years old, it may be wasting as much as 30% of the energy it burns, meaning you could only be using 70% of the gas you’re paying for. If you are ready for a boiler replacement you need to know which boiler is right for your home.

The majority of old heating systems will have a boiler, a cylinder and possibly a hot water tank in the loft. You can choose for your new boiler to keep the current set-up or switch to a Combi boiler.

Combi boilers don’t need cold water tanks or hot water cylinders; they heat water on demand, when you turn the tap on, as well as powering your central heating. However, Combi boilers are best for smaller households – they can only deliver hot water to one tap or your central heating at a time. If you regularly have two or more hot taps running, a Heat Only or System boiler will be more appropriate; they store hot water in a tank, so several hot taps can be run simultaneously.

Want to know more about the different types of boilers? Head to our guides below:

Find Your Ideal Heating Solution

Our Product Selector Tool is a quick and easy way to find your Ideal boiler replacement. Plus, you can find your local Gas Safe registered installer using our 'Find an installer' tool.

Your installer will help to specify the most appropriate new boiler for your home and conduct the boiler replacement.

You’ll find further advice on gas safety, servicing, and boiler care in our FAQs, as well as more in-depth guides on the Ideal Heating blog.