Condensing Boilers Vs. Combi Boilers | What are the Differences? Re February 6, 2023

Condensing Boilers Vs. Combi Boilers | What are the Differences?

Engineer repairing a boiler

It’s easy to think (and many people do) that when it comes to boilers, it’s a one-size-fits-all model; after all, a boiler’s a boiler, right? Wrong. There are various different types of boilers, with condensing and combi boilers the two most popular and most commonly found throughout the United Kingdom. But whilst they might enjoy similar levels of popularity, they’re far from being the same in the way they function.

Which of these two boiler types you have will affect various things, from upkeep to efficiency, from price to physical footprint. In this blog, we’ve listed some of the key differences between condensing boilers and combi boilers, so that you know what you’re looking for when next you’re in the market for an upgrade.

Are Combi Boilers the Same as Condensing Boilers?

No! They may look similar from the outside (in the sense that most boilers are bulky, cuboid-shaped objects) but they operate in different ways. Below, we’ve outlined the main differences in the way the two boiler types operate:

Condensing Boilers

Using either oil or gas as its fuel, a condensing boiler has a burner which fires up; the burner then transfers that heat into what’s called a primary heat exchanger. In this regard, condensing boilers are similar to more traditional boiler models, which also have a heat exchanger. Where they differ, however, is that condensing boilers also feature a secondary heat exchanger.

A conventional boiler will feature cold water entering the (sole) heat exchanger, ‘picking up’ heat before then circulating on to be used in radiators. With a condensing boiler, by contrast, sees its fluids enter the secondary chamber first, picking up latent heat from the cooling flue gases.

With the fluids already partially heated, it then passes the primary heat exchanger, heats up in the same way as a conventional boiler and is used to heat radiators and central heating.

This condensing method drastically improves a boiler’s efficiency; for comparison, a conventional boiler typically offers efficiency rates of 65-80%, whilst a condensing boiler can achieve efficiency rates of almost 99%. It’s no surprise, then, that they’ve become so popular over the past couple of decades. How, though, do combi boilers differ from these condensing boilers?

Combi Boilers

Combi boilers work by receiving signals from the home’s main thermostat; when the temperature falls below a set point, a signal is sent to the boiler which fires it up; heat is then pumped around the central heating system until the set point on the thermostat has been re-reached.

The ‘combi’ part comes from the fact that when the hot water tap is turned on, a valve diverts the heating towards the water supply, providing hot water on demand, without the need for a storage tank.

How Much Does a Condensing Boiler Cost to Buy (and Install)?

The price of purchasing a condensing boiler depends on the complexity and quality of the model, however average prices range from £500 on the budget end of the spectrum, through to almost £2,000 for top-of-the-range models from industry-leading manufacturers. These prices don’t include the cost of labour for boiler installation, which can range from between £250 and £1,000, depending on where you are in the country. For example London boiler installation prices will be higher than Newcastle installation pricing. 

How Much Does a Combi Boiler Cost to Buy (and Install)?

Combi boilers cost a similar amount to their condensing counterparts, and installation/labour will also cost similar. The cheapest combi boilers will set you back under £500, however, their power output will be significantly lower than more expensive models, meaning they’re less likely to be suitable for larger homes, or those with greater heating/hot water requirements.

What are the Advantages of Condensing Boilers?

The main advantage of a condensing boiler is its efficiency; this in turn leads to lower energy bills, something which is incredibly attractive especially at the minute, as well as a lower overall carbon footprint. When compared with an older, conventional boiler model, condensing boilers can save you anywhere up to 30% on your annual energy bills, though this will of course depend on the model in question.

What are the Advantages of Combi Boilers?

One of the primary advantages of combi boilers is that they take up less space overall (in that they eliminate the need for a separate hot water tank), as well as providing hot water on-demand. What’s more, they achieve similarly high-efficiency rates as most condensing boilers.

Regulations for Condensing and Combi Boilers

There are several important regulations for condensing and combi boilers that you need to know about before purchasing/installing one. In short, there is main regulations you need to be aware about, and it pertains to a condensing/combi boiler’s overall efficiency rating:

  • Condensing boilers fitted after 2005 (April 2005, to be exact) must have a minimum SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK) rating of B. A ratings are always preferable, however.

The Popular Boiler Brands in 2023

The most popular (and reliable) boiler brands are VaillantWorcester Bosch, Glow-Worm, Viessmann and ideal. At this point, most modern boiler models – even on the budget end of the spectrum – are highly capable and efficient, so differences will vary only slightly, whichever boiler you end up choosing.

Final Thoughts…

Both condensing boilers and combi boilers are better options than older, conventional boiler types, with both offering high-efficiency rates and the ability to last a long time, provided they’re looked after properly.

Condensing boilers are a good option for those with the space for a hot water tank, whilst combi boilers are ideal for those families and homes where space is at more of a premium. Both, however, are very good options to go for when you next replace your boiler!

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