Difference between Combi, Condensing and Heat Only Boilers

Welcome to the Surrey Heating Services blog. I am Richard Chelton, the owner of the company and on this blog I will try to add content that I feel will help you save time and money e.g. little tips and tricks you can try yourself to avoid a callout charge.

I will also give you information on boilers, heating systems and plumbing, so you are in a better position to make the right decisions when you wish to go ahead with any future gas central heating installations, boiler installation or new bathroom installation.

First thing I will talk about is the differences between the various boilers on the market today.

Condensing boilers

All boilers fitted these days are condensing boilers. They are so much more energy efficient than the older boiler, as their clever design feature of reusing the heat from the flue gases (that otherwise would have been wasted) makes them around 90% efficient.

Because the flue gases are reused what eventually comes out the flue is cooler and contains water vapor which can produce plumes especially on a cold winters day and can be a nuisance to neighbours so consideration should be taken when choosing the position of the new boiler.

 

Combination boiler (combi)

Combi boilers are a high efficiency water heater and a central heating boiler all in one, hence the name (combi). They have become increasingly popular in the last 10 years in fact they account for over half the boilers sold in the UK due to their ingenious space saving design.

When you have a combination boiler, you don’t need to have any stored cold water tank in the loft space as well as a hot water cylinder in the airing cupboard as they are feed directly from the cold water mains supply and heat this water on demand. This produces great showers without the need for noisy pumps and will save you money as you’re not constantly heating stored water.

Pros of having a combi boiler

  • Instant and unlimited hot water supply
  • Mains pressure at taps and showers flow rates up to 18 litres
  • An economical choice as you’re not storing hot water in a tank all day
  • No need for water tanks in the loft so good choice if planning a loft conversion

Cons of combi boilers

  • Not suitable for larger houses with several bathrooms
  • There’s a delay from when you open the tap as the boiler has to fire up to heat the water
  • Takes longer to fill baths
  • If the boiler breaks down you are without hot water and heating as you don’t have an immersion heater as a backup

Heat only boilers

These boilers simply heat water inside a heat exchanger, which is then pumped and diverted around either the radiators or the coil in the hot water cylinder to indirectly heat that water. They in most cases feed from a small tank in the loft.

Pros of heat only boilers

  • Large tank of stored hot water
  • Suitable for larger houses with higher hot water demands
  • Can run more than one shower at one time
  • Can have a secondary coil on your hot water cylinder to allow a solar panel to heat the water

Cons of heat only boilers

  • Takes up more space as need stored water tanks, external pumps and valves
  • You are limited by the size of you cylinder and once all hot water is used, you need to wait for it to be heated again
  • To get powerful showers you need booster pumps that are expensive and noisy

System boilers

These also have to be fitted to a hot water cylinder but contain the heating pump and pressure vessel and diverter valves inside the boiler

Pros of a system boiler

  • Large tank of stored hot water
  • Suitable for larger houses with higher hot water demands
  • All components are built in the boiler, making installation neater and quicker (also covered in the warranty from the manufacture)
  • More economical
  • Possible to have a secondary coil on your hot water cylinder to allow a solar panel to heat the water

Cons of a system boiler

  • Takes up more space as need stored water tanks external pumps and valves
  • You are limited by the size of you cylinder and once all the hot water has been used, you need to wait for it to be heated again
  • To get powerful showers you need booster pumps that are expensive and noisy