Types of Boiler

Condensing, Conventional, System, Combi, Biomass

Types of Boiler: Condensing, Conventional, System, Combi, Biomass

Find out everything there is to know about the different types of boilers – Condensing, Traditional/Conventional, System, Combi, Biomass boilers!

There are many types of boilers available, and selecting the right one for your property – in this case, we are looking at residential properties rather than commercial – can be an exceedingly tricky task.

In the following list, we walk you through the types of boilers that are available at the moment.

We look at which boilers are best suited for different environments and discuss the costs to help you find out which boiler is the one for you.

What should you consider before reading? Have a think about the variables in your property.

  • How many radiators will this boiler be expected to serve?
  • How many showers/bathrooms do you have? And how many of those will be running at once.
  • Check your area water pressures.

All of this will have an impact on the performance of your boiler and which one will be best for your property.

When you’ve got this clear in your mind, move on to the list below and take your time exploring the options.

Recommended reading: What Size Boiler Do I Need?

Condensing Boilers

Condensing boilers are a type of boiler which is pretty much standardised across the domestic UK market.

In fact, when it comes to system or combi boilers as well as traditional boilers (read on below), the law actually states it much be a condensing boiler.

So with that in mind, it is worth stating that condensing boilers are less of a ‘type’ of boiler and more of a technology behind boilers that most units will need to be using in order to be certified in the UK.

Condensing boilers are far more efficient due to the way they can use heat from the waste flue gas to pre-heat cold water.

Rather than spilling any waste fuel out into the atmosphere, this boiler will create energy, resulting in condensing boilers being seen as an incredibly green heating solution – making the average boiler a much greener option than many people realise.

As mentioned above, all boilers must be condensing boilers whether that’s system, combi or conventional units. So what are the main differences between these three systems, if they are all condensing boilers?

Traditional/Conventional Boilers

Seen less and less, a conventional boiler is now more suited to large properties that can house the equipment needed to make it work.

Open vent or heat only boilers have a cylinder for storing hot water as well as a water storage tank.

Conventional boilers take water from the tank, rather than the mains. The water is then heated and stored in a cylinder before it is distributed around the property.

Due to the sheer size of this kind of boiler, a large volume of hot water can be stored at any one time and then delivered to multiple bathrooms across the property.

Meaning you can run more than one bath at a time. However, it is worth remembering if everyone runs a bath, you could end up with no hot water for a short period of time as you’ll need to wait for the tank to refill.

While you might not pick this for your average, modest terraced property where wasted space is not an option, large, traditional properties that have a very traditional heating system in place are perfectly suited for this types of boilers.

Properties that have conventional boilers often have a large space in the loft for the tank/storage.

If your property already has a conventional boiler installed that may need replacing, it is worth considering another conventional boiler.

This will protect or maintain the existing pipework throughout the property, rather than having to redo an entire system.

The chances are, if you have a traditional system, the property may be quite large and replacing an entire network of pipes to suit other boiler formats could incur much large costs.

If you want to make this option a greener solution, these traditional boilers work very happily with solar heating systems so you can rest easy knowing that your planet and wallet will thank you in the long run.

Key Notes:

  1. Works well in large properties with multiple bathrooms/showers/taps etc.
  2. Does take up a significant amount of space but can hold plenty of water.
  3. You will need to wait for the tank to refill with hot water between peak hot water usage periods.
  4. Good in areas of low water pressure.
  5. Compatible with greener, solar heating systems.
  6. Installation can cost more if the property isn’t already on a conventional system due to the extra storage equipment, however, if you’re replacing an existing conventional boiler, this is your best approach.

System Boilers

A system boiler is suitable in a house that has multiple bathrooms because, like the conventional boiler, it stores pre-heated water.

However, unlike the conventional boiler:

A system boiler only has the storage cylinder element, rather than the extra water tank as well, meaning a system boiler will take water directly from the mains to heat up.

No water tanks also free up the fear of any damage in colder weather and the cost/damage risk of problematic water leaks in the house.

The lack of tank also saves a significant amount of space, making this a great option for smaller properties that still have multiple bathrooms.

Key Notes:

  1. With fewer parts and less space required, a system boiler’s installation is quicker and more affordable.
  2. The cylinder will require space, so it’s not suitable for very small properties. In order to keep the water warm, the cylinder will need to be well insulated.
  3. No water tank reduces the risk and cost of damage or leaks.
  4. Hot water supply is more constant – as water comes straight from the mains.
  5. However as it does store its hot water, you may need to wait for the cylinder to refill.
  6. Also compatible with green/sustainable energy solutions such as solar power.

Combi Boilers

For many residential properties, the combi boiler (combination boilers) is one of the most popular and cost-effective.

This type of boiler does not need a tank or a cylinder to store any water.


A combi boiler takes water directly from the mains and heating it to demand when the tap is on. This means you never have to wait for hot water.

This also means you save maximum space and with a simpler boiler, comes a simpler installation.

Combi boilers are also popular for their eco-friendly approach, usually ranked highly for their efficiency and ability to reduce heating costs.

Key Notes:

  1. Hot water on demand – no waiting time.
  2. Compact option for smaller properties.
  3. Easier to maintain / cheaper to install due to fewer and less pipework.
  4. Incredibly low risk of any frozen pipes.
  5. Low water pressure properties can struggle with combi boilers.
  6. Not advised to try to run two showers/baths at once.

Biomass Boilers

A biomass boiler is a renewable boiler alternative – which can be compatible with traditional radiators as well as more modern underfloor heating systems.

Biomass boilers run off wood pellets or wood chips, which can be bought or created/farmed on your own land.

The biggest pull toward biomass boilers is the fact they are seen as more sustainable.

In fact, you can be eligible for a renewable heat incentive for having one.

While the cost of the fuel to run these kinds of boiler is cheaper, it does come at a cost – space.

Biomass boilers can be large and also require a storage building for the wood pellets.

With space, comes the cost. Despite it being cheap to run and maintenance costs being fairly low – average installation for a boiler like this can be as high as £20,000, depending on the property.

Key Notes:

  1. Renewable fuel alternative – government incentives/bursaries available – paying you for the energy you produce.
  2. Expensive initial cost, but cheaper running costs.
  3. Works in most properties, but does require large amounts of space for boiler and storage.
  4. Despite being “renewable” the combustion of wood in this way does not remove the negative impact on the environment.

These types of boilers are the most suitable for the majority of properties, so hopefully, we’ve suggested something that suits your needs – whether you’re replacing a boiler or building a solution from scratch.

Our top tip is to remember to consider the number of your bathrooms as well as the water pressure levels in your area and you should find the perfect boiler for you.

If you have doubts or concerns, please give PHS a call and an engineer can talk through your options with you or even visit the property to take a closer look at what you’ve got and help you make a decision.

We are currently available to visit properties in the Home Counties, London, Suffolk, Essex, Kent and Hertfordshire.