Underfloor Heating with a Combi Boiler

Last updated: November 15, 2023

Can you install underfloor heating with a combination boiler? How do these installations work together and what are the costs involved?

Underfloor heating is seen as a luxury by many and something only observed in new build properties, but that’s no longer the case.

Underfloor heating can typically be retrofitted into existing homes with very little adjustments to the existing heating system having to be made, even if you heat your home with a combi boiler.

Can You Install Underfloor Heating with a Combi Boiler?

The short answer is yes you can and many people have, but there are some important things to be aware of.

If your current central heating system is composed of a combi boiler attached to your radiators and you wish the underfloor heating to use the same combi boiler you will need to have a two port valve installed.

As you may have guessed, a two port valve controls the flow of water in a central heating system, in particular the water that goes from the boiler to other parts of the heating system.

If you install an underfloor heating system with a combi boiler and don’t bother with the two port valve the boiler may try to supply hot water to both the underfloor heating and your radiators simultaneously.

This can result in the boiler overheating and eventually locking out and displaying an error code.

Installing a two port valve will help prevent this problem from ever occurring.

Learn all about the different types of boilers, including condensing boilers, LPG boilers, oil boilers, Opentherm boilers and calculating boiler size in our guide.

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Best Type of Combi Boiler to Use With Underfloor Heating

The majority of combi boilers will have adequate power output to supply hot water to your underfloor heating.

As mentioned, the one thing that is essential is the two port valve to ensure the hot water flowing to your radiators and underfloor heating are separated.

To determine the size of combi boiler you require (measured in kilowatts) you will need to determine how many rooms you want to install the underfloor heating.

The more rooms you have underfloor heating = the higher the power output of the boiler.

The good news is that the power required to heat your underfloor heating is lower than what is required for the typical radiator.

For reference, you can use the following guide to determine what size boiler you need:

  • A 24kw boiler is sufficient for one room installation.
  • A 30kw boiler for two rooms.
  • A 35 – 40kw boiler for underfloor heating installation in many rooms.

Of course, you will need to factor in the number of radiators in your home too, so it’s always advised that you seek the help and assistance of a qualified Gas Safe engineer.

Wondering how much a new boiler costs? Check out our guide on options available if you need a new boiler but can’t afford it, as well as boilers on finance and government boiler grants here.

Which Underfloor Heating System Works Best with a Combi Boiler?

There are two main types of underfloor heating referred to as wet and dry systems.

In the case of combi boilers, a wet underfloor heating system is going to be required.

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A wet system utilises pipes to transport hot water that has been heated by the combi boiler.

In essence, a wet underfloor heating installation operates like a regular central heating system that uses radiators, only the pipes are installed over a much larger surface area and much closer together.

Temperature regulation is also a major part of the system. The underfloor heating system contain a temperature sensor that helps regulate the water and therefore floor temperature.

This sensor detects the water temperature flowing through the network of pipes and if necessary will communicate with the combi boiler to either re-heat the water if it’s not warm enough, or to keep circulating the water through the system if it’s still hot enough.

Is Underfloor Heating from a Combi Boiler Worth It?

Underfloor heating is incredibly versatile and can be installed under almost any type of flooring including wood, tile and ceramic.

It also means you can avoid those terribly cold floors on winter mornings and instead be greeted by a warm floor instead.

Another major benefit is the way underfloor heating’s heat, unlike radiators they don’t leave the centre of the room cold. This is all because underfloor heating warms the entire surface area of the room.

Lastly, underfloor heating is ideal in rooms where radiators can’t be installed or there are limited installation options, for example kitchen areas where cabinets take priority.

Do You Need Radiators with Underfloor Heating?

You can install underfloor heating without radiators, but it’s typically not advised in case your underfloor heating ever fails.

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In addition, the majority of UK properties that do have wet underfloor heating install do not have it installed throughout the whole property.

In fact, on average, underfloor heating is installed in just one room in the UK, typically the kitchen or bathroom.

Additionally, one of the major disadvantages of underfloor heating is that it can be expensive to run, therefore, by only using it in certain rooms, you can help to limit your heating costs.