What is the difference between undertile & inscreed heating?

If you have been considering Underfloor Heating for your home, you may have noticed or heard someone mention about systems for undertile and systems for inscreed. Yes, there are different systems for these applications so to help you understand what the difference is we have put together this article for you.

Hopefully, by the time we have finished explaining these points, you will have a thorough understanding as to which system is going to be best for your application.


What is meant by undertile & inscreed?

Let’s begin by understanding undertile heating, it’s pretty straightforward. This is where your Underfloor Heating is installed directly below the tiles. The Underfloor Heating is laid on top of the substrate, either concrete or timber, and ideally with insulation, and then the tile glue is spread over the heating and tiles laid on top. This means your floor heating is sitting in the 6-8mm of tile glue and doesn’t add to your height build-up.
To understand the inscreed system we need to understand what a screed is. The primary purpose of a screed is to give a smooth and level floor on which to lay your chosen floor finish however it is also used to adjust or slope the levels of a floor, especially in a bathroom.
A screed is typically a mix of sand and cement that is spread out over the floor so another way of understanding it is to consider it as a mini slab that is spread over the substrate before the floor finish is laid. The thickness of the screed will vary based on the application but would typically be a minimum of 20mm and up to 50mm thick.

Typically when it comes to Underfloor Heating and screed, the screed would be used to cover the Underfloor Heating to give a smooth surface for laying the floor finish. Most commonly though, a screed is actually used in a bathroom to help shape the slope of the floor to help the water drain to the floor waste. In most cases where there is a screed the Underfloor Heating would be installed below the screed, hence the two different systems.


What are the different systems?

There are different systems that are designed for either going below the screed or directly below the floor finish. Whilst the systems are essentially the same, it comes down to a difference in the wattage. If you are going below the screed then you want to ensure that you use a higher wattage system, so that it effectively heats through the screed as opposed to a system installed directly below the tiles. We will discuss this further when we get to the pros and cons.

A mat or loose wire system doesn’t necessarily mean one is for screed and the other is for undertile, there are typically both loose wire and mat systems for both applications. A credible Underfloor Heating supplier should have both systems.


What are the pros & cons of going undertile or inscreed?

Pro’s Con’s
  • Fast heat-up time
  • Can be used in renovation applications where the screed is not being removed
  • Less electricity draw per m²
  • Faster cool-down times
  • More difficult for the tilers to tile over (it is still straightforward but slightly more challenging than the screed method)
Pro’s Con’s
  • Heats up the screed, turning the screed into a heat bank so it remains warm for longer
  • Reduced likelihood of the system being damaged while the screed is being laid
  • Easier for the tilers
  • Slower heat-up time
  • Draws more electricity per m²


Why do you use screed wattage in bathrooms?

An inscreed system going below your screed will typically be around 200W/m² to help heat through the thickness of the screed. However, we recommend using 200W/m² in bathrooms regardless of if it is below the screed or the tiles.

The reason for this is, that for Underfloor Heating to be the primary heat source in the room, 75-80% of the floor area must be covered. In a bathroom, this is sometimes difficult to achieve when you take out the areas with floor-mounted fixtures such as toilets, baths or showers etc.

Further to this, bathrooms are typically one of the coldest rooms in the homes and are mostly used early morning and evenings, the coldest time of the day, so again we are trying to put as much heating in, as possible to heat the room effectively for you.

As a result, we prefer to use the 200W/m² system to get an increased amount of heating for the available floor space. For an undertile install in a bathroom, we would use either the Thermonet 200W mats or the Vario loose wire system working on 200W/m².

This doesn’t mean that you can’t use an undertile system below a screed or an undertile system below the tiles in the bathroom. The systems will still work, we are just recommending the 200w/m²  systems as the best option for providing suitable heat up and performance.


Other helpful information

We have included some links below to some other helpful information.

  • Best systems to use – this will help you work out what system is best based on your floor build-up or room type.
  • Heat-up times – this blog will help you with understanding the heat-up times of your Underfloor Heating.



We trust this article has provided you with an understanding of the difference between undertile and inscreed systems and allows you to make a decision on which option is the best for you.

If you are unclear or have any questions regarding your specific application, please don’t hesitate to get in contact and we will be happy to speak with you about your requirements.



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