Can electric underfloor heating be used as a primary source of heat?

When you ask a group of people if electric underfloor heating can be used as a primary heat source, more often than not you’ll get a mix of responses. Some say it can and others say it can’t. 

If you want the simple answer, yes, electric underfloor heating can be used as a primary source of heat but there are several factors to consider ensuring running costs are kept to a minimum. In this heating blog, we outline some key considerations before you go full steam ahead and install electric underfloor heating for your primary source of heat. We will be covering:

• Heat loss calculations and why they are a must have
• The importance of insulation
• What type of underfloor heating system to consider
• Electric load and control considerations

Why heat loss calculations are vital

For anyone looking to replace their home heating system or simply looking to upgrade their boiler, getting a heat loss calculation is well worth it. Best practice is to get a heat loss calculation because it ensures that the heating system that has been specified effectively and efficiently heats the space based on the heating demand. Lack of a heat loss calculation can often lead to either under or over specified systems being installed which can result in higher running costs and uncomfortable living spaces.

What is heat loss?

Heat loss occurs from hotter spaces to colder spaces and can happen via conduction, convection and radiation. In fact, it can happen using a combination of all three. When it is colder in the winter months, the rate in which heat is lost will increase, because of the higher temperature difference between inside your home and outside. If you have poor insulation, the rate of heat loss will be greater and the more expensive it will be to maintain your comfort levels (more on that later).

How heat loss is calculated

A heat loss calculation works out how quickly heat will escape out of the fabric of your home on the coldest day of the year, no matter if it’s from conduction; convection; or radiation.
The calculation for heat loss is:

q = (U x A) x Δt

Total heat loss = (Coefficient of heat transmission x Area) x difference in temperature between the inside and outside

Example of a heat loss calculation:

What is the heat loss from a building with a 50m² area, a coefficient of 0.8 and a temperature difference of 22^oC?

The answer: 880W 

(0.8 x 50) x 22 = 880W

By running a heat loss calculation, you will know exactly the specification of the electric underfloor heating system that you need without compromising your comfort level.

The importance of insulation for electric underfloor heating

Unfortunately, the UK has some of the worst insulated homes in western Europe. According to Northern Energy, around 35% of heat is lost due to poorly insulated walls and 10% of heat is lost via windows (Department for Business, Energy & Industrial Strategy).

No matter what heating system you are planning to install, hot air rises so another important part of insulating your home is to ensure you have adequate insulation in your loft. According to the Energy Saving Trust, a staggering 25% of heat is lost through the roof in a poorly insulated home.

As well as the above, heat can very easily be lost through the floor, which is why we always specify insulation boards with all electric underfloor heating systems. An uninsulated floor will cause 50% of the heat generated by the underfloor heating system to be lost through the substrate. This will cost you more to run because it will take twice as long for your room to reach your desired temperature. This is particularly important if you are planning to use electric underfloor heating as a primary source of heat as there will be larger heated spaces rather than just smaller bathrooms or kitchens.

What type of electric underfloor heating system is better as a primary source of heat?

If you plan to use electric underfloor heating as a primary heat source and you have a heat loss calculation, you will know what output of system you will need based on the heating demand of the building. The lower the heat loss the lower the output of the underfloor system you will need to maintain a perfect level of comfort. As an electric underfloor heating manufacturer, we can customise heating systems to meet the lower heating demand of a well-insulated home.

In addition to the right output specified, questions we would also ask include:

• Type of project? – new build or retrofit
• Type of subfloor? – concrete, timber, or a mix of both
• Type of floor finish? – tile, stone, wood, carpet or vinyl
• Are there any restrictions on floor build-up?

Type of project

Electric underfloor heating such as pre-spaced mesh mat, heating and decoupling membrane and foil systems are more commonly used in renovations. This is because there is little impact on floor height, and they have a faster installation time (depending on the size of the room). 

However, it’s not solely used in renovation projects, it’s rising in popularity for new build projects too. For new build projects and where there is screed being laid, in-screed electric underfloor heating systems are popular because the heating cable can easily be installed in the screed layer during the building phase of the project. These systems are ideal for rooms that are in almost constant use (usually larger floor areas) as they have longer heat up and cool down times. They provide a great opportunity to take advantage of low-cost energy tariffs like Economy 7 because of the slower heat up and cool down time.

Type of subfloor

The reason why knowing the type of subfloor is important is to ensure the right insulation board is specified. 

• Coated insulation boards: The best fit for timber subfloors. Manufactured from a high-density extruded polystyrene core with a fibreglass reinforced cement coating on both sides which adds rigidity and strength.
• Uncoated insulation boards: A cost-effective thermal insulation for concrete and screed substrates. They are manufactured from a high-density extruded polystyrene and can be installed using a flexible cement-based tile adhesive.
  

Type of floor finish

You will find that there are electric underfloor heating systems that have been specifically designed for different types of floor finish.

• Tile & stone: For tile or stone floor finishes, we would recommend a heating and decoupling system (ThermoSphere Membrane) or a pre-spaced mesh mat system (ThermoSphere Mesh). However, a heating and decoupling system is designed to prevent cracking, lifting and delamination of tiled floors. It acts like a decoupling layer which allows the tiled surface to move independently from the substrate.
• Wood, carpet & vinyl: For wood, carpet or vinyl floor finishes, we would recommend a foil system (ThermoSphere Foil). These systems can be installed without using adhesives and have a specific output such as 140W/m² which is designed to not overheat soft floor finishes. Foil systems provide great thermal conductivity and fast heat up times because the heating cable is wrapped by two layers of foil which is a great thermal conductor.
  

Restrictions on floor build-up

The heating component of electric underfloor heating systems only adds a minimal amount to the total height of the floor. Where floor height is impacted is in the installation process and what component parts are in the floor build-up itself. For example, the thickness of insulation board or adding a decoupling membrane to help protect tile or stone floor finishes will all impact the total height of the floor.

For more detailed information on floor build-ups, read ‘How thick is underfloor heating?’

Electrical load and control

When considering electric underfloor heating as a primary heat source, you need to be mindful of not exceeding the load of the building. For residential buildings this is usually between 60A and 100A. However, there are a couple of things you can consider:

Load management devices

A load management device helps to balance how much electricity is used at any one time. They are designed to reduce the peak demand and improve energy efficiency which will also help to keep energy bills from sky rocketing. 

It is incredibly rare for a home that uses electric heating as its primary heat source to have all power-hungry appliances on at once. What could happen? Without a load management device, the main fuse could blow and will need to be replaced by a qualified electrician.

Zoning your heating

Electric heating works brilliantly if you plan to create heating zones. But what do we mean by ‘zoning’? By creating heating zones, you can control and set different temperatures for different spaces around your home. For example, you will probably want your lounge, where you may spend most of your time, to be a different temperature to that of a guest bedroom which would only be used infrequently. By creating heating zones, you minimise energy usage which will result in saving money off your energy bills.

To summarise

Electric underfloor heating can be used as a primary source of heat for your home. With a heat loss calculation, it is possible to design a system that provides enough warmth to be a primary heat source. However, there are key considerations, especially for larger properties where the electrical load will need some sort of load management, but your electrician or heating engineer should be able to give you the right information you need to be sure.

If you are considering Solar PV or similar for your home too, electric underfloor heating can provide an alternative option for primary heating, especially as it unlocks more design freedom that radiators simply can’t.

Next steps

If you have any questions about using electric underfloor heating as a primary source of heat or if you have questions regarding electric heat generally, please contact one of the ThermoSphere team who will be happy to help.