Why Use floor insulation for Underfloor Heating?

Adding underfloor heating to your home’s heating system is an effective way of ensuring that your living space is heated uniformly. However, for the underfloor heating system to reach its maximum energy efficiency, it’s important to install the right amount of floor insulation. In this article, I’ll show some of the benefits you’ll get from using floor insulation for underfloor heating. 

Let’s get into it! 

Importance of using floor insulation for underfloor heating  

Underfloor heating insulation is installed underneath the flooring to increase the underfloor heating process and maintain optimum heat levels. 

Ideally, installing floor insulation below the UFH pipe helps to prevent the heat from going downwards to the subfloor. As a result, the heat is pushed upwards onto the floor surface and into the room, thus allowing the heating system to work efficiently at lower floor temperatures. In addition, this results in an effective, economic underfloor heating system. 

When creating an underfloor heating design, it’s important to consider the fabric and insulation level of the building since it affects the system’s performance. It’s highly recommended that you conduct a heat loss calculation if you’re planning to buy an electric UFH system. This will help you to determine if your house is well-insulated and how big the heat loss is.

 If the building is well insulated, the underfloor heating system can be designed to the lowest temperatures. This will help it retain the produced warmth inside the room, thus saving you both money and energy usage. In addition, the insulation enhances the heat produced by the underfloor heating system and distributes it uniformly across the room. 

Reduced thermal mass 

In underfloor heating, thermal mass refers to the size (volume) of the floor surface heated by electric floor heating mats/ cable. When you install an underfloor heating mat/ cable over a concrete slab without insulation, the slab becomes part of its overall thermal mass and absorbs the heat produced by the electric UFH system. However, with insulation, only the finished floor becomes the thermal mass since a thermal barrier is created between the UFH system and the concrete slab. 

How thermal mass affects the heating system’s efficiency & heating costs 

A large thermal mass requires more energy to get to a pre-set temperature, leading to higher energy costs. However, with proper insulation in place, the system operates at high efficiency, transferring almost all the heat to the flooring surface. 

In addition, the size of the thermal mass determines how long the UFH system will take to heat the flooring surface. For instance, a large thermal mass takes longer to heat to the desired temperature. On the contrary, reducing the thermal mass means that only a portion of the flooring needs heat. Therefore, the amount of time needed to effectively heat the floor will be significantly reduced. 

How much floor insulation is needed for underfloor heating? 

To enjoy the above benefits, it’s important to consider the location and depth of the floor insulation. First, you should ensure that the insulation is above the thick subfloor layers to prevent the UFH system from heating the subfloor surfaces. Also, this will minimize the time taken by the heat to get to the room above. With that in mind, make sure you install the floor insulation at the correct depth when laying single-zone or multi-zone UFH systems in your home. 

In general, underfloor heating systems require a U-value of about 0.13 – 0.25 to meet the set building regulations, depending on the type of construction. To achieve a U-Value performance of 0.13 with typical rigid foam insulation, the minimum insulation thickness for underfloor heating should be at least 125 mm. Unfortunately, this can increase the overall thickness of the build-up, thus affecting the door thresholds and floor levels. This makes it necessary to consider the type of flooring you’re installing in your home for better heat output.

Best Type of flooring for underfloor heating insulation 

Both types of underfloor heating systems (wet & electric) are suitable for use in almost all kinds of flooring. However, some types are better than others in terms of heat output. 

Wooden floors work well with underfloor heating insulation, thanks to their ability to stay stable under temperature fluctuations. For optimal performance, this kind of flooring should have a thickness of less than 22 mm, while its width-to-thickness ratio shouldn’t exceed 4;1. Moreover, the moisture content of the flooring should be between 6% and 8%, and the floor temperature shouldn’t exceed 28 deg C. 

Other floor materials that work well with underfloor heating insulation include; stone, ceramic tiles, and concrete. With proper insulation, these types of flooring provide a uniform background heater with hydronic underfloor heating. 

Different types of Floor insulation for Underfloor Heating 

There are various types of floor insulation that are compatible with underfloor heating systems. However, board insulation is the most popular and common type of installation and it’s available in various forms. These include; 

• Extruded Polystyrene (XPS)

Typically, XPS has a better insulation performance and is more durable than EPS. It’s manufactured through an extrusion process. This process involves melting polystyrene polymer and other ingredients. The formed liquid is then continuously extruded through a dye and expands as it cools. More notably, this forms closed rigid foam insulation and usually features a colored dye like red or yellow. The only downside of XPS is that it involves a more complex manufacturing process, making it more costly than EPS. 

• Expanded Polystyrene Insulation (EPS)

EPS is a popular and cost-effective underfloor heating insulation. As the name suggests, this insulation is made by expanding a polystyrene polymer and features a white plastic foam appearance. A mold is used to hold small foam beads that are then heated or steamed, causing the beads to expand and fuse. This process results in closed cell insulation. 

• Rigid Polyurethane (PUR) & Polyisocyanurate (PIR) boards 

Rigid PIR and PUR boards are mostly used in ground floor applications, especially in new-build screed flooring. These boards are highly effective, lightweight, and compatible with most materials. In addition, they have a high strength-to-weight ratio, and excellent thermal conductivity and are available in various options to choose from. 

Other types of Insulation types 

On the downside, board insulation poses some challenges in certain situations because of flexibility and size. Luckily, there are other types of floor insulation for underfloor heating to choose from like; 

• Foil Insulation 

Foil insulation is commonly used when height restriction is a problem. Various multi-foil insulations range from 5 – 10mm and deliver excellent performance, thanks to the minimal height build-up. In addition, they have a series of layers of plastic and foil, giving them an incredibly high insulation value. According to some manufacturers, the insulation value of foil insulation is almost equivalent to that of 40mm EPS boards, while being a fraction of the size. For that, they’re suitable for refurbishment projects where the floor build-up height should be kept to a minimum. 

• Mineral wool 

Also known as mineral fiber, mineral wool is commonly used to insulate joist voids, thanks to its flexibility. Moreover, this type of insulation is created by drawing or spinning synthetic or molten materials. This results in a porous material that traps air, making it an excellent thermal insulator. Even better, this form of insulation is incombustible and does propagate or fuel flames.

• Cork  

Cork is another popular option of insulation for UFH systems for several reasons. First, it’s a natural material and doesn’t emit toxic vapors when heated such that it’s even approved by the Tile Council of America (TCA). Plus, it has relatively low expansion and moisture absorption ratios, yet it’s highly affordable. 

In terms of insulation, a ¼” thick cork provides the same R-value as a ¾” thick plywood. Most cork insulation for electric underfloor heating is available in various thicknesses ranging from ⅛” – ⅜”, but ¼” is the most popular size option. In addition, you can find cork floor insulation in tiles or rolls. 

• Polystyrene 

Polystyrene panels are some of the best types of floor insulation for electric UFH systems. They have an incredible R-value of about 5.0 per for 1” thick panels. On top of that, these panels have high water resistance and prevent the growth of mold & mildew. Best of all, the insulation forms a flat finished surface, making it ideal for the installation of stone or floor tiles. The only drawback with this material is that it loses its thermal resistance capabilities over time. 

Conclusion 

After choosing the best floor insulation for underfloor heating, the next step will be to install it in place, followed by a UFH mat or cable installation. Luckily, most floor insulation is compatible with almost all underfloor heating systems since most options have an adhesive backing. This eliminates the need for using tape or glue, especially if you’re using one of the best electric underfloor heating mat kits.