Underfloor Heating – Materials & Insulation

Selection of materials and integration of UFH into the form of a building is a key aspect of underfloor heating (UFH). Materials include floor finishes, concrete screeds and insulation. Floor screeds and finishes are covered by BS 8204 (2005) Parts 1-7, BS 8203, and DIN Standard 18560 Parts 1-7. Insulation products are covered by a range of standards, including ISO/TC 163/SC 3 , by Irish and British Agrement Boards and the insulation of buildings must conform to the European Energy Performance of Buildings Directive (EPBD). Insulation materials alongside the insulation of buildings are new major areas of study.

Flooring materials and their suitability for use with UFH is based on a material’s thermal conductivity, meaning how well heat transfers to the floor surface. Flooring with good conductivity heats up more quickly, has greater heat output and is more efficient to run. UFH systems work for almost any type of floor finish, but specific floor finishes need to be checked out with the supplier in question. Finishes floor temperatures generally should not exceed 27 degrees C but some permit higher temperatures.

Finished solid floors, such as ceramic, porcelain and terracotta tile comes out as the best conductors and are at the top of the list. Polished screed, slate and flagstones are also in this best category. Marble is a bit slower in terms of heat transfer. As regards wood flooring, there are different categories, as those that are denser and thinner work better with UFH. Engineered timber is regarded as the best wood type finish for UFH as solid wood floors can shrink when heated. Most laminate and vinyl finishes also work well with UFH. Carpet is at the bottom of the heat transfer “pile”, as one must consider the properties of the carpet and underlay in terms of slowing down heat transfer. Generally the total tog of all items used in carpeting should not exceed 2.5 tog (thermal resistance property used in the textile industry) – 1.5 tog is preferable.

The primary function of a sub floor, in which the underfloor piping / tubing is normally embedded, is structural and provides a key element of the building form – with the heating pipes being integrated into such a sub floor. UFH works with both concrete / screed and timber joist approaches. With modern energy efficiency demands and UFH, thermal insulation is an integral part of the sub floor composition, enabling the heating system to function properly. The physical integration of UFH and insulation with the sub floor structural components must be planned for on an integrated basis within overall floor design and not as an afterthought.

Insulation

Insulation is a key component of any building. Its specification depends depends on the type of building, the building fabric / elements, the materials used, the ventilation throughput, the energy demand & profile of the building, the heating system and the standards set for energy efficiency for the building. Insulation and its use in a building is a complex matter and unique to the design of a particular building. Buildings have become hugely more energy efficient over the last 20 years and insulation has played a major role in this. Insulation has reduced considerably the overall demand for heating capacity for buildings and heavily impacted the rate at which heat dissipates from floors and other building elements. It significantly affects the design of a UFH system for any building and strengthens the need for formal design of a UFH system in a building.

Warm up Times

Warm up times have historically been a challenge for UFH. In the past, it has taken up to three hours for a floor to warm up a room to provide a comfortable level of heat at that location. One effective response to this is to have a back drop temperature of 16 degrees C during the heating season (along with weather compensation), so that a room can then heat up within an hour or so to the desired level. It is desirable in this country in any case to avoid having a room drop below 12 degrees C, which is the “dew point” – the temperature at which condensation can occur on the walls of the room, thus causing damage and potentially leading to mould and other problems.

More recently, low-profile systems can be laid on top of existing concrete or suspended timber floors – and so is very suitable for retrofitting UFH to an existing house. The standard height for low-profile UFH is 15mm, so maybe 25mm to 40mm in total thickness to include the floor covering. Low-profile UFH tend to have smaller diameter pipes and run at a higher temperature (45 to 55 degrees C). The impact of this is that the floor heats up and cools down more quickly than conventional UFH (approx. 30 minutes). From a physical perspective, this primary areas affected are generally doors and skirting boards. Hopefully there is a minimal impact on room doors – although in a modern airtight house, ventilation through doors must also be accounted for.