Antony White, technical director at Warmup looks at the reasons insulation is such a key feature when designing a home and how it affects the installation of underfloor heating.
If you are including underfloor heating within a new build property or extension, you should be aware that Building Regulations Part L require the property to be well insulated in order to create an energy efficient dwelling.
You should also be aware that significantly refurbished thermal elements (ceilings, walls, windows or floors), will also need to be insulated in line with the current regulations wherever practicable. This requirement is often overlooked, and consequently the insulation required is often omitted. If you are unsure if this applies to your project, we recommend that you speak to your Local Authority Building Control for further information.
There is more than one way of improving the energy efficiency of a dwelling with insulation. The obvious effect of including either more or higher performance insulation, is that the heat escapes the dwelling at a slower rate in the winter. It will also enter it slower during the summer, a time where the efficiency of Low Emissivity Windows is more apparent than in the winter.
However, the location of the insulation within the ceilings, walls and floors is equally important. If there is no insulation within the floor, or if the insulation is located beneath what may be a 100mm concrete slab, a 65mm screed, or even both, when the underfloor heating activates it will take longer to reach its desired temperature. Think of it as boiling a full kettle of water verses boiling just enough water for one cup.
As the floor takes longer to reach its design temperature, it takes longer to heat up the room, and when the heating turns off, the stored heat within the floor will cause the room to cool down slower too. This can be beneficial for those wishing to use the floor as a thermal store, in combination with an economy energy tariff, but it is wasting energy for the majority of users who would be heating their rooms on a schedule. Energy is wasted because the room is warmer for longer than is required, both before and after the room is in use, so the room is losing more heat than it would if it was cooler at these times.
Results from tests conducted at a leading research centre in Germany have proven that installing insulation in the correct location makes a significant difference. In cases where the insulation required to comply with building regulations is already installed beneath the sub floor, the addition of a thin layer of insulation directly beneath either electric or hydronic underfloor heating, insulating it from the sub floor, will reduce the heat-up time (the period taken for the heated floor to reach the design temperature). A thin layer of insulation separating the underfloor heating system from the mass of the floor can cut the heat-up time from as long as 2.5 hours to as little as 20 minutes. Depending on the heating schedule, this can reduce the running costs of the heating by as much as 50 per cent.
There are underfloor heating systems available for all floor constructions and companies can provide guidance on how to optimise them all for both energy efficiency and comfort. Compared with other forms of heating, i.e. radiators, underfloor heating systems are cost effective solutions that offer improved comfort and reduced energy usage with little or no maintenance.
Choosing the right system to suit the project and the occupant’s lifestyle is vital. There are two main underfloor heating variants to choose from – electric and hydronic. Electric underfloor heating systems work by passing electricity through resistive wiring within the floor which is either supplied as loose wire, adhesive mats or foil mats. The most technically advanced systems use robust multi strand heating cores that are doubleinsulated in an advanced fluoropolymer for a finished cable that is just 1.8mm thick and very tough. As explained above, it is recommended that the system is installed directly over an insulation layer before the floor finish of choice is laid. This can be wood, carpet, stone or vinyl. This approach ensures the benefits of a low mass system are realised.
Hydronic underfloor heating is a particularly popular choice for new floors. Hydronic systems operate by circulating warm water at a regulated temperature through pipes installed within the floor. Many such systems embed the pipes within a layer of screed and these systems can be optimised by using a thin (35-45mm thick) and highly conductive (λ≥2.2W/mK) screed. However in order to achieve the most responsive hydronic system, it is best to choose a system which uses highly conductive aluminium diffuser plates to distribute the heat beneath a low mass floor deck, creating a system that heats up and cools down quickly.
Whatever heating system is installed, whether underfloor heating or radiators, smart heating controls can further optimise the energy usage. Advanced smart controls can calculate what time the heating should be turned on so that the room it is controlling reaches its target temperature at just the right time and when to turn off again, ensuring the room loses as little energy as possible.