Underfloor heating

[edit] Introduction

Underfloor heating (UFH) is a form of heating in which the floor surface of a space is heated and this heat is then radiated (and convected) throughout the space to create comfortable thermal conditions. It has been used for thousands of years as a form of space heating, most notably by the Romans, whose hypocaust system consisted of a raised floor through which warm air and smoke were drawn to heat the floor before being discharged through flues.

Modern underfloor heating tends to use either electrical resistance elements or fluid-flowing, hydronic systems to heat the floor.

Underfloor heating systems tend to be low-temperature systems, as the heating surface covers a much larger area than conventional radiators which because of their relatively small size have to operate at a high temperature.

Underfloor heating can be installed on new-build projects, or retrofitted into existing spaces. It can be installed as the primary heating system or used to provide additional, localised heating in specific spaces such as bathrooms. It may be used in combination with renewable heat sources, thermal mass and night-time purging.

Systems can be modular or custom designed and installed, and will generally include insulation under the heat source to reduce heat loss.

[edit] Electric underfloor heating

Electric underfloor heating systems can sit beneath stone, tile, wood or even carpeted surfaces. A series of electric wires installed beneath or within the floor finish provide the heating element. There are a number of product types available, including loose-fit wiring, modular systems and heating mats.

The design of the installation will depend on the space size and dimensions, how well insulated it is, the nature of the flooring structure and the type of flooring covering. Generally, on new-build projects, cables or electric heating sheets are fitted beneath the floor finish on a layer of screed and insulation which ensure the floor is level and that the heat travels upwards into the space.

[edit] Hydronic underfloor heating

A fluid flowing hydronic system generally consists of a series of looped pipes connected to a boiler that circulate warm water through the floor. This needs enough space for the installation of piping and insulation and so floor levels may need to be elevated which can be difficult when retrofitting, increasing costs and disruption. For this reason they tend be better suited to new-build projects.

They can be more expensive to install than electrical systems, but may be less expensive to operate.

Because they are low-temperature systems, they can easily incorporate renewable energy sources such as solar thermal panels, ground source heat pumps, air source heat pumps and so on.

Water-based systems can be used to provide cooling as well as heating.

[edit] Planning permission

The installation of underfloor heating in an existing property does not need planning permission. If you are building an extension or a conservatory, then planning permission will be needed, however, the heating system would be part of the overall plans for this construction and would not require separate planning permission.

[edit] U-values

A significant impact on the construction industry relates to energy and the efficiency of the build. The heating is covered under part L of building regulations. This regulation refers to the conservation of fuel and power – and requires a set U-value of floors in the new dwelling. The lower the U-value, the less the heat is lost through the floor. The value when underfloor heating is used is more stringent, with a value no greater than 0.15w/m2K. This means that you will need to ensure there is insulation beneath the flooring to stop seepage of heat into the ground.

Despite more strict standards for the U-value, underfloor heating can help with part L of the building regulations thanks to the efficiency of heat emission. The water heats to a lower temperature, which means that the efficiency of the boiler is improved, as heat is not wasted in the flue gases. Also, as the heating is zonal, it lends itself to precise time and temperature control for each room, and so makes the whole house heating system more efficient.

When planning energy requirements for a community heating system, underfloor heating works particularly well. The low return temperature supports the efficient design of community heating systems. A heat interface unit is usually installed in each home from where the hot water is delivered to the underfloor heating manifolds.

[edit] Choosing screeds

One of the biggest concerns project managers may have is the heat up time and its relation to cost effectivity. A conventional screed is a mix of sand and cement, sometimes with a glass-fibre reinforcement, up to a depth of 60mm to 75mm. This acts as an effective heat sink, but it can take up to three hours to heat up and cool down. As an alternative, there is flow screed. This can be restricted to 40mm and so gives a much shorter warm-up time of about an hour. Whatever system is chosen, it will impact on the insulation, clip rail, pipe and reinforcement used.

Before considering the design of underfloor heating, it is best to consult with a manufacturer early in the design process. They will be able to advise on the construction of the floor – as well as the final finishes proposed. The manufacturer will also be able to guide on the standards that are expected in installation and commissioning.

[edit] Handover

There comes a point when a building or system is handed over to the owners. It is easy to presume that they are a) aware that there is an underfloor heating system and b) that they know how to use the systems – and the potential maintenance issues it might pose.

It is a good idea to presume that they are non-technical. Selecting a system that has intuitive controls is advisable, and there should be clear, easy and non-technical instructions for use.

[edit] Pros

• Underfloor heating can be considered more healthy, separating heating from ventilation, and so reducing draughts and problems associated with dust, pollen and other pollutants.
• It can be more durable, quieter and easier to maintain.
• It creates a more comfortable, even temperature distribution.
• It can be space saving and unobtrusive.
• It can be quieter than conventional radiators or HVAC systems.
• It can be less expensive to run in certain situations.

[edit] Cons

• It can be expensive and disruptive to install.
• It may restrict the selection of floor coverings.
• It may restrict room layout.
• It can be less effective at cooling, and cool surfaces can create condensation issues.
• It can be difficult to repair.
• Depending on the system, it can take longer to heat up and cool down than conventional systems.

[edit] Related articles on Designing Buildings Wiki

• Building services.
• Building services engineer.
• Click and lock flooring.
• Cooling.
• Corrosion in heating and cooling systems.
• Heating.
• Heat pump.
• Laminate flooring.
• Pipework.
• Radiant heating.
• Radiator.
• Radiation.
• Screed.
• Thermal comfort.
• Tiled floors with underfloor heating: A guide to minimising and repairing cracking.
• Types of heating system.
• Underfloor air conditioning at London Grade II listed landmark.

[edit] Resources

• Infographic showing the benefits of underfloor heating