A Simple Guide to Underfloor Heating

The concept of underfloor heating is not a new one. It is known that smoke channelled through covered trenches was used to heat the stone floors of dwellings as far back as 5000 BC. Nowadays underfloor heating is a popular choice and consequently there is a wide range of sophisticated systems available which are suitable for projects ranging from large new build houses to the simple renovation of a bathroom. But what is underfloor heating and why would you want to install it?

What is under floor heating?

Underfloor heating works by using the floor as a radiator to warm the room from the ground up.  By heating the floor radiant warmth is created which rises slowly, producing an even temperature that tends to provide comfort at levels below that of a traditional radiator heating system.  Due to lower operating temperatures underfloor heating can often be a more efficient way of heating a home.

What are the potential benefits of underfloor heating?

Underfloor heating can have many benefits over traditional radiator heating systems:

  • Removing radiators creates space and makes it easier to position furniture.
  • Rooms are heated evenly, eliminating hot and cold areas.
  • Heat is released from the thermal slab slowly keeping areas warm for longer.
  • Cost savings can be achieved as a lower temperature is required to heat the room.
  • Rising heat keeps the feet and body warmer and head cooler, providing a more comfortable and less stuffy environment.
  • Underfloor heating will help to control moisture and dry floors in wet areas such as bathrooms, wetrooms and kitchens.
  • It is thought that there are also hygiene benefits to underfloor heating.  The even heat produced helps to prevent drafts and reduce dust particles and the reduction in humidity helps to prevent and control dust mites.
  • Warm floors allow for practical surface finishes such as tiles to be used without feeling cold.

Are there any potential disadvantages associated with underfloor heating?

Underfloor heating has few disadvantages but there are some aspects that should be considered.

  • The reaction time of some systems can be quite slow because the thermal slab has to be heated to working temperature.  It should be noted that some electric systems can reach working temperature in a little as 5-10 minutes.  Warm up times are dependent upon the type of system used and the thermal efficiency of the floor slab.
  • Wet underfloor heating systems can be expensive and difficult to retro fit into existing buildings and are better suited to new builds and extensions.
  • Not all electric underfloor heating systems are compatible with wetroom tanking systems.

What types of underfloor heating are available?

Underfloor heating systems are available in either wet (piped hot water) or dry (electric) formats and it is important to select the right system for your project.  So what exactly are wet and dry underfloor heating systems?

Wet underfloor heating systems

Wet underfloor heating systems channel hot water, supplied by your boiler or equivalent heating source, through a grid of plastic water pipes which are laid beneath floor and encased in heat conducting screed.  The hot water heats the floor slab turning it into a radiator.

A wet underfloor heating system can be as much as 25-30% more efficient than a comparable radiator heating system because the water used to heat the thermal slab is cooler and therefore costs less to heat.  However, a wet underfloor heating system can take up to two hours from cold to reach working temperature because the thermal slab must first be heated which can partially offset a proportion the cost savings.

Installing a wet underfloor heating system is not a simple task, floors will have to be excavated and manifolds for controlling the system will be required.  For this reason Wet underfloor heating is best suited to new builds or extensions and professional advice should be taken in regard to both the design and installation of your heating system.  The applications for wet underfloor heating are wide and varied and it is therefore difficult to provide a definitive indication of cost, however, for a rough guide budget for £25 – £30 per square metre for supply and installation.

Dry underfloor heating systems

Dry underfloor heating systems use electricity to radiate heat through a grid of wires which are available in either “loose wire” or “matting” formats.  Typically electric underfloor heating is laid over the top of the existing sub floor, although insulation board must be laid first.  However there are electric underfloor heating systems such as “Thermoduo” by “Thermogroup” which are designed, like piped hot water systems, for use in concrete screeds.

Electric underfloor heating is generally not quite as efficient as a wet system.  However, it is significantly cheaper to buy and install and because it is laid on top of the existing floor warm up times can be significantly less than for an equivalent wet system, as little as 5 – 10 minutes in many instances.  Again, systems and specifications vary and therefore it is difficult to give a definitive indication of price, however, budget for a minimum of £15 per square metre.  The cost of installing an “in screed” electric underfloor heating system should be comparable with a wet piped hot water system.

Electric underfloor heating systems can be purchased as kits containing all of the required components including a time clock and comprehensive instructions.  Installing electric underfloor heating is relatively straight forward and can be undertaken by any competent person.  However, the system should be tested and commissioned by a Part P qualified electrician.

So which is better, wet or electric underfloor heating?

The answer to this question is largely dependent upon your own circumstances, requirements and budget.

Wet underfloor heating systems are generally more efficient and can be cheaper to run than electric systems but they are more difficult, expensive and intrusive to install.  These complex systems are a sensible option if you are considering a large extension or new-build, however, they are generally not well suited to smaller scale renovations.

Electric underfloor heating, although not generally as efficient as a wet system, is significantly cheaper to buy, easy and simple to install and perfect for smaller projects such as renovating bathrooms and kitchens or installing a wetroom.

What types of floor covering are suitable for use with underfloor heating?

There are hot water and electric underfloor heating systems available to suit most types of floor construction and covering.  It is, however, important to consult the manufacturers of the floor covering and heating system to ensure that the two are compatible.

Stone, ceramic and porcelain floors

Stone and tile floors have become increasingly fashionable, not only in traditional spaces such as bathrooms and kitchens but now also lounge’s, hallways and dining rooms.  Both electric and wet underfloor heating systems are suitable for use with tile and stone finishes and will keep floors warm and free of moisture.  However, the warm up response time may vary depending upon the thickness of the floor covering, ultra-thin tiles such as Porcel-Thin can speed this up.  Consideration should also be given to adhesives, grouts and wetroom tanking systems which should be suitable for use with underfloor heating.  Contact the floor and underfloor heating manufacturers for advice.

Wooden floors

Natural and engineered wooden floors can be used in conjunction with wet and electric underfloor heating.  However, you should select a product that is specifically designed to work with underfloor heating and expansion gaps will be required to accommodate movement.  Speak to the flooring retailer or manufacturer for advice on installing the floor and selecting a compatible underfloor heating system.

Vinyl floors

If Vinyl is your floor covering of choice it must be of good quality and designed to work specifically with underfloor heating.  It is likely that the underfloor heating will need to be covered by a thin layer of screed or levelling compound to provide a suitable surface for the vinyl and It is therefore advisable to seek advice from a flooring expert or manufacturer regarding products, compatible underfloor heating systems and installation.

Carpets and wooden floors

Underfloor heating systems such as “Thermocarbon” by Thermogroup, have been specifically developed for use with carpet and floating wooden floors.  Systems of this type feature an ultra-thin carbon fibre heating element that is designed to lay flat under the finished floor.

However, for guidance it is worth noting that carpets and underlays should not have a combined thermal resistance of greater than 2.5 Togs.  A higher rating may impede the heat from radiating effectively.

Natural and engineered wooden floors can be used in conjunction with wet and electric underfloor heating.  However, you should select a product that is specifically designed to work with this type of heating system and expansion gaps will be required to accommodate movement.

It is always advisable to seek professional advice when choosing underfloor heating and floor coverings in order to ensure that they are compatible.

What does underfloor heating cost to run?

Although underfloor heating can have a beneficial effect on the efficiency and running costs of a heating system it should not be overlooked that comfort, health, environment and design are equally important factors for consideration.

That said, potentially significant cost savings can be achieved and that is a compelling incentive for many people.  However, it is very difficult to provide accurate information regarding running costs and potential savings as this is largely dependent upon the type and complexity of the system used and, possibly of most importance, the thermal performance of the floor and building.  Installing electric underfloor heating in bathroom may be a luxury or practical choice rather than a decision lead purely by running costs, whereas a wet underfloor heating system combined with a ground source heat pump could provide significant savings.

For a more accurate indication of running costs it is advisable to obtain energy and performance data from the manufacturer of your chosen system.

Is there anything to consider before installing underfloor heating?

Insulation, for underfloor heating to work efficiently the sub floor or slab must be adequately insulated.  The manufacturer’s installation instructions should provide the insulation requirements.  If the sub floor is not adequately insulated the heating system will take longer to warm up and more energy will be consumed maintaining the temperature.  Insulation is therefore one of the most important underfloor heating considerations.

Both wet and dry underfloor heating systems work in conjunction with thermostats, and are often connected to a time clock, which will need to be wall mounted in a convenient location.  Furthermore, wet underfloor heating systems often require flow control manifolds to be sited in each room.  The position and accessibility of all these controls should be carefully considered, take professional advice even if you intend to install the system yourself.

Ensure that floor coverings, screeds, tile adhesives, grouts and wetroom tanking systems are compatible for use with your chosen underfloor heating system.

This guide is intended only to provide an introduction to the concept underfloor heating.  The choice of underfloor heating products is vast and many are highly sophisticated and it therefore important to consult a tile or flooring expert and seek their recommendations.

Notes about this guide

The purpose of this article is to provide an introduction and overview of underfloor heating systems and it is not intended to be a detailed technical guide. Room H2o is a stockist and retailer of Thermogroup electric underfloor heating products.  Images of electric underfloor heating products accompanying this article have been kindly provided by Thermogroup.

If you would like advice regarding electric underfloor heating please contact us or if you wish to experience the warmth for yourself please do visit our bathroom showrooms which are located in New Malden Surrey and Wareham in Dorset.