How Underfloor Heating Works

Underfloor heating is becoming more and more popular in the UK as an alternative to central heating. Building design today focuses on energy efficiency and the reduction of carbon emissions, and underfloor heating is one of the systems which are being specified more regularly, with this in mind.

Electric radiant heat coils in Underfloor Heating

So how does it actually work? And why is it more efficient? What types of systems are there? And can they be fitted anywhere?

This article will look at the different types of underfloor heating available, how they work, and how they match up to more conventional systems.

The temptation for many people, particularly those embarking on a self-build, is to choose products simply because they appear to be more energy efficient without really researching the products suitability.

It is important to consider all aspects of underfloor heating to ascertain whether it is the right choice for your property or design; it may not always be the best form of heating for every application.

The science behind underfloor heating

The principle of underfloor heating is to supply an even distribution of heat throughout a room or an entire property. Underfloor water pipes or electric cables transmit heat into the flooring, making it one large surface area of heat.

Much of the heat generated by underfloor systems is radiant heat rather than heating by convection.

The heat energy from the floor is either reflected or absorbed by furniture and objects in the room. When it is absorbed, the furnishing effectively becomes another heat source radiating heat into the room.

This creates a mediate temperature throughout the space, from the floor up to the ceiling and to each corner.

On average, a comfortable level of heating is maintained by underfloor heating systems at a 2°c lower temperature than convection heating systems.

How conventional systems work

Unlike underfloor heating, radiators emit heat via convection. As the heat rises it produces higher temperatures at the highest point in the room, and leaves the floor much colder.

They tend to create uneven temperatures at every level in the room, as it is hotter close to the radiator but can feel colder further away.

The excess of heat at high level results in greater heat loss through the roof of a building, making convection heating less efficient and resulting in a higher air temperature to achieve the same level of comfort as an underfloor system.

Electric underfloor heating

Electric underfloor heating consists of a network of cables laid into the flooring, or heated mats that can be laid onto existing flooring and re-covered. The principle involves using electrically resistant cables which produce heat and transfer it to the flooring or concrete.

The cables and mats can be cut to size to fit into any room layout, or to avoid fixed objects. Cables are most commonly used in concrete floors or wooden sub-floors, while mats are highly versatile and can be used for almost any type of flooring or room shape.

Electric systems work on the same basic principles as storage heaters, but rather than heating bricks they heat the entire floor to create a larger heat emitting surface.

Each electrical circuit within a system is connected directly to the electric supply via its own circuit breaker for safety purposes, and the heating elements and cables are insulated and earthed.

Thanks to the larger surface area, and the benefit of radiant heat, the operating temperature of an electric system tends to be around 30-40°c, much lower than a conventional heating system which would operate at about 70°c.

Electric underfloor heating is more viable for refurbishments as installation doesn’t involve digging up floors, where fitting a wet system might; in general they are very quick and inexpensive to install.

It is often popular in properties which do not have a gas supply, and therefore a boiler to heat a wet system.

The systems have a very low profile which also makes them ideal for properties where headroom is a concern as the floor would not need to be raised significantly.

The systems can also be zoned much like any other heating system, whereby each room can have a different temperature setting, and can be heated individually as necessary.

Wet underfloor heating

Water based underfloor heating consists of a series of pipes laid into the concrete or the subfloor. Warm water is pumped around these pipes from a boiler or another heat source such as solar panels.

Wet underfloor heating system

The advantages are the same as electric heating, in that heat is transmitted to the floor and radiated into the building.

The water temperature is considerably lower than the water circulated through a radiator system, and systems can operate at around 50°c.

Wet underfloor heating is not always viable for existing buildings as installation can involve a great deal of upheaval digging up floors, laying pipe work and making alterations to plumbing.

However, it is ideal for new builds as the installation can be done at ‘first fix’ which is much quicker and cheaper than retrofitting.

The pipes are usually fitted into the floor screed, and insulation is added to reduce downward heat loss.

A manifold assembly consisting of various valves will control the flow and temperature of the water to each room, and these valves along with the timer unit can usually be fitted in one discreet location such as a cupboard.

Although wet systems are usually more expensive to install than electric systems, the running costs are generally lower; and a wet system could be up to 30% more efficient than using radiators if the property is suitably insulated.

Summary

The principle behind underfloor heating systems is to provide radiant heat, similar to that produced by the sun, which creates an even and ambient temperature throughout a building.

In doing so it avoids hot and cold spots, excess heat at ceiling level and unnecessary heat loss through the roof.

By running pipes or cables in a matrix underneath the floor, heat is transferred into the floor itself, which becomes a single, large heat emitting surface.

With a much larger area to transmit heat, it is possible to run the systems at much lower temperatures than traditional convection heating systems, and the same level of comfort can be maintained at a lower air temperature.

As property developers look to maximise the energy efficiency of their projects, underfloor heating is becoming an increasingly popular choice as an alternative to radiators.