Time for the UK to Rediscover Underfloor Heating

The History

In the 1960s, most underfloor heating (UFH) Systems were electric systems in which electric resistance cable was incorporated into thick concrete floors. The idea was to treat the floor as a heat sink for surplus electricity which was available during the night - to make the floor a massive storage heater.

Such systems were poorly controlled, the floors were allowed to overheat and this made your feet uncomfortable, the rooms were too hot at the beginning of the day, the floors themselves were uninsulated and this wasted energy which made the systems expensive to run. And, due to the quality of the technology which was available at the time, these systems were often unreliable.

It is unfortunate that many influential people in the UK building today, while readily accepting that since then there have been improvements in almost every other facet of their lives - in computing, in motor cars, in the way we travel around the world - still believe that UFH remains the way it was in the 1960s and that has not changed.

The fact is, it has changed considerably and underfloor heating is the fastest growing part of the heating industry. Sales have doubled in the past four years and are set to double again in the next four years. It is a subject you need to know more about.

Today's UFH

The majority of modern UFH systems are warm water systems. Most systems integrate high tech plastic pipe either within or just below the floor - Warm water at temperature of 45-65°C is circulated through this pipe and this warms the floor to a temperature of 25-28° C, which is about the same as the palm of you hand. Whereas radiators transfer heat from a small surface area which is very hot by comparison with the room, UFH transfers heat from a very large surface which is only slightly warmer than the room.

There are variants of UFH to suit every form of concrete of timber floor construction. Modern systems have effective controls, they are economical to run, very reliable and virtually maintenance free. Most importantly, they provide the most comfortable all-round warmth of any heating system. In concrete floors, it is typical to set out the heating pipe or cable on top of insulation before the screed covers it over and completes the floor construction. In timber floor constructions, there are several different ways of incorporating UFH. There are methods which suit the full range of joisted and battened floors, fully floating floors and even acoustic floors.

How does UFH Transmits its Heat?

A radiator system transfers energy into the room largely by convection. This convection results in the floor being the coolest part of the room and leaves a mass of warm air at ceiling level. It also picks up fine dust from the floor and distributes it into the air and over the furnishings. An UFH system heats mostly by radiation. This is the most natural and comfortable form of heating, just like the sun. Radiant energy emitted by the floor is partly reflected by each surface and partly absorbed. Where it is absorbed, that surface becomes a secondary emitter. After a while, all surface becomes a secondary emitter. After a while, all surfaces and the furnishings themselves radiate energy and the room becomes evenly and uniformly warmed. The energy reaches into every corner of the room - no cold spots, no hot ceilings and no cold feet!

With radiators, the air in the room heats the room and its furnishings. With UFH, it's the other way round - the room and its furnishings heat the air.

Heat from radiators

Heat from underfloor heating

Application

UFH is applicable to every type of building, whether it is new-build construction or refurbishment. Its much greater comfort is appreciated in the home and the office. It frees wall space in shops, pubs an clubs. Its safety and cleanliness is beneficial in schools and hospitals. Its obtrusiveness is useful in student accommodation and hostels.

Time for attitudes to change

In other countries, where users are more demanding about quality of heating systems installed in buildings, and where heating running costs are great concern, UFH is very widely used. In the UK, however, UFH currently represents just 2.5% of heating market. The primary reason for this disparity is because the choice of heating system for a building has, in the past, invariably been made by builders and developers rather than by users, and their decision has focused entirely on finding the cheapest system to install, without regard to the subsequent running costs of users' comfort.

Although they have to live with, and pay the running costs of, whatever heating system is installed, users have hitherto had little influence of the choice of heating system which they are being offered. This situation is changing, and changing rapidly.

House buyers are becoming increasingly aware of UFH and the benefits it offers in terms of greater comfort and convenience, and lower running costs. There has been a sea-change in interest in the residential sector. A recent conference in London, held to examine the creation of the ideal productive workplace, took delegates to two state-of-the-art buildings, both of which have UFH as the form of heating.

The time has now arrived for all professionals, who are involved with any aspect of specifying, designing, building or running buildings, to take a fresh look at UFH. There is a need for greater education in this area and this re-education is underway.

Modern electric underfloor heating

Modern electric systems use high tech heating cable in place of warm water pipe. Better systems monitor and control offer fast-response and lower running cost than before. Room, floor and outside temperature are often monitored for maximum comfort and energy savings.

Energy Savings

With UFH, there are four primary areas of energy saving by comparison with radiators.

1. Losses through the window are much lower
2. Losses through the ceiling are lower because the temperature at ceiling level is lower
3. Losses through the wall and through air changes are lower because room air temperatures are lower with UFH, for the same comfort level
4. Transmission losses between heat source and room are lower because the water temperatures used with UFH are much lower.

Other Advantages of Underfloor Heating

Energy savings apart, UFH provides other advantages.

1. It is the most comfortable form of heating
2. It is unobtrusive, safe and quiet
3. It is virtually maintenance free
4. It complements other energy-saving developments in heating, such as condensing boilers, solar panels, heat pumps and combined heat and power systems
5. It's simple to install
6. When used in conjunction with displacement ventilation, UFH makes a superb alternative to conventional air conditioning.
7. Crucially, because it uses water at much lower temperatures than radiators, UFH keeps many more options open for the future with regard to water heating. Installing radiators can lock you in to having to burn fossil fuels and this is likely to become very expensive in the future.