Under-floor heating - cost £25-£75/m2 installed, depending on system and materials.

This might be electric or hydronic (‘wet’), and is generally considered to be radiant heating - although it actually uses conduction, convection, and radiation. Underfloor heating can be installed as the primary heat distribution method, or localised for one or two rooms.
The electric heating elements or hydronic piping might be cast within a slab (‘poured floor’), placed on top of the floor and under the covering (‘dry system’), attached directly to a wooden sub floor, or installed from below. With any type, it is vital that the ground floor is well insulated.
Hydronic systems are fed by central heating boilers, and have the added advantage over electric systems that they can also be used for cooling with the right extra components (a heat exchanger). 
Because underfloor heating utilises such a large surface area, and because it heats in part by radiation, it requires much less energy to produce the same thermal effect as conventional radiators.

Some science...

Underfloor heating emits low temperature long wave radiation, which is much better at warming interior surfaces.This in turn suppresses body heat loss resulting in a perception of heating comfort. Thermal comfort is further enhanced through conduction (through your feet on the floor) and through convection, by the surface's influence on air movement.
The same system can be run in reverse in order to provide cooling - underfloor cooling works by absorbing both short wave and long wave radiation resulting in cool interior surfaces. These cool surfaces encourage the loss of body heat resulting in a perception of cooling comfort. 


Hydronic systems require a certain level of skill to install, and the process is longer and costlier, whereas electrical systems pretty much just plug in. Hydronic systems will require at least 100mm of ground floor depth, whereas electric systems require millimetres. However, heating electrically is very expensive.
Another healthy advantage is that because of the type of radiation and temperatures involved, more of one’s home is heated evenly and conditions become less favourable to mould, bacteria, viruses and dust mites. Moisture levels are also better modulated.

Floor coverings

It is important with underfloor heating that the right floor covering is chosen. Ideally the pipes/elements will be cast into a thin concrete screed with tiles laid directly over the top, as this thermal mass will evenly distribute the heat. Make sure that the floor is insulated underneath and around the sides! Timber can be used as a floor finish, although it is more insulative and must be well dried otherwise it is liable to warp and bow. Any synthetic material or carpet is not recommended, because it will block the heat.

Please Note! Your floor will get hotter quicker than most flooring manufacturers are likely to be used to, and it is important that you make it clear what your application is. This won't necessarily change your options, but you will have to buy well-seasoned floorboards otherwise they may twist and bow for example, or have a flexible matting installed underneath your non-fired tiles so that they don't crack.

Because of the materials that are ideally used as floor coverings, such as tile, slate, terrazzo and concrete, underfloor heating can also have a positive effect on indoor air quality. Masonry surfaces such as these typically have very low VOC emissions in comparison to other flooring options.
So long as they have been installed correctly and undamaged, underfloor heating pipes should never require maintenance or repair.
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