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Hot water systems use a form of boiler (conventional, condensing, solar etc.) to warm up water which is then pumped through layers of tubing underneath the floor of a room.

In the UK the most common sizes are 15-16mm. The type of tubing used includes cross-linked polyethylene (PEX) and polyisobutylene piping. These plastic based pipes have the advantage of being able to turn right angles without the need for elbow joints and it is because of this reason that the rigid copper tubing is not commonly used in underfloor systems.

All types of boilers are suited to hot water systems and they often work more efficiently (and therefore more cheaply as well as eco-friendly) than the same boiler on a conventional radiator based heating system. This is because an underfloor system requires the water to be at a lower temperature to achieve a similar level of heat. Temperatures of as low as 35 degrees Celsius can be used.

The lower temperature required in a hot water underfloor system lends itself perfectly to the eco house principles. When combined with sustainable wooden flooring it creates an insulating effect and heats quicker than when built into more dense concrete.

The lower heat also enables solar heated water to be used, although in solar based systems small (30-40 Watt) pumps will need to be used to prevent air bubbles from forming within the pipes which reduce the system's efficiency. These pumps are only used occasionally and are not required to run all the time so cost is minimal both environmentally and monetary.

Hot water systems have the advantage over electrical power based systems in the summer months. Cold water can be pumped through the system in order to remove heat from a building. However care is needed when considering such systems as if the temperature reaches to low a point moisture will form on the floor causing a safety hazard. The water will also need to chilled before pumping around the system and this will require energy and therefore reduce the ecological contribution a system makes.

The savings an underfloor hot water based heating system can make are considerably. A system using a condenser style boiler can save up to 40%, and even a normal boiler can save 15%. When used with solar heating costs can be reduced even further. Installation costs are higher then a standard radiator based system so consideration is needed however the cost is a one off payment and energy prices are only likely to go up.

Hot water Underfloor heating Whichever system is used in a building, the main advantages remain constant. Underfloor heating is far more efficient than radiator based systems, and allows designers far more freedom when designing the spaces we live and work in.

See introduction to underfloor heating >