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Hydronic Heating Systems


Hydronics – is a heating system in which heat is transported using circulating water.

A hydronic heating system is beautiful in its simplicity. Heated water is distributed via plumbing throughout the home.  The sealed system can be used to heat towel rails, concrete floor slabs, wall radiators, swimming pools etc. Wall radiators are the most common and come is a wide range of sizes and styles.

Hydronic Heating heats water at its source via a Hydronic Boiler.  The boilers can be powered by combustion heat from wood, gas or pellet fuel. Electricity can also be used to create a heat source (resistive) however this method is expensive to run.  Heat Pumps can also be used but are limited due to the low temperatures produced and only suitable for concrete slab heating.

Once used the water is returned to be reheated via a reticulation system. This ‘heating’ system is separate to the homes domestic hot water supply. Panel radiators operate as ‘Heat Emitters’ in each room, pushing out natural radiant heat which spreads evenly.  The radiators can be individually adjusted to provide ultimate comfort in each room, living areas can be warmer than bedrooms.  Unlike air forced central heating systems there are no airborne particles, providing a totally dust free and allergen free form of heating making it ideal for medical conditions such as Asthma.

Basic Schematic

Selecting a wall radiator

Radiators are one of the most important elements of central heating installation, and a well-specified radiator is essential to ensure the homeowner does not waste money or energy on overheating their home.

PURMO offers a multitude of radiators, which cater for all tastes and requirements. Our wide range means that you will be able to find just what you need to complement your personality and your interior – not only in terms of heat outputs and controllability – but in shapes, styles and colours that you probably never knew existed.

Link to the Purmo-Hydronic-Heating brochure

Heat loss calculations are essential in order to establish the radiator output and size required in a particular room. The final heat loss figure (given in Watts) can be matched up with a radiator of a similar or higher output.  If this figure is underestimated, the room will not reach the required temperature in the depths of winter, and the house will be under heated.  

When calculating the heating requirement of a room, it is important to consider other factors which can affect the rate of heat loss, for example:

  • Outdoor temperature. The amount of heat lost from a building can depend on its location.  The lower the outdoor air temperature, the higher the heat loss is.
  • Building location and wind conditions. Buildings situated in open space and in windy regions lose heat at a higher rate than identical buildings located in a settlement protected from extreme weather.
  • Age of building. Modern buildings are usually better insulated than old, leaky buildings. They have a low rate of heat transfer and therefore need less heating to maintain a comfortable temperature.
  • Windows and glazing. High quality windows reduced the rate of heat transfer and cut the costs of heating for the homeowner.
  • Position of external walls. Rooms without any external walls will have a lower rate of heat transfer.
  • Indoor temperature. The purposes for which the room is used should be considered – the higher the required temperature is, the larger the radiator should be.
  • Wherever possible, radiators should be installed on the external wall under the window.  This way, the cold air flowing in through the window is heated by the radiator and distributed evenly around the room.  Also, using several small radiators in a large room rather than one bulky radiator will ensure better heat distribution.  The physical size of a radiator is also important, so that the room looks well balanced. 
  • In rooms with high air humidity, such as bathrooms and saunas, panel and decorative radiators should not be used unless adequate ventilation is present.  PURMO radiators come with a variety of different connections to suit the nature of the installation, and can be supplied from the side or from below.  If a radiator is to be installed under a window, the height of the radiator depends on the distance between the windowsill and the floor. The lower edge of the radiator should be placed at least 10 cm above the floor and the upper one at least 10 cm below the sill.