Using a simple illustration from the motor car world, one can refer to the boiler as the engine of the central heating system. Subsequently, the radiators are the wheels that transfer the energy to the road, and helping the system deliver its potential. Radiators make a major difference to the effectiveness and performance of a domestic central heating system through their design, location and size. Quite often it is the boiler which is the focus when discussing your domestic heating needs. However, the heat that is generated by the boiler has to pass through the radiators to ensure it actually radiates out into the living space in the most effective way.
It might come as a surprise that those sleek looking stainless steel radiators offered by most UK plumbing and heating merchants date back more than 150 years. The first radiator was registered as a patent in 1855 by Franz Sangalli, a German engineer. In effect, despite considerable visual differences, the main working structure of the radiator is the same as the ones registered initially by Mr. Sangalli. The radiators are effectively a hollow case made of metal, shaped as a flat box and attached to the wall to maximize radiation of heat into the room.
Most UK made radiators are constructed from sheet metal with brazed fins (normally internal within an outer casing). Using a simple pump (normally located in the boiler or by the hot water cylinder), hot water is circulated through the central heating loop. The hot water is pumped into the radiator and gradually loses its heat to the surrounding atmosphere. As the water cools off it drops and eventually is pumped out via the return valve (normally at the bottom of the radiator). The air surrounding the radiator absorbs the heat from the water within the radiator and rises to the top of the room. Consequently, cooler air is drawn towards the radiator to get heated up. This convection effect is a simple physical phenomenon that keeps our homes warm in the winter.
Despite their long life and history, radiators suffer from common problems such as air pockets. These pockets of gas are believed to be a result of two potential sources. One source is tiny bubbles that creep into the central heating loop through microscopic cracks in the piping (for example through holes in the brazing). A good installation and connection of piping should reduce the risk of such cracks.
Another common explanation for these air pockets it that they are the result of a chemical reaction that occurs when copper piping and other metals come in contact with very hot water. Such pockets (normally made of hydrogen) get trapped inside the system and find their way to the top most point of the system. This is why your radiator does not get hot at the top side, as it is filled up with air pockets rather than hot water. As this reduces the efficiency of the radiator and the central heating system as a whole it is recommended to bleed out such air pockets from the system. This can be easily done by using a bleeding key (which can be purchased in all major DIY stores in the UK). The bleeding key fits into a bleeding screw at the top of the radiator that lets the air pockets escape and return the system to good operating mode.
Another common problem affecting radiators is a build up of sludge. Since hot water rubs against iron, copper and other metals within the closed central heating loop, the resulting chemical reaction creates not only gases but also chemical deposits. Such chemical deposits remain in the sealed system and clog the pipes, reducing their performance and effectiveness.
Most boiler manufacturers these days require the heating engineer installing the central heating system to power flush the central heating loop prior to commissioning. This ensures the system is clean from any debris that might have accumulated during the years (for example inner corrosion in older systems). Furthermore, most engineers recommend adding a corrosion inhibitor chemical into the closed loop circulating water, to inhibit production of corrosive gases and deposits.
About the Author:
Tal Potishman is editor of Heating Central, which publishes information about UK boilers, plumbers, underfloor central heating and solar thermal systems. He focuses on helping save money and the planet by consulting on high-efficiency central heating.
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