Practical Home Energy Saving
Updated: 13-Aug-2014
Central Heating Radiator

Radiator Efficiency

Central Heating Radiator eith Thermostatic ValveGeneral Information

To work properly radiators have to be set up correctly and the heat radiated efficiently in the right directions. This means the temperature drop across the radiator needs to be correct (12C or 20F) - see central heating set up for more information. There must be no air in the radiator and the air flow around the radiator must be unrestricted - this means keeping furniture as far away as is sensible. Painting radiators is not a good idea since every layer of paint acts like an insulation reducing it's efficiency, the proper solution to rusting radiators is to remove them, strip all the paint off and start again with a proper radiator paint which is a big job and not for the faint hearted. Make sure thermostatic valves are set properly. Another way to stop radiators working properly is to hang towels or clothes over them or in front of them. Some radiator have radiation fins on the rear of them to improve air flow and heat transfer, these can get clogged up with dust, cobwebs and other debris which reduces it is well worth hoovering behind radiators (can be difficult due to limited space) once a month.

It is also important to maintain efficiency that the central heating system is free of debris and corrosion products which build up over time if the system does not contain an inhibitor which is effective.


Radiator Covers

Sometimes radiators are fitted with decorative enclosures which look nice but they do reduce the radiator efficiency quite a bit. For this reason covers/enclosures are not recommended. Where these covers are fitted the thermostatic valve should be outside the cover to ensure adequate air flow and the correct operating temperature range of the control.

Radiators On Outside Walls

Radiators mounted on outside walls can lose a lot of the heat through the wall, especially if there is no cavity wall insulation. A simple way to reduce this loss is to fit reflective foil and insulation behind the radiator. Rolls of combined foil and insulation can be obtained from most large DIY chains, it is very simple to fit without removing the radiator. A more effective solution is to mount radiators on insulating boards (this moves the radiator further away from the wall) with a reflective foil surface. Placing a small shelf above the radiator also helps since it means the heat tends to be forced more into the room rather than just rising up the wall - leave a gap of around 25mm to 50mm between the radiator and the shelf to allow the heat to get out. It is quite likely that the balance of the radiator will be affected by additional insulation and adjustment of the radiator flow control valve may be needed - for more information see central heating set up. Where radiators are situated beneath windows make sure that curtains are not hanging over them. If curtains hang above radiators then unless the curtain makes a good seal with the window sill otherwise heat will be lost behind the curtains, fitting a shelf above the radiator can solve this. It is also important to make sure the airflow beneath radiators is not blocked so make sure there is nothing underneath radiators. Radiator efficiency will also be affected by any draughts through cracks around windows so it is well worth checking all holes and cracks are sealed to prevent draughts.

An Alternative Method Of Insulating Radiators On Outside Walls

Radiator insulating board without the insulationWhere there is space an alternative is to mount the reflective foil and insulation on a board similar to the pictures here. The board is 6mm MDF with 12mm wide strip board round the edges to protect the insulation from damage. Picture 1 shows the board made up before the insulation and foil has been glued to it which can be seen in the second picture. The hooks cut into the board on either side fit over the radiator mounting brackets.

Radiator insulating board with the insulationThis method works fine provided there is enough space at the top of the radiator to slide it into place, apart from looking neat, the big advantage is it can be easily removed for cleaning or decorating. Obviously it only insulates the central part of the radiator from the wall but even that makes a big difference.

Measurements were carried out before and after fitting on a number of radiators with thermostatic radiator valves fully open, the outside temperature was -4 degrees C. Typical results were that the wall temperature behind the radiator reduced by around 20 degrees C and the temperature drop across the radiator reduced by 2 degrees C for a large radiator. Reducing the drop across the radiator meant the flow valve could be turned down slightly to increase the drop to the recommended 12 degrees C, which in turn reduced energy consumption. Once the thermostatic valves had been reset it was noticeable the rooms achieved temperature more quickly than before. An even more efficient way would be to remove the radiator and mount the board behind the mounting brackets directly to the wall covering the whole width of the radiator.


The build up of corrosion products over time will lead to the system efficiency being reduced and increase the chances of premature failure. To stop this the system need to be filed with an inhibitor that meets BS759. It is vital to top up or replace the inhibitor if any part of the system is drained or there has been a leak. When the inhibitor is ineffective the water in the system will be black (iron oxide or magnetite) and the system may need flushing before new inhibitor is added. A sign that the inhibitor is missing or ineffective is usually that radiators need bleeding regularly, this is caused by the formation of hydrogen and other gasses in the system due to corrosion.

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