To get rid of the air, put a radiator key or small screwdriver (depending on the type of hole) into the radiator’s bleed valve and open it (see my How-to Tip). Don’t do this when the heating is on or the radiators are still hot.
Radiator output is measured in btus (British thermal units) - to work out the btus required to heat a room, use an online btu calculator, although they vary in the questions they ask and the results they give. Lots of factors affect how cold a room is, such as the direction it faces, the number of outside walls and whether the windows are double or single glazed. You’ll want some rooms warmer than others and a btu calculator will take account of this.
If you want to replace the radiators or add more radiators and you’re not replacing the boiler, check with a heating engineer that the boiler has sufficient capacity. When choosing new radiators, go on the btus rather than the size - powerful radiators no longer need to be big.
The position of the radiators can affect how well they work. Radiators are traditionally placed under windows, but be careful not to block the heat with curtains. To bounce heat back into the room, fit radiator foil behind your radiators, although this doesn’t work with column radiators because you can see through them.
Old heating systems often lack adequate controls, such as adjustable radiator valves, so you can’t turn the radiators up or down - they’re either on or off. You also need the right controls for the boiler, to improve its performance and efficiency. Up-to-date controls enable the boiler and radiators to communicate, giving you a much better central heating system.