Firstly, you will need to find out what kind of wall you will be mounting the radiator. There is a number of internal walls such as masonry plaster, stud wall (either plasterboard or lathe and plaster), plasterboard dry lining. Which type of wall you have, will affect how you fix the radiator brackets but first of all you need to decide upon the position of the radiator and its brackets.
Positioning the radiator
We would suggest placing any radiator central to a feature; a window, alcove or wall - where a door opens back onto a wall, radiators are normally positioned central on the exposed wall with the door open. None of the following are compulsory as there could be better positions to mount the radiator.
The first thing to do is to mark a vertical centre line on the wall to help with the placement of the radiator.
Then, on the back of the radiator, measure the distance between the middle of the supports mountings, divide this distance by 2 to establish the offset required on both sides of the line marked on the wall.
For the vertical position of the radiator, it's normal for the bottom of the radiator to be 4 to 6 inches above the floor - try to use existing radiators as a guide for the placement on the new radiators.
On the back of the radiator, measure up from the bottom to the lower edge of the support bracket. This distance plus the required distance from the floor is the required height from the floor for the lower support on the wall bracket.
Note that most radiator wall brackets have faces of unequal depth, both machined to support the radiator - it does not matter which support face is used but the deeper one may be necessary for the pipes to the radiator to clear any skirting board.
The method of fixing the brackets to the wall depends upon the type of wall construction.
Once the brackets are fixed in place, hang the radiator on the brackets making sure that it is supported by both the upper and lower supports.
After all the above is complete you have successfully mounted the radiator to the wall and it is ready to be installed and piped up.