That's a pretty general type of question so here's a pretty general type of answer.
Depends on what you want to do in the room really. If it's just to take the chill off and be left on for a long time then you can opt for an oil filled radiator. These have a long time constant when it comes to storing heat. They don't get that hot but retain the heat for quite a while and so are ideal for keeping an ambient background temperature. They are also thermostatically controlled so you can choose your temperature quite reasonably.
If you want heat rapidly then a fan heater is ideal for warming up the air. However they eat electricity and temperature is impossible - ON/OFF.
A convector heater lies somewhere between the two. You can get thermostatically controlled ones (recommended - by me). These will provide hot air into the room which will circulate by convection. They tend to dry out the air a bit and I find they make the room stuffy unless there's some ventilation.
Finally, how cold does the room get? How quickly will it lose heat? The answer to that will give you a clue as to the form of heating you want and the amount of output required from the heater.
A thermostatically controlled 2-3kW convector should be OK for most rooms. At full blast a 3kW heater will cost about 25p an hour to run, however with the thermostatic control it will come down below half that (depending on the outside temp!!)
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local