when we use a room heater to heat the room, heat is transferred from the heater by all three modes: conduction,convection and radiation. can you explain how ?

Dear student, 

Refer to the link to a similar query.
https://www.meritnation.com/ask-answer/question/the-heat-that-we-obtain-from-the-room-heater-is-through-bo/academics/3238833

Once convection current of hot air is set up, it is spread out in the room through radiations.

Hope this clears your doubts.
Regards