3 links have been added on this idea.
  1. I used to put a heater under my chair so the backs of my knees and calfs rested on it. Very nice till I saw the purple veins this was causing. So yeah, stick them under the desk and don’t use freestanding ones if you are tempted to cosey up to it. Just read this which argues against putting them under the desk.

  2. yeah, these are a good idea as long as they are ventilated. loads better than the free-standing ones you burn your legs on. Which are still being sold for in and outdoors use.