What material to use to patch a hole near a heater?

Question

The previous owner installed a base-board heater in the bathroom, but did a really poor job. Below the heater, there is a hole in the drywall where the wiring goes into the wall about the size of silver dollar where cold air is blowing into the bathroom. The hole is well concealed (only visible when I get down on my hands and knees), so I'm not worried about it from a cosmetics point of view, I just want to seal it so to stop the draft.

What material(s) should I use that close to a heater?

Answer 1

Use a fire retardant expanding foam:

Be sure to turn off the electricity to the heater first, then simply spray it in the gap, wait for it to expand and dry, then cut it flush with the wall and paint over it.