The thermostatically-controlled heat tape that you plug in and comes on automatically? Or a plain electric heater?

That could be dangerous. The heat-tape works well, but you need to seal the leak.

: : I have an electric heater on pipe right now,will putting pipe insulation on pipe stop from freezing in the future?

: No.
: It will only slow the freezing (and thawing) process.
: Deb
: The Pipewench