I want to build a roof deicer. Please don't laugh.

I am looking for a small inline heater that can be exposed to the
elements. It will be installed inline with small copper pipe which
will lie in a roof valley. The pipe will be full circuited with the
lower sections built with flexible tubing; allowing it to snake
thru gutters and drain pipes. I am hoping the circulation will
provide just enough heat to keep the drain open allowing
occasional melt to head for the street.

I suppose this inline heater could be affected with heat tape. The
inline
heater could also be placed under the eves in a protect position.

Ideas?