My partners and I are considering this preheater:
http://aerothermheaters.com/

It's advantages seem to be that, unlike Tannis and other sump heaters, it's
not permanently attached to the airplane, and therefore doesn't require an
STC or W&B recalculation (unless you forget it and leave it attached :-).
Anyone ever use something like this?

--
Bob (Chief Pilot, White Knuckle Airways)