Abstract: A resistance heating apparatus for rapidly heating a liquid or gas to a desired temperature includes a porous mat of fine electrically-conductive elongated elements selected from the group consisting of metal coated non-metal whiskers and polycrystalline metal whiskers electrically connected at their points of contact by metallization from the gaseous phase or by electron beam welding so as to be electrically conductive. The porous mat is disposed in and substantially fills all of the length of an electrically non-conductive tubular structure having an inlet opening at one end and a discharge opening at the opposite end. The tubular structure may be conical in shape with the inlet end being larger than the outlet end. Heating current may be supplied directly to the mat by electrodes connected thereto or the current may be induced therein from an induction means around the tubular structure.