A facility for assembly of well heaters includes a well of sufficient diameter to receive coiled tubing; a scaffold supporting a coiled tubing injector, wherein the injector is configurable for injection of coiled tubing into the well and configurable for injection of one or more resistive heating cables into coiled tubing in the well; a coiled tubing guide system supported by the injector or the scaffold; and one or more cable guides for guiding the resistive heating cables from respective cable reels into the injector, wherein the cable guides are supported by the scaffold.