A cable-based heater for providing underground heat and a method of assembly of the cable-based heater are provided. The heater includes a length of coiled tubing having a sealed down-hole end and an open-ended cable support adapter attached to the up-hole end of the coiled tubing. One or more conducting cables are contained within the coiled tubing and a wedging tube is placed in the open end of the adapter for supporting the weight of the one or more cables against the interior sidewall of the adapter when the heater is deployed underground. The wedging tube has an inner surface shaped to conform to the outer shape of the one or more cables and an outer sidewall configured for weight bearing frictional contact with the interior sidewall of the cable support adapter.