Knob and tube wiring

Knob and tube was built to be surrounded by air. The U.S. Department of Energy notes that this older wiring was intended by code to have free air movement to cool the wire as it carries current. Its notice adds that laboratory tests show retrofitting thermal insulation around wiring can cause it to overheat, which creates a fire hazard.

Do not cover it with insulation. Many homes with it also have an ungrounded outlet. Compare aluminum wiring. A licensed electrician should evaluate and plan any change. See electrical warning signs.