The Electrical Safety Authority (ESA) in Ontario studied 160 electrically caused fires spanning five years, and identified only three instances where defective knob and tube wiring were involved - and in all cases the homeowner had been playing with the wiring. This, and inspector etc. experience, supports the statement that knob and tube wiring itself is not inherently hazardous. If it has been unsafely modified, or if the insulation is brittle or cracked (sometimes caused by high temperatures) then it can be a different story. If the wiring is in original condition ideally it should be possible to rewire only as necessary to correct deficiencies such as lack of grounds on outlets, overloaded circuits, poor splices, .. and leave the original knob and tube ceiling lighting circuits that are not causing a problem. But even when the wiring is not dangerous, the homeowner may have difficulty if home insurance companies refuse coverage for houses with knob and tube. In BC, an electrical inspection company partnered with BCAA Insurance to offer an electrical inspection service for $250 - if identified deficiencies are fixed house insurance can be obtained with a premium surcharge of 10% for knob and tube wiring. If deficiences have not been remedied or the house not inspected the surcharge is 50%. Assuming that deficiencies are fixed and safety is not an issue, the homeowner could decide to compare the costs of leaving the good wiring in (premium surcharges, inspection charges) versus the costs of replacing it, or they may just wish to replace all the knob and tube in order to eliminate difficulties with insurance.
