The original purpose of knob and tube systems (K&T) was strictly for lighting. There had been no other appliance or electrical invention available for purchase at the time of its inception. This wiring is not practical in today's electronic age. The system is only two wires which means it lacks a grounding conductor (the third wire designed to carry fault current to the panel to open breakers in event of a short circuit) and it lacks the capacity to carry the demands of today's modern home. If you have knob and tube in your home there is a high probability that someone has worked on it over the years that wasn't qualified. Adding load or improper connections on a K&T system can turn a benign system into a fire starting menace. Most Insurance Companies choose not to insure a home with a certain percentage of its wiring system as K&T. Covering K&T Systems with insulation causes excessive heat to build up on the wiring and can cause fires quickly. NEVER PLUG A SPACE HEATER INTO A K&T SYSTEM
as resistance elements play havoc on the terminations or connections, that were soldered or just twisted together and taped. K&T systems were great for their original intended purpose but if you have this wiring in your home it would probably be best to have it evaluated sooner than later!