I have a house build in the 1920's. I recently had a HVAC system installed, and i have to insulate my actic (Unfinished). The three bedrooms and one bath on the floor below have a center ceiling electric light, wired with the original knob and tube electric. What would be the best form of insulation around this area of the attic?
None. K&T was designed to have an air space around the wires. If you fill that space up with insulation--any kind of insulation--you're defeating that part of the design and causing a major fire hazard. Keshlam is right--the best solutions is to bite the bullet and have the house re-wired. Then you can install whatever kind of insulation you'd like, including in the walls, which right now are most likely empty and uninsulated--another consequence of K&T wiring.