Knob and tube wiring is an older type of electrical wiring that's no longer used and generally not considered safe. However, some homes still have it, or may have a knob and tube wiring system that was incorrectly modified or rigged to work with a modern electrical system. Knob and tube wiring may contain asbestos insulation, but the only way to know is to have the material professionally tested.

Professional asbestos testers or environmental consultants are the best people to call to test for asbestos. An asbestos testing company specializes in collecting and analyzing samples and will be the most qualified to do the job for you. An environmental consultant may not specialize in handling asbestos, but should still have the knowledge and know-how to safely collect a sample and send it off for analysis.

No, but it’s common that they do. Gravity furnaces weren’t terribly efficient so wrapping either the ductwork in asbestos, the furnace itself, or both, was something done regularly. This allowed the system to retain more heat. At the time, this greatly enhanced the efficiency of the furnaces but it wasn’t until later that we became aware of just how carcinogenic and dangerous asbestos could be.

Whether or not to buy a home containing asbestos is ultimately a decision for the homebuyer, and there are several things to consider. When in good condition and contained, asbestos is unlikely to present a health risk—it’s when those tiny fibers are loose and airborne that they become a problem. Consider any renovations you plan on doing to the home that could disturb existing asbestos and the cost of removal. If an inspection finds asbestos in a home on the market, you could negotiate with the seller for a lower price, though this isn’t a sure thing.