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.

If you have an older electrical system with fraying wires and other signs of damage, removal  may be the best course of action. When asbestos begins to break down, it's more likely to become airborne, increasing the risk of health issues when it's inhaled.

However, if the system is in good condition and doesn't have visible signs of wear or damage, leaving it alone may be the safest course of action. An asbestos abatement and removal professional can help you determine the best way to proceed.

Many homeowners may never have to test their homes for asbestos. Asbestos particles are only dangerous if they become airborne. If you plan to do construction or notice damage to piping, siding, or drywall, you should hire a specialist to test for asbestos. 

If you plan to remodel your home or have any concerns, you should have your home tested for asbestos just to be safe.

The microscopic asbestos fibers do not cause eye irritation, throat irritation, or lung irritation. If you are inhaling fibers, you will not know it. This lack of immediate symptoms is one of the reasons why asbestos is so dangerous. You cannot know for certain if you are inhaling fibers, which is why you must wear safety gear if you could have any chance of an exposure while working.