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.

There are products that still contain asbestos, but they were typically installed decades ago. Common places where you may still find asbestos-containing materials are in siding, wrapped around ductwork, in older appliances (i.e., stove and gravity furnaces), and in floors. Asbestos was primarily used as an insulator, so anywhere in an older home where you lose heat is where you will most likely find asbestos.

Sampling typically takes 1-3 hours, and depending on the provider, lab results are available within 2-7 days.

While a professional can always help, there are some common plumbing culprits you can check yourself to see if you can find the sewer gas smell. For example, you should check your water traps, sometimes called P-traps and S-traps, which are located under sink, shower, and laundry drains. The wax ring beneath the base of your toilet, which creates a watertight seal with the plumbing, could also have gone bad.