I appreciate all your responses. We are pretty sure the house no longer has knob and tube. The electric on the 1st floor is older than the 2nd floor which was done we estimate in the 60's when the basement was remodeled into a livable part of the house. There are some grounded plugs and a GFCI in the bathroom. Some switches and plugs don't work and there are many 2 prong outlets or 3 prong not gounded. We are not exposing the walls downstairs like we are with the 1st floor. Do you think it adequate to put GFCI on the ungrounded 3 prong plugs with label "not grounded"? Is there a way to tap into the outlets that are gounded without major damage to the walls?
