A long ... long ... long ... long .. and-even-longer ... time ago.
As long as (here's that *if*) by "closet" you are referring to a "clothes closet" or another type of closet with "readily ignitable" material in it.
*Most* closets would: a) not be large enough, and, b) be used for storage of materials and items which would make the panel not suitable or allowable to be installed in the closet.