Indoor & Outdoor Fireplaces, Plus Accessories

Installation of a pellet stove insert?

We’re installing a pellet stove insert in our existing fireplace. The manufacturer, Harman, instructs that a steel plate should be installed with rock wool (mineral wool) inside the chimney. The rock wool is handy for condensation as well as fire retardant purposes, but what’s the purpose of the steel plate?

My guess is that the steel plate is some kind of heat reflector or barrier. It may also be a fire stop if the wool burns through.