Do fireplace doors really help heat a home more efficiently?

Fireplace heat from the flame goes up the chimney! It is the radiant heat you are looking for, and that will happen, fireplace doors or not! The doors will prevent the heat you am from flying up the chimney also...so yes, they do increase the efficiency of a fireplace. You will be able to damp down the fire by limiting the amount of air available also, but be careful here, for a damped down wood burner is subject to depositing creosote in the flu...and that stuff is flammable. Be particularly careful about pine, for it's ability to make creosote is more than other woods. The problems I have with gl doors is the soot buildup on them...keeping them clean is a full time job!