We’ve just come through one of the coldest spells in many years. We have a heat circulating fireplace so I use it when we’re anticipating really cold weather.
The firebox is designed so that when it is hot enough a thermostat circuit turns of a fan which moves air from outdoors around the box and into the heating ducts. There is also a vent opening to the room which can draw off heat locally. It works well and my only complaint is the noise of the fan. If I had it to do over I’d locate the fan where it couldn’t be heard as much.
Several years ago my chimney sweep advised putting in a fireback to give extra protection to the back wall of the firebox. He has seen cases where the back wall had burned through and that was more difficult to repair than to prevent. I think it takes users a while to realize a small fire works well in these units and that, in itself, goes a long way to protecting the steel of the firebox.
The design we worked out conforms in shape to the back wall. It stands a inch or more away from the liner and it made from 7 gauge HRS sheet. There are four slots along the bottom which allow the plate to rest on the firebrick floor by straddling the four grate bars. There are triangular fins welded to the plate which creates good standing stability. On each side there set screws made from 9/16” x 3” bolts sharpened to a point so they don’t tend to “walk around” when tightening.
The final touch was to add a few forged flame-like elements for a decorative touch as well as extra thickness in the hottest zone.
For years I’ve wanted to make a set of custom fireplace doors to replace the store-bought ones we’ve used since the house was built. The ones I’ve made for clients are better in several ways and the doors are much easier to remove for glass cleaning. Maybe, I’t get to that this spring or summer.