A cracked fireplace firewall is not terribly uncommon in a metal fireplace insert, AKA the zero-clearance fireplace.
You've seen them - they have the metal floor and surround, with the cement panels in the fireplace. Those panels are made to deflect heat into the room and make for more efficient operation.
However, those cement panels can crack.
Hairline cracking is not rare and often is not a problem.
Severe cracking can be more problematic however, as heat can escape into areas of the assembly it is not intended to. The framing around these fireplaces, all the way to the chimney cap, is usually wood with some form of siding. It is not made for too much heat.
This fireplace was converted from wood burning to gas.
And in this house the gas is Liquid Propane.
While there is nothing wrong with that, they did crack the firewall severely when they drilled the hole for the gas line.
There is something stuck inside to seal the hole, but I don't know what it is.
What is the best course of action? Have a professional look at this to see what should/could be done.
It might be that with a proper sealer all is well.
My recommendation: fireplaces are a critical item in the house, wood burning or gas. They have to be right! If they are not right, they can surely be dangerous. It's always best to be on the safe side and have a professional look at them when they are suspect. And this one is suspect!
Jay Markanich Real Estate Inspections, LLC
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560