I posted this question before but got no replies. searched through the forums but didn't find a straight answer. I have a Heatilator ec 42 metal ZC fireplace. I have decided on the OSburn 1801 insert. What, if anything can be removed from the Heatilator? To fit an insert into mine it appears that I will have to remove the smoke shelf and some of refactory lining, placing the insert on the sheet metal. Is this acceptable?