I'm now hoping to have a local installer put in a Breckwell p23i but he brought up something that was new to me. All the dealers I have talked with never asked or checked if my zero clearance unit was UL listed to accept an insert. I would like to put the Breckwell into my Desa B42LI zero clearance fireplace which shows a UL listing of UL 127-CAN/ULS-S610-M87. This means nothing to me!! Anyone have an idea if my insert is certified to accept a pellet insert or should I not worry.