I am installing a Pacific Energy Super Insert. The manual specifies 21" clearance with a heat shield between the top of the insert and any combustible above, and 30" without the heat shield. I have a wooden mantel hanging from the brick above, as seen in the photo. When the installer came out to measure, he told me that without the heat shield, I would need to raise the mantel up another 8 inches; with the heat shield I could leave it where it is. After he left, I did some measurements and discovered that this could only be correct if he was measuring from the insert top to the underside of the shelf. Isn't this incorrect? In order to have the proper clearance, wouldn't I need to measure from the top of the insert to the bottom of the three large wooden supports that are part of the mantel since they too are combustible? If this is the case, then the mantel will have to be placed ridiculously high, so I will remove it altogether and forgo installing the heat shield.