I've been running my Buck pretty hard the last few days (as most of us have with the weather) and I occasionally throw the IR thermometer on the brick around the insert. The whole fireplace heats up and stores and releases lots of heat. You can see the temps registering 2 and 4 courses of brick up from the insert. The inside of the fireplace is getting anywhere from 150 to 220 depending on where I shoot it. I can't help but believe the block off plate is keeping that heat inside the living area and radiating it back into the house rather than up the chimney. That much mass throws a lot of heat and does it for a very long time. Anyone else ever measure this and what kind of results do you get. Here's a picture of the blockoff plate. Got the idea from a thread here called 'Poor mans blockoff plate" or something like that. Thanks to whoever posted that. Not that hard and highly recommend for anyone doing an insert install.