How much heat is lost on my BK Princess Insert without using a Block Off Plate in a masonry chimney? The chimney is lined with 6" Stainless Pipe and there is a plate blocking off or sealing off the flue at the top. Right now it is in the 20's here and I thought my living room would be much warmer with the insert in there. During the Shoulder Season it was plenty warm as we had to open the windows a lot from too much heat. Am I loosing heat up the chimney? I do have the surround installed around the chimney opening. Thanks Pete