I am a total noob and am getting my first insert installed on 1/11. I spoke with the installers today and asked about a block off plate because of what I have read here. The installers said they block off at the top of the chimney with a piece of stainless steal that they fit around the pipe. Obviusly this is not like the set up I have read about on this web site. Will this help keep the heat in/cold out at all? Should I also have a block off plate like described here installed? Any help or suggestions would be appreciated. The chimney is about 25 ft high on the southern end of the house.