Hey guys...just following up on this thread I posted from last February. I had the dealer install a block off plate this September and I wanted to wait until we had some frigid temps this season to respond regarding how the BOP has worked. We had a string of pretty cold temps over the last 3 or 4 days and in my area of eastern PA two of those recent nights got down into the mid 20s. All I can say is thanks to everyone on this site that pushed me to get the block off plate (bholler, hogwildz, Begreen, etc.) because it is literally night & day from what I was experiencing last winter without it. Bottom line is the HI300 heats up much, much faster, burns much more efficiently and maintains firebox temperatures much, much longer. I first noticed the difference in shoulder season when I was easily getting cooked out of the family room with just small loads in the firebox. I was getting the downstairs up to 78 without even wanting it that hot and the upstairs around 74...had to build much smaller fires because of this and keep the insert fan off.
During the recent cold front when it got down into the mid 20s overnight I was able to keep the downstairs of my 2000sq ft Center Hall Colonial at 73 to 74 and the upstairs at a comfortable 70 to 71!! Last winter during the frigid temps without the block off plate it was taking me 60 to 90 minutes to get the insert up to cruising temp...and the temps would start dropping pretty quickly soon after I got it up to 500 or so. Also noticed that I can now get very long, efficient overnight burns with plenty of hot coals left over in the early morning to start a roaring fire again in a very short time.
So my conclusion is...if you have an exterior chimney don't let any dealer ever tell you a block off plate is not necessary because they are full of it. I can attest to this fact and feel like I have a whole new insert this year. Even though the HI300 is only rated to heat up to a 2000sq ft house...I can honestly say it is now heating my 2000sq ft house fairly easily
Just want to thank you all for the guidance and give you all an update.