The stoves are way past any warranty issues and there are holes all in the back of the hopper to release any extra heat that may build up. But in all reality if the stove it's self is getting up to 600+ degrees than there are other issues to deal with than an extra 40lbs of pellets. But I know where your coming from and I def weighted the options and took a logical approach to building these, I mean i don't want to have something horribly go wrong just so I can store 40 extra lbs of pellets. And the Lancaster is the same stove as the Pepin only a multifuel and they make a extension for it, so i weighted that in as well. I have measured the heat in the center of the pellets with and with out the hopper and the differential is minimal. It works for me might not work for everyone else.