We recently purchased a home that has a gorgeous fireplace which has been identified as a Napoleon High Country 6000. I noticed that this model does not seem to have an kind of air control. I am coming from a Regency wood stove insert and I can load it up and get a good 8-10 hours of heat from it. With this Napoleon, it has about double the firebox size, but only a damper and with it loaded up I get maybe 4 hours of heat from it. Any suggestions on how to get better burn times with it? Thank you in advance for your time.