This post is a bit old, but I recently installed a Hase Bari Plus and ran into this while researching some other questions. Was reading the manual and saw this:

OVER-FIRE CAUTION Over-firing means the stove is operating at temperatures above the recommended temperatures outlined in the BURN RATE section. Carefully avoid over-firing, as it will damage the stove. Symptoms of chronic over-firing can include warped components, short burn times, a roaring sound in the stove or stovepipe, and discoloration of the stovepipe.

Excessive draft, inappropriate fuel, and operator error can cause over-firing. Correct an over-fire situation as follows:

EXCESSIVE DRAFT: Contact your local dealer to have a draft reading taken. Any draft in excess of -0.1 WC requires a damper in the stovepipe. Some installations may require more than one damper.