I've made several calls to the liner people, the chimney sweep people, and to Heatilator. Here is what it boils down to (I as much figured this is where it was headed). Since it has never been tested no one can tell you its a legal install. Heatilator said they have tested their pipe to 1700 degrees. Logic says to me that if you stuff a 2100 degree liner into a 1700 degree pipe you would at least have the 2100.