we have a Englander model 28-3500 and only burns good if door is open. it going into a brick exterior chimney with a teracota flue size 13x9. manual recommends a 6inch flue. thinking of buying a pre insulated liner will this help? only getting 2-3 hours burn time 4-5 hours coaling time. stove flue come 2feet strait out of stove to a 90 2 more feet to a 90 into thimble then strait up chimney 30 feet no cap. any advice would be very helpful.