Any of the various energy modeling programs would give you a starting place. Model the ducts in various places and with different insulation levels. I know you will not forget to seal the ducts.
It is called the Distribution Efficiency Table. Here is a link to a PDF of it:
Hope that helps
10-12" liners are not made. Biggest made I find is 6" Flue temp on gravity is above 800' most 80% gas or lp are in the 350-380'. If a low end replacement is put in goes from quite to very very noisy
For example: if a furnace has an AFUE rating of up to 98%, which means that up to 98 cents of every $1.00 of heating energy expense warms your home.
Before purchasing this appliance, read important information about its estimated annual energy consumption, yearly operating cost, or energy efficiency rating that is available from your retailer.