I am looking into coal boilers. I have a 2500 sq ft house with oil fired forced hot water. I want to install a coal boiler unit and have narrowed it down to a Harman 160 or a New Yorker Coal Boiler 90,000 btu fuel saver. I am limited by a 6" existing metalbestos flue. My question is can the New Yorker Coal Boiler unit do the job of heating the entire house and how long will the burn time be for a 40 lb load of anthracite coal. What is the burn time for the Harman boiler (by the way a 6-9 month backlog of orders)? And does anyone know of a comaparably priced coal boiler alternative in the 2800-3500 dollar range that has a 6" exhaust flue?