We live in a 65 –yr-old home in Arlington, VA that has wonderful radiator heat. The old oil boiler needs replacing, and we consequently found a 2-ft chimney tile had fallen within the flue, which prompted us to consider switching to a high efficiency natural gas boiler for side venting, thus saving on the repair of the (boiler) chimney flue. Our concern with side venting is exactly how much exhaust is created with a direct venting system? Or, should we bite the bullet and install a standard efficiency gas boiler along with a stainless steel liner for the flue? Since we’ve been quoted a range of $1,500 to $3,000 for the flue liner, should we just simply put that money into a high efficiency system? Has anyone had similar issues with replacing a boiler? By the way, we are getting boiler estimates, but the high efficiency quotes seem sky high to the gas boilers ranging from 82-85 percent efficient. Help, and thanks in advance! By the way, I've learned a lot from all all the previous posts...what a gold mine of information!