Can I Use My Chimney With My New Furnace?

There can be several reasons for furnace-chimney incompatibility. Chimney has to match the size of the flue coming out from the furnace flue pipe. High efficiency furnaces generate  more heat into your home and discharge less heat up the chimney than older style low efficiency furnaces (less-efficient units). So this also means that the existing chimney might be too large for the new furnace. The result could be improper ventilation of flue products, which can cause condensation problems inside the chimney causing bricks or exterior material to get damage.