The arch is the structure used to support the evaporator and to supply heat. For the hobbyist can be an old stove or an improvised fireplace. The easiest wood-fired each to build consists of four or eight concrete blocks and a smoke stack. Dig a shallow pit underneath where the pan will be and place the blocks in a manner to support the evaporator or sap kettle. A smoke stack aids in drawing the smoke and in heat efficiency. A general rule is that the stack should be twice as tall as the pan is long. Fill your pan with sap and start the fire inder it. Fill your "finishing pan" with sap an start it cooking. Transfer concentrated sap from the sap pan to the finishing pan as needed. Because sap will not burn easily, the fire can be quite hot. Nearly finished syrup WILL burn if not watched. Using this two pot system is much better than using single pot. If a single pot is used, new sap will constantly be added to the concentrated sap. The sap that was added first will constantly be cooked fron the beginning to the end of this process. This extended period of cooking results in a dark syrup that may taste burnt if the cooking requires a very long time. Using two pans allows one to concentrate the sap and then most of the sap is transferred and replaced by unprocessed sap. The finished unit brings the syrup to appropriate density.