The Furnace

The first step in building the furnace is the layout. The inner circle is critical and must be just large enough for the kettle to slide down into it with the lip resting on the bricks. The masons got the dimensions, drew the layout, and began the first run of bricks.

My furnace, built to accommodate an 80 gallon kettle is 67" wide, 101" front to back. The chimney is 28" x 28" and the kettle rests at 12 runs of brick high and the firebox and exhaust port are 14 runs high.  I would make it one or two runs lower in order to get the kettle closer to the fire if I had it to do over again.

The firebox, as you see, is on the right side of the furnace and is designed for the flames to wrap around the kettle before exiting the chimney on the left side.  Notice the fire bricks on the bottom.  Since concrete will explode at high temperatures the code for our area calls for one layer of fire bricks on the bottom when building a fireplace on concrete.

To create the circle into which the kettle fits, the masons used pieces of angle iron. 

In this way they are able to get a perfect circle strong enough to hold up the kettle and 80 gallons of juice.

Nothing was used to fill the space between the inner and outer walls, but a syrup-making friend, Tommy Clayton, and I found one furnace which had the walls spaced farther apart and the space filled with red clay.  This was probably excellent insulation and kept the outer layer from cracking so badly.

A machine shop build the 21" W X 28" H hinged fire door and it has been a wonderful asset.  The furnace has such a terrific draw that I have to keep it closed tightly during cooking. If the syrup begins to boil over, we throw open the door and it cools down immediately.

The chimney was the last step in construction and soon I had...

... a completed furnace in which an 80 gallon syrup kettle had been set. The cost of materials and the price of professional masons makes a gallon of syrup sell for a bundle.