Carlisle Furnace is in excellent condition.
The outer stack has a number of evenly spaced gaps in the brickwork. There are blind holes that appear to contain structural support rods. Additionally, the upper portion of the furnace is surrounded by a iron band (tie rod). It is not clear why this additional structural support was required, as the furnace appears to be well constructed. This type of structural support is quite prevalent in Pennsylvania iron furnace sites.
The inner cupola is in excellent shape. It appears to have been partially rebuilt (note the red bricks), but the vast bulk of the cupola is original firebrick. As the inner portion of the furnace is gated, I was unable to determine the condition further up the stack, but the lower portion is a wonderful example of iron furnace construction. There is also some refurbishment work on the inner rear portion of the stack, and around the tuyeres.
This furnace was built in 1762 by J.S. Rigsby & Company.