# SPECIAL REPORT: Weighing Your Insulation Options

February 2, 2006

Upgrading your furnace insulation can mean the difference between saving energy and pouring profits down the drain.

Natural gas future prices have doubled since May 2005 to reach \$12 per million BTU by December, with no relief from the increasing prices in sight. Now is the time for owners and operators of high-temperature furnaces to reexamine their options with regard to energy efficiency. Aside from the obvious area of burner combustion efficiency, one other key place to look is the wall thermal efficiency in the furnace. Upgrading to a higher-performing insulation can provide energy savings-but how do you know you'll get your money's worth?

## Modeling the Options

In a recent experiment, three different types of insulation were evaluated for their energy saving potential in a typical high-temperature furnace (2300°F):

• 12 in. of dense refractory material
• 12 in. of typical dense refractory material plus 2 in. of a patented foam/ fiber insulation* on the furnace hotface
• 12 in. of patented ceramic fiber modules**
To perform the heat loss evaluation, engineers used 3E Plus(r), a computer program that is available free of charge from the North American Insulation Manufacturer's Association. The model assumed that the furnace was located in a factory with an 80°F ambient temperature and no wind speed, that natural gas costs were \$10 per million Btu (typical in December 2005, although this price will likely increase to \$15 or \$16 in 2006), and that the furnace operates 6500 hours per year (about three quarters of the time) with 75% combustion efficiency. The results are summarized in Table 1.

Clearly, the continued use of standard dense refractory materials will result in a large rate of heat loss from the furnace walls, and this energy use will cost the owner/operator about \$90 per square foot each year. By veneering this dense refractory material with 2 in. of foam/fiber insulation, the owner/operator can reduce that heat loss by more than half, resulting in an annual energy cost of less than \$43 per square foot. Replacing the standard dense refractory material with the ceramic fiber modules provides the greatest efficiency improvement-73%.

## Saving Energy

The estimated energy savings shown in the model are dramatic and can be achieved in a real manufacturing plant. Furthermore, as shown in Table 1, the owner/operator can reduce the furnace skin temperature by almost 200°F, thereby significantly improving worker safety.

To determine the best course of action in your facility, balance the cost to retrofit the furnace interior with a veneer of foam/fiber insulation against the cost to remove the conventional dense refractory material and replace it with ceramic fiber modules. Either option will dramatically reduce energy use. However, the latter will save the greatest amount of energy and can therefore make the greatest improvement.

In today's world of high energy costs, it pays to carefully consider your furnace insulation options.