Allowing equipment to deteriorate and slowly deviate from its specified performance levels is VERY expensive. You might save a little on maintenance costs in the short run but you will pay through the nose in energy terms. Particular attention should be paid to the following:

Wall Losses: Ensure that existing insulation or refractory lining is doing its job. Discolored paint, blistered sheet metal or other signs may indicate that the lining is breaking down. A systematic survey of exterior skin temperatures should be done at least annually. Finding losses before they become obvious will save a lot of energy and minimize repair costs.

Radiation Losses: In high temperature processes, radiation losses can result in huge energy costs. Furnace doors should not be opened any longer than necessary. If certain openings must be left open for access by material-handling equipment, (conveyors, fork lifts etc) they should be fitted with radiation shields of made of flexible ceramic fiber or textile.

Shutdown Losses: When equipment is shut down and restarted in batch operations, some of the heat required to bring the unit up to operating temperature will be lost and must be replaced. If shutdown is unavoidable due to lack of product, maintenance or less than 3 shifts, fuel consumption should be monitored to compare the effect of a complete shutdown with maintaining a low temperature.

Exhaust or Flue Gas Losses: The single biggest heat loss in furnaces and ovens is exhaust gas. The goal is to keep the volume and temperature of those gases to the minimum consistent with your process.

Controlling the volume of exhaust gases can involve several different parameters, depending on the process. For high temperature furnaces, setting the combustion ratio for no more excess air than necessary, is important. The amount of ambient air drawn into the furnace by stack draft should also be limited, because this air behaves the same as excess air going through the burners, absorbing heat from the furnace and then leaving the stack without doing any useful work.

On processes with exhaust fans, the flow through the exhaust system has to be balanced against the incoming flow of combustion products and makeup air. If the incoming flow doesn’t satisfy the exhaust system, the oven chamber will operate at a negative pressure, pulling ambient air in through any available opening, wasting fuel and creating cold spots at the entry points. The opposite situation is when an exhaust system is unable to remove all the gases entering the oven. This results in high positive chamber pressures forcing hot gases out to heat the surrounding area, instead of the product.

To keeping exhaust gas temperatures in balance, two parameters should be monitored carefully - product loading and heat transfer inside the oven or furnace. Processing too little product increases energy consumption per unit of production. Processing too much product is worse. As hot gases enter the heating chamber, they begin transferring heat to the product. The longer this takes, the more complete and efficient the transfer. In an overloaded furnace or oven, the product can only be heated properly by over-firing the combustion system, either by raising the burners’ firing rate (higher gas flow, shorter residence time, less efficient heat transfer) or by raising the set-point temperature, thus forcing the exhaust gases to leave at higher temperatures.