If you operate a large heater for process heating, it may be possible to cut its fuel costs significantly. If the heater has a net thermal efficiency of 80 percent or less, it is wasting a lot of fuel. That is well below the efficiencies of heaters currently available.

By changing to a heater with high thermal efficiency, it may be possible to achieve substantial savings over the course of a year. Obviously, the amount of savings depends on several variables such as the cost of fuel, the number of hours the heater operates, its heat load, etc.

The first thing you need to determine is the net thermal efficiency of the heater you are using. To do that, simply measure the temperature of its exhaust gas. Then use the chart shown here to find its net thermal efficiency.

Now examine the table shown. It is based on a heat load of 8 million Btu/hour and shows fuel usage for a wide range of thermal efficiencies. You can use the hourly usage shown to compare fuel usage of your heater with heaters that have thermal efficiencies from 87 to 92 percent. You can then calculate usage over a year using variables applicable to your operation.

As an example, consider a facility with a heater that provides 8 million Btu/hour for a production process. Assume it has a heater with a thermal efficiency of 80 percent. If that heater operates only 50 percent of the time, it will burn 330,159 gallons of No. 2 fuel over the course of a year. At $3.90 a gallon that amounts to $1, 287,619 a year!

A heater operating at 87 percent thermal efficiency could reduce that fuel usage from 330,159 gallons to 303,594 gallons. That would cut usage by 26,565 gallons and save you $103,604 dollars a year. And remember, this is for a single heater.

If your heater has a lower thermal efficiency than the example cited, the savings would be even greater. And if the size of your heat output is more heat than our example, the savings would be greater yet.

Reducing the amount of fuel you use not only saves you money: it also conserves energy. And that is one of the biggest concerns of our nation at this time.

If you are concerned that your heater may be wasting a lot of fuel, consider having an on-site analysis. Heatec Inc. in Chattanooga, Tennessee, provides free on-site analysis of heaters at industrial facilities. The analysis will show possible savings you could expect by switching to a heater with higher thermal efficiency.

Heatec offers thermal fluid heaters with basic thermal efficiencies of 87 to 89 percent. With optional heat exchangers, efficiencies range up to 92 percent.

Heatec is a leading manufacturer of heaters for a variety of industries and has been in business since 1977. You can contact them by calling toll free (800) 235-5200.

About Net Thermal Efficiency

Net thermal efficiency is defined as a measure of a heater’s usable heat input vs. its heat output. Thus, thermal efficiency indicates how much of the heat released actually ends up as usable output compared to the amount lost through the exhaust stack and walls.

Consider a heater that runs on No. 2 fuel. The net amount of heat released by each gallon burned is usually about 132,200 Btu. This is the fuel’s low heating value (LHV), which is always lower than its high heating value (HHV) because some heat is lost through moisture and this is unavoidable. If its burner consumes 69.5 gallons an hour, the input or the net amount of heat released is 9.2 million Btu/hour. If the usable portion of that heat released is 8 million Btu/hour, the thermal efficiency would be 87 percent.

The formula for calculating the net thermal efficiency of a thermal fluid heater is shown in the accompanying drawing, which also illustrates where the heat goes. But a simpler method of determining thermal efficiency with reasonable accuracy is to measure stack temperature and use the accompanying bar chart that shows efficiencies for various stack temperatures.

Thermal efficiency and combustion efficiency should not be confused with each other. Thermal efficiency is affected by flux rate and many other details of a heater’s design. Combustion efficiency is affected mainly by the burner and combustion air.