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Selecting Watt Density

Choosing the correct sheath material and watt density for an application requires an understanding of the relationship between the sheath material, the watt density, and the solution being heated.  The following recommendations are based on information compiled over many years of actual use under normal conditions.

These Recommendations can, however, be upset by unusual factors which can effect both the heater life and the media being heated.  It is to your advantage to check with both the supplier of the solution and the supplier of the heater in question before using.  We cannot guarantee heaters against premature failure due to corrosive action over which we have no control, so please check before having heaters installed.

 Suggested Watt Density Ratings

Note: These watt densities may be adjusted when heat taken-away or flow velocity rates are increased or when operating temperatures are altered. 

Because it is not possible to anticipate all conditions under which this information and our products may be used, Therm Coil Mfg. Co.  cannot be responsible for any electric immersion heater failure that is attributed to corrosion.

Materials Being Heated

Operating Temp.

Max. Watts
Per Square Inch
Acid, Solution or Electro –Plating Tanks 180°F 40 W/in²
Alkali & Oaklite Cleaning Solution 212°F 40W/in²
Asphalt, Tar, Heavy Compounds, etc 200°F
10 W/in²
8 W/in²
7 W/in²
6 W/in²
Bunker C Fuel Oil 160°F 10-16 W/in²
Caustic Soda 2%
45 W/in²
25 W/in²
25 W/in²
Downtherm A
liquid phase
vapor phase


22 W/in²
10 W/in²
Downtherm E 400°F 12 W/in²
Ehtylene Glycol 300°F 30-35 W/in²
Freon 300°F 3 W/in²
Fuel Oil Pre-heating 180°F 9-16 W/in²
Gasoline, Kerosene 300°F 3-5 W/in²
Glue Heat indirectly using water bath
Lead-Stereotype Pot 600°F 35 W/in² on casting
Liquid Ammonia Plating Bath 50°F 25 W/in²
Machine Oil, SAE-30 250°F 18-20 W/in²
Metal Melting Pot 500-900°F 20-27 W/in²
Mineral Oil 200°F
20-26 W/in²
16-20 W/in²
Molasses 100°F 4-5 W/in²
Molten Salt Bath 800°F-950°F 25-30 W/in²
Molten Tin 600°F 20 W/in²
Oil Draw Bath 600°F
20 W/in²
24 W/in²
Paraffin or Wax 150°F 16-25 W/in²
Sodium Cyanide 140°F 40 W/in²
Steel Tubing Cast into Aluminum 500°F-750°F 50 W/in²
Steel Tubing Cast into Iron 750°F-1000°F 55 W/in²
Socony Vacuum Type Transfer Oil 600°F 22 W/in²
Therminols and Heat Transfer Oils 500°F
22 W/in²
22 W/in²
Therminol 66 650°F 22 W/in²
Therminol 77 700°F
22 W/in²
15 W/in²
Vapor Degreasing Solutions
20 W/in²
Vegetable Oil (fry kettle) 440°F 30-50 W/in²
Water (process) 212°F 50-60 W/in²
Water (washroom) 140°F 80-90 W/in²

Corrosion Guide For Immersion Heaters

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