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How to Choose an Immersion Heater

Immersion heaters are the quickest and most efficient way to heat water, oil, coolant, and chemical solutions through direct contact. To choose an immersion heater that will work with your liquid, there are a few things to consider.


Determining the Watts You Need for an Immersion Heater

This chart shows the minimum watts needed to heat a container of room-temperature liquid with a six-hour warm-up time. Thick liquids, low initial temperatures, and shallow, uninsulated containers increase warm-up time and watt requirements. The watt requirements shown for chemical solutions were calculated for solutions with up to a 6% chemical concentration.


Minimum Watts Required
Heat to 100°F Heat to 130°F Heat to 150°F Heat to 170°F Heat to 190°F
Gallons Water Oil & Coolant Chemical Solutions Water Oil & Coolant Chemical Solutions Water Oil & Coolant Chemical Solutions Water Oil & Coolant Chemical Solutions Water Oil & Coolant Chemical Solutions
5 60 20 50 130 50 100 170 70 130 220 90 170 260 110 200
10 130 50 100 260 110 200 350 150 270 440 190 320 530 220 400
15 200 80 150 400 170 300 530 220 400 670 290 500 800 340 600
25 330 140 250 670 290 500 890 380 670 1,100 480 840 1,300 580 1,000
50 670 290 500 1,300 580 1,000 1,800 780 1,300 2,200 970 1,700 2,700 1,200 2,000
100 1,300 580 1,000 2,700 1,200 2,000 3,600 1,600 2,700 4,500 1,900 3,400 5,400 2,300 4,000
200 2,700 1,200 2,000 5,400 2,300 4,000 7,200 3,100 5,400 9,000 3,900 6,700 10,800 4,700 8,100
300 4,000 1,700 3,000 8,000 3,500 6,100 10,800 4,700 8,100 13,400 5,800 10,100 16,100 7,000 12,100
400 5,400 2,300 4,000 10,800 4,700 8,100 14,300 6,200 10,800 17,900 7,800 13,400 21,500 9,300 16,100
500 6,700 2,900 5,000 13,400 5,800 10,100 17,900 7,800 13,400 22,400 9,700 16,800 26,900 11,600 20,200

Choosing the Right Watt Density for an Immersion Heater

Watt density is the amount of power (in watts) an immersion heater produces per square inch of its surface area. One of the main causes of immersion heater failure is using a watt density that’s too high, so it’s critical to choose the lowest watt density possible. As long as you’re using enough watts to heat your liquid, the watt density can never be too low.

Small immersion heater
When a small immersion heater
distributes power, the heat energy is
closely concentrated over a small surface area.
Large immersion heater
But when a larger immersion heater distributes the same amount of power, the heat energy spreads out over a larger surface area. For the lowest watt density, always choose the largest heater that fits in your container.

Maximum Recommended Watt Density
Liquid Maximum Watt Density
(Watts/Sq. In)
Clean Water 100
Oil and Coolant 25
Chemical Solution with
up to 6% Concentration		 35

Exceeding the maximum recommend watt density can damage the heating element and shorten the immersion heater’s service life. With water, a high watt density causes rapid scale and mineral deposit buildup on the heating element. With oil and coolant, it creates hot spots and overheats the heating element until it burns out. And with chemical solutions, it speeds up corrosion and quickly degrades the heating element.


Even at a low watt density, sludge, scale, and mineral deposits will still build up on the heating element. To remove buildup and extend the immersion heater’s service life, frequently clean the heating element with a scraper or a wire brush.

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