Immersion Heater Selection Criteria

Before choosing an immersion heater, you need to ask yourself a few questions, that if answered correctly, will ensure optimal heater performance. We highlighted some important questions and common mistakes below that will help you choose a heater. If you have any questions after reading this, you can get in touch with us by sending us an e-mail, filling out a contact form, or giving us a call at (866) 685-4443.

Do You Need an Immersion Heater for a New Project, or Are You Looking for a Replacement?

Although we have a wide selection of immersion heaters available for purchase on our site, we are more than happy to help you select the right heater for your application. We've found that most of the folks we talk to who are replacing immersion heaters on a regular basis have just used stock immersion heaters that are readily available from many general industrial product distributors. Unfortunately, most of those heaters are designed for heating water or oils. Why is that unfortunate? Because many people aren't aware that immersion heaters are specific to the fluid they are intended to heat. For long service life from your immersion heater, you need to make sure that the heater's sheath material and the power density of the elements are both appropriate for your application. This page will lead you through some of that stuff and more.

Now, if you're not sure about the specs for the immersion heater you need, you can always get in touch with us: we'll help you figure it out. You can give us a call at (866) 685-4443, send an e-mail to info@oemheaters.com, or fill out one of our contact forms. If you choose to contact us electronically, please make sure to give us as much information about the application as possible (e.g., fluid being heated, ambient temperature, tank dimensions, available voltage, etc.). Don't worry about giving us too much information; there's no such thing. Also, if you're replacing an immersion heater that has had a long life, tell us what you're looking for by using our Immersion Heater Configuration Tool, and we'll get you a quote within one business day.

Why Am I Replacing My Immersion Heater So Often?

We don't hear that question from the customers we've helped, but we do hear it from folks who've misapplied heaters that were not designed for the fluids they're heating. Sometimes we hear it from customers who've received immersion heater specification "help" from someone who sells pumps or motors, but doesn't know heaters. Calculating the correct immersion heater (or any type of heater, for that matter) isn't rocket science. The first thing you need to do is figure out how much power—i.e. how many Watts—you need. (We'll have a calculator up on the website soon to help you figure that out.) Getting the right amount of power for the job means that you'll be able to get your fluid up to temperature in the time you require, and that you'll be able to hold the desired temperature. However, applying the right amount of power alone isn't going to ensure long heater life. To get the best immersion heater life possible, you need to do two things:

1. Specify the correct sheath material for the fluid being heated
2. Specify the correct power density (e.g., Watts/in2 or Watts/cm2)

Heater Sheath Material

Determining the right heater sheath material for a given liquid isn't difficult either, it just takes some time. First, if you've done a bit of research on immersion heaters, and you've looked at the sheath selection tables from a few different manufacturers, you have probably found what appears to be contradictory information. For instance, most everyone agrees that, among the lower cost sheath materials, Incoloy gives the longest service life in potable water applications. But, after that, you'll find some manufacturers who rate copper as a 'Best' material while others rate it only as a 'Good' material. Who are you going to believe!? Well, we've gone through all of the selection tables from all of the manufacturers, compiled our own table from that and our own experience to create our own Immersion Heater Sheath Selection Table that lists what we feel are 'Good', 'Better', and 'Best' sheath materials for application in specific fluids. You'll see some asterisks and notes in there—for instance, we don't recommend heating flammable liquids directly, and, although it would be a case of overkill, even though most liquids can be heated with PTFE sheathed heaters, we don't show that since a less expensive alternative will work just fine—but we think you'll find it useful.

What happens if I don't specify the right sheath material?

In a nutshell, your heater is going to have a very short life. Here's a common scenario: some guy calls us up and says, "I need to heat up a few hundred gallons of 5% nitric acid; quote me a heater." We get the details on the application, figure out how much power the customer needs, and call him up and say something like this: "You need a 24kW PTFE sheathed heater, and it's going to set you back a little over $3 grand." There's usually a pause, then the customer on the other end of the phone says, "but I've had this 316 stainless tank and it's been working great, quote me a heater with a 316 stainless sheath."

Why can't the heater elements' sheath material be made of the same material as the vessel the liquid is contained in?

The reason is that applying heat directly to a material acts as a corrosion catalyst. In other words, a 316 stainless steel tank full of 5% nitric acid might last several years before a leak forms, but an immersion heater with a 316 sheath in that same acid concentration might last a few days before it fails.

If I don't go with the appropriate sheath material, what will happen to my immersion heater?

It will fail...perhaps spectacularly. The most common cause of destruction in metal-sheathed immersion heaters is failure due to corrosion. In fact, there are no manufacturers of immersion heaters who will provide a warranty against corrosion—not even us. If the sheath of the heater isn't gobbled up by the chemistry it's heating, over time, even a properly specified immersion heater will develop small pinholes in the sheath. As long as the heater remains turned on, this might not be a problem. However, when the heater turns off and starts to cool, liquid will seep in to the heater element through the pinholes. Then, the next time the heater is turned on, the trapped liquid heats up very quickly—perhaps even vaporizing. Typically, the heated liquid that is trapped in the heater element can't escape quickly enough through the pinholes that let it in, a pressure build-up occurs, and the heater sheath "explodes". Heaters that have died this way look pretty impressive, and it's a good shock to the system when you're around an immersion heater in an open tank that is going through its death throes...not to mention the fact that it creates a safety hazard for anyone in the vicinity.

True Story:

A couple of years ago, a guy called us wanting to heat a few hundred gallons of a 5% nitric acid solution...just like in the example above. We told him that the metal sheathed heaters just wouldn't last, but since two (one for immediate use, one as a spare) of the metal sheathed heaters cost less than 1/3 the price of the PTFE sheathed heater, he decided to go with the metal. We set up a pool here in the office, betting how long it would be before we heard from him again; the winner was the guy with 5 days after delivery. That's right, the 316 stainless steel sheathed immersion heater lasted exactly five days after it went in the tank. The customer asked us to rush a PTFE sheathed heater to him, and the next time we heard from him was when he was expanding his operations and needed another heater (PTFE sheathed, of course) for the new tank.

Why aren't immersion heaters guaranteed against corrosion?

That's because those of us who provide immersion heaters have no way of knowing what liquid the immersion heater is really going to be used in. For instance, various proprietary solutions—for example, solutions for pickling metals—may have as their primary constituent a chemical for which we know the appropriate sheath material. But, there may be other chemicals present in those solutions that would indicate use of a different sheath material, and we (or you) have no way of finding out what those other chemicals are. Another example is when customers tell us they are buying an immersion heater for use in 'plain water'—where we would recommend a regular Incoloy sheath—but tell us later, after the first heater has failed that their 'plain water' is really de-ionized water—where we recommend the use of passivated Incoloy (Best), passivated Inconel (Better), or passivated 316 Stainless Steel (Good).

Power Density a.k.a. Watt Density

There are really two reasons you need to specify the correct power density for your immersion heater:

Prevent localized overheating or scorching of the liquid being heated
Prevent excess heat buildup in the heater

And, what is interesting is that failure to accomplish 1. usually results in failure to accomplish 2....or vice versa. Why is that? Well, to get the best life out of any type of heater, it is important to efficiently remove the heat from the heater. (You might want to think about that for a second or two...for instance if you're heating water, the heat needs to be removed from the heater and put into the water.) So, if we build an immersion heater for use in water at the maximum allowable power density (75W/sq.in.) it will work well in water. But, if you put that heater in oil and turn it on, the heater sheath will rise to an unacceptably high temperature thus scorching the oil that is in proximity to the sheath. That temperature rise occurs due to oil having lower thermal conductivity than water. If the heater is left on long enough, eventually so much heat will build up that, if the oil doesn't catch fire first, the heater element will melt down.

Which Product is Best for My Application?

If after reading this, you’re still not sure which product to use, we’ll be glad to help you figure it out. Give us a call at (866) 685-4443, send us an e-mail at info@oemheaters.com, or fill out a contact form.