Heating Blog

How to choose an immersion heater

February 23, 2022 by Jamie Bristoll

There are several different considerations that apply generally to all types of immersion heater, regardless of what liquid they are to be immersed in or what type of application they are part of. If we deal with the generic aspects first, then readers can follow the links below, which will tie dowm the specifics of the various types of application you may be purchasing for.

An immersion heater is, simply put, a number of elements, usually 3, elements, a screwplug and a IP rated terminal box to protect the connections.

screwplug sizes — One of these, drilled through, for the elements to be braised or welded into.

First off, you need to decide on the necessary IP rating required for your terminal box. This will be dictated by your application, its location and position. As the name suggests, Ingress Protection ratings grade the terminal boxes ability to keep stuff out, thus protecting the connections, thermostats, contactors, etc, inside. See our IP entry for details as to the specific meanings of the 2 digits, but you need to match your application & situation, ie, indoor/outdoor, installed near to floor which is jet washed daily, in a chemically hazardous environment due to fumes from heated liquid, etc, to a minimum required IP rating. Our stock heaters range from IP54 (suitable for outdoor use) to IP 67. It is unlikely that you IP need will exceed what we supply, unless you are in the market for explosion and flameproof, flanged heaters, which we can supply, but in a rather different cost bracket and massively increased leadtime, as they are sourced from Italy.

Next on the list of considerations is the screwplug. The standard size in this fine country of ours is 2.25″ or 2 & 1/4″ BSP, which is probably a historical hangover that has, as yet, resisted the metric march of Brussels and the Eurocrats. It is indeed a quirky system, which I found downright confusing to begin with.

“What does a 2.25″ BSP screwplug measure across the thread?”
“2 and a quarter inches, stupid!” would be most folks reply (including me a couple of years ago!).
WRONG, its a little over 2 and a half inches, or 2.537″ or 2 & 5/8, if you prefer.

Have a look at the screwplug blog entry if you need further detail, & good luck.

Next thing to consider is what are you heating? Hopefully the answer is nice, clean, fresh council pop, or water, as it is known in more affluent areas. Our PII Range has Incoloy 800 sheathed elements, which are ideally suited to water heating and, if you believe the manufacturers is a “superior stainless steel” which has the “…ultimate chemical properties for high-temperature strength and resistance to oxidation, carburization and other types of high-temperature corrosion.”

Unfortunately, all waters are not created equal, and problems can occur with bore water and even good old tap water in hard water areas, usually due to calcium and magnesium, forming limescale deposits, attacking the elements, causing corrosion and splitting. Such problems are not insurmountable, but are more costly. Make sure to let your supplier know of any such potential issues ahead of time, so you can look into the costs associated with prevention, and if they can’t provide such solutions, contact me, because we can!

The easy way to maximise the working life of your immersion heaters, whether in a hard water area or not, is to minimize the Watts density. The article explains in detail a simple concept which we are using every day, maximise the element length THUS minimising the watts density THUS maximising the working life of the element, all other things being equal.

How to choose a brewery heater

Click above for the specifics relating to brewery immersion heaters.

Selecting an oil heater

…and above for oil immersion heater specifics.

Water hardness and it’s implications when choosing a water immersion heater

…and above for further information on water hardness and it’s implications when choosing a water immersion heater.

How to calculate the kW required to heat a volume of water in a particular time.

August 28, 2021 by Jamie Bristoll 15 Comments

Click for our online water heat up time calculations page HERE.

One question which comes up time and again is “How many kW do I need to heat up my tank?”

Or phrased a different way, “How long is it going to take my ? litres of solution to raise ? °C using my ? kW heater?”

If we can calculate the volume of water and the required temperature rise, we can answer these questions using the following formula.

It is used to calculate the power of heating element needed to heat a specific volume of water by a given temperature rise in 1 hour.

volume in litres x 4 x temperature rise in degrees centigrade / 3412

(4 being a factor and 3412 being a given constant)

for example 100 litres of water, to be heated from 20ºC to 50ºC, giving a temperature rise of 30ºC would give –

100 x 4 x 30 / 3412 = 3.52

meaning that the water would be heated in 1 hour by 3.5kW of applied heat.

Also we can use this information to extrapolate both ways. To heat the same water volume in half the time (30 minutes) would need twice the heating power, ie, 7kW.

Converesely, if we only use half the heating power, 1.75kW, it will take twice as long to heat up to desired temperature, ie, 2 hours.

If we only have a 1kW element available, we will expect a heat up time circa 3.5 hours.

Also we can use this formula as the basis of similar calculations for heating oil. Generally speaking, oil heats up in about half the time of water, due to its viscosity & density. However, oil requires a much lower watts density element than water, as described here in the “How to choose an oil heater” article.

Another variant of this formula, given here at the excellent website Sciencing.com gives the following varaint of the formula & subsequent explanation-

Pt = (4.2 × L × T ) ÷ 3600

Calculate Kilowatt-Hours

Calculate the kilowatt-hours (kWh) required to heat the water using the following formula: Pt = (4.2 × L × T ) ÷ 3600. Pt is the power used to heat the water, in kWh. L is the number of liters of water that is being heated and T is the difference in temperature from what you started with, listed in degrees Celsius.

Solve for Thermal Power

Substitute in the appropriate numbers into the equation. So imagine you are heating 20 liters of water from 20 degrees to 100 degrees. Your formula would then look like this: Pt = (4.2 × 20 × (100-20)) ÷ 3600, or Pt = 1.867

Divide by Heater Element Rating

Calculate the amount of time it takes to heat the water by dividing the power used to heat the water, which was determined to be 1.867 with the heater element rating, listed in kW. So if your heater element rating was 3.6 kW, your equation would look like this: heating time = 1.867 ÷ 3.6, or heating time =0.52 hours. Therefore, it would take 0.52 hours to heat 20 liters of water, with an element with a rating of 3.6 kW.

Which made better sense in my little brain when I put a multiplication sign between P and t, allowing 30+ year old math class memories to clarify that if you move the Power (P) or the Hour (t) to the other side of the equals symbol, we gotta divide by that number also. “Change the side, change the sign” Thanks Mr Phipps, some of it actually stuck, hope you are still above ground, happy & healthy.

P x t = (4.2 × L × T ) ÷ 3600

…which doesn’t usually “show” as t = 1 hour, as in kW(1)h.

Hope you found this useful.

Any feedback, suggestions, improvements, etc, PLEASE COMMENT, I promise to read ’em.

How to choose an oil immersion heater

August 17, 2021 by Jamie Bristoll 1 Comment

In addition to all the requirements for water immersion heaters, for oil heaters our target is to get the watts density down, requiring more element or less power, that is the compromise facing the customer, who is always right, even when they are wrong!

For HEAVY INDUSTRIAL OILS we are aiming for <=12w/in².

For LIGHT COOKING OILS we are good with up to 25w/in².

If we stray above this, the sheathe temperature is too high, the oil caremelizes onto the elements, thus preventing dissipation of the heat, so it gets hotter & more stuff sticks, until something goes BANG!

POIL Oil Imersion Heater — Oil Imersion Heater

The FOIL Range has many benefits, including bespoke screwplug size, immersed length, double stat pockets, etc, all with a 2 week leadtime. The 8mm elements can be double looped to fill your maximum available immersed length with a large overall length of element.

On 2″BSP & above screwplugs, the elements drop from the screwplug to your maximum available immersed length, before looping back up to within a few inches of the screwplug (taking care not to stray into the cold section), before dropping back to full immersed length, then returning back up to the screwplug. This allows us to fit nearly twice the length of element possible in a plain U bent element. For example, in 24″ of maximum immersed length, we could use an 84″ element double looped. Thus, nearly halving the resultant watt density.

If you are in the privilidged position of having a very large tank with a massive space available for immersed length, you may choose not to double loop, but to have plain U bent elements over a meter in length.

But for most folks, size is important! And this is where compromise is required to achieve the target watt densities shown above.