Remember all of the stuff that applies to all water immersion heaters, plus for oil heaters our target is to get the watts density down to 12w/in² or below.

POIL Oil Imersion Heater

POIL Oil Imersion Heater

The POIL 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. As can be seen in the fifth image on our PII web page, the elements drop from the screwplug to your maximum available immersed length, before looping back up to within a few inches of the screwplug, 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.

if you have a very large tank with a massive maximum available immersed length, you may choose not to double loop, but to have plain U bent elements over a meter in length.

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.


3 of these (preferablynot chopped up)

screwplug sizes

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

Terminal box

…and one of these to attatch to the screwplug, to house the terminals and wiring.

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.

For the full shilling version, see the web authority on everything, Wikipedia, or an informative, if uninspiring, site referenced on the wiki page.

The extremely abridged version – its an electrically powered tube which applies direct heat to liquids and gases.

And finally, the Process Heating Services version. Here is one I chopped up earlier –


Video for those that are allergic to reading.

The top end is the terminal, sometimes a spade connection, but more usually a thread, washer and bolt combination, geared at holding the electrical connection, ie, incoming wire, in place.

Below the nuts is a white plastic plug which serves as a seal against ingress of moisture and also to hold all of the important bits inside in the middle of the tube, away from the sheathing.

The sheathing material is the outer housing, the solid casing, usually made of a metal, in this case Incoloy 800, a stainless steel variant. This serves to encase and protect the important bits, protecting them from whatever is being heated, ie, oils, chemicals, etc.

The white compacted powder inside the tube is magnesium oxide powder, which serves as an insulator against electrical leakage, but as a conductor of the heat generated by that electrical current.  It serves to hold the filament wire centrally within the tube so that contact with the sheathing material is all but impossible.

Finally, the tiny wire seen protruding at the bottom of the picture is the filament wire which creates the heat in the core of the element.  Usually Nickel Chromium, this converts electricirty very efficiently into heat, with only a little wastage as light, as with the filament of an old light bulb.  Whilst it is straight in the picture above (due to being hacksawed), under normal circumstances it would be coiled centrally in the magnesium oxide, as shown below, in this very cool x-ray.


The picture above also helps to explain the terms cold end, cold section, dead length, etc.  The bit before the wiggly filament, that looks a bit like a hose pipe, is the other end of the terminal pin, the nuts & washers electrical connection as described above. Usually mild steel, this section is not going to create a great deal, if any heat, and so this is termed the cold section.  All elements have two terminals, one at either end, to complete an electrical circuit, and both ends will have a cold section of 2 – 6″ dependent on the application.

This length would have to be subtracted from the element length when calculating watts density, ie, a 48″ 1000W element with 6″ colds has only 36″ active length (48″ – 6″ – 6″ = 36″), so the watts density of this element is 1000 / 36 = 28w/in².

So that is a plain heating element, but what about finned heating elements?

Mainly for use in air duct heaters, finned heating elements are merely plain elements as detailed above, but with finning added by a very clever machine.


This allows for better dispersion of the heat, basically by creating more surface area of heated element in the same available space.

Thanks for your interest. Any comments, feedback, additional information, please feel free to use our contacts page.

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

At Process Heating Services, we have 2 types of customer.  There are those who tell us what they want as they know their exact requirements.

There are others who need guidance and advice as to what they need.  One question which comes up time and again is “How many kW do I need to heat up my tank?”

If we can calculate the volume of water and the required temperaure rise, we can answer this question.

The following formula 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 in excess of 3 hours.

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

Following a great deal of hard work and patience on the part of our Website Team at, our new WordPress website is ready to view at

There is a lot more content on the site, much more product detail, and hopefully, all laid out in a way that a first time visitor in search of a UK based supplier of immersion heaters or heating elements, can drill down through the content to find information about exactly the product that they are after.

For example, someone in search of a 1kW finned heating element, may land on our website from natural listings or from adverts, on the ‘heating elements‘ page, they would then select ‘Finned Heating Elements – PEF Range (250W – 7kW)’ where they would then find a list of the various lengths and kW ratings available as finned elements, from which they would select 1kW, taking them to the PEF Range – Finned Heating Elements 1000w / 1kW page, which lists the various lengths of element that are available with a 1kW rating (20″, 24″, 26″, 30″, 32″, 34″, 36″, 40″, 42″, 48″, 54″, 60″, 66″, 72″, 78″, 84″, 90″, 96″, 104″, 114″, 120″, 132″, 144″, 170″, 180″). They can then choose the length which best suits their application, then ring us on the phone numbers ever present in the right hand bar, to place their order.

Also new additions are many of the photographs, showing much greater detail of terminal boxes, element looping, element diameter, etc.


Again, these are for the benefit of new customers, to get a feeling for the dimensions, quality, etc, of the heaters they are considering purchasing.  These pictures are complemented on the specific Range pages, by tables showing all available kW ratings, plus sub pages for each individual heater in that range.  We hope that the intuitive nature of the information allows ‘viewers’ to navigate to exactly what they want, then ring us and tell us what they want, rather than ringing ‘blind’ and asking if we supply something suitable to their needs.

The ‘OddBins’ page is also new, and is my attempt to sell off some of the accumulated bits and bobs at bargain prices, just to get rid of it and reclaim some space.  These are items, sometimes ordered in error, sometimes sent as samples by prospective suppliers, but just oddments that may fit somebodies exact requirements.  I’d never even heard of a ‘Hopper Heater’ but now you can buy one from us!

The website will grow, as will this blog, over the coming months and years, and we welcome any feedback, input, guidance, etc, from anyone with the interest and motivation to give it.

Just to repeat our enormous gratitude to all at for teaching a man to fish. Cheers!

My first blog entry, excellent.

Hello, I am Jamie Bristoll of Process Heating Services Ltd, based in Tamworth & Lichfield, in the UK.

We sell a range of electrical heaters, mainly screwed & flanged immersion heaters and elements, but also air duct heaters, vat heaters, drum heaters and inline heaters.

Whilst the company has been going now for 22 years, I have only been involved for the past 18 months, having spent the previous 15 years teaching in primary, secondary and special schools.  I am learning the business from scratch, most of which is fairly dull, ordering, invoicing, deliveries in/out, etc.

The bit I am hoping will be useful and relevant for blogging purposes is the technical side of things.  I have already become aware, through my interactions with suppliers and customers, that this is a VERY specialist world, even down to the use of terminology.  What one customer calls an element, another calls an immersion heater.

I am hoping to be able to use my own learning process, by recording it in a series of blog entries, to give an overview of electrical heating, defining the relevant terminolgy, using images to illustrate where necessary, providing the relevant formulas for calculation purposes, to expand upon aspects of the design process, and eventually, to provide a repository for others to share their own specialist knowledge of the subject matter.

A big task indeed, but I like a challenge.  That’s why I had 2 kids! It’s probably also why i’m a Wolves fan, but we’ll avoid that subject for the moment.