What it is called, by market
One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.
United Kingdom
No local equivalentimmersion heater
also immersion, immersion element, backup immersion
Normally a BACKUP in a cylinder heated by a boiler or a heat pump, on its own circuit with its own switch, used when the primary source is off or has failed.
Australia
Close, not identicalelement
also heating element, booster element, immersion heater
Electric storage water heating is common, so the element is frequently the primary source rather than the backup — and a solar hot water system's element is called the booster.
United Statesyours
No local equivalentheating element
also upper element, lower element, water heater element
There is no separate word, because an electric water heater IS a tank with elements: typically two, upper and lower, staged so the top of the tank recovers first. Nothing is being backed up.
Canada
No local equivalentheating element
also upper element, lower element
As the United States, with the same two-element staged arrangement standard.
The governing standard, by market
United Kingdom
BS EN 60335-2-73 / BS 7671
Safety of fixed immersion heaters, and the electrical installation requirements for the circuit serving one.
United States
UL 174 / NFPA 70 Article 422
Household electric storage tank water heaters, and the branch circuit and disconnect requirements for appliances.
Calculators for this
Each works in either measurement system, and the terminology on the page follows whichever market you have selected.
Frequently asked questions
- Why is an immersion heater a backup in Britain and the main thing in America?
- Because the systems grew from different starting points. British houses are overwhelmingly heated by a gas boiler, and once a boiler is present it is by far the cheapest way to heat water too — so the cylinder takes a coil from the boiler and the electric element is there for summer, for a boiler breakdown, or for a cheap overnight tariff. American electric water heating grew up without that boiler in the picture, so the tank and its elements are the whole appliance. The consequence when reading across markets is that a specification saying 'water heater' in American usage names a complete appliance, while a British cylinder specification names a vessel and says separately what heats it. Ordering one against the other leaves either a tank with no heat source or a duplicate.
- Why does an immersion heater take so long, and why does the top get hot first?
- Because the power is modest and the water stratifies. A typical domestic element is around three kilowatts, and raising a 150 litre cylinder through 45 degrees takes roughly nine kilowatt hours of energy — so about three hours at full power even before losses, against a boiler putting in five or six times that rate. The stratification is the useful part: hot water is less dense, so it sits at the top and does not mix downward, which means the top of the cylinder reaches temperature long before the bottom. That is why an element near the top gives a usable amount of hot water quickly while a full reheat takes hours, why American tanks stage an upper and a lower element deliberately, and why a British cylinder often has two immersion positions for exactly the same reason.
- What actually fails, and what does that say about the water?
- Three things, and each points somewhere different. The ELEMENT itself burns out, usually after scaling up in a hard-water area — scale insulates the element from the water, so it runs hotter than it was designed to and fails, which makes a short element life a statement about the water rather than about the part. The THERMOSTAT fails, and the symptom is either no heat at all or water far too hot, which is the dangerous one and is the reason a system has a separate non-resettable thermal cut-out behind the thermostat. And the SACRIFICIAL ANODE in the cylinder is consumed — it is there to corrode instead of the tank, and once it is gone the tank starts. An element replaced repeatedly in the same cylinder is usually a water-treatment question.