Immersion Heater & Tank: Switch Off to Cop On?

The immersion - have you ever even been to Ireland if you don’t know what one is? As anyone who has ever lived in our country can tell, the immersion heater has been integral to hot water in Ireland for many years. Even the comedian Des Bishop did a skit on the fear of leaving the immersion turned on, and the ruinous bills that could accompany such folly.


Nowadays, in our move towards a greener and cleaner economy, does the immersion still have a place in Irish households or should it be relegated to the past? Read on and find out everything and anything you needed to know about immersion heaters, the immersion switch, timers, the age-old sink or bath problem, and whether it could be a good fit for your household.

What is an immersion heater?

A large immersion tank

Many people refer to the cylindrical-boiler-like contraption in the hot press as the immersion heater, but actually the immersion heater is an electric water heater that sits inside the cylinder (also known as the immersion tank). Strong currents of electricity pass directly into the immersion heater which then uses the energy to warm the water around it.

Basically, an immersion heater is like the element of a kettle and performs the same function, heating up water. Some households which are not connected to the gas grid will use immersion heaters as their only source of hot water. Others will use the immersion in addition to their central heating/boiler set up, as a backup or “top up” supply of hot water.

Immersion heaters can be particularly useful for businesses which require a large quantity of hot water, for example, a hairdressing salon, due to the fact that you can get immersion tanks with a large capacity.

An immersion water heater and tank can also be useful in the summer months for households as the central heating has usually been turned off and people may prefer not ot fire up the whole system just for hot water.

How much does it cost to run an immersion heater?

Rough estimates are that it costs around 50 cent to run an immersion heater for an hour. If you have a more efficient immersion heater, say a 6KW element instead of a 3KW one, it will heat the same amount of water and cost the same, but do the job in half an hour instead of a full hour. Heating water with electricity is much more expensive than heating it with gas.

How can you reduce the costs of running the immersion?

a calculator with an electriciy bolt over it

The two most important factors to reduce the cost of running the immersion are thermostats and insulation. Make sure your immersion heater has a functioning thermostat and set it to a reasonable temperature - there is no point in spending money overheating water to the point where you need to mix cold water with it to shower in.

However, you do need to remember to heat the water in the immersion tank to above 50ºC to kill off any bacteria which may be lurking inside.

Although many modern immersion tanks come with an insulating layer built-in, if you have an older tank you should definitely invest in a lagging jacket. Lagging jackets can be bought at any local hardware store.

Do not leave your immersion heater running all the time - no matter how well-insulated the immersion tank is, it will still lose heat and the drop in water temperature will cause the immersion heater to run repeatedly (like your kettle coming back to the boil over and over again).

Unless you are sure that your immersion heater thermostat is just the ticket, the tank is insulated as much as possible, and that you need copious amounts of hot water all throughout the day, switch it off until needed. Otherwise, the only thing you will be saving is saving up for a big (nasty) surprise when you receive your electricity bill.

Fitting a timer will only cost around €45 and will solve the neverending arguments over who left the immersion on. It will also allow you to heat water for less if you have a Nightsaver meter and can program the immersion to come on before everyone gets up to shower in the morning.

Our last tip to reduce the costs of running the immersion is to set it to the sink switch for quick showers. As everyone knows, the immersion has two switches, an on-off one and a sink-bath one. In theory, the sink switch is for enough hot water for washing dishes and washing hands etc. while the bath switch is enough for a bath or a shower.

If you’ve ever kept the plug in the bath while having a shower you’ll have noticed that you usually only use a third as much hot water as you would for a bath. Setting the immersion to the sink side of the switch will use roughly a third of the amount normally heated for a bath. So set the switch to sink and take a shower, because not only will you be using less water, you’ll only be using a third of the amount of electricity as when you set it to bath, and your pocket will thank you.

Are there energy-efficient immersions?

No. Due to the nature of the function they perform, exchanging electricity energy for heat energy, there are no energy-efficient immersion heaters whereby you can get more heat energy bang for your buck.

When immersion heaters are referred to as being “efficient”, it just means that they are more powerful and can produce more hot water in the same amount of time, but they still need to use the same amount of energy.

It is possible to use solar panels to power your immersion heaters, and this would result in clean renewably produced hot water.

The pros and cons of immersion heaters

Pros Cons
Initial economical purchase price and later cheap replacement costs of up to €130 only, as the heater can be replaced separately to the tank. Slow to heat up water, requires planning in advance.
If your boiler breaks down you will still have hot water through the immersion, and vice versa. More expensive to run than heating hot water with gas.
Well-insulated immersion tanks can keep water hot for hours after being switched off. The majority of Irish households would need to run the immersion for hours each day to produce enough hot water for their household.
Nightsaver customers can set the immersion to come on during cheaper electricity hours, and wake up to plenty of hot water. Gas boilers are considered to be far cheaper to run.
Easy to operate, simply switch on or off. Electricity dependent - you’ll have no access to hot water if the power goes out.

KRIB - a viable alternative to the traditional immersion tank and heater?

A green lightbulb

As mentioned above, a gas-fired boiler is usually a cheaper alternative to an immersion heater. But did you know there is a new kid on the hot-water block in Ireland, the KRIB device?

KRIB heats water at the top of a water tank rather than the bottom, and it heats it fast, so that only the required amount of hot water is produced, rather than heating up the whole tank. It has a modern digital controller which comes in a variety of colours, and can also be accessed from anywhere via an app on your smartphone.

KRIB can be retrofit to existing hot water cylinders for €999 (which includes the touchscreen control and app as well as the retrofit equipment) or installed from scratch for €1850. The KRIB is touted to save energy, reduce water consumption, and lower heating costs. It also qualifies for an SEAI Better Energy Home grant.

Initial reports are that while immersion heaters can take up to an hour to heat enough hot water for a bath or shower, the KRIB can do so in just six minutes.

Investing in a KRIB is a much bigger initial outlay than investing in an immersion heating system. This means that it may not be suitable for you if:

  • You’re on a tight budget.
  • You plan to be using the property sporadically.
  • The property is a rental.

However, if you’re planning on living in the property where you’ll be installing a hot water system for a long time, then you could definitely make some considerable savings long-term with the KRIB system.

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