The time it takes to heat water depends on the heater type, power, and tank capacity. Considering how you use this water, and how much of it can make a big difference to your energy consumption. For example, it takes an immersion system, According to the ESB a traditional immersion system takes 2.5 hours to heat up 120 liters from cold.

Based on SEAI reports it’s generally cheaper to heat water using the central home heating system, as the system is already running to heat your home. This means you can take advantage of its operation without much additional expense. When it gets warmer, switch to using your immersion heater, which heats water without needing to run the whole heating system, which can save energy and money.

Bonus Tip: Installing a timer on your immersion heater means it’ll turn off on its own, saving you from those "oops, I left it on" moments and helping to keep your energy bills in check

A significant level of washing machine energy use is related to heating water. If you run your machine at a lower temperature, you will use less energy. Don’t worry, your clothes will still get clean, most washing powders are now designed to work just as well at 30°C as they do at higher temperatures. Only using the machine when you have a full load of washing is another great way to avoid wasting energy and water.

Installing lagging jackets on your hot water cylinder can help them lose as little energy as possible. If the tank has a good insulating jacket, it will keep the water hot all day, without needing to be constantly reheated. Buy a quality, 80mm (3-inch) thick version and with the energy savings, it will pay for itself in a few months.