Last updated: August 2026
Hot water is the biggest electricity habit in most Irish homes - bigger than the TV, the washing machine and the lights combined. Between the immersion, the electric shower and the boiler, a family of four can easily spend €600-€900 a year just making water hot, and most households have never compared their method against the alternatives. The differences are not small: the same ten-minute shower can cost 55c or 28c depending on how the water was heated and when. Run your own numbers in the calculator below, then steal the fixes.
⚡ Quick Summary
🌿 The hierarchy (cheapest first): night-rate immersion → gas boiler → day-rate immersion ≈ electric shower.
🌿 A 10-minute electric shower costs ~50-55c; the same shower from a night-rate-heated tank can cost around 25-30c - or ~12c if the tank heats inside an EV tariff's boost window.
🌿 An immersion left on costs ~€1 an hour at day rates - the timer is the highest-payback gadget in Irish energy.
🌿 Lag everything: a €20 cylinder jacket and pipe lagging pay back in months, not years.
🌿 Solar owners: a diverter turns surplus generation into free hot water instead of 19.5c exports.
🌿 All figures indicative at ~35c day / 18c night / 11c gas per kWh - adjust the calculator to your tariff.
🧮 Compare Your Options
💧 Why the Same Shower Costs 55c or 28c
An electric shower is a 9.5kW instant heater - it makes hot water the most expensive way possible, at full day rate, at the moment you use it. A tank shower uses water heated earlier - and when and how that tank was heated sets the price:
🌿 Immersion on day rate (~35c/kWh): convenient, dear - the default in too many homes.
🌿 Immersion on night rate (~17-21c/kWh): the same element, the same tank, roughly half the price - just timed after 11pm (and a quarter of the price inside an EV tariff's 6-11c boost window).
🌿 Gas boiler (~11c/kWh): cheap per unit, slightly less efficient in conversion - lands between the two immersion options.
🌿 Heat pump or solar diverter: the endgame - a heat pump makes hot water at roughly a third of gas cost, and a solar diverter makes summer hot water essentially free.
🛠️ The Fix List, In Payback Order
🌿 1. Immersion timer or smart plug (€15-€60): heat water for when you actually use it, ideally in the night window. Payback: weeks.
🌿 2. Cylinder jacket and pipe lagging (€20-€40): an unlagged cylinder leaks heat all day; a jacket cuts standing losses dramatically. Payback: months.
🌿 3. Shower discipline (free): minutes are money on a 9.5kW shower - a family shaving 3 minutes each saves €100+ a year.
🌿 4. Night-rate tariff (free to switch): if you have a smart meter and any tank heating, the night window changes the whole equation - see our night rate guide.
🌿 5. Solar diverter (€400-€600 with an existing array): surplus generation heats the tank before exporting - free hot water most bright days.
The wider context - which appliances cost what across the whole house - is in our appliance running costs guide, and what it all adds up to in our average bill breakdown.
⚠️ Common Mistakes to Avoid
🌿 The always-on immersion: €5+ a day if forgotten - the single most expensive accident in Irish kitchens. Timer. Today.
🌿 Heating a full tank for one wash-up: use the sink element (many immersions have bath/sink settings) or the kettle for small jobs.
🌿 Ignoring the cylinder's age: a modern well-insulated cylinder holds heat overnight; a bare 1980s copper one is a radiator in a cupboard.
🌿 Switching to an electric shower to "save on heating": it swaps cheap tank heat for the dearest instant heat - usually backwards.
🌿 Never checking the thermostat: 60-65°C is right for the cylinder - hotter wastes money (and scalds), much cooler risks legionella.
❓ Frequently Asked Questions
🔹 What is the cheapest way to heat water in Ireland?
With existing kit: the immersion on a night-rate tariff (~18c/kWh, or 6-11c in an EV boost window), well lagged and timed. With investment: a heat pump or a solar diverter beats everything.
🔹 How much does the immersion cost per hour?
A 3kW immersion costs roughly €1 an hour at day rates, or around 55c at night rates. A full tank heat is typically 2-3 kWh.
🔹 Is an electric shower expensive to run?
It is the dearest common way to make hot water: roughly 50-55c per 10-minute shower at 2026 day rates. Fine occasionally; expensive as a family default.
🔹 Should the immersion be left on all the time?
No - heat water for when you need it. A modern lagged cylinder holds usable heat for many hours, so a timed night-rate heat covers most households' whole day.
🔹 Is gas or electric cheaper for hot water?
Gas beats day-rate electricity comfortably; night-rate electricity beats gas. The calculator above ranks all three at your own tariff figures.
🔹 What temperature should hot water be?
Store at 60-65°C. Lower invites bacteria; higher wastes energy and scalds - mixer valves at taps are the safe way to deliver cooler water.
📚 Related Guides
🌿 Best Electricity Provider
🌿 Electricity Prices & Average Bill
🌿 Night Rate Electricity
🌿 Pay-As-You-Go Electricity
🌿 MPRN & GPRN Numbers
🌿 ESB Smart Meter Error
🌿 Appliance Running Costs
🌿 Electric Heater Running Costs
🌿 Dehumidifiers
👉 All guides and calculators
Climate Jargon Buster is an independent resource providing plain-English information on climate, energy and sustainability topics for an Irish audience. All running costs are indicative, based on typical 2026 tariffs and equipment - your tariff, cylinder and habits will vary. Check your own bill for exact rates.