How much can I realistically save by scheduling heating?

It depends on how much heating you can shift and on the spread in your market. The widget above uses last winter's real hourly prices per country: a 2 kW load shifted for 3 hours a day is typically worth tens of euros per winter in calm markets and well over a hundred in volatile ones. Add a hot-water tank and an EV and the total multiplies.

Will my home get cold during the expensive hours?

Not if the schedule pre-heats before them. Walls, floors and furniture store heat, and a well-insulated room drops less than a degree over a two-to-three-hour pause. Your thermostat remains the safety net: if a room falls below its minimum, it heats regardless of price.

Do I need a spot-price contract for this to work?

You need a price that varies during the day. Spot (hourly) contracts capture the full spread; day/night grid packages capture part of it. On a flat fixed price, scheduling changes nothing on the bill.

What equipment do I need?

For radiators and water heaters, a metering smart plug or relay such as a Shelly costs 20–40 euros and pays for itself within the first winter. Cloud-connected heat pumps and EV chargers can often be scheduled with no extra hardware at all.

Will winter 2026/27 prices swing as much as last year?

Nobody can promise the level, but the shape is structural: cold, dark evenings raise demand while wind and solar output vary hour by hour, so the cheapest and dearest hours will keep drifting apart in winter. A schedule earns more the more volatile the market is, and costs nothing when it is calm.

I have district heating or a gas boiler. Is any of this for me?

The heating itself cannot be shifted, but hot water, EV charging, appliances and any electric top-up heaters can. The checklist items on contracts, grid packages and appliance timing still apply.

Wissens-CenterWater heater as a battery

Energy Storage

Your Water Heater Is the Cheapest Home Battery You Can Buy

Home batteries promise to buy electricity when it is cheap and use it when it is dear. A hot-water tank does exactly that for the energy you spend on hot water anyway, with no conversion losses, no permits, and a controller that costs about as much as a pizza. Here is how to turn the tank you already own into storage, and what it is worth.

A tank of hot water is a battery

Heating 200 litres of water from 20 °C to 70 °C takes about 11.6 kWh. That is the same order of energy as a mid-size home battery, and the tank holds it for hours with only slow standby losses. If you heat the water in the cheapest hours of the day and let the thermostat hold it, you have bought your hot water at the night price and used it at the evening price. Nothing about your shower changes.

The difference is what it costs to get there. A battery has to be bought, installed by an electrician and, in many countries, registered with the grid operator. A water heater only needs a switch that knows the electricity price. If you want more storage, a second or larger tank is still a fraction of the price of a battery, and it never wears out from cycling.

Energy in a 200 L tank

11.6 kWh

heated from 20 °C to 70 °C

Controller cost

≈ 25 €

Shelly smart plug with metering

Conversion loss

heat goes straight into water you would heat anyway

Battery vs water heater, side by side

Both shift energy from cheap hours to expensive ones. The table shows where a battery is better and where a tank simply wins.

Criterion	Home battery	Water heater tank
Upfront cost	Several thousand euros installed for 5–10 kWh	You already own it; ~25 € smart plug or ~35 € relay
Usable storage	5–10 kWh typical	6–12 kWh for 100–200 L; add a tank for more
Round-trip losses	8–15% lost charging and discharging, plus inverter idle draw	No conversion loss; 0.5–1.5 kWh/day standby loss that exists with or without a schedule
Lifespan	10–15 years, capacity fades with cycles	10–20 years, no cycle wear; element and thermostat are cheap parts
Installation	Electrician, often a permit or grid registration	Plug in, or one relay fitted by an electrician for hardwired heaters
What it can power	Anything in the house	Hot water only, but that is 15–25% of a household's electricity
Payback	Typically 8–15 years on price arbitrage alone	Weeks to a few months

Upfront cost

Home battery: Several thousand euros installed for 5–10 kWh
Water heater tank: You already own it; ~25 € smart plug or ~35 € relay

Usable storage

Home battery: 5–10 kWh typical
Water heater tank: 6–12 kWh for 100–200 L; add a tank for more

Round-trip losses

Home battery: 8–15% lost charging and discharging, plus inverter idle draw
Water heater tank: No conversion loss; 0.5–1.5 kWh/day standby loss that exists with or without a schedule

Lifespan

Home battery: 10–15 years, capacity fades with cycles
Water heater tank: 10–20 years, no cycle wear; element and thermostat are cheap parts

Installation

Home battery: Electrician, often a permit or grid registration
Water heater tank: Plug in, or one relay fitted by an electrician for hardwired heaters

What it can power

Home battery: Anything in the house
Water heater tank: Hot water only, but that is 15–25% of a household's electricity

Payback

Home battery: Typically 8–15 years on price arbitrage alone
Water heater tank: Weeks to a few months

A battery is the right tool if you need to run the whole house on stored power or ride out outages. If the goal is simply to stop paying peak prices, start with the tank: it is the cheapest kilowatt-hour of storage in the building.

How the tank works as storage

Left to itself, a water heater reheats whenever the water cools below the thermostat setting, which means it also fires during the most expensive evening hours. With a price-aware switch in front of it, the heater is only powered in the cheapest window of the day. It heats to the thermostat's maximum in that window, then holds the heat until the next cheap window.

The thermostat stays fully in charge of temperature and safety; the switch only decides when power is available. Because the tank is well insulated, a full heat in the night still means a hot shower in the evening. Households that use a lot of hot water can add a second cheap window in the early afternoon, when solar pushes prices down in many markets.

Want more storage than one tank offers? Fit a larger tank, or a second tank in series, and set both to heat only in cheap hours. The extra capacity costs a few hundred euros, not a few thousand, and lets you skip the expensive hours entirely even on heavy-use days.

Set it up in five steps

From an ordinary heater to price-aware storage in about 15 minutes, plus an electrician visit if the heater is hardwired.

Pick the right switch for your heater

Plug-in heaters up to 2.5 kW (12 A) run through a Shelly Plug S Gen3: plug it in between heater and socket, done. Most tank heaters above 2 kW are hardwired; those get a Shelly Plus 1PM or Pro 1PM in the circuit, fitted by a licensed electrician. Both models meter energy, which is what lets Elewatt show real savings later.

Shelly Plug S Gen3 guide →

Add your contract and a price filter in Elewatt

In Elewatt, add your electricity contract under Contracts so prices include your grid tariff and taxes. Then create a price filter under Filters: for a water heater, the usual choice is the N cheapest hours of the day, with N set to the time your tank needs for a full heat, typically 2–4 hours.

Connect Shelly to Elewatt

Under Integrations, open Shelly and connect your Shelly Cloud account. Your plug or relay appears in the device list within a few seconds. Elewatt reads its power and energy so the savings you see later are measured, not modelled.

Link the heater to the filter

Select your heater and assign the price filter you created. From now on, Elewatt rebuilds the schedule every afternoon when tomorrow's prices are published, and switches the heater on only in the chosen hours.

Per day

17.96 Kč

Per month

538.89 Kč

Per year

6565.35 Kč

Set the thermostat and watch the savings

Set the heater's thermostat to 60–70 °C so the tank stores as much heat as possible in each cheap window, and fit a thermostatic mixing valve at the outlet if the tap water would otherwise be too hot. Then let it run; the calculator below shows what a typical tank saves, and the Elewatt dashboard shows what yours actually did.

Figures come from the calculator below; adjust it to your tank.

Safety and hygiene: three rules

Hardwired means electrician

Any heater above 2.5 kW, or one without a plug, must be switched through a relay installed by a licensed electrician. Never bypass the heater's own thermostat, pressure relief valve or overheat cut-out.

Keep Legionella out

Water stored between 25 and 45 °C is where Legionella grows. Heat the full tank to at least 60 °C regularly, ideally daily and at minimum once a week. Scheduling to the cheapest hours does not change this: the tank still reaches the thermostat setting each cycle.

Mind the tap temperature

Storing at 65–70 °C is excellent for capacity but scalding at the tap. A thermostatic mixing valve on the outlet gives 45–50 °C water from a hot tank, which is how most new installations are done anyway.

What does a scheduled tank save?

Enter your tank volume and temperatures. The calculator uses your country's real hourly prices from the last twelve months, your grid tariff and VAT, and compares heating in the cheapest hours against the most expensive ones.

Volumen (L)

Min. Temp. (°C)

Max. Temp. (°C)

Energie · Zeit

11.6 kWh · ~6 h

Nord Pool Mittel (Mär 2025–Mär 2026) · ct/kWh

0:00 · 14.0c

1:00 · 13.9c

2:00 · 13.0c

3:00 · 12.6c

4:00 · 12.5c

5:00 · 13.1c

6:00 · 16.1c

7:00 · 22.2c

8:00 · 24.5c

9:00 · 26.3c

10:00 · 24.0c

11:00 · 22.5c

12:00 · 18.3c

13:00 · 18.2c

14:00 · 18.2c

15:00 · 18.6c

16:00 · 23.0c

17:00 · 24.6c

18:00 · 27.2c

19:00 · 29.2c

20:00 · 26.3c

21:00 · 24.6c

22:00 · 18.6c

23:00 · 16.2c

Günstigste 6hSpitze 6h

Mit Elewatt

13.2 ct/kWh

38.79 Kč

Ohne Elewatt

26.4 ct/kWh

77.62 Kč

Ihre Ersparnis

Pro Tag

38.82 Kč

Pro Monat

1164.73 Kč

Pro Jahr

14170.89 Kč

Jahresdurchschnitt der Nord-Pool-Preise, Estland. Annahme: 1 Zyklus/Tag, 2-kW-Heizstab. Netzentgelt: Elektrilevi.

Why Elewatt insists on metered energy

A tank heater only draws power while its own thermostat calls for heat, so relay-on time tells you nothing about consumption. When we compared 91 days of real meter readings from two water heaters against the usual nominal-power estimate, the estimate overstated consumption by 63%, and the two identical heaters differed from each other by 3.2×. That is why Elewatt only reports savings from devices with a meter, and why the Shelly models above all have one.

Turn your tank into storage today

Connect a Shelly plug or relay, pick a cheap-hours filter, and Elewatt heats your water when electricity is cheapest, every day, with metered savings you can check.

Kostenloses Konto erstellen Funktionen

ZurückCut Your Winter Electricity Bill 2026/27: The Complete Checklist

WeiterTransparenter Strompreis: Was 1 kWh wirklich kostet

KI-gestützt, menschlich geprüft – jeder Artikel wird vor der Veröffentlichung redaktionell kontrolliert. Unsere redaktionellen Grundsätze lesen

Häufig gestellte Fragen

Weitere Leitfäden

Alle Leitfäden

Transparenter Strompreis: Was 1 kWh wirklich kostet

Klare Aufschlüsselung des kWh-Preises: Börsenpreis, Netzentgelte, Steuern und Marge — und wie Sie Ihren echten Strompreis live nachvollziehen.

Leitfaden lesen

Smartes E-Auto-Laden: Geld sparen durch Laden zur richtigen Zeit

E-Autos sind in Spitzenzeiten teuer im Betrieb. Erfahren Sie, wie Sie das Laden automatisieren, um immer den günstigsten Strom zu nutzen.

Leitfaden lesen

Elektroheizungen & smartes Heizen: Senken Sie Ihre Winter-Stromrechnung

Heizen ist der größte Stromposten in baltischen Haushalten. Erfahren Sie, wie Sie Elektroheizungen so automatisieren, dass sie nur in den günstigsten Stunden laufen.

Leitfaden lesen