Storage or instantaneous
An instantaneous water heater heats water at the moment of use. It is compact but needs a lot of power: 6-8 kW for one tap and more for a shower. For a typical apartment electrical supply this is often too much.
A storage water heater heats water in advance and keeps it in a tank. Its power is 1.5-2.5 kW, suitable for a standard socket on a dedicated circuit. It provides a stable temperature and good water pressure.
For an apartment or a house without gas, a storage water heater is the most practical option.
How many litres you need
| Who uses it | Volume |
|---|---|
| Kitchen, washing up | 10-30 l |
| 1-2 people, shower | 50 l |
| 2-3 people, shower | 80 l |
| 3-4 people, bathtub | 100 l |
| Large family, 2 bathrooms | 150 l or more |
The water in the tank is hotter than needed for a shower and is mixed with cold water. 80 l of water at 75 °C gives about 190 l of water at a comfortable 40 °C.
How many watts and how fast it heats
Most household models draw 1.5-2.5 kW. Heating time can be estimated as follows:
Time (h) = volume (l) × temperature rise (°C) / (860 × power, kW).
An 80 l, 2 kW water heater will heat water from 15 to 60 °C in about 2 hours. A 100 l model takes about 2.5 hours.
Vertical or horizontal
A vertical model heats more efficiently: hot water collects at the top, cold water stays at the bottom and they hardly mix. A horizontal one is needed when height is limited: above a door, under the ceiling, in a niche.
What to look for when choosing
- Tank protection. Enamel or glass-ceramic coating protects the steel from corrosion. A magnesium anode extends the service life.
- Heating element type. A dry heating element in a sleeve does not touch the water, builds up less scale and can be replaced without draining the tank.
- Thermal insulation. Good insulation keeps the water hot for a day or longer and saves electricity.
- Controls. Eco mode, frost protection, temperature display.
Safe connection rules
- A dedicated circuit with a circuit breaker and an RCD, always earthed.
- A safety valve on the cold water inlet. Do not block its drain outlet.
- If the mains pressure is above 6 bar, fit a pressure reducer.
- Mount it on a load-bearing wall: a 100 l water heater full of water weighs more than 120 kg.
Important: if the house has a gas boiler, it is cheaper to heat water with it via an indirect water heater. An electric water heater is convenient as the main option in an apartment or as a summer backup.
Write to ThermoHouse how many people are in your family and where the water heater will be installed. We will select a 50-150 l FERROLI E-Glasstech water heater. Contact us →
