What Size Termoacumulador Do You Need? 50, 80, 100 or 150 Litres

How much hot water a shower really uses

A typical shower head uses somewhere between 7 and 12 litres of water per minute. You never shower at the tank's full temperature — hot water is mixed with cold — so a tank at 60 °C gives you more "shower water" than its size suggests.

Roughly, an 8-minute shower uses 30 to 50 litres of hot water from the tank. That is why a 50-litre tank is fine for one person, tight for two people back to back, and not enough for a family.

A simple sizing table

50 litres: one person, short showers, or a small studio used part-time.

80 litres: two people, or one person who likes long showers.

100 litres: three people, or two who shower one after the other.

150 litres: four or more people, or anyone who uses a bathtub.

If you are between two sizes, go up. The extra cost of a larger tank is small compared with living with one that is too small.

Recovery time: the number nobody mentions

Recovery time is how long the tank takes to heat again once it is empty. It depends on the element's power and the tank size, and it is typically between one and several hours.

If your household showers in a burst (everyone between 7 and 8 in the morning), a bigger tank matters more than a faster element. If showers are spread through the day, a smaller tank can cope because it has time to recover.

Vertical or horizontal?

Vertical tanks are more efficient: hot water rises and cold water stays at the bottom, so you get more usable hot water before it cools. Choose vertical when there is height available.

Horizontal tanks fit above doors, in false ceilings or on top of cupboards, which is often the only option in small Lisbon kitchens and bathrooms. They deliver slightly less usable hot water for the same size, so size up a little.

Cutting the running cost

Set the thermostat sensibly — around 55 to 60 °C is common. Higher wastes energy and speeds up limescale; much lower is not recommended for hygiene reasons.

Use a timer, or an off-peak electricity tariff, to heat the tank at night. Good insulation matters: a newer tank loses much less heat than one from fifteen years ago.

If you are replacing and have the space, a heat-pump water heater uses far less electricity for the same hot water. It costs more upfront and needs ventilation.

Installation details that matter

A full 100-litre tank weighs well over 100 kg, so the wall must be solid and the fixings right. The tank needs a safety valve with a drain pipe — it drips a little as the water heats, which is normal.

The electrical circuit must be suitable for the element's power. In hard-water Lisbon, the magnesium anode inside the tank protects it from corrosion and should be checked every few years.

When we replace a tank we also replace the safety valve and flexible connections: old ones are the most common source of small leaks afterwards. See water heater repair and replacement.

When the problem is not the size

If a tank that used to be enough suddenly is not, the size did not change — something else did. The element may have partly failed, the thermostat may be set lower, or the tank may be full of scale that takes up space and insulates the element.

Other signs of trouble: rusty water, a tank that makes crackling noises, water around the base, or a safety valve that pours instead of dripping. These need a professional look. See also no hot water in your apartment.

A worked example

Three people, one bathroom, showers of about 8 minutes, all in the morning. Each shower uses roughly 40 litres of hot water from the tank at 60 °C, so the morning needs about 120 litres of hot water. A 100-litre tank covers the first two comfortably and the third partly — a 150-litre tank covers all three.

The same three people showering at different times of the day could manage with 100 litres, because the tank recovers in between.

Power: what the element means for you

Tanks are sold with elements of different power ratings. A higher-power element heats the water faster (shorter recovery time) but draws more current, so it must suit your electrical installation and your contracted power with the electricity supplier.

If you already trip the main breaker when the oven and the washing machine run together, adding a more powerful water heater will make that worse. We check this before recommending a model.

Smart and eco modes

Many newer tanks have programmable timers, "eco" modes that learn your usage, and Wi-Fi control. The useful part is simple: heat the water shortly before you need it, preferably during cheaper tariff hours, instead of keeping it hot all day.

A basic external timer does most of the same job on an older tank.

Where to put the new tank

Close to the main points of use: long pipe runs mean waiting for hot water and wasting it. In small flats, above the bathroom door, in a kitchen cupboard or on a service balcony (with protection from weather) are typical.

The drain from the safety valve must go somewhere suitable — usually into a waste pipe. Leaving it dripping onto the floor or into a bucket is not an installation.

Frequently asked questions