Esquentador vs Termoacumulador: Which Is Better for Your Flat?

How each one works

An esquentador heats water as it passes through. Open the tap, the gas burner lights, the water comes out hot a few seconds later and keeps coming for as long as the tap is open. There is no tank and nothing is kept hot while you are not using it. See what an esquentador is.

A termoacumulador is an insulated cylinder with an electric element inside, like a large kettle that keeps water hot. Common sizes are 50, 80, 100 and 150 litres. It heats the whole tank, keeps it hot, and when you use hot water, cold water enters at the bottom to replace it.

Hot water: endless vs limited

With an esquentador the only limit is flow. One shower is always hot; two things at once may be cooler, depending on the model's capacity (11, 14 or 17 litres per minute).

With a termoacumulador the limit is the tank. Once the hot water is used up, the next person waits — often an hour or more — for the tank to heat again. A tank that is too small is the most common complaint we hear about electric water heaters, especially in flats where the landlord chose the cheapest size. Our tank size guide explains how to choose.

Running costs

There is no universal answer, because it depends on your gas and electricity tariffs and on how you use hot water. A few principles do hold true:

A tank loses some heat all day, even when nobody uses hot water. Setting it to a sensible temperature and using a timer, or an off-peak electricity tariff (bi-horário) to heat at night, reduces that loss considerably.

Bottled gas is usually the most expensive way to heat water per litre, and running out mid-shower is part of the deal. Piped natural gas tends to be cheaper to run.

If running cost matters most and you have the space, a heat-pump water heater (bomba de calor) uses a fraction of the electricity of a standard tank. It costs more to buy and needs more room and ventilation, so it is not a fit for every flat.

Space and installation

An esquentador is compact and hangs on a wall, but it needs a gas supply and a flue to take the fumes outside. In a flat without either, adding them is usually impractical or not allowed by the building.

A termoacumulador needs a wall strong enough to hold 100+ kg when full (or floor space for a vertical model), a water connection, a safety valve with a drain, and a suitable electrical circuit. No gas and no flue — which is why it is the default in flats that never had gas.

Safety

Both are safe when properly installed. With gas, the risks are leaks and bad combustion producing carbon monoxide; that is why ventilation, the flue and periodic checks matter. Room-sealed (estanque) models remove most of that risk.

With an electric tank, the key safety part is the pressure relief valve — it drips a little when the water heats, which is normal, and it must never be blocked. A tank that leaks from the body, or a valve that pours constantly, needs attention.

Changing from one to the other

Gas to electric: usually possible if there is room for the tank and the electrical installation can take the extra load. The old gas supply is capped safely and the water connections are adapted.

Electric to gas: needs a gas supply and a flue route, which rules it out in many flats. Where it is possible, it is a bigger job than a like-for-like swap.

Either way the connections, valves and safety devices are adapted to the new appliance. See water heater repair and replacement.

Our rule of thumb

Two or more people who shower back to back, with gas already in the flat: esquentador.

One or two people, no gas in the flat, or you want to stop buying gas bottles: termoacumulador of the right size — ideally on an off-peak tariff.

Renovating and planning to stay for years, with space available: consider a heat-pump water heater.

A real-life example: a couple in a T1

Two people, one bathroom, showers in the morning within half an hour of each other. With an 11-litre esquentador both showers are hot and there is no waiting. With a 50-litre tank, the second shower is often lukewarm; with an 80-litre tank it is usually fine; with 100 litres there is margin for a longer shower.

If that flat has no gas and the couple want to stop buying bottles, an 80 or 100-litre tank on an off-peak tariff is the sensible choice. If it has piped gas and a working flue, keeping the esquentador is cheaper and more comfortable.

A real-life example: a family in a T3

Four people, two bathrooms, evening showers one after another. A tank needs to be 150 litres or more, takes space and still risks running out. A 14 or 17-litre esquentador — or a heat pump if there is room — handles it better.

This is the case where the choice of water heater makes the biggest difference to daily life.

Maintenance compared

Esquentador: batteries once a year if it uses them, a service every one to two years (burner, flue, filter, scale), more often if it is an older open-flued model.

Termoacumulador: check the safety valve occasionally by lifting its lever briefly, and have the magnesium anode and scale checked every few years — in Lisbon's hard water the anode is what protects the tank from rusting through.

Neglected maintenance is the main reason either type fails early.

Lifespan and replacement cost

Both typically last 10 to 15 years with reasonable care. A like-for-like replacement is the simplest job; changing type means adapting connections and possibly electrical or gas work, which costs more.

Repairs start from 75 €. For replacements we quote after seeing photos of the current heater and its connections.

Frequently asked questions