Atmosférico, Ventilado or Estanque: Which Esquentador Should You Buy?

Atmosférico (natural draught)

It burns gas using air from the room and sends the fumes up a flue by natural draught — hot air rises. No fan and no electricity needed (apart from ignition on some models).

Pros: simple, robust, cheaper to buy and repair. Cons: it depends on permanent ventilation openings in the room and on a flue with a good draw. If the flue is blocked, too long or affected by wind, fumes can come back into the room. Most models have a safety device that shuts the heater off if that happens, but it must never be tampered with.

Ventilado (fan-assisted)

Same principle, but a small fan actively pushes the fumes out through the flue. That makes it much less dependent on natural draught and allows longer or more complex flue routes.

Pros: more reliable exhaust, more installation flexibility. Cons: needs a socket nearby, and the fan is one more part that can fail. It still uses air from the room, so ventilation openings are still needed.

Estanque (room-sealed)

The combustion chamber is sealed from the room. A concentric pipe (a pipe inside a pipe) brings fresh air in from outside and sends fumes out, usually through an outside wall.

Pros: the safest option, because the heater never uses or contaminates the air inside your home; it can go in rooms where an open-flued heater would not be allowed. Cons: needs a route to an outside wall for the concentric pipe, and it is usually the most expensive to buy.

Capacity: 11, 14 or 17 litres per minute

The number on the model is how many litres of hot water per minute it can deliver at a comfortable temperature rise.

11 litres: one shower at a time, typical for a one-bedroom flat. 14 litres: a shower and a tap at the same time, a good default for couples and small families. 17 litres: two bathrooms, or a family that often uses hot water in two places at once.

Bigger is not always better: an oversized heater costs more and can struggle with very low flows, like a small hand basin.

What your flat allows

Start from the existing flue. If there is a vertical flue into a shared building duct, you are usually looking at atmosférico or ventilado. If the heater is on or near an outside wall, estanque becomes possible.

The room matters too: open-flued heaters need permanent ventilation and are not suitable for every space. The building may also have rules about new openings in the façade.

This is exactly why we ask for photos of the old heater, its label and the flue before quoting: it tells us what will fit without surprises on the day.

Other features worth paying for

Thermostatic control keeps the temperature stable even when flow changes — very welcome in older buildings where pressure varies.

Hydro-generator ignition (no batteries) removes the most common cause of breakdowns. Low-NOx burners produce fewer emissions.

Brand matters less than the availability of parts and technicians locally. Vulcano, Junkers/Bosch, Ariston and Baxi are all widely supported in Portugal.

What affects the price of a replacement

The heater itself, whether the flue has to change (a new concentric pipe and wall opening costs more than reusing a flue), whether gas and water connections need adapting, and access.

A like-for-like swap on an existing flue is the simplest and cheapest job. Changing type, position or gas is more work. For the full comparison with electric tanks, read esquentador vs termoacumulador.

Mistakes we see when people buy a heater themselves

Buying for the wrong gas: a heater for natural gas when the flat uses bottles, or vice versa.

Buying a type the flat cannot take: an estanque with no route to an outside wall, or an atmosférico for a room without proper ventilation.

Buying the wrong size: an 11-litre model for a family, or a 17-litre model for a studio with low water pressure.

Forgetting the flue: a new heater often needs a new flue adaptor or pipe, which is not in the box.

Send us photos before buying and we tell you what fits. It costs nothing and avoids a heater that cannot be installed.

What happens on installation day

The water and gas are shut off, the old heater is removed and the connections are checked. The new heater is fixed, connected to gas, water and flue (and power, if needed), then tested: gas tightness at every joint, combustion, flue draw and hot-water temperature.

You are shown how to use it, where the gas and water valves are, and what the warning signs are. The old heater goes with us.

Keeping the new heater healthy

Service it every one to two years, keep the room ventilation clear, and in hard-water Lisbon, pay attention to early signs of scale — slower heating, fluctuating temperature. A well-kept heater lasts years longer.

See also esquentador and carbon monoxide.

Frequently asked questions