What Is an Esquentador? The Portuguese Water Heater Explained

How an esquentador works, step by step

When you open a hot tap, cold water starts flowing through the heater. A small valve inside detects that flow and opens the gas supply. At the same moment an ignition system creates a spark — powered by batteries, by the mains, or on some models by a tiny turbine driven by the water itself — and the burner lights.

The water then passes through a copper heat exchanger sitting above the flame and leaves at the temperature set on the front dial. Close the tap and the flow stops, the gas valve closes and the flame goes out. Nothing is kept hot between uses, which is why an esquentador wastes very little energy when you are not using it.

Because it heats on demand, it never "runs out" of hot water the way a tank does. The limit is flow, not quantity: every esquentador has a capacity measured in litres per minute (you will see 11, 14 or 17 on the label). An 11-litre model is comfortable for one shower at a time; running a shower and the kitchen tap together can make the water noticeably cooler.

The three types you will find in Lisbon flats

Atmosférico (natural draught): the older, simpler design. It takes the air it needs for combustion from the room and relies on hot fumes rising naturally up the flue. It works without electricity, but it needs a well-ventilated room and a flue with a good draw. Many older Lisbon buildings still have these.

Ventilado (fan-assisted): has a small fan that pushes the combustion fumes out through the flue. That makes it less dependent on the flue's natural draw and more flexible about where it can be installed, but it needs electricity — look for a plug or a cable next to it.

Estanque (room-sealed): takes combustion air from outside and sends the fumes back outside through a sealed, concentric pipe. It does not use the air inside your home at all, which makes it the safest option and the usual choice for new installations and replacements where the wall allows it.

If you are about to replace an old heater, the type you can install depends on the room, the flue and the building rules — see atmosférico, ventilado or estanque for how to choose.

Which gas does it use?

Every esquentador is set up for one gas at installation. In Lisbon you will see three situations: natural gas (gás natural) piped from the street, propane piped from a tank shared by the building, or butane or propane bottles (garrafas) connected to the heater by a rubber hose and a regulator.

The type of gas is written on the label on the heater. Using the wrong gas is dangerous — a heater set for natural gas will not burn bottled propane correctly, and vice versa. Converting a heater from one gas to another means changing burner parts and adjusting it, which is a job for a qualified gas technician, not a DIY swap.

If you use bottles, the most common reason for "no hot water" is simply an empty bottle. The second most common is a regulator that has failed or was not reconnected properly after the swap. See gas bottles and your water heater.

How to tell which model you have

Look for the label on the front, the side or the underside of the casing. It shows the brand (Vulcano, Junkers, Bosch, Ariston, Baxi and others are common in Portugal), the model, the capacity in litres per minute and the gas type.

A plug or cable means a ventilado or estanque model. A battery compartment at the bottom means battery ignition. A large round flue going straight up into the ceiling is typical of an atmosférico; a double pipe through an outside wall suggests an estanque.

Take a clear photo of the label before calling anyone. It is the first thing a plumber will ask for, and it lets them bring the right parts on the first visit instead of coming back.

Looking after an esquentador

Change the batteries once a year if your model uses them — weak batteries are behind a surprising number of breakdowns. Keep the area around the heater clear: nothing stored on top of it, nothing blocking the air vents in the room.

Lisbon's water is hard, and limescale slowly builds up in the heat exchanger and the water filter. Symptoms are water that takes longer to get hot, temperature that goes up and down, or a heater that switches off during a shower. A service every one or two years cleans the burner, checks the flue and removes scale before it becomes a repair.

Never cover the air vents in the room to keep draughts out. With an atmosférico heater, those vents are what supplies the air it burns.

Warning signs you should never ignore

A flame that is yellow or orange instead of blue, black soot marks around the casing, a smell of gas, or headaches, dizziness or drowsiness while the heater is running all point to incomplete combustion — and possibly carbon monoxide, which you cannot see or smell.

If you notice any of these, switch the heater off, close the gas valve, open the windows and do not use it until it has been checked. We explain the risk in more detail in esquentador and carbon monoxide.

Repair or replace?

An esquentador typically lasts 10 to 15 years. Most faults in that time are small: batteries, the ignition electrode, the flame sensor, the water valve diaphragm or a clogged filter. These are usually worth repairing.

Once a heater is old, has repeated faults, or the heat exchanger is leaking, replacement usually makes more sense. A good plumber gives you both prices when both options exist, so the decision is yours. If you are weighing gas against electric at the same time, read esquentador vs termoacumulador.

Useful Portuguese words around your water heater

Esquentador: gas water heater. Termoacumulador: electric hot-water tank. Caldeira: boiler (heating). Chaminé or conduta de exaustão: flue. Garrafa de gás: gas bottle. Redutor or regulador: the regulator on the bottle. Pilhas: batteries. Torneira de gás: gas valve. Válvula de segurança: safety valve.

Knowing these helps when you read the manual, buy parts or explain a problem to the landlord.

Frequently asked questions