Portugal has relatively mild winters but if apartments do not have heating (central or partial), it should be cold and damp inside in winter.
How common are heating systems in Portuguese apartments and how well they work?
Is there any mold growing in some corners where air circulation is poor?
Do locals pay attention to it or they just consider all this inevitable?
@Masha,
Normally new houses or refurbished houses in older neighbourhoods, have central heating, double walls and double glasses. This is true for upper middle/high range houses. For middle/lower range houses, central heating is not common/does not exist. There is an idea that Portugal is a warm country, but winters can be very cold and wet, although it is not comparable to the rest of Europe concerning cold winters. But now with climate change, all this is more and more uncertain...
The certificate of energy is MANDATORY since 2013 in the purchase and rental of houses. In real estate agencies, each house advertised is always marked with the energy certification assigned to it by a certified technician (A+, A, B, B-, C, D, E and F).
@JohnnyPT
What kind of rating should apartment have in order to be able to maintain comfortable conditions (say, around 20C) in winter?
What about summers? Do you need a lot of air conditioning or it's pleasant enough without?
The energy certificate doesn't exactly answer that question. It will help give you an idea how much heat you will have to put into the apartment, to keep it warm - i.e., the efficiency of its insulation - but even there, it is influenced by other considerations, particularly whether the input involves renewable sources or not.
In addition, you have to consider potential limitations to the heat source. For example, if using electrical heat, if I'm right, a 10 ampere circuit will support no more than 2000W - and that may be about the limit for the entire dwelling. If it has a recuperador de calor fireplace+radiator system, you won't likely be operating that around the clock. Etc.
This is an example of an energy certificate:
https://www.sce.pt/certificacao-energet … sumidores/
Download it by clicking at:
"Clique aqui para descarregar uma versão exemplificativa do certificado Energético de Edifício de Habitação"
It includes issues related to the efficiency of heating and cooling of the house.
You can translate PDF into English using a Doctranslator, such as:
From my experience with a T2, which was classified as C, I would use the Energy Certificate only as a guidance. I do have gas central heating and I try to keep the bedroom at above 18C and the living areas at above 20C. In summer it can get pretty warm in the apartment, but that's what I like anyway.
Regarding humidity I would always recommend buying one or two larger dehumidifiers. Otherwise the likelihood of getting mold is the not so well ventilated areas is huge.
Also the certificate reflect what was there, when it was created. So with the overall degeneration of the building the real value might deteriorate as well.
When I came to lisbon I got shocked by not having a heating system in the apartment. I found out that Portuguese house doesn't use heating in central that much even in new apartments almost they are using air conditioner not radiator nor floor heating
Regarding humidity I would always recommend buying one or two larger dehumidifiers. Otherwise the likelihood of getting mold is the not so well ventilated areas is huge. -@nz7521137
Having a dehumidifier at home is a quite good investment 
@Negar Nasiri Sad reality. We found out the hard way !
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