Opening windows or closing them might be good advice against humidity.

Disclaimer: Humidity is an important topic at Portugal; and at a lesser level at Italy; and at an even lesser level at the North of Europe. Moisture is not a focus of my profession. I offer this webpage for gratis as hints to protect you and your properties from fungi, but I do not perform truly conclusive experiments or analyses of mildew. I do not know! Clyde Windows and Construction Limited and Community Energy Plus advise that condensation is complicated. A good source contradicts a different good source. A single recommendation might be good but its opposite might contrarily be good at a different time (e.g. night versus day; or Summer versus Winter); and/or at a different location (e.g. west Portugal versus east Portugal versus Italy); and/or with a different climate; and/or with different conditions which I do not enumerate! Misinterpretations and invalid generalisations are too easy! Do not rely on this webpage and do not prosecute me over it! Buy a hygrometer and a dehumidifier and open windows and doors and close windows and doors to find out what technique or techniques works or work for you. If you offer evidence or counterevidence or data or counter-data, then I might consider it or them. Thanks!

A good real-estate agency (Nest Property Management at Louth) gave me a pamphlet about mustiness. I failed to find an Internet version. Similar webpages are WWW.FNREM.com.Au/pages/real-estate/blog/4526/the-menace-of-mould-and-how-to-manage-it and WWW.PropertyTribes.com/down-in-the-damps-t-2084.html and HTTPS://CEP.org.UK/landlords/damp-condensation-and-mould-advice-for-landlords and WWW.ClydeWindows.com/blog/windows/internal-window-condensation/?srsltid=AfmBOoqcZ_pLawhwSvMLowDgwFgEhKB3CHnemvmvGaeNgW-XnmkBepGX and WWW.DIYdata.com/problem/condensation/condensation-overcoming.php and WWW.Netmums.com/coffeehouse/home-garden-194/cleaning-14/110656-condensation.html etc.

Coimbra and Oporto and Montemor-o-Velho and Matosinhos and Condeixa at Portugal are too humid. The map of humidity which this sentence hyperlinks to does not show Azores, which is even worse more humid than Coimbra according to a lady who used to reside at both Azores and Coimbra.

I bought a dehumidifier (during 2008) and 2 hygrometers at Portugal. A dehumidifier significantly reduces a house’s humidity. A hygrometer also showed me that open doors and open windows during non-night times much more significantly reduce a house’s humidity than a dehumidifier accomplishes. WWW.Netmums.com/coffeehouse/home-garden-194/cleaning-14/110656-condensation.html alleges that a "a positive pressure unit" is better than a dehumidifier.

The 2nd Republic of Portugal robbed a hygrometer etc. of mine. “I keep my expectations low.” said an advocate about regaining my properties that Portugal robbed on 5th July 2023.

The metrological forecasters here predicted that humidities here can be e.g. worse than 80% throughout 23rd August 2025 and between 80% and 100% between 7p.m. and 2p.m. earlier during the same week or similar humidities between 8p.m. and 10a.m. even earlier during the same week. (E.g. 100% at 3a.m.; 80% at 7p.m.; and 86.3% at 9a.m.)

“indoor humidity of 80% or higher
[. . .]
•In winter, you still need to open windows on a daily basis (wait till the warmest time of day)
[. . .]
•[. . .] opening blinds during the day”
says First National Real Estate Maitland at Australia. Cf. WWW.PropertyTribes.com/down-in-the-damps-t-2084.html and HTTPS://CEP.org.UK/landlords/damp-condensation-and-mould-advice-for-landlords and WWW.DIYdata.com/problem/condensation/condensation.php etc.

However Clyde Windows and Construction Limited says: "During the beginning of the winter when you start to heat your home, condensation occurs. After a few weeks, your home will begin to dry out and you’ll see less condensation. Opening a window briefly is a quick temporary solution. The dryer cold air will enter the room while the moist air is allowed to escape."

Clyde Windows and Construction Limited says: "During the winter months, condensation will be seen on the inside of the window. Condensation will present itself on the outside of the window during the summer months." Moisture on opened and closed windows here was on their outsides, not insides, on 18th August 2025 (i.e. a warm day during a warm month) shortly after 6a.m. o'clock.

"I bought a wardrobe and chest of drawers for my lo and the backs of them have gone mouldy I keep wiping down but it returns. As I said before the windows are so wet in the morning and I never leave windows closed fully plus we have a few wall air vents in every room." says a person who reports worse dampness than I ever lived with.

Mother owns a printout of a document. That document seems to be a webpage of a newspaper. It recommends to avoid fustiness by never opening curtains. That document does not convince me. Cars’ windows do not have curtains. Cars’ windows gain moisture before 6a.m. o’clock. I keep a subset of this house’s curtains opened and different subsets closed and opened for different amounts of times. I do not detect an overwhelming difference of moisture between any of these windows.

Italy is too humid. Many persons attempt to dry clothes outside at Italy during nights. An educated gentleman at Italy said that that is normal and bad because nighttimes humidities are against drying. He said that many persons at Italy do not know that that is a bad technique.