Shutting every window in winter feels sensible, but it keeps in the moisture you make. Here is how little fresh air can do the job, cheapest step first.
Keeping every window and vent shut does not reduce condensation, because the moisture from cooking, showers, laundry and breathing has nowhere to go. Council and GOV.UK guidance favours short, regular ventilation: open a window wide after cooking or bathing and close it once the air has changed, or open a few windows a little rather than one fully. You do not need to leave windows open all day.
Streaming glass in the morning, a stuffy room, mould that creeps along a cold wall, and a feeling that opening a window just lets the heat out. Sefton Council points out that cooking, washing, drying clothes indoors and even breathing all produce water vapour. If that vapour cannot leave, it settles on the coldest surface it finds.
Whatever type of home you have in Ashford or nearby, for example in Kennington or Willesborough, the rule is the same: moisture made indoors has to leave somehow. Tighter, newer homes depend more on trickle vents and fans, so read the new-build condensation guide if that is you.
Fresh air will not stop a leaking gutter, a failed seal or rising damp, and a dehumidifier will not either. If a wall is wet in a way that follows the rain rather than the weather indoors, find the leak first. If you rent, a portable unit is more realistic than a loft-mounted system. If noise, security or cold is why you keep windows shut, GOV.UK guidance recognises those worries, and the vent position and trickle vents are the compromise.
A Dryzen system is a loft-mounted dehumidifier and fresh air system with insulated ductwork to the central area or stairway of the home. Each unit covers up to 150 square metres, extracts about 12 litres a day and costs about 20 pounds a year to run, with an adjustable ratio of fresh and recycled air, both dehumidified and filtered. It suits owner-occupied homes with a loft and is not suitable for rentals unless the landlord authorises the changes. It helps stop the conditions mould and dust mites need, but it does not remove mould that is already there, which must be cleaned off. A free survey can measure humidity through the day and tell you honestly whether a system would help. See the healthy humidity guide for the target range.
The guidance gives no single figure. GOV.UK advises opening wide and closing once the air has changed, and Basingstoke Council suggests short, regular periods. Watch for glass and mirrors clearing, or a hygrometer reading falling back towards 40 to 60 per cent.
Short bursts limit heat loss, according to Basingstoke Council, and keeping windows and vents shut to save heat will not reduce condensation. Sefton Council adds that it should not be necessary to leave all windows open all day.
Sefton Council notes that how much ventilation you need varies with the weather and how much water vapour you are making. On colder days keep to short bursts, use extractor fans and keep trickle vents open.
Sources: Basingstoke and Deane Borough Council: Condensation and mould; Sefton Council: Condensation, damp and mould advice; GOV.UK: Understanding and addressing the health risks of damp and mould in the home; Centre for Sustainable Energy: Damp and condensation
Last reviewed 2026-10-17. General guidance only; this is not a survey of your home.