You can keep an unheated guest room dry in winter by not letting the room cool down completely, airing it briefly every day, keeping the door to the rest of the house closed, and running a dehumidifier when humidity is high. Cold walls and windows attract moisture, and in a room that no one uses, this often only becomes apparent when it starts to smell musty.
Why does an unheated guest room become damp?
Moisture does not originate in the guest room itself, but comes from the rest of the house. Cooking, showering, and breathing release water vapour, which spreads throughout the home. When this warm, moist air enters a cold room, it cools down against the walls, window, and mattress. Cold air can hold less water vapour than warm air, so the relative humidity rises and condensation forms on the coldest surfaces.
The RIVM states that dampness problems arise when moist air remains trapped due to insufficient ventilation. That is exactly what happens in an unused room: the door is left ajar, the window remains closed, and no one opens the vent. Now that the first really cold days are approaching, with the KNMI forecast predicting grey days with temperatures around 6 degrees Celsius and a chance of light frost, it is time to keep an eye on the guest room.
How cold can a guest room get in winter?
There is no official minimum temperature for a guest room. The colder the room, the greater the temperature difference with the rest of the house and the faster moisture condenses on the walls. Therefore, it is advisable not to turn the radiator completely off, but to leave it on a low setting. For comparison: Milieu Centraal recommends setting the thermostat to 15 degrees when you are away for a few hours for a central heating boiler. A guest room does not need to be as warm as the living room, but a room that is significantly colder than the rest of the house for weeks at a time runs a greater risk of damp walls and a musty smell.
If the room has no radiator, or if it is deliberately turned off, the door becomes even more important. The less moist air enters from the hallway and bathroom, the less moisture can condense.
Keeping the guest room dry: what works in practice
The basics are simple and inexpensive. Keep the door closed, air the room briefly a few times a week with the window wide open, and leave a ventilation vent open if there is one. Milieu Centraal advises ventilating day and night all year round, even in winter. Place the bed and wardrobe a few centimetres away from the exterior wall so that air can circulate behind them. And do not dry laundry in the guest room: that is exactly where moisture is hardest to remove.
| Measure | Why it helps | How often |
|---|---|---|
| Keep the door closed | Reduces warm, moist air from the rest of the house | Always |
| Air briefly with the window wide open | Moist air is replaced by drier outdoor air | A few times a week |
| Radiator on a low setting | Prevents walls and windows from cooling down too much | During cold periods |
| Furniture away from the exterior wall | Allows air to circulate, preventing cold, damp corners | Once |
| Measure humidity | You can spot a problem before you smell it | Check weekly |
| Run a dehumidifier | Actively removes moisture from the air | When humidity is consistently high |
A simple hygrometer will show whether more action is needed. You can find out how to do this in how to measure humidity in your home.
When can a dehumidifier help in a cold guest room?
If you notice that the humidity in the guest room remains high for weeks, the bedding smells musty, or you see spots in the corners, a dehumidifier can make a difference. You can run it for a few hours a day with the door closed, for example. Be realistic, though: in absolute terms, cold air contains less water than warm air, so a dehumidifier will generally remove less water from a cold room than from a warm, damp bathroom. The device also does not remove the cause; airing the room and preventing it from cooling down too much remain necessary.
If you are going away for a while, similar principles apply to the entire house. You can read more about this in how to keep your home damp-free when you are away for a week in winter. Note: dampness and mould in the home are linked to respiratory problems. The RIVM states that exposure to damp living conditions or mould increases the risk of asthma. A dehumidifier is not a treatment; if you have symptoms, consult your GP.
The AirPure DH251 dehumidifier
The AirPure DH251 is a compact dehumidifier that is easy to move from room to room, which is useful if you only need it in the guest room occasionally.
Dehumidification: up to 900 ml per day
Water tank: 3800 ml, with a safety sensor that switches off the device when the tank is full
Space: suitable for rooms up to 55 m²
Power consumption: 80W
Features: timer from 1 to 24 hours, night mode with display off, ambient light in various colours
Size and weight: 24 x 13.4 x 37 cm, 2.51 kg
Direct answer: do not let an unheated guest room cool down completely, keep the door closed, air the room briefly a few times a week, and measure the humidity. If it remains high, use a dehumidifier.
Want to keep the guest room dry and fresh this winter? Check out the AirPure DH251 dehumidifier or the full range of dehumidifiers from Dynter.
Frequently asked questions
Should you heat a guest room if no one is sleeping there?
Full heating is not necessary, but turning the radiator completely off is also not ideal during a cold period. A low setting prevents walls and windows from cooling down significantly and attracting moisture.
Should the door to an unheated room be open or closed?
Closed. With the door open, warm, moist air flows in from the rest of the house and then condenses on the cold walls and windows.
How often should you air a guest room?
Airing briefly a few times a week with the window wide open is usually enough. In addition, leave a ventilation vent open if the room has one.
Why does the bedding in the guest room smell musty?
Textiles absorb moisture from the air. In a cold, poorly ventilated room, they do not dry out properly, which creates a musty smell. Airing the room and reducing the humidity helps.
Does a dehumidifier work in a cold room?
Yes, but usually less effectively than in a warm room, because cold air contains less moisture. Therefore, combine the device with airing the room and using a low heating setting.