Indoor climate and energy in your home: damp, ventilation and heating

Indoor climate is about more than airing the rooms: the home's construction, its installations and the way you use the rooms also play a part.

In brief

A good indoor climate requires a balance between:

• Fresh air
• Damp
• Temperature
• Ventilation
• Cleaning
• The home's construction

The Danish Health Authority (Sundhedsstyrelsen) recommends, among other things, airing several times a day with 5 to 10 minutes of cross-ventilation, using the cooker hood, airing after a bath or shower and a room temperature that is not below 18 degrees.^[1]

If you find persistent damp, a musty smell or larger areas of mould, the cause should be assessed. Simply washing the surface is not enough.

What is indoor climate?

Indoor climate is the conditions you spend your time in indoors.

It includes, among other things:

• Air quality
• Temperature
• Humidity
• Ventilation
• Dust and particles
• Chemical substances
• Noise and light

In this guide we focus on damp, ventilation, heating and energy, because they are often closely linked in a new home.

The Danish Health Authority describes how a poor indoor climate can cause, among other things, tiredness, headaches and irritation of the eyes, nose, throat and airways, and can make illness worse.^[1]

Get to know your home in the first month

Use the first few weeks to observe the home.

Note:

• Where condensation forms
• How quickly the bathroom dries
• Whether the basement smells different after rain
• Whether the ventilation grilles are open
• Whether the cooker hood extracts the air outside or recirculates it
• Whether some rooms are noticeably colder
• Whether marks appear behind furniture
• How your heating consumption develops

Take dated photos if you notice something. That makes it easier to see whether the problem is growing.

Damp and condensation

Damp occurs naturally in a home.

It comes from, among other things:

• Baths and showers
• Cooking
• Drying clothes
• Plants
• Cleaning
• People and pets
• Leaks and water damage
• Moisture from the ground or the building structure

Condensation forms when warm, humid air meets a cold surface. A little misting can be temporary. Persistent condensation can be a sign of high humidity, cold surfaces or inadequate ventilation.

Moisture on a pipe after a shower is not necessarily the same as damp coming through a wall. The cause has to be found before the solution is chosen.

Signs of a damp problem

Keep an eye out for:

• Persistent condensation on windows
• Dark patches in corners
• A mouldy or musty smell
• Peeling paint
• Wallpaper coming loose
• Swollen wood
• Salt deposits on basement walls
• Damp around pipes and drains
• Discolouration after rain

If the issue was already there at the handover, it may be relevant to compare it with the condition report (tilstandsrapport), the purchase agreement (købsaftale) and photos. See the first 14 days after the handover for documentation and next steps.

Mould

Mould can grow where there is enough moisture and organic material.

The Danish Health Authority states that visible mould should be removed as quickly as possible.^[1]

But removing the visible area does not necessarily solve the problem. If the source of the damp continues, the growth can come back.

If you suspect mould, you can:

1. Document the area
2. Look for an obvious source of damp
3. Limit further moisture, if it can be done safely
4. Have the extent and cause assessed if the problem is larger or keeps coming back

Health symptoms should be assessed by a healthcare professional. BoligKlar cannot determine whether a mark is mould or what it means for your health.

Airing with cross-ventilation

The Danish Health Authority recommends airing several times a day with 5 to 10 minutes of cross-ventilation.^[1]

Cross-ventilation replaces the air quickly. A window left ajar for a long time can cool the surfaces down without giving the same rapid change of air.

The need depends on, among other things:

• Number of people
• Size of the home
• Ventilation system
• Cooking and bathing
• Drying clothes
• Season and weather

If the home has mechanical ventilation, the system is normally designed to work together with how airtight the home is. Do not close vents without understanding the system.

Bathroom and kitchen

Bathing and cooking add a lot of moisture.

The Danish Health Authority recommends:

• Using the cooker hood while cooking
• Airing after cooking
• Keeping the bathroom door closed during and after a bath or shower
• Airing after a bath or shower^[1]

Check whether the extractor fan starts and whether the grille is clear. If the moisture lingers for a long time, the ventilation may need to be assessed or cleaned.

Drying clothes

Clothes release moisture as they dry.

The Danish Health Authority recommends drying outdoors or using a tumble dryer vented to the outside or a condenser tumble dryer.^[1]

If clothes are dried indoors, the need for ventilation increases. A small closed room without airing is particularly exposed.

Temperature

The Danish Health Authority states that the room temperature should not be below 18 degrees and should be the same in all the rooms of the home.^[1]

Very cold rooms can have cold surfaces where moisture condenses more easily. At the same time, energy use depends on the type of home, insulation, heating system and how you use it.

The aim is not necessarily the same precise temperature in every home, but to avoid large and persistent differences without understanding the consequences.

Basement

A basement is often cooler and more affected by damp than the rest of the home.

Check:

• Whether the basement is approved for habitation
• Whether there is a drain and a pump
• Whether walls and floors show signs of damp
• Whether the ventilation works
• Whether organic materials are placed directly against walls and floor
• Whether the smell changes after rain

A dry basement on the day of the viewing is no guarantee of the conditions throughout the year.

The energy label

The energy label (energimærke) shows the building's energy performance on a scale from A to G and points to possible energy improvements.^[2]

The report can describe, among other things:

• Insulation
• Windows and doors
• Heating system
• Calculated energy demand
• Suggested improvements
• Estimated costs and savings

The energy label is based on standard assumptions. Your actual consumption may be higher or lower depending on your household, temperature, weather and habits.

Read the in-depth guide on the energy label when buying a home.

Energy and indoor climate must be considered together

When you draught-proof or add insulation to the home, the rate of air change can change.

A project should therefore not only be about heat loss. Ventilation, damp and construction need to be factored in.

Examples:

• New airtight windows can reduce natural air change
• Added insulation can change surface temperatures
• A new heat source can change how the rooms are used
• Mechanical ventilation requires correct operation and maintenance

If you are planning larger changes, you can read the guide on renovating after buying a home.

Owner-occupied flat

In an owner-occupied flat (ejerlejlighed), the indoor climate can be both your own responsibility and the owners' association's (ejerforening).

A problem can be linked to:

• Shared facade
• Roof
• Soil stack
• Basement
• Shared ventilation
• Heating system

Document the issue and contact the managing agent if the cause may lie in a shared part of the building. The articles of association and the specific cause determine who is responsible.

Your checklist

• I have found the ventilation grilles and extract vents
• I know whether the home has mechanical ventilation
• The cooker hood and bathroom ventilation have been checked
• I am keeping an eye on condensation and damp
• Signs of mould have been documented
• I know the home's heat source
• I have read the energy label
• I have compared calculated and actual consumption
• Ventilation is factored in when making energy improvements
• Shared matters have been clarified with the managing agent

Common misconceptions

Condensation on windows always means building damage

No. It can also be caused by high humidity and cold surfaces. Persistent problems should be investigated.

Mould can be solved by painting over it

No. The cause of the damp has to be found and dealt with.

A good energy label guarantees low consumption

No. The label is based on standard assumptions, while actual consumption depends on use and conditions.

More airing always solves the problem

No. If the damp comes from a leak or the building structure, the source has to be dealt with.

Vents can be closed if there is a draught

That can affect how a ventilation system works. Have the system explained to you before you change any settings.

In summary

A good indoor climate starts with observing the home.

Air the rooms, use the ventilation, keep an eye on damp and act on persistent signs. Use the energy label as a planning tool, not as a guarantee of your bill.

See also the guide on heating and electricity when moving and the guide on maintenance.

BoligKlar gives you a second pair of eyes and an overview. Damp, mould, installations and health may require an individual assessment from the relevant professionals.

Frequently asked questions