Questions regarding ventilation units

Below we have listed some of the most common questions and answers regarding ventilation units.
If you need further information, please contact one of our dealers or service partners.

Choose from the following topics:

  • Ventilation in general
  • Indoor climate
  • Economy
  • Service and maintenance
  • My house gets too hot during the summer
  • The ventilation unit does not work as expected
  • When should I contact someone, and whom?

Contact our business partners

Whether you need to buy a new filter or need assistance with troubleshooting or adjusting your Nilan unit, our partners can help you.
You will find links to both Danish partners and abroad here.

Ventilation in general

A ventilation unit with heat recovery extracts warm, humid and vitiated air from the kitchen, bathroom and utility room in the dwelling. Fresh outdoor air flows into e.g. living-room, bedrooms and study. The cool outdoor air gets heated up in the heat exchanger by the warm extract air. That way the energy from the extract air is recovered and recycled.

Passive heat recovery is a process that takes place in a high-efficiency counterflow heat exchanger (heat exchanger). Warm extract air flows into the exchanger from one side. From the other, cold outdoor air flows into the exchanger. When the two bodies of air meet inside the exchanger, the heat from the extract air is transferred to the fresh outdoor air, which then flows into the dwelling.

Active heat recovery occurs when a heat pump draws out the energy from warm extract air via an evaporator. The reclaimed energy is then transferred to cold outdoor air via a condenser.  Active heat recovery is not indicated in percentage, such as passive heat recovery, but as a COP (coefficient of performance). COP indicates the energy output in kW compared with the energy in kW used for operation. A COP of 4 therefore means that for every 1 kW energy consumed by the heat pump, you get 4 kW energy in the form of heating. With a heat pump, heat recovery therefore often exceeds 100%.

The heat pump has a reversible cooling circuit, which means that it can heat the supply air in the winter and cool the supply air in the summer. 

Some of Nilan’s ventilation units are equipped with both a counterflow heat exchanger and a heat pump. Heat recovery is primarily carried out in the counterflow heat exchanger. However, if it becomes necessary to heat the dwelling by means of the supply air, the heat pump will start up and transfer more heat to the supply air. On the other hand, if cooling is required, the heat pump will reverse its cooling circuit and cool the supply air.

In all new builds, you can decide already at the planning stage that a ventilation unit is to be installed.

In already existing dwellings it can sometimes be a challenge to run the ventilation ducts throughout the building. You should therefore seek expert advice regarding the possibility of running the ducts through your dwelling, and also about which ventilation unit would best suit your situation. 

The level of noise from a ventilation unit depends on whether it has passive or active heat recovery.  Ventilation units with passive heat recovery generally produce very little or no noise. Ventilation units with an integral heat pump are slightly more noisy, but typically no more than an ordinary refrigerator or freezer.

Nilan produces ventilation units of different sizes and with duct connections placed on top or on the side of the unit.  A top unit is typically installed in a tall cabinet, whereas a unit with duct connections on the side may be installed in, for instance, an unused attic. 

You do not need permission from the council in order to install a ventilation unit with air to air heat recovery. However, it is important that it meets the requirements specified in the existing Building Regulations regarding power consumption and heat recovery.

If you have no experience with dimensioning and installing ventilation units, we recommend that you get an expert to carry out the installation.

Indoor climate

You should ventilate your dwelling in order to achieve a comfortable and healthy indoor climate that helps protect you against illness, and the building against mould and dry/wet rot.

The air in the dwelling is continuously being polluted from different sources such as furniture, carpets, wall paints and electrical appliances that all emit chemicals and gases. In addition, particles from candles and cooking (roasting and baking) cause cardiovascular diseases. It is therefore important to remove these as particles well as chemical gases from cleaning products. This can be done through ventilation.

Another source of pollution is dampness. If the humidity level is too high during the winter, it can harm your health and damage the building. If the humidity level exceeds 60%, dust mites will thrive easily, and if it exceeds 75%, mould and dry/wet rot may occur and cause damage to the building. 

It is therefore important that the dwelling is properly ventilated.

In winter, during prolonged periods of subzero temperatures and especially when it is also below freezing in the daytime, ventilation can cause the humidity level in the dwelling to fall to just 20%. This can lead to cracks appearing in e.g. wooden furniture, wooden floors and in walls. To the inconvenience of the residents of the dwelling, dust will also spread more easily.

These issues cannot be ascribed to the ventilation unit as such. The unit is simply ensuring that the requirements stated in the Building Regulations are met with regards to the minimum level of air exchange. Natural ventilation causes the same issues, provided the Building Regulations are met.

All Nilan’s ventilation units have an intelligent humidity control system that can be set to reduce ventilation during those short spells during the year when the humidity level in the dwelling could potentially become very low. This prevents the humidity level from becoming too low and causing issues in the dwelling. 

Scientists recommend that we keep the humidity level in our homes between 30% and 60% as this creates the least favourable conditions for bacteria and viruses.

Most people with allergies experience a considerable improvement after having had a Nilan ventilation unit installed because of the subsequently improved indoor climate. For any of Nilan’s ventilation units, you can purchase a pollen filter as an optional extra. It filters out pollen from the outdoor air so you get affected as little as possible inside the dwelling.


All ventilation units by Nilan have CE marking and they are therefore officially approved to sell throughout Europe.

Building Regulations include requirements to power consumption, heat recovery and noise that must be met. Nilan’s ventilation units easily meet these requirements as the units are highly energy efficient and comparatively noiseless.

Within the EU, ventilation units with passive heat recovery must comply with the Ecodesign Directive. Nilan therefore has to supply product data in a particular way so you, the consumer, can compare different products. In addition, the EU carries out market surveillance on products to ensure that the data supplied by manufacturers are correct.

It depends on your individual requirements. It depends on the size of your house and whether you want the unit to also provide heating and cooling of the dwelling as well as domestic hot water, or perhaps a combination. 

Please, contact a Nilan dealer to get a quote for your particular requirements.

The power consumption depends on which model of ventilation unit you choose and how you use it. The power consumption varies from 300 to 2,000 kWh a year.  You can see the indicative power consumption in the data sheet for the individual ventilation units under “Ecodesign Data”.

You can find examples of calculations on the Danish Energy Agency’s website.

A Nilan ventilation unit typically has a service life of more than 20 years.

Service and maintenance

There are no legal requirements preventing you from installing the ventilation unit yourself. You can download Installation and Software Instructions from our website under Downloads.

However, we recommend that a certified dealer carries out both installation and balancing. It requires expertise to be able to install the unit so you achieve maximum operation with the lowest possible power consumption and low level of noise. 

It is important that you carry out maintenance to your ventilation unit in order for it to operate properly for many years. You can compare it to a car that will eventually break down if it is not maintained.

The most important thing is to replace the filters when they are dirty, which typically means 4 times a year. In addition to this, the unit will need an annual check-up. You can find a detailed description of the maintenance requirements in the User Manual for the individual ventilation unit. The manual can be downloaded from Downloads.

You can buy filters from our dealers and service partners either online or over the phone. Please state which ventilation unit and model you have and its approximate age so you are sure to get the correct filter.

The primary function of the filter is to protect the ventilation unit.  You will be able to purchase the same type of filters that the unit had been fitted with when it was delivered, called ISO Coarse > 65% (previously called G4 filters).

If anyone in the household has allergies, we will recommend that you purchase a pollen filter ISO ePM1 50-65% (previously called an F7 filter).  It filters out most of the pollen from the outdoor air. The filter area of the pollen filter is bigger than the standard filter and it therefore does not need replacing quite as often.

With a ventilation unit with passive heat recovery, you can carry out service inspection and replace filters yourself.  However, if you want to check the balance of the whole system, you will need a specialist to do this. 

If your ventilation unit is equipped with a heat pump, the service inspection of the heat pump must be carried out by a certified cooling technician or a Nilan service partner.

When the unit is fully installed with ducts and valves, it will need balancing. This ensures that the unit runs with the right air volume to the individual rooms. 

If, by accident, you alter the setting of the valves, you will need to get the ventilation system balanced again. Otherwise it will not operate as intended.  If the valves are set incorrectly, the ventilation unit may consume more energy and the quality of the indoor climate may be reduced.

The dirt that potentially gathers around the valves does not come from the ventilation unit.  A turbulent flow occurs around the valves when air flows in or out.  The turbulent movement causes dust in the room to whirl around and settle in the ceiling around the valves. 

When you clean the valves and the area around them, it is important that you do not change their setting as this may spoil the balance of the entire system.

My house gets too hot during the summer

In dwellings with large, south-facing windows or poor insulation, you will often experience that the temperature fluctuates considerably from early spring to late autumn whenever the sun is shining. During summer it can be almost unbearable and a real problem to the residents.

It is therefore often blamed for making the dwelling too hot during summer. In reality, however, an ordinary ventilation unit does not contribute much to the heating of the dwelling during the summer. Even if it does not have 100% bypass and it supplies air at outdoor temperature, it has only limited impact on the temperature in the dwelling due to the air exchange being only ½ a time every hour. 

We are often asked if a ventilation unit can cool the dwelling in the summer, but this is not the case. The air exchange rate in a standard dwelling is ½ a time every hour. In order to achieve efficient cooling, however, the air exchange rate needs to be 7-10 times per hour. A ventilation unit for a dwelling is unable to do this.

Nilan sells ventilation units with an integral heat pump. Its primary function is to heat the dwelling during winter. In the summer, the reversible heat pump can cool the supply air with up to 10 °C. However, the cooling effect remains limited due to the low air exchange rate.

When cooling the outdoor air, humidity is extracted from the supply air. Instead of an indoor temperature of e.g. 28 °C and a humidity level of 80%, you may end up with an indoor temperature of 25 °C and a humidity level of 60%. The reduced humidity level makes it easier to cope with the heat. That is why we call it “comfort cooling”.

The best solution is to stop the heat from entering the dwelling in the first place by using external screening in the form of blinds or curtains.

A window with low-e glass and no sun screen gives off approx. 600W heat/m2. You can then calculate yourself how much heat is transferred into your dwelling. With window sun screens, windows will give off approx. 90 W heat/m2. This is a considerable reduction that requires very little energy.  

If you decide to use external screening, we will recommend that you choose screens with a control system that detects outdoor and indoor temperatures. They will then only screen out the sun when it gets too hot inside the dwelling, and not during periods when you would like the sun to help heat the dwelling.

If your ventilation unit does not work as expected

Contact the dealer from whom you purchased the unit. This is also the case if you purchased the unit online.

When the outdoor temperature is very low, ice may form in the counterflow heat exchanger (heat exchanger). This is normal in a ventilation unit with a high level of heat recovery.

Ice formation occurs when cold outdoor air meets humid extract air in the counterflow heat exchanger. The moisture in the humid air will turn to ice inside the exchanger, and over time more and more ice will form.  The ice needs to be removed regularly; a process that is controlled by the integral control system of the ventilation unit. During de-icing, the supply air temperature may be lower than it would otherwise be during ordinary use of the unit. For de-icing to occur, you make the cold outdoor air bypass the counterflow heat exchanger by opening the bypass damper. The heat from the extract air is then utilised to de-ice the counterflow heat exchanger.

In extreme cases, the counterflow heat exchanger may not be de-iced effectively. Ice will then slowly keep forming until the counterflow heat exchanger eventually closes up completely. This is a very rare occurrence. Should the counterflow heat exchanger ice up completely, you can remove it from the ventilation unit and rinse it in hot water in the shower. 

If you want to prevent the counterflow heat exchanger from icing up altogether, it is recommended that you install a pre-heating element for frost protection. The heating element ensures that the outdoor air that flows into the ventilation unit does not fall below 0 °C. This will prevent ice formation. This is also a financially good solution. See detailed explanation in the datasheet for the ventilation unit. You can find it under the menu item Downloads.

When should I contact someone, and whom?

If you want to purchase a Nilan ventilation unit, please contact one of our authorised dealers. They can offer advice and ensure that you get a unit that meets exactly your requirements.

Contact the dealer from whom you purchased the unit. This is also the case if you purchased the unit online.

If the unit is not working and it is still under warranty, please contact the dealer from whom you purchased the unit. This is also the case if you purchased the unit online.

If the warranty has expired, please contact one of our service partners.

Nilan collaborates with some companies that carry out balancing. You can contact any of these to get your unit balanced.

The dealer from whom you have purchased the unit will be able to talk you through exactly how the unit works and how to operate it.