Heat recovery with decentralised ventilation systems

It is a common misconception that airing the house by opening all windows at once is a cheap way to bring fresh air inside. However, this is only a quick fix, because even though this means no installation or electricity costs for you, this method proves to be utterly ineffective when drawing an energy balance, and offers no heat recovery at all. Indoor air that has been brought to an agreeable temperature escapes to the outside, but the energy that was used for heating the air is never gained back. If you really think about it, this is a great loss! Ventilate and save costs the smart way while doing something good for the environment. You can do this by applying a fan-supported home ventilation system in combination with a hear recovery device.

Decentralised ventilation systems are easily implemented in newer and older buildings respectively as they do not require much effort when it comes to installation, which also makes it perfect for individually ventilating single rooms.


  • Humidity and mould
  • Functionality of decentralised heat recovery
  • At a glance: advantages and disadvantages of a system
  • Tips for use in kitchens and bathrooms
  • Measures in summer and winter
  • Cleaning, maintenance and care 

Humidity and mould

It is currently a trend to renovate old buildings or build new homes in a way that they consume about 30 % less primary energy than it is the case in traditional, conventional buildings, meaning that consumption is reduced by keeping the loss of energy at a minimum. However, this „air tight“ insulation cannot transport humidity from inside the house to the outside without any further means of ventilation, which has proven to be a main cause for mould and damage of building materials. The prime reason for installing a ventilation system is the prevention of high humidity by ensuring sufficient air exchange and transportation of humidity. It either functions as a support for regular airing with windows or as the only supply of fresh air in rooms without windows.

The formation of mould is more than just a visual problem: Resistant mould spores are extremely bad for your health, irritate your respiratory tract, provoke headaches and are suspected to cause cancer. The basic structure of the building can experience irreversible damage if mould penetrates the organic materials deep enough. Sometimes the infested wall becomes porous and the affected spots starts to disintegrate, which leads to the suffering of the complete construction. Spores already begin to form under a humidity level of 60 – 80%, particularly in places where warm indoor air meets a cold exterior wall or surface, for example in corners above the windows or directly on the window sill. Curtains, wallpapers and the beloved decoration on the window sill are often the victims. Mould stains and serpula are unfortunately not always formed in obvious places, but rather like to thrive and flourish behind closets and cover panels. Condensation and melting water on windows only become visible once they reach 100% humidity and are a sure indicator that humidity inside the house is too high! Especially rooms where laundry was drying over night and now have fogged windows should never be left to natural regulation alone. If you spot the first black spots on your wall you still have the possibility to easily remove them with cleaning agents from the supermarket, aggressive agents with clorine are available for tenacious stains. It is also imperative to change your ventilation and airing habits, prevent over 200 kinds of fungi with sufficient and regular ventilation through a modern system. 

Functionality of decentralised heat recovery

If supply and exhaust air is controlled by fans, heat recovery comes into play. That means the ventilation system takes the thermal energy from the used air that is transported to the outside and passes it on to supplied air. A heat recovering system for rooms that are being heated is a good investment, because, without too many extra costs, it kills two birds with one stone: On one hand you have a regular supply and exhaust air cycles in your premises and on the other hand reutilisation of thermal energy that was taken from air that has already been heated.

In our product range, with a ceramic unit for storage:

The energy requirements of fans may add to your expenses, but stays absolutely manageable thanks to energy-saving devices, partially equipped with direct current motors. The models we offer at creoven.co.uk consume as little as 2.8 to 6.1 Watt, for example. The flow rate of these models has a maximum of 58 m3/h and ventilates rooms with up to 50m2.

The decentralised ventilation system with heat recovery is compatible with all types of heating and combustion methods. However, the device must be installed in accordance with strict safety measures if they are installed with heat-producing appliances that require indoor air, like furnaces and fireplaces, so that harmful exhaust fumes do not end up in the air. If necessary you can talkt o your chimney sweeper about compliance with the guidelines.

The installation of a ventilation system is done without too many structural measures: A specialist is going to drill a hole through the outer wall of the room and the device is inserted with one opening facing the inside of the room and the other opening reaching the environment on the outside. In case several rooms are to be equipped a small cut-out in each of them is required. However, there is not need for connecting ducts, which is an advantage compared to centralised ventilation systems. In that, decentralised ventilation offers you constant, improved air quality for a low price with easy installation and manageable amount of maintenance efforts. Supply and exhaust air go through the same device so that heat recovery is achieved through one of the following methods:

Recuperators These heat exchangers absorb the energy of the exhaust airflow that crosses the supply airflow. This leads to a directy exchange of heat.

Regenerators e.g. with high-quality storage units made of ceramic that absorb thermal energy from the exhaust air and later pass it on to the supply air.

The filters that are inserted for both supply and exhaust air protect your device from pollution from the inside and outside and relieve breathing air from germs, bacteria and smells. The filter classes G1 to G4 are coarse filters and refer to their permeance. The higher the number, for example G4, the more small particles can be filtered. Filters classified as “fine“, F7 and higher“ are even more capable, and are a blessing for people with allergies or weak immune system. They even remove viruses from the air and therefore comply with strict guidelines for hygiene in doctor’s offices and hospitals.

The fans are usually designed to have a practical and simple design that does not attract too much attention. Generally the compact device is hidden by shells and grilles on the outside wall and on the inside of the room, their subtle, light and neutral colours matching the walls. The housing is weather-proof and easy to clean from the outside and inside. When going through with the purchase pay attention to brand quality with extended warranty, the filter should be replaceable without any troubles. Before it comes down to the actual installation, think of a place where electricians can reach the control unit of the device effortlessly. Apart from that, the wall break can be round or square and, in case of the latter, horizontally, vertically or even inclined. This is mostly a matter of space and personal taste, and does not have any influence on the efficiency of the fans. 

At a glance: advantages and disadvantages of a system

Suitable for:

  • Decentralised systems are particularly recommendable for old buildings and single rooms with high heat density, e.g. in living rooms and other main rooms that are used frequently. However, they are also suitable for single rooms in newly built passive houses and are mounted directly to the wall.
  • permanent support of natural ventilation with windows or in rooms without windows
  • for energy efficient renovation of old, reconstructed or new buildings
  • Under certain circumstances, for example a heat recovery of more than 80 %, the financing of ventilation systems may grant entitlement of government aid. Ask a representative of your bank, energy consultant or architect.


  • financially foresightful, environmentally friendly and sustainable
  • At least 75 % heat can be recovered from exhaust air, depending on the manufacturer this number can even increase to 90%! That way you gain energy savings through ventilation. Check the rate of heat recovery of your desired system before purchasing, we recommend at least 80 %.
  • Closed windows mean less chances of cunning burglars, reduced harrasment by pollen, grass and insects, less noise – all while the supply of fresh air remains the same, thermal insulation is improved significantly and prevention of mould. Also, the rain will not get inside anymore if you leave the window open, the wall stays dry, just like it should.
  • Prevention of mould and damages through humidity
  • Targeting single rooms: benefit from the possibility to individually adjust airflow in each room
  • Easy installation, no big structural alterations / changes: suitable for renovation in old buildings
  • Constant operation ensures good indoor air quality without having to check frequently
  • Low investment costs (compared to centralised systems)
  • A blessing for people with allergies: pollen, dust and germ filters
  • Energy-saving devices are available
  • No central ducts are required


  • When looking for the suitable manufacturer it is imperative to pay attention to the sound level of the system! Bedrooms and studies in particular are affected by constant loud noises. With a sound pressure level of less than 25 dB(A) on the lowest setting you reach a level that can be compared to whispering or the ticking of an alarm clock, which is still quite acceptable in bedrooms. For the purchase, please keep in mind that is easier to get used to a steady background noise than a device that produces a changing sound with high and low pitches.
  • If the entire house is supposed to be equipped with a ventilation system, a centralised system might be better for you.
  • Condensation water should be able to flow to the outside through the device (not directly on the exterior wall).

Tips for use in kitchens and bathrooms

Especially in rooms that are constantly exposed to high humidity, e.g. kitchen, bathroom, washing room and toilet, it makes sense to support ventilation with windows with a mechanical ventilation system. That way even rooms without windows can reach ideal air quality, a decentralised ventilation system is an excellent way of preventing mould, keep breathing air at a good quality level and extract smells.

Kitchens, bathrooms and toilets are rooms with so-called extract air. Inside these rooms we usually encounter a higher amount of humidity and heat, which means that they need to comply with stricter guidelines: If you are considering to use models in these rooms that work based on alternating operation (air extraction phase followed by air supply phase), you might be obligated to install two of those device in each room with extract air. A device that combines a heat exchanger and two integrated fans is also permitted. Extract air rooms without windows are a special case where the air needs to be exchanged sufficiently with a mechanical ventilation system, in a kitchen this can be done by regular airing. It should be made sure that all rooms inside the house without windows can be ventilated at the same time if necessary. Due to bad smells it can actually make more sense to install only extractor fans in these rooms that are complemented by decentralised systems in other rooms.

Heat recovery is also recommendable in cellar rooms if is being heated as well, for example when it is used as a hobby room or laundry room. 

Measures in summer and winter

On cold days and a high potential of heat recovery in winter (through permanent heating) condensation water can develop on the inside of the ventilation system. It is either collected in a container inside the device itself which needs to be emptied regularly, or the water is lead outside through a ventilation grille and can drip off with a safe distance to the exterior wall of the house. The manufacturer should always include the problem of condensation in the item description and offer an adequate solution for the particular product. If that is not the case for your system, we recommend a fitting grille for external walls in our accessory range.
During summer rooms tend to get hot and muggy, the cold air at night is a welcome change. A summer ventilation feature offers you the possibility to supply fresh air at night without heat recovery. This means you are reducing heat inside your home without an air conditioning system.

Tip: In order to let in a summer breeze that smells of flowers and grass or to feel the cold winter frost on your skin, you are of course allowed to open the window for a short time. If you are looking to permanently switch over to ventilation through opening the windows in summer, simply turn of the system. 

Cleaning, maintenance and care

If the cover of your system got a bit dirty, for example because of water spots with limescale, greasy fingerprints or in the outside area due to wind and weather and other dirt, the ABS material on the outside can easily be cleaned with a cleaning agent. Smells are extracted quickly and discreetly before they can settle in wallpapers and textiles. The same goes for greasy particles, e.g. sizzled food in a pan. However with constant use, the filters are also clogging over the course of time.

In order for the filter screens to do a good job, they need to be replaced or cleaned every six to twelve months. This time frame however varies from manufacturer to manufacturer, some filters have to be cleaned monthly, which demands quite a good amount of time and effort in short intervals. Depending on the manufacturer, maintenance is more or less complicated can also be done by the owner with a little skill and experience. However, you should always be very careful, insufficient cleaning of the device can lead to mould formation in the system itself, it collapses, the manufacturer’s warranty does not cover these events. In case of doubt contact a handicraft business you trust.


Image sources:
Image 1: © K.-U. Häßler - fotolia.com
Image 2: © Kadmy - fotolia.com
Image 3: © Shestakoff - fotolia.com
Product images © Creoven.de