Improve indoor air quality


  • Indoor air quality
  • Particulate pollution in the street
  • NASA study: Plants for better air quality
  • Plants in the bedroom?
  • What to do against bad air quality 

Air quality indoors

Image originator: Antonioguillem, 

How comfortable we feel in a room depends on several factors, including the CO2 content, temperature, temperature difference on surfaces, humidity, odour, bacteria and toxic particles. Apart from subjective factors like the smell of garlic there are also threshold values for harmful gas. In enclosed rooms the concentration of harmful gas can increase to a point where it becomes dangerous for the health. For example, the concentration of carbon dioxide (CO2) in the Earth’s atmosphere near the ground is about 0.04 percent. Ever since the big age of industrialisation starting around 1850, the concentration has increased steadily. In addition to its impact on the climate, the greenhouse gas leads to physical illness in high concentrations. The concentration of 0.1% indoors is generally regarded as a threshold value between healthy and unhealthy air quality.

Tip: In order to extract stuffy air, the space requires manual or automatic ventilation on a regular basis. This can be done manually simply by opening the windows each hour for about 5 minutes. If this is not possible, for example if there is no window or occupants are not present, opt for automated ventilation systems that operate with sensors. Among other factors, the required air change rate ACH is based on the number of people in the room.

Particulate pollution in the street

Various models come with an integrated sensor that analyses the indoor air quality and indicate results for the user. 

Unfortunately, the quality of air inside buildings is oftentimes worse than outdoor air. Despite frequent air change, there is still the possibility of pollutants that are infiltrating the building from the outside, for example CO2 from the street. These agents corrupt indoor air quality. Environmental pollution caused by exhaust fumes of combustion engines and power plants are a serious problem, especially in metropolitan areas. Until all combustion engines have been replaced by more environmentally sound alternatives, air purifiers help improve air quality. Depending on the model, the appliances feature prefilters for hairs and pollen, HEPA filters for contaminants measuring 0.07 and more micrometres, as well as activated carbon filters for unpleasant odours, formaldehyde and volatile organic compounds (VOC). Some devices are equipped to cover rooms with a size of up to 75m2.

NASA study: Plants for better air quality

However, not only pollutants from the outside impact indoor air. Chemicals are also released directly inside the building. Brand-new textiles, furniture and appliances usually take a few days to evaporate. In most cases, this process happens without leaving any odour, but that does not make it less dangerous. Even cleaning agents, paint and insulation material of the building can influence the quality of air. The “Sick Building Syndrome SBS“ is a medical condition that can occur after moving into a different building.

Compound found in the air

Source of pollution

Health effects


Building material, furniture made from chipboard or compressed wood, carpet, waterproof or fire-resistant products, natural gasoline, kerosene, tobacco smoke

Irritated mucuosa (eyes, nose, throat)
Allergic dermatitis

Benzol, Xylene

Petroleum products, oil, paint, synthetic materials, rubber, tobacco smoke, open fireplace

Irritated eyes, nose, throat and skin
Headache, loss of appetite, drowsiness

Carbon monoxide

Exhaust fumes from vehicle engines (from the street), burning of wood and gas, tobacco smoke

Headache, dizziness, nausea


Chemical cleaning agents, printing ink, paint, lacquer, glue

Fatigue, carcinogenic

The American space agency NASA has researched a simple yet effective solution for improving the quality of indoor air. Plants absorb CO2, produce fresh oxygen and break down pollutants. Plants are particularly suitable to remove ammonia, formaldehyde, benzol, xylene, carbon monoxide, ozone and trichloroethylene. In some cases, plants were able to decrease pollution by about 89.8% within 24 hours (e.g. common ivy for benzol and absorbing mould spores).

The golden pothos (Epiperemnum aureum) is efficient against formaldehyde, trichloroethylene, xylene and benzol.

The spider plant (Chlorophytum comosum) considerably reduces formaldehyde and CO2.

A list of indoor plants that help improve air quality has been published in the Clean Air Study. It has been conducted by Dr Bill Wolverton in 1989 and was later confirmed by further research.

Some of these popular and low-maintenance plants such as the white adder’s mouth and rubber plant have become a common sight in offices and doctor’s practices over the last years. They are also a great choice for less formal surroundings.

Plants in the bedroom?

During photosynthesis chlorophyll converts carbon dioxide into sugars and oxygen. The sugars are used by the plant, oxygen is released as a byproduct. The plant also absorbs a small amount of oxygen to be used for cell respiration (growth), but this amount is smaller than the amount of produced oxygen.

Many plants require light for the photosynthesis. At night, the oxygen product decreases, however they still absorb oxygen. Sensitive people react to the slightest changes in indoor air quality, meaning they become unwell as soon as the quality decreases. That is why you will often hear that flowers and foliage plants should never be put in a bedroom.

Plants with a crassulacean acid metabolism (CAM) produce oxygen at night and are explicitly recommended for bedrooms. They originate from dry regions with little water which has caused to evolve in a way that allows them to open their cells without drying out – after sundown. They absorb carbon dioxide and transform it into malic acid which is stored for later.

CAM plants include bowstring hemp and aloe vera.

Video: Improving indoor air quality with plants

Golden cane, bowstring hemp and golden pothos produce enough air for a human in closed rooms. The effect can be remarkable on a global scale: less heat is lost because less ventilation is needed.

About 6 to 8 waist-high bowstring hemp plants are required per person in a bedroom. Also note that indoor plants increase humidity. Excessive watering of the plants can lead to mould in the soil. The moisture can be decreased to an optimum value between 40 to 60% by an automated dehumidifier with humidity sensor.

What to do against bad air quality

Apart from the mentioned minimum requirements for good indoor air (high amount of oxygen, low amount of CO2) the following factors impact our well-being:



More information

Humid or dry air

The relative humidity of the air is closely linked to the well-being inside the house. The interior climate should not be too dry or humid for humans and sensitive furniture. Ideal values between 40-60% make a significant contribution to the maintenance of the building materials as well as prevention of condensation and mould.

Optimise indoor air quality


Humidifiers and dehumidifiers are available for different room sizes in our shop⮩ category for improving air quality.

Room temperature too cool, too hot

Sweating employee

Image originator: Minerva Studio,

The ideal indoor temperature should be about 20-21°C during the day, at night 16-17°C will suffice. In the summer, buildings tend to be much warmer, particularly in the upper storeys heat builds up. A ceiling fan eliminates sweat on the upper layer of the skin. This causes people to feel cooler even though the room temperature itself has not changed. This is the most ecologically efficient method of regulating heat in the summer.

⮩ Ceiling fans in summer

⮩ More tips about cooling

Loss of heat

If the weather outside is cold, the interior of a building requires heat in order to make occupants feel comfortable. Uncontrolled ventilation leads to loss of heat. Ventilators with a built-in heat exchanger store the heat of the extracted air and pass it on to the incoming fresh air.

If the floor stays cold even though the heater is turned on, all the warm has accumulated on the ceiling. This layering of cold and warm air can be dissolved by a ceiling fan that is running in reverse. That way, the fan does not cool, instead it evenly recirculates heat.

Centralised heat recovery (new buildings)

Decentralised heat recovery (single rooms, old buildings)


Ceiling fans in winter


Allergens and mould spores

Allergens such as mites, pollen and animal hair make it hard to breathe. Other small matter, e.g. bacteria, fine dust and mould spores also impact the quality of life of all residents. Pollutants infiltrate the building through windows, to a certain degree they are also a natural part of our breathing air. Electric air purifiers remove coarse particulate matter and small germs.

Living with allergies

Odour, smoke

Bad air quality

Image originator: olly,

Smokers, dog owners and passionate cooks do not want to keep odours in their home forever. Air purifiers equipped with an activated carbon filter remove odour and vapour. A subtle smell from the fireplace can also be removed.

How to get rid of odour?

Sound, noise

Noise from the adjacent flat, electric appliances or the street spread in acoustic waves that are transmitted through the air amongst others. Long-term stress caused by noise affects the human health. In most cases noise is reduced easily by insulation materials.

Improve sound and noise


Blog “Leading a quiet life“


Neck pain

Image originator: absolutimages,

Draught can result in dry eyes and skin as well as problems with the ears, joints and muscles. Dry skin and mucosa suffer from tiny fissures. The latter are prone to infection by bacteria. This results in further susceptibility to catching the cold, only to name one example. Finally, a tense neck causes headache.

Preventing draught and providing sufficient ventilation are not mutually exclusive, though. Mechanic ventilation systems and heat exchangers provide the fresh air you need without cooling down the inside of the building.

Supply air guide



When using ceiling fans you can prevent draught by changing the rotation speed which is done by a variety of speed controllers.
The best rotation speed