Ventilation is one of significant aspects to be considered when building a new or renovating an existing housing. A properly chosen and constructed ventilation system will not only care for the quality of indoor air and comfort of people, but also for the longevity of the building and the efficient use of energy sources.

In Latvia, the requirements for ventilation are determined by MK noteikumi Nr. 310 par Latvijas būvnormatīvu LBN 231-15 "Dzīvojamo un publisko ēku apkure un ventilācija".

Indoor air quality

Recommended temperature and relative humidity

  • Today, people spend most of their lives indoors, so it is very important to take care of the microclimate of the housing.
  • Air quality requirements for rooms with different needs may vary. In addition, every person may also have a different comfort temperature, but it should preferably be maintained between 18°C and 22°C.
  • The recommended relative humidity of air is between 40% and 60%.
  • Low relative humidity can have adverse effects on the skin, airways, nasal membranes and eyes, causing irritation, and increases the ability of viruses and bacteria to spread in dry air.
  • On the other hand, high relative humidity increases the likelihood of dust mites as well as water drops that cause moulding may condense on cold surfaces, such as window frames.

CO2 level in the room

  • The concentration of carbon dioxide (CO2) in the room is a very important indicator of the microclimate. It is measured in parts per million or “ppm”.
  • The CO2 level in the room should not exceed 800 ppm above the outdoor air CO2, which is 350-400 ppm.
  • A CO2 concentration of up to 1000 ppm is considered to be acceptable air quality.
  • Beyond this value, oxygen is reduced in the room causing people feel tiredness, drowsiness and even headache.

Necessary air exchange

  • According to the Latvian construction standard, the quantity of fresh air supply in a room where one person is present and there are no other sources of air pollution should be 15 m3/h.
  • However, to maintain an optimal level of comfort and to remove all possible pollutants and humidity from the room, an air exchange of 20 to 30 m3/h should be ensured.

Three aspects – air supply, air circulation and air exhaust – are needed in order to ensure the correct exchange of air in a housing. There are different types of ventilation solutions – both natural and mechanical.

  • Natural ventilation is based on the characteristics of the air circulation as a result of pressure or temperature differences.
  • In the case of mechanical ventilation, the air exchange is ensured by a ventilation unit.

Natural ventilation

Historical air supply

  • Once, air supply was partially secured through the areas of the building structure, which were not airtight, through which the fresh air flowed in.
  • The outside walls of individual multi-apartment buildings have built-in channels for the supply of fresh air.
  • When renovating buildings, replacing windows, performing works to ensure heat insulation and airtightness of the building, as well as various indoor repairs, areas lacking airtightness and air supply channels are often closed with different solutions, resulting in a lack of natural supply of fresh air.
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Air circulation in housing

  • Air circulation in housing usually takes place through open doors, hallways or other gaps.
  • When replacing indoor doors, it is preferable to leave a small gap under them so that even in closed condition the air between rooms can be exchanged.
  • If doors are closed tightly, an overpressure condition may build in the room where air supply is provided, while the rooms with air exhaust channels will be in a low pressure condition.
  • It can be felt as a resistance in the process of opening or closing the door.

Air exhaust channels

  • Air exhaust channels in multi-apartment houses and private houses are installed in rooms with a high risk of humidity, such as the kitchen, bathroom and toilet.
  • This is done to ensure that the excess humidity and odours that occur during cooking or washing do not spread in the entire housing, but are extracted from it.
  • In multi-apartment buildings, air, through exhaust channels, enters the vertical air extraction shafts, which discharge the extracted air onto the roof of the building.
  • The air flow is ensured by the difference between the height of the room and the roof outlet.
  • The higher the air exhaust shaft is located on the roof, the better the air draught would be.
  • Similarly, external conditions, such as wind, also improve or worsen the draught. If the natural ventilation of the building has insufficient draught, deflectors should be installed on air outlet channels on the roof.
  • They look like pipe ends of an increased diameter, which intensify the draught of the ventilation system depending on the direction of the wind.
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Do not!

  • The natural ventilation exhaust channels must not be closed or fans not working 24 h a day must not be installed in front of them, as there is no air exhaust at the time, when the fan does not work and ventilation in the housing does not function.
  • The same applies to natural ventilation exhaust channels in the kitchen.
  • Apartments in multi-apartments, where gas cookers and heating equipment are used, should not interfere with the natural ventilation system.
  • Any intervention in main structures of the building, such as reconstruction of natural ventilation without coordination or connection of a stove hood to the exhaust channel in the kitchen, is not allowed and should be regarded as arbitrary construction.


The main element of mechanical ventilation is the installation or several installations ensuring the exchange of air in the premises.

Both centralised and decentralised mechanical ventilation solutions are available.

Types of mechanical ventilation

Decentralised ventilation systems

  • In the case of a decentralised ventilation system, separate installations ensure air exchange in individual rooms or groups of rooms.
  • There are solutions, where air supply and air exhaust are ensured by separate installations or simple fans.
  • Such solutions are suitable for multi-apartment buildings, where all the dwellers of the building do not want or cannot install a joint ventilation unit.


Centralised ventilation systems

  • Centralised ventilation systems are intended for both private houses and multi-apartment houses.
  • In this case, one installation takes care of air exchange with the air circulation through separate air channels.
  • It is recommended to install fresh air supply channels in the rooms where fresh air is needed primarily, such as the bedroom and the living room.
  • It is recommended to install air exhaust channels in the kitchen, bathroom and toilet.
  • It is not desirable to install fresh air supply channels and indoor air exhaust channels located on the outside of the building close to one another so that the ventilation unit does not suck back into the building the air that has just been extracted from the housing.

Heat recovery ventilation units recover heat from exhaust air and heat the fresh supply air. This makes it possible to recover up to 90% of the heat from exhaust air. If the exhaust air temperature is 20°C and the outdoor air temperature is 0°C, the air supply temperature will be 18°C. This type of heat recovery allows the costs of heating to be reduced.


The two most common types of heat recovery equipment are:

  • plate heat exchanger,
  • rotary heat exchanger.

Heat recovery ventilation

Plate recuperator

  • The plate recuperator consists of cross-shaped plates, between which isolated supply and exhaust air flows are flowing across and in parallel and their temperature equalises.
  • The advantage of the plate heat exchanger recuperator is very high efficiency of separation of exhaust and supply air – up to 99.9%.
  • Thus, it can be used to recover heat even from the warm air flowing out of the kitchen exhaust channel without worrying that unwanted smells will spread in other areas of housing.
  • This type of recuperator does not recover the humidity in the room.
  • In cases where the outdoor air is very dry, humidity levels in the room will also decrease.
  • The disadvantage of a plate recuperator is the possible formation of condensate in the heat exchanger itself.
  • This may occur during the winter period, when the outdoor air temperature drops below -2°C.

There are two solutions that are used to prevent condensate formation:

  1. to reduce the air supply intensity and to increase the air exhaust intensity, thereby reducing the efficiency of the recuperator and reducing the supply air temperature.
  2. to install an electric heater in the outdoor air supply channel and to heat outdoor air above -2°C, but this will result in additional electricity consumption.

Rotary recuperator

  • An aluminium plate rotor containing air flow channels is installed on bearings in the ventilation unit with a rotary heat exchanger. The exhaust air heats up the rotor and this heat is used to heat the supply air.
  • In this type of equipment, supply and exhaust air are slightly mixed – 2% to 5%.
  • Thus, there is a minimal possibility of transmitting odours from exhaust air to supply air.
  • The rotary heat exchanger partially recovers humidity from exhaust air, which is important during the winter period when the relative humidity of the outdoor air is low.
  • There is no possibility of condensate formation in the rotary heat exchanger, which eliminates the risk that the equipment may freeze.
  • It should be noted that at very low outdoor temperatures the effectiveness of this type of recuperator will reduce.

Enthalpy recuperator

  • An enthalpy heat exchanger has been created to combine the good properties of a plate heat exchanger and a rotary heat exchanger.
  • The enthalpy heat exchanger basically is a plastic plate heat exchanger.
  • Its plates are made of a special nanomembrane, the main property of which is the recovery of humidity.
  • The membrane structure is designed so that only compounds that are the size of water vapour molecules can move from one side of the membrane to the other.
  • The enthalpy heat exchanger has a high energy recovery efficiency.
  • Due to the nature of the recovery of humidity, the risk of freezing of the heat exchanger reduces significantly.
  • Such a recuperator allows the air humidity level in the rooms to be maintained at the same time and guarantees that the supply and exhaust air flows are separated from each other.

Management and control of equipment

When selecting both simple ventilation units and heat recovery units, attention should be paid to the control system of the equipment and to the possibilities of regulating air flows and temperature.

Nearly all ventilation units are equipped with a humidity or CO2 sensor that monitors air quality in the rooms and automatically adjusts the parameters to ensure the appropriate air quality in the rooms. A qualitatively chosen and installed ventilation system will work autonomously without human intervention and will not require much effort in its maintenance.

It should be borne in mind that ventilation units have air filters that need to be replaced on a regular basis so that air quality is not affected and the operation of the equipment is not disturbed by reducing their energy efficiency. The frequency of replacement of filters for each unit in devices of different manufacturers varies. This is also affected by the load intensity of the ventilation unit, outdoor air pollution and the geographical location of the building.

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