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Indoor air in residential buildings

General information about ventilation

Ventilation is a key factor affecting indoor air quality, which is used to supply outdoor air into indoor areas and remove “used up” air. In dwellings, air is typically supplied to the living room and removed from so-called dirty rooms (kitchen, sanitary rooms), which are the largest sources of impurities and moisture.

Natural ventilation

Natural ventilation is a traditional form of ventilation, where air is moved with the help of the pressure and temperature differences between the indoor and outdoor air. One of the benefits of natural ventilation is its ease of use, since it does not use machines that require maintenance.

The main drawback of natural ventilation is poor adjustability, since air currents fluctuate according to the weather. Adequate replacement air is a prerequisite for the functioning of natural ventilation. In old buildings, ventilation ducts can be in poor condition, which can result in smells being transferred from one room to another through the ducts.

Partial mechanisation of natural ventilation systems using hoods or channel blowers, for example, is not recommended since this can alter the pressure ratios of the building and ducts and thus disrupt the air flow.

Mechanical exhaust ventilation

The most common form of ventilation for dwellings is mechanical exhaust ventilation, where used air is removed from the dwelling by a machine and replacement air comes in through windows or air inlet valves. Mechanical exhaust ventilation is better for ensuring an adequate air exchange during all seasons than natural ventilation.

The recommended replacement air channels are air inlet valves, located either in the upper frames of windows or high up on outer walls. Another option is to remove insulation from the top side of windows.

Mechanical supply and exhaust ventilation

Mechanical supply and exhaust ventilation is a system where supply air is injected indoors mechanically and heated. Such systems can ensure adequate and draught-free ventilation in all facilities.

Mechanical supply and exhaust ventilation is ideal for facilities that require large amounts of air. The supply air fans can include efficient filters, thanks to which the supply air can be purified more thoroughly than when using other ventilation systems. A mechanical supply and exhaust ventilation system that includes supply air moistening and/or cooling systems is called an air conditioning system.

Mechanical supply and exhaust ventilation has the highest investment costs out of all ventilation systems, but the use of the system can save energy thanks to heat recovery systems.

Mechanical supply and exhaust ventilation always requires good maintenance. A poorly maintained ventilation system can cause significant indoor air quality problems.

Cleaning and maintenance of ventilation systems

Supply air ducts should be cleaned or at least inspected even more frequently, for example every five years. Supply air filters should also be replaced regularly, for example twice a year.

Cleaning the ducts is the responsibility of the owner of the property. Residents are responsible for the regular cleaning of ventilation valves located in their own flats.

Valves should be cleaned at least once a year and the condition of the hood grease filter should be assessed monthly and cleaned as required. Dirty ventilation valves and ducts reduce air exchange indoors. Dirty supply air ducts and valves also reduce the indoor air quality.

Indoor air temperature

The Ministry of Social Affairs and Health’s Housing Health Guide (STM:n oppaita 2003:1) defines good and passable levels for the indoor air temperature of dwellings and other comparable common areas as follows:

  Passable level oC  Good level oC
Indoor air temperature  18  21
Wall surface temperature 16  18
Floor surface temperature  18  20
Point-like surface temperature  11  12

Indoor air temperature should not exceed + 26 oC, unless the rise of indoor air temperature is caused by outdoor air temperature. Surface temperatures are measured as averages in accordance with the SFS 5511 standard.

Relative humidity of indoor air

The recommended relative humidity of indoor air in the heating season is 30 - 40%. Higher humidity during the heating season can be sign of inadequate ventilation, whereas lower humidity can be caused by effective ventilation and/or excessively warm indoor air. In the summer, weather conditions can cause the relative humidity of indoor air to rise to high levels (60–80%).


Vetoisuus johtuu yleisimmin ilmanvaihtoon liittyvistä ongelmista: Ikkunoiden puutteellisista tiivistyksistä, rakenteiden ilmavuodoista, väärän mallisista tai väärin sijoitetuista tuloilmaventtiileistä tai liian suurista ilmavirroista. Liian alhaiset rakenteiden lämpötilat saattavat myös aiheuttaa vedon tunnetta. Rakenteen liian alhaisen lämpötilan syynä voi olla riittämätön lämmöneristys tai ns. kylmäsilta, joka johtaa ulkoilman kylmyyden sisäpuolisiin rakenteisiin

Structure surface temperatures

Excessively low structure temperatures may be caused by inadequate thermal insulation or so-called thermal bridges that conduct cold from outdoor air into indoor structures. Excessively low indoor air temperature may also cause structures to cool down.

09.07.2020 13:14