Ventilation Systems for Your Home

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The Technical Building Code (CTE) in Spain, according to the basic documentation (DB) for quality of interior air, requires that all living spaces have the appropriate means to guarantee an adequate ventilation system. It states that they should provide the flow of outside air and ensure the extraction of contaminated air.

The aim of this system, as it is defined in the CTE, is to guarantee adequate ventilation in every room of a home. This is to provide sufficient air flow from the outside and guarantee the extraction and expulsion of contaminated air that is commonly produced during everyday life within the home.

How is air contaminated? It may be affected for various causes:

  • Lack of oxygen, on account of the occupants breathing.
  • Combustion processes for the technical equipment.
  • Excess of humidity, most often found in toilets and kitchens.
  • Excess of toxins in the home, etc.

Ventilation Systems in Line with the Spanish Requirements of the CTE DB HE:

  • System A: Natural entry and extraction
  • System B: Mechanical entry and natural extraction
  • System C: Natural entry and mechanical extraction
  • System D: Mechanical entry and mechanical extraction
  • Combined Systems

The basic documentation (DB) establishes that homes must contain a ventilation system (either hybrid or mechanical) that circulates air throughout the entire home from the driest parts of the homes to the more humid areas. This is due to the installation of  openings that help the interior to connect with the exterior. The partitions that separate each room contain openings in the hallways that also allow for air circulation.


System A

Natural ventilation systems without fans use the pressure from the wind on the side of the building and the air movements from the differences in temperature. This system is commonly found in older homes, where outside air entered in through the defective sealing of doors and windows. This system is no longer used in modern homes due to the inconvenience caused and the elevated energy consumption. In this ventilation system, the outside air enters through regulated openings in the walls and is expelled from the interior through vertical ducts that reach all of the different floor levels of the building and remove the air through the roof. Advantages of this system include that it does not make much loud noise and that it does not consume electricity. However, air flow is not guaranteed but rather depends on the thermal conditions and the pressure of the exterior wind.


System B

Mechanical ventilation systems use one or more fans to help the air circulate into the building. It has a fan that is connected to vertical ducts that provide service to all floors of the building where air is admitted. Extraction is done in an exterior system that functions naturally through grates in the humid areas that connect to a vertical duct connected to the roof. In this way, it fulfils the requirements set forth by the Spanish CTE DB HE.


System C

Using this system, clean air is obtained through regulated grates that are located in the wall through natural or mechanical means. The extraction and expulsion of contaminated air is carried out through an extractor connected to vertical ducts in the humid areas of a home. Its principal advantage is that air flow is guaranteed and that it hardly needs maintenance to be utilised in the home.


System D

This system uses mechanical entry and extraction, which means that air flow is guaranteed and that it uses electricity. Before it is installed, the sound level of the entire system should be taken into account, which may be negatively affected by low-quality motors making loud noises. The most frequent is a centralised system of entry and extraction by mechanical means, using the system of ducts throughout the entire home. This system may be combined with a heating recovery formed by a heating exchange, air filters, fan for expelling and another for extraction.


Combined Systems

The most common combination is made between system C and system D, which is more comfortable in common areas of the home.


The minimum ventilation flow required by the CTE DB HS 3 for each room in the home is the following:

Flow of Entry:

  • 5 l/s (18 m3/h) per occupant in bedrooms.
  • 3 l/s (10.88 m3/h) per occupant in living spaces and eating areas.

Flow of Expulsion:

  • 15 l/s (54 m3/h) in toilets and wash rooms.
  • 2 l/s (7.2 m3h) per useful m2 in kitchens.
  • 0.7 l/s 82.52 m3/h) per useful m2 in storage units and common areas.
  • 10 l/s (36 m3/h) per useful m2 in reserved areas for storing waste.


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