One of the most important aspects in the maintenance of our home is its ventilation. Poor ventilation is not only detrimental to the health of residents (unpleasant odors, stuffy environment, breathing problems, appearance of mold , etc.) but, in addition, it can cause deficiencies in the construction systems of the interior of our home.

In another article we talked about the kitchen ventilation , in this case we will focus on the so-called health ventilation, that is, the one that makes homes healthier.

Context and regulations

It is very likely that, if you live in a building built before 1979, spots will appear on the inside of the facades, in cold times; the walls, behind the radiators, behind the cabinets and even on the ceilings of the rooms. This is due to the humidity that is generated by condensation since Royal Decree 2429/1979, of July 8, was not published until 1979, approving the Basic Building Standard NBE-CT-79, on thermal conditions. in buildings. In an economic context of recession as a result of the 1973 oil crisis, this regulation forced all constructions to incorporate a minimum thermal insulation to reduce consumption. In the field of construction pathology, better insulation not only improves energy demand but also favors the reduction of condensation, in a previous article we explained it.

But this regulation from 1979 only emphasized insulation, ignoring indoor air quality; Many years passed in which fortunately, the tightness of the windows of that time left much to be desired, the clean air from the outside entered the buildings in abundance through the joints. However, from then on the building improved a lot, even outside of a reference regulation (until 2006 there will not be a mandatory regulation), committing the mistake of prioritizing hermeticity and insulation to the detriment of good ventilation. This has generated that many buildings have a low energy demand, but are unhealthy because, as we will see, ventilation (increases energy demand) and insulation of buildings (reduces energy demand), and these are two parameters that have contradictory aspects but that we must combine to obtain healthy homes.

This tour has led us to a specific regulation of ventilation parameters that began with the CTE DB HS approved in 2006 (Basic Hygiene and Health Document of the Technical Building Code) where ventilation flows required, according to numerous experts, were excessive and the improvements thereof with the approval of the CTE DB HS modified in 2017 (Basic Hygiene and Health Document of the Technical Building Code) in which ventilation flows are relatively reduced.

The CTE also established, which is common sense, that the admission of clean air should be done through the “clean rooms” (living rooms, bedrooms, etc.) while the extraction should be done through the “dirty rooms” (kitchens , bathrooms, etc.) this generates a flow in the house from the clean and dry part to the dirty and humid part, avoiding odors and excess humidity. This operating scheme is basic in all systems, the following image, extracted from the CTE itself, represents it:

ventilacion hibrida cte - planta

Deficiencies caused by poor ventilation.

We can consider poor home ventilation as a constructive pathology that can cause the following deficiencies:

  1. Aggravate or motivate the appearance of condensation moisture and associated deficiencies (see article of the presence of mold on the walls)
  2. Poor indoor air quality (excess humidity, CO, CO2)
  3. Pathogens in indoor air

Poor ventilation causes excess CO2, CO, NO in the air and encourages the presence of allergens and pathogens in the environment.

These deficiencies can cause problems for people. An excess of pathogens in the environment, be they molds, fungi or bacteria that could cause allergies, respiratory problems, etc. The presence of oxygen-poor air due to the accumulation of other gases (CO 2, CO, NO, etc.) can cause headache, dizziness, nausea, fatigue, dry skin, eye irritation, sinus congestion and cough. . To learn more about the consequences for people of poor air quality, see guide to good practices in the National Institute of Safety and Hygiene at Work.

There are studies that directly link humidity in homes with the increased occurrence of respiratory problems. Here you can consult a study made in 8918 Swedish homes.

Types of ventilation 

We can mainly distinguish two types of ventilation, natural and controlled ventilation. The natural one is generated by the opening of the windows and the air flow does not depend on any type of fan but on environmental provisions regulated by the laws of thermodynamics. It should be noted that these types of ventilation are not contradictory or exclusive and can be complementary.

Next, we will briefly explain the characteristics of the different types:

  1. Natural ventilation (generally without mechanical fans or ducts)
  2. Hybrid controlled ventilation
  3. Dual flow controlled ventilation
  4. Dual flow controlled ventilation with heat recovery

Natural ventilation

There are many ways to configure good natural ventilation in a building, but they are all based on the laws of physics, that is, for there to be an air flow there must be a pressure difference or a larger scale convection (wind) .

A good architectural configuration can make our home have totally natural ventilation al, that is, free and completely sustainable.

We will not stop to analyze all passive natural ventilation systems in this article, we will explain them soon. Without wishing to be exhaustive, this would be a summary list:

Crossed ventilation

In order to have good cross ventilation, it is necessary to ensure that there is a pressure difference in the outside air in two exterior openings, then the air will flow from one to the other. This is achieved by arranging the windows on opposite facades or located in different orientations. Due to the effect of the outside wind, or due to changes in temperature between the air that remains in the different orientations (due to the variation in sunlight), a pressure change occurs.

ventilacion natural - cruzada

Venturi effect ventilation

Venturi effect ventilation is based on Bernoulli’s theory in which it was shown that an increase in the velocity of a fluid necessarily reduced its pressure.

ventilacion natural - venturi efecto

Stratification ventilation and / or solar chimney

The difference in density of the same flow (in this case the air) depending on the temperature at which it is motivates an air movement: the warmer air rises. These temperature changes can be created intentionally with passive natural ventilation systems such as solar fireplaces.


Hybrid controlled ventilation

Hybrid controlled ventilation is by default the one proposed in the CTE (Technical Building Code) is based on the ventilation system, which ideally should have a clean air intake arm and a stale air extraction arm It will only have ducts and mechanical fans in the extraction arm. So the admission will be made freely through openings in the windows or facades.

ventilacion hibrida cte - seccion
ventilacion hibrida cte - planta

As you know, the CTE is a provision and this should not be taken as a normative prescription. This system is correct to meet a minimum standard, but the systems that we will see below are better for the benefits they can achieve.

Dual flow controlled ventilation

This system, unlike the one explained above, has a controlled and distributed intake by means of an intake at specific points (chimneys or specific intake openings) and internal channeling through ducts.

This allows, unlike the previous system, that the intake air is chosen from a specific point and this will facilitate the inclusion of filters for pollen, bacteria, particles, etc.

We can add different types of filters to avoid the entry of:

  • Pollution of the external environment NO particles or another type, CO2, etc.
  • Of insects and other small-sized living beings
  • Viruses, bacteria, very fine particles, spores, mold and pollen. These filters are called F7 and have a more specific character
filtros-de-sistemas-de-ventilacion - fuente siber

 Dual flow controlled ventilation with heat recovery

The previous double-flow system can be improved by adding an element to the system: the heat recovery unit (either enthalpic or sensible heat). The scheme presented in the image below represents this type of system. The intake is conducted by ducts, as well as the extraction ducts, and this allows the two flows to join together at a point where the heat recovery unit is installed.


In an energy balance of a home with high levels of insulation, that is, with a very low energy demand, we can see how the parameter that would penalize the most is energy losses due to ventilation.

In other words, energy costs due to ventilation can be the equivalent of everything a low-demand house spends on heating, domestic hot water and lighting and appliances.

As can be seen in the attached graph (source: passipedia ) that represents an “evolution” of the energy balance of a typical building up to the “Passive House” standard, the yellow stripe represents ventilation losses.

Note that in the standard building of EnEv 2002 it is the German Energy Conservation Law and the next bar represents a “passivhaus” building, the yellow stripe, which came from the first bar being of the same dimension (that is, the air ventilation had remained without recovery in the evolution of rates, while insulation losses were gradually reducing) sharply reduced to more than half with the inclusion of the heat recovery unit.


Ventilation with a heat recovery system allows to recover up to 80% of the heat that would be lost by the ventilation system, which is why it is essential in a low-consumption house.

Below, you can see a diagram of the operation of a heat recovery unit:


The best ventilation system for a home depends on the outdoor climate, the needs of the users and the budget of the client. However, it can be said that for a home located in cold or temperate latitudes like ours, the best ventilation system will be the “controlled dual flow with heat recovery system”. The advantages it brings in terms of energy efficiency and air quality are indisputable.

aroom arquitectes ventalló