How to Ventilate Your Home

Houses used to be naturally ventilated by design. Large chimneys, single glazed windows, doors without seals, floorboards, underfloor crawl spaces and large loft spaces. All of these gaps in the fabric of the building contributed to a constant airflow from the outside to the inside. The drawback was draughts and the ingress of cold air.

As house design became more focused on energy efficiency and preserving the escape of warmth, we began to seal our houses in more and more air-tight boxes. As we increased the energy efficiency, the side effect was a lack of natural ventilation. This impacted the quality of air in the home.

House design is now focused on ensuring there is a balance of energy efficiency with ventilation for healthy homes.

What Is Ventilation?

Ventilation is the introduction of fresh air from the outside to the inside and the distribution throughout a building and all the rooms.

Good ventilation systems will introduce fresh air to dilute stale air and moisture whilst extracting pollutants and also minimising a loss of room temperature.

Healthy indoor air will minimise condensation, mould growth, dust particles, mites, C02 and maximise oxygen to keep residents feeling awake, energised and healthy.

With homeowners spending more time at home working or relaxing, Building Regulations have made changes to ventilation requirements. Ventilation is now considered an integrated solution into new house designs and not an afterthought.

Ventilation strategies use a combination of the following main types of ventilation:

• Mechanical
  Mechanical ventilation uses fans to draw air into a building from the outside. Combination systems will exchange air flow by drawing air from the outside and extracting air from the inside.
• Natural
  Natural ventilation introduces the passive flow of natural air from the outside to the inside without using fans. Well-designed natural ventilation is similar to old-fashioned ventilation which relies on the manipulation of air pressure and cross ventilation.
• Mixed-mode hybrid ventilation
  Mixed-mode ventilation is the most commonly used and combines both natural and mechanical ventilation. For example, mechanical extract ventilation.

Why Do We Need Ventilation?

As mentioned above, good home ventilation is essential for healthy living spaces and healthy people who live in them. The impact of poor air quality and toxins such as mould spores are seriously damaging to health and should not be underestimated.

As we become better at designing houses to retain more heat and keep out more draughts. We have become very good at creating airtight boxes that can hold moisture, dust mites, C02, VOCs and a collection of other pollutants.

As we breathe, we naturally consume oxygen and exhale carbon monoxide (C02) from the air. The ground beneath us can exude Radon. Our pets and furniture can breed dust mites and allergens from shed skin. Cleaning products and even candles all contribute to creating a soup of harmful Volatile Organic Compounds (VOCs) in the air.

Normal everyday activities can be an issue as they contribute to excess moisture in the air. Showering, cooking, laundry and even breathing. Cooking alone will produce up to 3 litres of moisture per day. And all of that moisture has to go somewhere. Usually, it forms as condensation on cold windows and walls.

Read more: What causes condensation and how to stop it...

In pre-war built homes, that was easily solved by opening doors and windows every day to let fresh air stream through our homes. Today, that isn't as straightforward.

Energy efficiency has become critical in the fight against climate change, with a need to reduce the usage of fossil fuels and also to keep our household bills to a minimum as fuel prices become more volatile.

Home design needs to be focused on retaining heat whilst also being ventilated for maximum health. Passivhaus (see below) is a progressive design system that creates a highly-insulated building combined with controlled mechanical ventilation.

All homes can benefit from being better insulated through the installation of triple glazing whilst improving natural and mechanical ventilation.

Household Toxins That Need to Be Ventilated

Airborne toxins are a considerable risk to health that most people don't even think about. Awareness of the dangers of mould growth is growing, but what about the other hundreds of toxins that the air in our household can contain?

• Carbon Dioxide (CO2)
  Produced by gas cookers, boilers and from breathing. An excessive buildup of CO2 is lethal. Even a mild concentration can cause headaches, fatigue and increased asthma attacks.
• Volatile Organic Compounds (VOC)
  Airborne pollutants from aerosols, cleaning products, paint, candles, tobacco smoke and other solutions contribute VOCs into the air we breathe. VOCs are especially harmful in concentrations causing tiredness, headache, breathing problems, allergy and can potentially be carcinogenic.
• Radon
  Radon is a naturally occurring radioactive gas that exudes from the ground. Some areas have a higher concentration than others and need a radon pump. When you bought your home, the searches would have indicated the known radon level in your area, or you can buy a radon test kit. Radon can cause health issues and possible cancer.
• Allergens
  Dust mites, dust mite droppings, shed skin, pollen and household chemicals are a big cause of allergic reactions such as eczema, rhinitis and asthma. Dust mites thrive in atmospheres with excessive moisture, again highlighting the need to control condensation.
• Mould
  Mould is an organism that thrives in damp atmospheres and grows on cold surfaces prone to excess moisture such as around window frames. There are several types of mould, white, green, blue and toxic black mould is the most damaging to health. Wheezing, itchy eyes and rashes are the mildest symptoms of mould exposure. Asthma, allergic rhinitis, hypersensitivity pneumonitis and allergic alveolitis in adults but children are especially vulnerable to acute idiopathic pulmonary haemorrhage.

The Benefits of Ventilation

Proper ventilation is essential for maintaining a healthy, comfortable, and energy-efficient indoor environment in a house.

• Improved air quality
  Ventilation helps to circulate fresh air into the house, which reduces indoor air pollution and the buildup of harmful pollutants.
• Reduce condensation
  Proper ventilation can help to reduce excess moisture in the house, which can prevent mould growth, dampness, and other associated health problems.
• Temperature control
  Purge ventilation, continuous ventilation and mechanical ventilation all help to regulate the temperature and remove excess heat from a room in summer.
• Energy efficiency
  By removing excess moisture and reducing the buildup of pollutants, ventilation can help to keep a house at a more consistent temperature, which can reduce energy costs.
• Healthier living environment
  Ventilation helps to reduce indoor air pollution, which can improve air quality and reduce the risk of health problems such as allergies, hay fever, asthma, and other respiratory issues.
• Longevity of building materials
  Good ventilation helps to prevent damage to building materials due to moisture buildup, which can extend the life of a house and reduce repair and maintenance costs.

Ventilation in Period Properties and Older Houses

Period properties and especially Victorian houses were designed to be heated by coal fires and use air circulation to ventilate and move heat around the house.

Open fires need a circulation of air to maintain the fire and to move the heat around. Fires also need ventilation in a room to maintain healthy oxygen levels.

Victorian houses had several design features that helped with ventilation:

• Large bay windows with facing windows that opened and encouraged cross ventilation
• Sash windows that could be opened at the top and bottom for extra ventilation
• Air bricks to draw air directly from the outside to the inside
• Chimneys that draw the air upwards from the fire creating pressure to draw air from windows and air vents
• Transom windows over the front door that open and draw the warm air from the fire up the stairs
• Transom windows at the back door that create cross ventilation through the house in summer

The natural design of a Victorian house follows the same principle as Passive Stack Ventilation (see below).

Apart from the design, older houses also have more gaps than modern builds so they naturally ventilate through draughts.

The problem with Victorian houses today is that they do not use coal fires and are being retro-insulated to try and retain heat and to meet EPC rating standards. Trying to heat an old house like this is very expensive and the insulation blocks the natural ventilation of the house. Moisture is trapped and the property is prone to condensation, dampness and an unhealthy atmosphere.

It's a difficult balance to achieve energy efficiency with healthy ventilation in a house not designed for that purpose.

Ventilation in Energy Efficient Homes

Why is ventilation important for energy efficient houses?

As insulation increases in a building, it becomes more airtight and ventilation is reduced. Without an exchange of air, pollutants start to condense, oxygen reduces and the overall quality of air rapidly declines to an unhealthy level.

The more energy efficient a house is, the more it needs the introduction of ventilation.

Building Regulations Approved Document Part F has been updated to ensure that houses have adequate ventilation.

What Is Passivhaus?

Passivhaus is a standard for low-energy building design and construction. The main aim of Passivhaus is to reduce the energy consumption of buildings to a minimum, specifically for heating and cooling.

Passivhaus buildings have high levels of insulation, airtightness and efficient use of passive solar gain, which helps to reduce the need for heating and cooling systems. Passivhaus buildings are also required to use mechanical ventilation systems with heat recovery, which help to ensure healthy indoor air quality.

Passivhaus buildings can be up to 90% more energy-efficient compared to traditionally built homes and designed to maintain a consistent and comfortable indoor temperature, with minimal fluctuations, and to ensure good air quality through effective ventilation. This results in a healthy and comfortable living environment, free from the harmful effects of dampness, condensation, and mould.

What Are the Different Types of Ventilation for a House?

As mentioned above, a ventilation strategy uses a combination of mechanical and natural ventilation systems. It starts to get a bit more complicated when we then factor in that Building Regulations refer to three types or approaches to ventilation that all have different applications. And these can be either mechanical or natural.

Purge

Purge ventilation is the ability to quickly remove any odours or buildup of fumes in a living space. Particularly toxic fumes from cleaning, DIY, smoking or cooking. Purge ventilation is also required by Building Regulations for the ability to cool and room and remove a build-up of excess heat.

The volume of air contained in a room must be completely replaced four times in one hour.

To meet Building Regulations, windows are required to have an opening angle of at least 15 degrees and be at least a tenth of the floor area of the room. Windows that can open more than 30 degrees can be a twentieth of the room floor area.

All habitable rooms must be able to purge ventilate through either a window, door or a mechanical extraction system.

Extract

Extract ventilation is used to quickly remove any excess moisture or cooking smells before they spread to other areas of the house.

Especially critical in bathrooms and for cooking to avoid a build-up of condensation.

Extraction can only be achieved using mechanical ventilation on either an intermittent or a continual basis.

For a bathroom or utility room, the extraction rate must be 15 litres per second. For a kitchen, the extraction rate must be 30 litres per second.

Kitchen extraction cooker hoods that only filter air and don't extract externally must be 60 litres per second.

Rooms that require extract ventilation include:

• Kitchens
• Utility rooms
• Bathrooms
• Toilets

Whole Dwelling

Purge and extract are both on-demand ventilation methods to be used as and when needed. Aside from ensuring that excess moisture and fumes are cleared, a house also needs a constant flow of background ventilation to remain healthy.

Older houses will generally fall into less airtight dwellings and modern builds should be built to certain airtight standards. Passivhaus is designed on the basis of being as airtight and insulated as possible to minimise the need for heating.

If a house has an air permeability higher than below it is considered 'less airtight':

• A design air permeability higher than 5m3/(h·m2) at 50Pa.
• An as-built air permeability higher than 3m3 /(h·m2) at 50Pa.

For less airtight houses, they have the option of natural background ventilation and can use a combination of trickle vents on windows and passive stack ventilation.

For airtight houses, a continuous mechanical supply is required using a system such as continuous mechanical extract ventilation (MEV) or Mechanical Ventilation with Heat Recovery (MVHR).

Passive Stack Ventilation (PSV)

Passive stack ventilation works on the same principles as how older houses were ventilated. By using natural air flow manipulated by natural pressure.

For example, old sash windows could open a gap at the top, which allows warm air to escape from the room. By also opening a gap at the bottom of the window, the pressure caused by air being sucked out of the top means that cool air can be sucked in through the bottom (based on the principle of warm air rising). Old chimneys also worked, in the same way, to allow the heat from the fire to move up through the walls of the house creating pressure and this would suck cool air into the room through air vents.

Imagine the same principle, but a skylight or vent at the top of a house which allows heat to escape and in turn the pressure created allows cool air to be drawn in through vents on the ground floor at a lower level.

Wind moving across a roof vent creates pressure that sucks air up and out of the vent. In turn, this creates airflow upwards through the house.

Using cross ventilation also creates pressure to draw air through rooms so all parts of a house are ventilated.

Passive Stack is designed to use natural air pressure through a system of vents and ducts for natural extraction and air flow ventilation.

However, it can be draughty and requires manual intervention unless you install an intelligent system that opens and closes the vents automatically.

Mechanical Extract Ventilation (MEV)

The mechanical extract ventilator (MEV) is a multi-room integrated system that has a central extraction unit usually fitted in the loft space. It has ducts to the bathrooms, wet rooms and kitchens that continuously extract moisture from the air.

As a progression of the natural passive stack system, the MEV system uses mechanical ventilation. The extraction ducts create pressure that draws in air through external background vents and trickle vents in the windows. This generates an air flow and cross ventilation through the rooms to ensure whole house ventilation.

The system also has a boost facility for accelerated extraction on demand to remove excessive moisture and fumes.

A mechanical extract ventilator can usually only be fitted to new build properties as the ducting is integrated into the fabric of the building. Retrofitting can be difficult and expensive.

Mechanical Ventilation with Heat Recovery (MVHR)

Mechanical ventilation with heat recovery (MVHR) is a multi-room system that uses centralised extraction the same as an MEV system. The difference to an MEV is that the MVHR extracts and supplies the air from the same system.

Ducts to bathrooms and kitchens extract the humid air and then pass it through a heat exchanger to warm it before recirculating it into other living spaces.

MVHR systems are highly efficient and economical when used in airtight houses and are a central part of the design standards of Passivhaus.

At Everest, energy efficiency is at the core of what we do and we are committed to offering a range of products with the lowest U-values in the UK.

Triple glazed windows with trickle vents and a mechanical ventilation system or a passive stack system can ensure your home is effectively ventilated. Keep your home healthy.

Information is correct at the time of publication: March 2023.