Ventilation In Bedrooms: How Many Air Changes Are Needed?

Ventilation is essential for maintaining a healthy home environment. Without it, a house can become damp and unhealthy, and can even develop structural issues. The amount of ventilation needed depends on the room size and the type of HVAC system installed. For example, for a standard residential HVAC unit, you need one supply vent and one return vent for every 100 to 150 square feet of living space. This means that a 10-foot by 12-foot bedroom (120 square feet) would need one air vent. However, this is just a rule of thumb, and the number of vents may vary depending on other factors such as room characteristics and HVAC system type.

Bathroom ventilation

Good airflow is essential in any home to prevent the build-up of chemicals and odours, and to maintain healthy humidity levels. This is particularly important in bathrooms, where washing habits can contribute large amounts of water vapour to the air, leading to problems with condensation and the development of mould.

Exhaust Fans

Bathrooms should be equipped with exhaust fans to remove excess moisture from the air. Exhaust fans should be installed as close to the ceiling as possible on an external wall. The power required will depend on the size of the room, but the fan should be able to extract at least 15 litres of air per second when in use, according to building regulations.

Intermittent vs Continuous Ventilation

HVI (Home Ventilating Institute) recommends intermittent ventilation rates of 1 CFM (cubic feet per minute) per square foot of floor area for bathrooms less than 100 square feet. For larger bathrooms, the CFM requirement for each fixture should be added: 50 CFM for a toilet, 50 CFM for a shower, 50 CFM for a bathtub, and 100 CFM for a jetted tub.

Alternatively, continuous ventilation can be used at a minimum rate of 20 CFM instead of an intermittent 50 CFM exhaust fan.

Timer Controls

To ensure that ventilation continues for a sufficient amount of time after each use of the bathroom, a timer or other control should be installed to keep the fan running for at least 20 minutes.

Steam Rooms

For steam rooms, a separate fan should be installed and turned on after use to clear the heat and humidity.

Placement

Fans approved for installation in wet areas should be located over the shower or tub whenever possible. Bathroom doors should have at least 3/4" clearance from the finished floor to allow proper entry of makeup air.

Whole-House Ventilation Systems

Positive Input Ventilation (PIV) systems can be retrofitted into existing properties to create airflow throughout the entire house, preventing condensation and mould growth in all rooms. These systems use a central unit mounted in the loft to draw fresh air into the property from outside. PIV systems are also recommended for controlling radon concentrations in areas with high radon levels.

Kitchen ventilation

The design of an effective kitchen ventilation system depends on several factors, including the kitchen's workload, the amount and type of cooking equipment, the kitchen's layout, the number of kitchen staff, and the need for easy cleaning and maintenance. The system typically consists of an extractor hood or canopy and a filtering system, with the fan located in the kitchen or its ducts.

There are two main types of kitchen ventilation systems: external venting and recirculation. External venting systems use a chimney to expel hot air from cooking outside the building. Recirculating systems, on the other hand, clean the air and direct it back into the kitchen. This type of system is used when external venting is not possible.

To improve kitchen ventilation and maintain healthy air quality, it is recommended to always use a range hood when cooking and to maintain it properly. This includes regularly changing disposable filters or cleaning metal mesh and baffle filters. Additionally, using a splatter screen can help minimise grease and reduce airborne particles.

If a range hood is not available, fans positioned in or near kitchen windows can be used to improve ventilation. Opening windows and creating a draft by keeping interior doors open can also enhance airflow and ventilation. For better air purification, consider using an oscillating fan with an ionizer feature.

In addition to these measures, a HEPA air purifier can be beneficial, especially when cooking with gas or for individuals with asthma or other cardiovascular ailments. Ensuring proper ventilation during cooking is crucial not only for maintaining air quality but also for reducing the risk of health issues associated with air pollutants.

Utility room ventilation

Utility rooms are often used for household tasks such as laundry, and they usually contain appliances that emit moisture, such as washing machines and tumble dryers. As such, they require adequate ventilation to ensure the good health of their occupants and to prevent issues such as condensation and damp.

According to the Building Regulations, utility rooms need "extract ventilation to the outside". Extract ventilation can be intermittent or continuous. Intermittent extract fans are often used only when required during tasks that produce moisture, and background ventilation such as trickle vents in the windows is also required. Continuous mechanical extract ventilation (MEV) can be either a centralised system, typically located in a loft space or hallway cupboard, or a decentralised system with individual room fans.

For a utility room, it is recommended to have 20 air changes an hour, or a minimum of 108 m³ an hour (or 30 litres a second). This can be calculated by multiplying the volume of the room by the recommended number of air changes per hour. For example, a utility room that is 3 metres long, 2 metres wide, and 2.4 metres high would require a fan with a capacity of 288 m³/hr or 80 litres a second.

When selecting a utility room fan, there are several factors to consider in addition to price. These include noise level, extra functions such as a humidistat, design, and environmental impact. It is important to choose a fan that is suitable for the size of the room and complies with building regulations.

Whole house ventilation

Whole-house ventilation systems are an effective way to improve indoor air quality and circulate fresh air throughout your home. These systems use ducts and fans to bring in clean air and expel stale air, ensuring proper airflow and ventilation. There are four main types of whole-house ventilation systems: exhaust-only, supply-only, balanced, and energy recovery. Each system varies in complexity, cost, and suitability for different climates.

Exhaust-only ventilation systems work by depressurizing your home and exhausting all the spent air. The exhausted air is then replaced by natural ventilation through building openings like cracks, holes, windows, and doors, as well as passive air vents. This type of system is relatively inexpensive and simple to install, making it a cost-effective option. However, it is only suitable for cold climates as depressurization can draw moist air into the building in warm, humid climates, potentially causing condensation and moisture damage.

Supply-only ventilation systems, on the other hand, pressurize your home and force fresh air inside. Spent air escapes through holes and cracks in the building's facade and wall or floor vents. Similar to exhaust-only systems, supply-only systems are also relatively inexpensive and simple to install. They offer more control over the airflow compared to exhaust-only systems. However, they are best suited for warm climates, as pressurization can create moisture issues in cold climates.

Balanced ventilation systems maintain a neutral pressure in your home by bringing in fresh air and exhausting an equal amount of polluted air. These systems are often the most preferred option as they are adaptable to all climates. They typically have separate fans and duct systems for fresh air supply and exhaust air removal, ensuring proper ventilation in every room. However, balanced ventilation systems are more expensive to install and operate than exhaust-only or supply-only systems due to the requirement of two fans and twice the ductwork.

Energy recovery systems, including energy recovery ventilators (ERV) and heat recovery systems (HRV), are the final type of whole-house ventilation. These systems circulate fresh air throughout your home and can also transfer moisture to reduce humidity levels. ERV systems are ideal for hot or humid climates as they effectively remove humidity from the air. However, they can increase electricity bills, especially in mild climates or when the HVAC system is not frequently used. HRV systems, on the other hand, are better suited for cold climates as they have defrost systems to prevent freezing.

When choosing a whole-house ventilation system, it is essential to consider your specific climate and budget. Exhaust-only and supply-only systems are the most affordable options, but they are limited to cold and warm climates, respectively. For homes in more moderate climates, balanced ventilation or energy recovery systems are recommended, although they come with a higher installation cost.

Ventilation and its impact on indoor air quality

Good ventilation is essential for maintaining healthy indoor air quality. Ventilation involves moving outdoor air into a building or room and distributing it within that space. This process helps to dilute and remove indoor pollutants, improving air quality and reducing health risks.

Types of Ventilation

There are three main types of ventilation: natural, mechanical, and hybrid (mixed-mode). Natural ventilation uses natural forces like wind and thermal buoyancy to drive outdoor air through openings such as windows, doors, or solar chimneys. Mechanical ventilation, on the other hand, relies on mechanical fans to move air, either directly installed in walls or windows or through air ducts. Hybrid ventilation combines natural and mechanical methods, using mechanical ventilation when natural ventilation is insufficient.

Impact on Indoor Air Quality

Ventilation plays a crucial role in maintaining good indoor air quality by addressing issues related to humidity and airborne contaminants.

Humidity Control

High indoor humidity can lead to mould growth and damage to buildings. Proper ventilation helps control humidity by removing moisture from the air. In cool climates, natural ventilation through open windows or mechanical ventilation systems like fans may not be sufficient to remove moisture, especially during winter. In such cases, a heating, ventilation, and air conditioning (HVAC) system with dehumidification capabilities can be beneficial.

Airborne Contaminant Control

Indoor contaminants can come from various sources, including construction materials, appliances, and outdoor air. Ventilation helps to dilute and remove these contaminants, improving indoor air quality. Spot ventilation, which focuses on specific areas like bathrooms and kitchens, and dilution ventilation, which addresses the entire living space, are effective strategies for controlling airborne contaminants.

Best Practices for Improving Indoor Air Quality

• Open doors and windows for at least 15 minutes daily to increase natural ventilation.
• Use exhaust fans in bathrooms and kitchens to remove moisture and gases.
• Install and use exhaust fans or windows when cooking to eliminate fumes, particles, and moisture.
• Utilise ceiling fans to improve airflow, preferably with open windows.
• If using paints, hobby supplies, or chemicals indoors, ensure extra ventilation by opening windows and using portable window fans.
• Regularly maintain and clean HVAC systems to prevent the spread of pollutants.
• Use filters with a MERV rating of 6-8 or higher to effectively capture particulates.
• Consider using heat or energy recovery ventilators (HRV or ERV) for continuous indoor air quality ventilation.

In conclusion, proper ventilation is crucial for maintaining healthy indoor air quality. By understanding the different types of ventilation and their impact on humidity and airborne contaminants, individuals can take appropriate measures to improve the air they breathe in their homes and buildings.

Frequently asked questions