Balanced ventilation in new buildings: How Much Fresh air in Each Room

How to have a balanced ventilation system in your new building: the correct amount of fresh air in every room

By Ruth MacEachern

Product Manager

A perfectly airtight building, improved air quality with a reduction in allergens and pathogens, improved heating and ventilation efficiency resulting in lower heating bills and reduced carbon emissions… These factors are among the benefits and selling points of a mechanical ventilation system, and can take your new project to the next level in terms of selling potential and eco-credentials. While the cost of running an individual extractor fan may not seem like a lot, if not properly installed and commissioned, an inefficient whole house mechanical ventilation system can incur significant running costs without offering the full benefit in terms of an improved living environment. In this article we will first consider why balance is so important to an efficient ventilation installation, before turning our focus to how one might achieve a balanced ventilation system, with an appropriate air flow rate in each room.

The importance of balance

Whole home mechanical ventilation systems are an excellent means by which to improve the air quality in your new build project, avoiding the build-up of allergens and irritants, and reducing damp and mould. Mechanical ventilation heat recovery systems also represent a verifiable means by which to improve thermal efficiency and reduce heating costs. More information on the cost-saving potential and efficiency of heat recovery systems can be found in our article, here.

However, the initial financial outlay and effort involved in installing the system will be for nothing if the system is not correctly balanced and configured during design and commissioning. If the air flow rates in the various rooms are not correctly balanced, this can result in excessive noise in certain rooms (definitely to be avoided in bedrooms), with insufficient ventilation or even dead spots in other rooms. This can actually encourage the build-up of damp, mould, and the associated pathogens. Furthermore, an unbalanced system can significantly reduce the system’s heat recovery rate. As well as balancing the air flow rates from one room to the next, it is also important to  consider the flow of air entering and leaving the building via external vents, to avoid pressuring or depressurising the house, resulting in further inefficiency.

A study conducted by BPE Specialists, “multidisciplinary Building Performance Experts" states that “where systems are out of balance, either large amounts of colder air are delivered to the dwelling leading to additional heat loads and discomfort, or else larger amounts of warm air are lost to the outside. A large imbalance can also lead to excess system condensation.”

With the potential issues and the importance of a balanced system having now been established, we shall now look briefly at what is required to achieve the desired balance.

Tips to help achieve a balanced MVHR system

1. As with many other aspects of mechanical ventilation installation, the solving, or ideally the bypassing of potential pitfalls starts from the early design phase. Your chosen ventilation system must be appropriately dimensioned to ensure even air flow throughout the property. The routing of ducts and positioning of ventilation openings must be carefully planned to ensure adequate air flow, particularly in sensitive rooms such as the kitchen or bathrooms, while avoiding noise disturbance in living spaces and bedrooms. 

2. Commissioning: this is when the real balancing act begins. In the aforementioned study conducted by BPE Specialists, “only 16% of systems [were] found to have been commissioned correctly with respect to air flow and balancing”. If you want to avoid adding to this statistic, it is essential that commissioning be performed correctly, calling in a professional if you are unsure as to what you are doing. To correctly balance a system you must first ensure that the extract flow rate is the same as the supply flow rate, to avoid the build-up of positive or negative pressure. Attention must then turn to the air flow rates in the individual rooms. Both outlet and inlet vents must be adjusted to ensure an adequate supply of fresh air and the removal of stale air. This can prove laborious, as adjusting the air flow in one room may affect that in a room that has previously been adjusted. It is therefore recommended that you begin in rooms with a larger air flow capacity, such as the kitchen. Commissioning requires the use of specialist equipment to obtain accurate measurements, such as a vane anemometer or even better, a powered anemometer if available.

3. Handover and maintenance: when handing the system over to the house buyer, it is essential that clarification be provided as to the operation and adjustment of the system. It may be necessary to adjust the system based on how frequently rooms are occupied. It is also essential that an MVHR system be regularly cleaned and maintained. Increased resistance from clogged vents and filters may result in a change in ventilation rates, which will result in disbalance and a reduction in the heat recovery rate.

A balanced system, healthy occupants, and a healthy bank balance

Whether it’s balanced carbon emissions, a balanced diet, or a healthy work/life balance – there is no denying that balance is the order of the day. Having read this article it should hopefully stand to reason that achieving balance in a mechanical ventilation is likewise essential. A successfully balanced and commissioned system will ultimately result in healthy and happy customers who are willing to pay a premium for a future-proof, efficiently ventilated home.