Ventilation: Fresh Air In, Stale Air Out
Ventilation is the process by which fresh air enters the home, and stale air exits. In the past, uncontrolled ventilation, also known as natural ventilation in building regulations, was the most common method.
Natural Ventilation
Natural ventilation is cost-effective, involving permanent wall vents or windows prefitted with vents. It is often complemented by extractor fans in bathrooms and kitchens to quickly remove moist, stale air.
Drawbacks of Natural Ventilation
While natural ventilation allows plenty of fresh (cold) air to enter the home, it also lets a significant amount of heat escape. This has led to practices like draught-excluding or boarding up vents, which can cause moisture problems and increase the risk of carbon monoxide buildup.
Natural Ventilation in Modern Homes
Natural ventilation is still common in most existing homes and remains an option under building regulations for new builds. However, in ROI, since the introduction of the 2019 building regulations, it has become challenging to design natural ventilation into new homes. The regulations require houses to be airtight and mandate mechanical ventilation if airtightness results are very good. This was already difficult under the 2011 regulations.
Air Supply for Combustible Appliances
A combustible appliance in your home requires a permanent air supply from outside. A stove with an air supply directly fed through a duct is preferable to a permanent vent in the wall, ceiling, or floor.
Mechanical Ventilation in Airtight Homes
Given that most new homes are built to be airtight, some form of mechanical ventilation has become mainstream. An airtight home allows only a minimal amount of air to enter or leave, making a dedicated system to bring in fresh air essential for maintaining good indoor air quality.
Role of Windows in Ventilation
Windows provide purge ventilation and are only part of a mechanized ventilation strategy. They cannot be relied upon for background ventilation, as a steady level of fresh air is needed for good indoor air quality.
Fully Mechanized Ventilation Systems
A fully mechanized system typically involves a centralized unit and ducting to each room. One popular option is Mechanical Ventilation with Heat Recovery (MVHR), which has become a go-to solution for self-builders due to its efficiency. MVHR recycles heat from within the home through a heat exchanger and may offer some cooling in the summer, depending on the model. However, MVHR is not an air conditioning device; it is designed to optimize air circulation.
Other Ventilation Options
- Demand Control Ventilation (DCV): This system features a centralized fan and uses humidity sensor vents in rooms to extract stale air.
- Positive Input Ventilation: An older system that relies on the passive stack effect but may struggle in areas with high winds. Variants of these systems exist.
Designing Ventilation Systems
Both natural ventilation and fully mechanized systems, as well as hybrid solutions, must be designed by a professional to ensure they work as intended. For example, creating voids in walls and ceilings allows for larger ducts, which reduce noise and improve overall system efficiency due to lower resistance.
Regulatory Requirements
In ROI, building regulations stipulate that the ventilation system must be both designed and commissioned (tested) by an independent energy assessor. In NI, for fixed building ventilation systems requiring commissioning, regulations do not specify who should perform it, but it must adhere to the procedures outlined in the Domestic Ventilation Compliance Guide as specified in the Building Regulations. It is advisable to have the company providing the equipment take on these roles to maximize efficiency.