A Breath of Fresh Air: Why Your Home Needs Mechanical Ventilation

New Zealand’s Healthy Homes standards are primarily concerned with insulation rather than ventilation, requiring insulation in the floor and ceiling along with at least one heating source in the house. However, insulation alone won’t solve all of a home’s problems. In fact, just increasing the insulation can sometimes do more harm than good.
 
Additional insulation reduces the amount of heat escaping, but this escaping heat can also help to dry out the walls, floor, and roof of the building. That means that adding insulation, while making it slightly less cold inside, can increase the internal moisture levels by inhibiting the building’s capacity to dry itself out. This can lead to an unhealthy and uncomfortable living environment, which is why an effective, efficient ventilation system is vital to maintaining good air quality and moisture levels in your home.

• In early 2020, MBIE published a report on the moisture issues caused by airtight buildings. View the report here.

​A holistic approach is necessary when you’re looking to upgrade or improve the health of your home; no single element can ensure optimal performance by itself. If you only have the budget for one substantive renovation, however, an effective ventilation system will likely have a bigger overall impact on your home becoming healthier, warmer, dryer, and more comfortable.

At Craft Homes, we understand the impact that mechanical ventilation can have in terms of the health and comfort our homes can provide. Learn more about mechanical ventilation systems below.
​
What are mechanical ventilation systems?
Mechanical ventilation systems cycle fresh air through a house or building. An easy way to think about different mechanical ventilation systems is to think about the kind of pressure they create within a house. When the atmospheric pressure inside a house is higher than it is outside, air will be pushed out of the home. If the pressure inside is lower, then air will be pulled into the home. Some ventilation systems can affect the pressure inside the home by design, to circulate air, while others such as MVHR systems are designed to maintain a satisfactory pressure. These systems can be classified as follows:

• Negative Pressure. A continuous extraction ventilation system constantly pulls moist air from the home (primarily from the bathroom and kitchen) and exhausts it outside through a vent. This creates negative pressure within the home that pulls air in through gaps in the building envelope. This is often the ideal ventilation system for older, leakier homes.
• Balanced Pressure. A mechanical ventilation system achieves optimal efficiency by extracting air through a series of ducts distributed throughout the house and then feeding fresh air back in, maintaining a balanced pressure at a comfortable level. Heat recovery systems use the outgoing air to heat or cool the incoming air, stabilising the temperature. These systems work best in homes with a high level of airtightness.
• Positive Pressure. A fan filters air from the attic and forces it into the house when it reaches an ideal temperature. This creates positive pressure that forces interior air out through gaps in the building envelope. While fairly common, this system is not recommended, as it creates a risk of condensation and moisture damage and may not work as intended in a home with a high level of airtightness.

Diagram from Oculus Architectural Engineering resources - Ventilation Systems

Why Mechanical Ventilation is Necessary
Mechanical ventilation systems are a great way for homeowners with lower budgets to make a meaningful improvement to their homes, and more and more experts are acknowledging their benefits. After years of scepticism, BRANZ finally embraced mechanical ventilation systems in late 2020, recommending that residential buildings be mechanically ventilated and built to an airtightness target. Jason Quinn, Director at Sustainable Engineering, continues to advocate for mechanical ventilation systems in all New Zealand buildings, not just new Passive Houses and high-performance buildings.
 
A continuous mechanical ventilation system in your home will:

• Reduce levels of relative humidity within your home
• Minimise the risk of condensation, mould, and dampness
• Reduce the risk of illness from indoor air pollutants
• Operate quietly and without disruption year-round

 
An MVHR system that uses filtered air will also:

• Provide cleaner air that is more comfortable for those with allergies or asthma.
• Improve indoor air quality

These benefits have a direct impact on our well-being. Stale humidity or dampness in a home can lead to condensation and moisture, which lead to mould. Mould releases tiny spores into the air that can aggravate—or even cause—respiratory conditions and other illnesses.
​

• Read more about the impact that New Zealand’s substandard housing quality has on our health.

In addition to a healthier environment, mechanical ventilation contributes to a more comfortable environment as well. By extracting moisture, humidity levels are kept within an optimally comfortable range. Also, heat recovery systems help to ensure that the temperature is even throughout the house.

Which ventilation system is right for you?
As with most features in your house, there is no single mechanical ventilation system that will suit all homes. For new build houses that meet higher efficiency and airtightness targets, a Mechanical Ventilation Heat Recovery (MVHR) system will likely be your ideal solution, this is also known as a balanced pressure system. These systems provide filtered fresh air and extract stale, moist air. An air-to-air heat exchange system then recovers as much as 90% of the heat produced within the home, helping to maintain a comfortable and even temperature throughout. However, these systems may not be as effective in older homes that already leak too much air.
 
For those older, leakier homes, a Continuous Extraction Ventilation system (also called a negative pressure system) may work better. This type of system extracts stale air from the indoor environment, normally from the kitchen and bathroom. The “fresh” air is then pulled into the house from somewhere through the building’s envelope, either from the crawlspace below the floor or from the attic or garage if the house sits on a concrete slab. This air is not filtered, and therefore is not necessarily clean and healthy.
 
Choose a healthier home
At Craft Homes, we specialise in every system and design element that contributes to a healthier and more comfortable home. We apply a holistic approach to ensuring the best possible indoor environment from the design stage and work with you from concept to completion. Get in touch with Craft Homes today to learn more about the role that mechanical ventilation can play in a healthier future for you and your home.