When discussing energy-efficient homes and sustainable building practices, Heat Recovery Ventilation systems (or HRV systems) often become a focal point. This topic can get complex because HRV systems are not just an add-on—they’re the final piece that ties a home’s comfort, energy efficiency, and health systems together.
HRV systems have far-reaching implications for a house, and while they are a cornerstone of Passivhaus, their benefits extend to any well-sealed, energy-efficient home.
(I’ll be referring to HRV, but Energy Recovery Ventilation or ERV, is a similar and interchangeable term for this article).
Why HRV matters
Australia’s building standards are often cited as being 20 years behind those in Europe. However, even in Europe, where energy efficiency standards are much higher, new homes are still sometimes built without HRV systems. So what are HRV systems, and why should you consider one for your home?
What is an heat recovery ventilation system?
An HRV system performs a simple yet vital task:
- Fresh air circulation: It draws in fresh air from the outside and circulates it throughout the home, delivering it to living and sleeping spaces.
- Air exchange: Simultaneously, stale air is extracted from wet areas, kitchens, and other key zones and returned to the central unit.
- Energy recovery: The conditioned (heated or cooled) indoor air exchanges its temperature with the incoming fresh air before being exhausted outside. This ensures the fresh air is tempered, reducing the energy load on the home’s heating or cooling systems.
Key benefits of HRV systems
- Moisture control:
By reducing the moisture load within the building, HRV systems help prevent mould growth and moisture damage, which are critical in homes with high-performance building envelopes. This function is critical in building health and asset protection. - Improved air quality:
Fresh air circulation maintains indoor air quality, protecting occupants from pollutants, allergens, and extreme outdoor conditions such as smoke from bushfires. - Comfort without energy waste:
HRV systems help maintain consistent indoor temperatures without the need for additional heating or cooling, leading to greater comfort and energy efficiency.
But why do I need an HRV system? Haven’t homes managed without them before?
Historically, homes relied on natural ventilation, often unintentionally, through leaky building envelopes. However, as building standards evolve, airtightness has become a key focus for improving energy efficiency.
The most cost-effective way to enhance a home’s energy efficiency is to ensure it is airtight enough to control the volume of air within the building. This is measured using Air Changes per Hour (ACH), which defines how often the air inside a home is replaced with outside air. (We’ve written more about airtightness here)
Where Australia stands on airtightness
- Current Australian building regulations assume an airtightness level of 8–10 ACH, which is relatively leaky.
- International standards in North America and Europe typically target 1–2 ACH for residential and office buildings.
- In Australia, if a home achieves an airtightness below 5 ACH, mechanical ventilation systems such as HRVs become mandatory.
It just doesn’t make sense to build a home, and leave lots of holes so that outside air can come in. What does make sense, is to build a great thermal shell and design windows that can be opened when it is appropriate to create airflow, and a mechanical system to maintain air quality when the house is closed up.
You need airtightness and you need HRV
The move from 8–10 ACH to 2 ACH is transformative. It significantly reduces a building’s primary energy needs, especially for winter heating, which is often the least sustainable due to reliance on coal and gas-fired power stations. This can be achieved through sensible detailing and upgrade measures.
As airtightness improves:
- Air quality becomes a priority: Without a leaky envelope, air quality must be actively managed. Although if you think about it, with a leaky envelope, you’re still at risk of poor air quality from outdoors: smoke, pollen, pollution – you just can’t do anything about it.
- Moisture risks need to be managed: Tighter envelopes are more prone to condensation, particularly in walls, which can lead to long-term damage. HRV systems are critical for preventing these issues.
- Heating and cooling systems work better: If you’ve got a split-system, research has shown it will be far more effective once the house is sealed up. It no longer has to work as hard to heat or cool the volume of air in the house.
- The building is more resilient to extreme climate events: HRV systems provide a buffer against outdoor air quality issues, such as bushfire smoke, high rainfall periods or extreme pollution events.
In short, a well-sealed home requires an HRV system to protect the building, maintain comfort, and ensure healthy indoor air.
The case for HRV in Australian homes
For Australian homes to move towards higher energy efficiency, tighter building envelopes must become the norm. However, with this shift comes the necessity of managing the internal environment effectively. HRV systems are the key to achieving this balance, ensuring homes remain comfortable, healthy, and energy-efficient while protecting against condensation and extreme outdoor conditions.
As we continue to advance building standards and adapt to a changing climate, HRV systems will no longer be optional—they’ll be essential.
They make up an integral part of the job of the building envelope, to relevant moisture coming in, to manage moisture generated internally, and ensure asset protection and occupant health.
You probably have more questions, so we’ll be writing follow-up articles shortly on:
- How to detail a HRV system with heating and cooling systems
- What are your HRV options?
If you’d like to get advice on getting airtightness and HRV right for your home, request a quote to work with our team.