HRV vs ERV in Australia — which suits Adelaide?

Once a home is airtight, ventilation stops being an accident and becomes a decision.

In a leaky home, fresh air arrives uninvited — through gaps, around windows, under doors — dragging in dust, pollen, noise and whatever the weather is doing outside. In an airtight home, none of that happens, so the fresh air has to be designed in. That is the principle behind the old building-science line: build tight, ventilate right.

The question is which ventilation system to design in. For most high-performance Adelaide homes that comes down to two acronyms — HRV and ERV — and the answer depends almost entirely on climate.

What is the difference between an HRV and an ERV?

Both move stale air out and filtered fresh air in while recovering most of the heat. The difference is whether they also move moisture.

An HRV — a heat-recovery ventilator — transfers sensible heat only. As warm, stale air leaves the home in winter, it passes its warmth through a heat-exchange core to the cold, incoming fresh air, without the two streams ever mixing. The heat is recovered; the moisture is not. Humidity simply leaves with the outgoing air.

An ERV — an energy-recovery ventilator — does the same with heat, but uses a moisture-permeable core that lets some humidity cross between the streams as well. In winter it keeps some indoor moisture in rather than venting it; in summer it sheds some of the incoming humidity before the air enters the home. The industry figures put an ERV’s latent (moisture) recovery in the order of 40–60%, with slightly lower sensible-heat recovery than an equivalent HRV.

That single distinction — sensible heat only, versus sensible heat plus some moisture — is the whole decision. Everything else about the two systems is broadly the same: continuous filtered fresh air to every occupied room, ducting, and a quiet box in the plant cupboard doing the work.

This is the system the pillar of any Passive House build is named for — mechanical ventilation with heat recovery, or MVHR. An HRV and an ERV are the two flavours of it.

Which suits Adelaide’s climate?

For most Adelaide homes, an HRV is the sensible default — and an ERV is the considered exception, not the rule.

Adelaide has a Mediterranean climate: hot, dry summers and cool, wetter winters. It also has the lowest humidity of any Australian capital. On a hot summer day, daytime relative humidity here often sits between 20% and 40% — the air outside is already dry. There is very little outdoor humidity to recover, and on the hottest days you generally do not want to drag the day’s moisture indoors at all.

That is the opposite of the case that makes an ERV shine. ERVs earn their keep in hot, humid climates — think Brisbane or Darwin — where the latent cooling load is high and keeping incoming summer humidity out of the home is genuinely useful. Adelaide does not have that problem for most of the year.

In an Adelaide winter, the logic is more even. The air is cooler and wetter outside, and a very airtight, well-occupied home can dry out indoors, because cold incoming air carries little moisture and the home’s own moisture is being continuously vented. An ERV’s modest moisture retention can keep winter indoor air more comfortable. But that is a comfort refinement, not a structural need — and it has to be weighed against the rest of the year, when Adelaide’s dryness means an HRV is the cleaner fit.

The honest position: in our climate, an HRV is the right starting assumption. An ERV is worth putting through the energy model when the brief calls for it.

When an ERV is worth modelling

An ERV becomes a real candidate when the home and the brief point that way, not because it is the newer-sounding option.

We would model an ERV when:

• The home is exceptionally airtight and tightly occupied, so winter indoor air would otherwise run dry.
• Stable indoor humidity is a stated priority for the people living there.
• The home sits in a microclimate, or a part of the brief, where summer humidity actually matters more than Adelaide’s averages suggest.

And we would default to an HRV when the home is a typical Adelaide custom build in a typical Adelaide suburb — Lockleys, Grange, West Lakes, Henley Beach — where the dominant condition is dry summer air, and there is simply not much moisture in the outdoor air worth trading.

Either way, the choice is made in the energy model before a brick is laid, alongside the rest of the envelope, rather than guessed at on site.

What both systems get right

Whichever core you choose, the work the system does for the home is the same — and it is the part most people underestimate.

It recovers heat. The Passive House Institute requires certified units to recover at least 75% of the heat from outgoing air; the certified units we specify typically reach around 90%. Most of the energy you have already spent heating or cooling the air stays inside the home, instead of going out the exhaust.

It filters. Continuous fresh air is delivered through a filter — F7 as standard, and up to HEPA-grade on a unit sized for it — so the particulate, pollen and smoke load inside the home is far lower than outside. In an Adelaide summer of bushfire smoke and high pollen, that is the difference between opening windows and not having to.

It keeps the fabric dry. Because the home is airtight, there is no uncontrolled air pushing moisture through the wall build-up. The ventilation handles the air the home needs; it does not let air smuggle moisture into places it can condense. That is the same logic behind why air leaks cause condensation in walls — uncontrolled air movement is the problem, and designed ventilation is the cure.

This is why ventilation is not an optional extra on an airtight home. It is the half of the equation that makes airtightness liveable. Build tight, then ventilate right.

The short version

If you are weighing HRV against ERV for a high-performance home in Adelaide:

• Default to an HRV. Adelaide’s dry, Mediterranean climate gives an ERV little outdoor humidity to recover for most of the year.
• Model an ERV when the brief earns it — a very airtight, tightly occupied home where winter indoor air would otherwise run dry, or where stable humidity is a priority.
• Don’t choose on the acronym. Both deliver continuous, filtered, heat-recovered fresh air; the only real difference is whether moisture comes along for the ride.
• Decide it in the energy model, with the rest of the envelope, not as an afterthought on site.

Ventilation is the quiet system that makes an airtight home work. Getting the right one is less about the latest product and more about the climate it has to live in — which, for a custom home built in Adelaide, usually points one way.