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Heat recovery ventilation · One honest page · Perth & south-west, Western Australia

Fresh Air Without Throwing Your Heating Out the Window.

"Your heat recovery capability is basically blown. It's gone."

Phil Pacak, Euroheat – on running ventilation ducts through an uninsulated WA roof space

A well-built modern house is sealed. That is the point of it – and it is also the problem. Sealed houses need air brought in deliberately, and the cheap way to do that is to open a window and let the heat you paid for walk out with the stale air. Heat recovery ventilation brings the fresh air in and keeps most of the warmth. When it is designed properly.

Here is when it is worth it, when it isn't, and the one detail that quietly wastes it – from the engineers who design and install these systems alongside the heating.

When it earns its keep

  • The house is genuinely sealed and well insulated. The tighter the build, the less air moves on its own, and the more you gain by controlling the air you do bring in. A well-built new home in Perth is the case heat recovery was invented for – though in Perth's mild climate the energy saving is modest, and the stronger reason is fresh, filtered air without opening a window on the heating.
  • Somebody in the house reacts to the air. Dust, pollen, damp, a stuffy bedroom by morning. Filtered incoming air is a different daily experience from a window cracked open, and it is the reason most of our clients raise it in the first place.
  • You are already paying to heat or cool the air. Recovery only has value where there is something to recover. In a house running hydronic heating through a Perth winter, the air you exhaust is air you paid for.
  • It is being designed alongside the heating, not bolted on later. Duct routes, plant space and control logic are cheap on a drawing and expensive in a finished ceiling.

When it doesn't

  • The house is leaky. An older Perth home with gaps around every window and door already changes its air many times over without any help. Seal and insulate first. Ventilate second. Spending on recovery before sealing is spending in the wrong order.
  • The ducts have to cross an unconditioned roof space and cannot be properly insulated. This is the common failure in WA, and it is fatal to the whole point – see below.
  • Nobody will maintain it. Filters are the one job the owner has. A system with blocked filters ventilates badly and costs more to run than no system at all.
  • It is chosen as a product rather than sized for the building. A unit picked off a spec sheet without an air-change calculation for the actual rooms is a guess with a warranty.
We design and install these systems, and we still tell people to fix the building envelope before they buy one. If a proposal cannot show you the air-change rate it is designed to deliver for your rooms, it is a product quote, not a design.
The detail that quietly wastes it

The recovery is lost in the roof space, not in the unit.

Heat recovery units are mostly European, and they are built for European installations where the ducts run inside the heated envelope of the building. In Perth they routinely get installed with long duct runs through a roof space that hits brutal summer temperatures and cold winter nights, with little or no insulation on the ducting.

At that point the unit is still recovering heat and the roof space is still taking it away again. The equipment works. The system doesn't. And on a commissioning sheet it can still look like a pass, because nobody measures what the air did between the unit and the room.

Why we keep repeating it: the same pattern shows up across hydronic work in Perth. A pipe or a duct carrying heat through an unconditioned space, uninsulated, giving that heat away around the clock, while every contractor on site points at somebody else's equipment.

We once traced a commercial building losing tens of thousands of dollars a year to exactly that – heat leaking out of uninsulated pipework buried in the structure. The gear was fine. The detailing was not. Ventilation ducting fails the same way, for the same reason: it is the part nobody photographs.

Two shapes of system, two different jobs.

Almost every conversation about heat recovery ends up as a choice between these. Neither is the right answer in general – they answer different questions about the building.

One unit, ducted through the house

Centralised

A single heat exchanger – the core where the outgoing air warms the incoming air without the two mixing – serves the whole house through a duct network: stale air out of the bathrooms, laundry and kitchen, fresh filtered air into the bedrooms and living spaces, the two air streams passing each other inside the unit.

Best when the building is still on the drawing board and duct routes can be planned inside the insulated envelope. Best performance, best filtration, quietest rooms – and the least forgiving of a bad retrofit, because the duct network is the system.

Small paired units, room by room

Decentralised

Pairs of small units sit in external walls and alternate: one pushes air out while its partner draws air in, each storing and returning heat in a ceramic core as the cycle reverses.

Best when there is no route for ducts and no ceiling to lose – typically an existing home, an addition, or a single problem room. Far easier to install, and honest about its limits: less filtration and less control than a well-built centralised system.

Heat recovery ventilation reduces the cost of fresh air. It does not make fresh air free.

Anyone promising a specific saving before they have looked at your building envelope, your duct routes and your air-change requirement is quoting a product, not designing a system. The honest answer is that a well-designed system keeps most of the heat you would otherwise open a window and lose – and a badly detailed one keeps almost none of it.

Watch it explained before you choose a system.

No scripts, no studio – the engineer who designs these systems answering the questions people actually ask about ventilation.

The full explainer · 18 min
Expert guide to centralised heat recovery ventilation systems
Watch on YouTube →
The other shape · 13 min
The pros and cons of decentralised heat recovery ventilation
Watch on YouTube →
Hiding it · 3 min
Compact centralised systems: concealed heat recovery explained
Watch on YouTube →
Where recovery pays · 6 min
Is a heat pump really worth it – and when is a heat recovery heat pump better?
Watch on YouTube →

Ventilation is decided with the heating, not after it.

Specifying or building it

Duct routes, plant space and control logic are cheap on a drawing and expensive in a finished ceiling. See how fresh air fits a house designed as one system, while the ceilings are still on paper.

See whole-home systems →

Heating your own home

Start with the running-cost number, not the equipment list. The Running Cost Calculator shows what your home models at built right versus built cheap – the gap that decides everything else. Modelled estimates, two minutes.

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