Ventilation near you

Ventilation is not one system but several jobs, each solving a different problem in a different part of the house. A quote should say which of these it is addressing.

Several of these are not merely disappointing workmanship. The first test the ACCC lists for a major problem with a service is one that creates an unsafe situation, and a fan discharging into a roof space, or extraction added to a house with an open-flued gas appliance without anyone weighing the negative pressure it creates, is capable of doing exactly that. Where a problem is major, the choice of remedy belongs to the consumer — cancel the contract for a refund, or keep it at a reduced price reflecting the problem — while a minor problem simply has to be fixed free of charge. These guarantees apply automatically and, as the ACCC puts it, cannot be taken away by anything a business says or does.

This is the part of ventilation work Australians most need to know about, and it is counterintuitive. A powerful extraction fan lowers the air pressure inside the house, and if there is an open-flued gas appliance running, the easiest place for replacement air to come from can be down its flue — dragging combustion products, including carbon monoxide, back into the room. Energy Safe Victoria's advice to households is direct: do not operate exhaust fans at the same time as your heater, because your rangehood, toilet or bathroom fan can create a negative pressure effect, drawing carbon monoxide into living areas.

The regulator has also flagged the underlying trend. Energy Safe Victoria's guidance for gasfitters states that the sealing of buildings to achieve higher energy efficiency, coupled with the increased use of extraction fans such as high-capacity range hoods and exhaust fans, can adversely impact the safe operation of internal open-flue gas appliances and lead to carbon monoxide spillage. The corresponding test is carried out with all extraction fans operating, precisely because an appliance that passes in a still house can fail in a working one.

Carbon monoxide is colourless and odourless, and Energy Safe Victoria is explicit that you will not be able to tell if your heater is leaking it because you cannot see it or smell it. The practical rules follow from that. Have gas heaters serviced at least once every two years by a qualified gasfitter. If you are worried about a heater, do not use it until a qualified gasfitter has checked it. And if you are adding extraction or sealing the house up, say so — Sustainability Victoria advises that where a home has unflued or open-flued gas heaters you should maintain adequate ventilation, not seal vents required for safe operation, and have a qualified gasfitter verify carbon monoxide levels after draught-proofing work.

The requirements to hold an installer to are in the ABCB Housing Provisions. Part 10.6 requires natural ventilation openings with a ventilating area of not less than five per cent of the floor area of the room being ventilated, and permits ventilation borrowed from an adjoining room where the connecting opening meets that same proportion and the adjoining room has openings equal to five per cent of the combined floor areas. Where mechanical ventilation is used instead, Part 10.8 requires exhaust from a kitchen, kitchen range hood, bathroom, sanitary compartment or laundry to discharge directly, or via a shaft or duct, to outdoor air — not into a roof space, a wall cavity or a subfloor.

The flow rates are minimums, not targets: at least twenty-five litres per second for a bathroom or sanitary compartment and at least forty litres per second for a kitchen or laundry. Where a bathroom or sanitary compartment exhaust system does not run continuously, it must include a run-on timer so the exhaust system continues to operate for ten minutes after the light switch is turned off. In climate zones 6, 7 and 8 the same part requires a roof space to be ventilated to outdoor air or sit under unsarked tiles, with a minimum roof space height of twenty millimetres.

On licensing, the electrical connection is the part that always applies: New South Wales requires an electrical licence before undertaking any electrical wiring work regardless of the cost or type of work, and in Victoria an exhaust fan installation falls into the non-prescribed category — the same category as lights, power points and air conditioning — for which you must be given a copy of the certificate of electrical safety within thirty days. In Queensland, ductwork and enclosures for air conditioning, air handling and mechanical ventilation systems fall within a specific air handling duct installation licence class. Anything touching a gas appliance or its flue is gasfitting and licensed separately again.

Start with the room, not the fan. The installer should establish the floor area of each room being ventilated, what the code requires for it, where the duct can physically run, and where it can terminate through a wall, eave or roof. A fan is then chosen with enough capacity to meet the required flow through that actual duct run, rather than at the laboratory figure on the box, because every metre of duct and every bend costs flow.

The installation itself has a short list of things that separate a working fan from a decorative one: the shortest and straightest duct run the building allows, duct pulled taut rather than left coiled in the roof space, properly clamped connections at both the fan body and the terminal, a terminal that actually opens, and the ceiling penetration sealed. Where the house has a gas appliance, the interaction with negative pressure should be raised before anything is installed rather than discovered later.

Commissioning is simple and almost never done: run the fan, confirm air is leaving the external terminal, check the run-on timer operates, and demonstrate it to the householder. Ask for that, and ask the installer to confirm in writing that the exhaust discharges to outdoor air. It is the single most common non-compliance in Australian housing and the one with the most expensive consequences.

Australian homes are being sealed up, and the code requires it. Part 13.4 of the ABCB Housing Provisions requires conditioned spaces, and habitable rooms in climate zones 4 to 8, to be sealed against air leakage: external doors and openable windows sealed, door bottoms fitted with draught protection devices, roof lights sealed or capable of being sealed, and ceilings, walls and floors constructed to minimise air leakage using close-fitting linings or sealed junctions. It even requires an exhaust fan itself to be fitted with a sealing device such as a self-closing damper, filter or the like, so the fan does not become a permanent hole in the ceiling when it is off.

The consequence is that draught sealing and ventilation have to be designed together. A house that has had its gaps closed no longer ventilates itself by accident, so the deliberate ventilation — the fans, their flow rates, their discharge to outdoor air and their run-on timers — carries a load that leakage used to carry invisibly. This is also why moisture problems often appear after an energy efficiency retrofit rather than before one.

There is one exemption in Part 13.4 that tells you how seriously the interaction is taken: permanent ventilation openings required for the safe operation of a gas appliance are exempt from the sealing requirements. If a vent in your home exists to keep a gas appliance safe, it is not a draught to be eliminated, and sealing it is the kind of well-intentioned improvement that has genuine consequences.