An Australian house is a lung with a mortgage. It takes in the afternoon, the wet season, the week the ranges are on fire, and whatever is burning on the hob. We talk about energy as if the only question were comfort and the bill. Air is quieter: what is in the room when you have closed it to keep the heat out, or opened it to keep the mould down, or both on the same Tuesday.
This is not medical advice. It will not interpret a cough, a child's asthma, or a reading on a cheap sensor. Those conversations belong with a clinician who knows the person. Buildings and appliances create indoor air. Bushfire smoke, tropical mould, a gas cooktop and an unflued heater are four Australian ways of doing that. Owners who seal a house for a warming climate — the work in home energy in a warming climate — inherit a duty: a tighter box needs a thought-out breath.
Bushfire smoke, which does not respect a postcode
Black Summer taught capitals that a fire two hundred kilometres away is household weather. The outdoor number that matters is fine particles. Close the windows when the air outside is worse than the air in. Run a recirculating cooler or a split system on a setting that does not drag the street in. A portable HEPA filter, sized to the room you sit in, earned its keep in those weeks. A tea towel under a door is folk theatre, not a plan.
The useful room is the one you can close: windows shut, filter on, a door that seals well enough. Do not "air the place" at noon on a red-air day. Air it at night if the outdoor reading has dropped. Agencies publish mask guidance when the smoke sits; follow that, not a reel. People with existing breathing trouble need a clinician's plan before the season. A house cannot replace that plan. It can stop being an extra chimney.
Smoke enters through the same gaps heat uses. If you have evaporative cooling, the smoke day is the day it stays off. The machine works by exchanging air with the street.
Mould in a house that was built to breathe
Australia does not have one mould story. It has a tropical wet-season story and a southern condensation story, and they are both about water that stayed.
In the north, a house closed for the air-conditioning, or closed because the occupants are away, can grow a green interior in a month of rain. The building answer is dry, light and movement: sun on a wall, a fan that exhausts outside, a cupboard pulled forward so air can pass, a dehumidifier if the wet season has made the suburb a cloud. Bleach is a visual reset, not a moisture strategy. Find the water.
In the south, the winter story is a family breathing in a sealed bedroom and a pane that runs with condensation. Insulation and a warm inner surface help. So does a night of slightly more air than you wanted to admit. Drying clothes on a rack in a closed room is how a lot of Australian mould begins. If the clothes must dry inside, open the door to a room that can take the water, or use a dryer that vents or condenses as designed. Renters cannot always re-line a black ceiling. They can photograph, ask in writing, and use the habitability words the state already wrote. Do not sleep in a room that smells like a wet towel because the bond felt more important than the air.
Gas cooktops, the indoor flame
A gas hob is a combustion appliance in the room where people stand. This journal will not convert the papers into a diagnosis. It will say what a building can do. Exhaust to the outside, not into the ceiling cavity. A rangehood that captures the plume — low enough, wide enough, turned on — is the minimum. A recirculating hood with a tired filter is a perfume.
Electric induction removes the indoor flame. In a rental it is often a fantasy. A renter can still use the hood, crack a window, and avoid using the hob as a winter heater. Using the cooktop to warm a kitchen is a common July habit and a way of treating the living room as a flue. What you cook with chemically — sprays, oven cleaners, long-lived compounds in dust — is opened in household chemicals, PFAS and safer swaps.
Unflued heaters, which are honest about the exhaust
An unflued gas heater puts its combustion products into the room on purpose: cheap heat, no chimney, a slightly wet house, a window that should stay cracked. Southern living rooms still contain boxes that were legal when installed and would not be anyone's first choice now. Flued gas, a heat pump, a split system in reverse: these move the exhaust or abolish it. An unflued unit that stays should be serviced, should not run while anyone sleeps in the room, and should have the ventilation the plate already asked for. People disable that ventilation because of the draught. The draught was the safety feature.
Portable unflued bottles in a closed granny flat are a worse version of the same idea. Combustion needs an exit. If you cannot name the exit, the room is the exit. Wood heaters are a neighbourhood problem: dry wood and a hot fire, or do not light. The romantic smell is someone else's indoor air.
Renters, and the levers that remain
A renter cannot easily replace a cooktop or flue a heater. Photograph the mould and the heater's plate. Ask, in writing, for a hood that ducts out and a dry room. Keep the emails; habitability language already exists in most states and is how a later complaint becomes more than a smell. A portable HEPA filter is one of the few machines you can take to the next place. A cheap particle sensor is a teacher, not a doctor. It will tell you when a bedroom has been closed too long, or when the smoke has arrived. It will not tell you what to do about a child.
Do not disable an alarm to manage a smoky kitchen. Do not run a generator in a carport that shares air with a bedroom. Sealing is an energy gift and a moisture problem. The civic work is minimum standards that include air, not only a working stove.
The rest of The House is chemicals, older fabric, the lead in a wall. This essay is the climate-shaped part. You cannot legislate a clean outdoor day. You can close a window at the right hour, give combustion an exit, and stop calling a closed, wet, unflued room character. For anything that feels like illness, close this tab and use the other number. The house can only do the house's work.
