Draughts, insulation and heating: fix the house before upsizing the system

When a heater or air conditioner can't hold the room, the instinct is to buy something bigger. Often the system isn't short of capacity. It is heating air that leaves through the ceiling, under the doors and up the exhaust fan almost as fast as it arrives.

Melbourne's west tests a house at both ends of the year. July at Laverton averages a minimum of 5.2 °C, and there are about 27 days a year at or above 30 °C. A leaky house loses on cold nights and hot afternoons alike.

Bigger isn't a cheap fix either. An oversized unit costs more to buy and connect and can cycle on and off. Sorting out the house first means the system you choose is sized for the house you will actually have.

Warm air rises, and in winter the ceiling is usually the biggest escape route. Lift the manhole cover and look with a torch, without climbing in. Is there insulation everywhere, or bare patches? Has it been pushed aside by tradespeople, flattened over the years, or never laid at all over a later extension?

Old halogen downlights are a common culprit. Many needed a ring cut out of the insulation to shed heat, and every ring is a hole in the blanket. Replacing them with complete IC-rated LED fittings, built to sit under insulation, lets the batts close over the top. Get the lights checked before any insulation work, because covering a fitting that isn't rated for it traps heat.

Don't climb in to rearrange insulation around fittings or cables yourself. Old cable can be brittle, and it is easy to put a foot through the plaster. An electrician can confirm which fittings may be covered and clear insulation from any that can't.

A bathroom or laundry exhaust fan is a hole in the ceiling. A fan without a self-closing damper lets warm air rise straight into the roof whenever it is off, all winter long. A sealed fan with a backdraft damper, ducted outside rather than into the roof space, closes that gap and clears steam better too.

Older homes, including many post-war houses around Altona and Laverton, often have fixed wall vents near the ceiling. Some were put there to ventilate gas appliances, so don't block them without advice.

Rangehoods and exhaust fans matter more if there is a gas heater. Energy Safe Victoria advises against running them while a gas heater is on, because the negative pressure can draw carbon monoxide into living spaces.

On a cold, windy evening, walk around with the back of your hand and feel for moving air at skirting boards, door frames, window sashes, floorboards, unused fireplaces, and around downlights and exhaust fans.

Weatherboard cottages in Newport, Yarraville and Seddon usually have suspended timber floors, and gaps between the boards and around the skirting let cold air up from underneath. Underfloor insulation is a separate project, but sealing the obvious gaps makes a noticeable difference on its own.

Sealing a house changes how air moves through it. Energy Safe Victoria warns that renovating or weather-sealing a home with an open-flued gas heater may change the ventilation needed to clear carbon monoxide, which could trap it inside. It also says open-flued heaters spill carbon monoxide more easily than other types.

Before serious draughtproofing, have a qualified gasfitter check any open-flued heater and advise on ventilation. Energy Safe Victoria recommends all gas heaters be serviced at least every two years, including a carbon monoxide test. Rentals will have their own rule: from 1 July 2027, a rental with gas appliances needs a gas safety check before draughtproofing starts, and the work must not go ahead if unflued or open-flued appliances are found.

Single-glazed windows lose warmth on winter nights and let heat pour in on summer afternoons. Close-fitting curtains with a pelmet or ceiling track, closed at dusk, stop warm air sliding down the cold glass and out under the hem. In summer, external shading on east and west windows does more than anything inside.

Double glazing is a bigger project. For most homes, ceiling insulation, draught sealing and good curtains come first, because they give more comfort for what they cost.

Once the ceiling is covered, the downlights sorted, the exhaust fans sealed and the draughts closed, run the existing system through a cold week. A heater that couldn't hold the lounge at 20 °C may now manage it easily. The Victorian Government suggests 18 to 20 °C for heating living areas and says each degree beyond that adds around 10% to running costs.

If it still can't cope, the sizing conversation is more accurate, because capacity is chosen for the room's real heat loss and a sealed room needs less. Reverse-cycle air conditioners move three to five units of heat for each unit of electricity, so a well-sized reverse-cycle unit in a well-sealed room is a strong combination when replacement time does come.

On ducted systems, check the ducts as part of the same exercise. Ducts should be insulated to at least R1.5 with sealed joints, and a torn or disconnected run in the roof is heating the roof space instead of the rooms.