Heating and cooling a double-storey home

Many double-storey homes in Point Cook, Werribee, Wyndham Vale and Tarneit follow a similar plan: an open kitchen, meals and family area downstairs, with the bedrooms, a rumpus and a bathroom or two upstairs. The floors are used at different times and behave differently, so one setting rarely suits both.

Upstairs sits right under the roof. On a hot northerly afternoon the roof space gets much hotter than the outside air and keeps pushing heat down through the ceiling well into the evening, just as everyone heads to bed. Warm air from downstairs drifts up the stairwell and adds to it. The Bureau of Meteorology's Laverton station averages 27 days a year at or above 30 °C, and those are the nights the bedrooms stay stuffy.

Winter turns it around. Downstairs sits on a cool slab, often with wide sliding doors to the yard, and the heat you put into the living area rises up the stairs. The landing ends up the warmest spot in the house while the family room feels cool near the floor. An open stairwell or void links the floors, so whatever you install has to work with that air movement, not against it.

Part of the imbalance comes from the building, not the equipment, and that part is usually cheaper to fix first. A bedroom with a large west-facing window and no eaves can take on more heat in an afternoon than a well-shaded room twice its size.

Insulation matters most in the ceiling over the upper floor, because that is the one under the hot roof. If you can look from the manhole safely, check it is there, even and not pushed aside by past trades. The ceiling between the two floors matters far less.

Then size equipment for what is left. A room needs less capacity once the sun is kept off its glass.

A single ducted reverse-cycle system can serve both floors well if it is zoned and sized for the whole house. The Victorian Government recommends zones for ducted systems so each area can be heated or cooled on its own, and suggests 1.1 to 1.4 kW of heating output for every 10 m² covered, depending on the home. In a double storey the natural split is one zone, or a group of zones, for each level.

What decides whether it works is where the temperature is read. If one sensor in a downstairs hallway runs everything, the system backs off while the bedrooms are still hot on a summer evening. With a sensor in each zone, the upstairs can run cooler than the living areas without one floor overriding the other. Return air matters too: a single return on one floor mostly draws that floor's air, which is why many two-level systems have a return on each level.

The hard part in a finished home is getting ducts downstairs. The indoor unit usually sits in the roof above the upper floor, so ducts to the ground floor have to pass between floors, through a cupboard or inside a bulkhead. YourHome says ducts should be insulated to at least R1.5 with sealed joints, and long runs squeezed through tight spaces are where crushed or poorly joined ducts lose capacity. Zoning moves air; it doesn't add capacity, so size the unit for the times both floors are in use.

Larger homes, and homes where both floors are busy at the same time, often do better with two smaller systems: one ducted unit for the bedrooms and another for the living areas, or ducted upstairs with wall splits downstairs. Each level gets its own capacity, controller and sensor, so there is no tug of war over one thermostat.

It also spreads the risk. If one system fails in January, half the house still has cooling, and a smaller unit matched to fewer rooms runs at a steady low speed, which suits bedrooms overnight.

The costs are real: two outdoor units to place, two systems to service and two circuits at the switchboard. Energy Safe Victoria says a manufacturer's requirement for a dedicated circuit or safety switch must be followed, and the original board in an estate home may not have the room for a second large system. Check that at the quote stage, not on installation day.

Plenty of estate homes came with gas ducted heating and no cooling, or with a ducted system that copes downstairs but loses the bedrooms on hot nights. Wall splits in the upstairs bedrooms are often the most practical answer. They cool the rooms where people sleep, run quietly at low speed and leave the existing system to look after the rest of the house.

Upstairs installs raise their own questions. The outdoor unit can sit on a wall bracket close to the room, or on the ground with a longer pipe run down the wall. Ground level is easier to service and keeps compressor noise away from bedroom windows, but the pipe route needs to be neat and protected. Each indoor head also needs a drain with a proper fall, which is simple on an external wall and harder on an internal one.

A multi-head system runs several upstairs heads from one outdoor unit, which saves wall and ground space outside. The trade-off is that every head relies on that one unit. If noise matters, the Zoned Energy Rating Label gives split systems separate indoor and outdoor noise ratings, so compare those for bedroom heads.

In summer, start cooling the bedrooms before they soak up the afternoon heat rather than at bedtime. Lower the blinds on the west side from early afternoon and close the doors of rooms nobody is using. The Victorian Government suggests 24 to 26 °C for cooling and 18 to 20 °C for heating living areas, and says each degree beyond that adds around 10% to running costs.

In winter, heat the living areas through the evening and the bedrooms for a while before bed. Because warm air rises, the upstairs zone can usually be set a little lower than downstairs and still feel comfortable. Victorians typically use more energy for heating than cooling, and Laverton's July mean minimum is 5.2 °C, so winter habits make the bigger difference to the bills.

A useful quote for a double storey starts with how the house is used, not just its floor area. Note which rooms are used together and when, and which rooms are hardest to keep comfortable in each season. Ask each installer to explain where the temperature will be read on each level and where the return air goes.

More than one licence is involved. In Victoria, refrigerated air-conditioning work is a class of plumbing work regulated by the Building and Plumbing Commission, and installing a system needs a Refrigerant Handling Licence. The circuits are electrical work: Energy Safe Victoria lists air conditioning as non-prescribed work, so the electrician completes a Certificate of Electrical Safety and must give you a copy within 30 days.