Where should the outdoor unit go? Noise, airflow, access and neighbours

The outdoor unit is where heat goes in summer and where it comes from in winter. It pulls air across its coil and blows it out, usually through the front grille. Anything that stops that air moving freely costs capacity and efficiency.

Manufacturers set minimum clearances behind, beside and in front of the unit. The usual mistake is the tight spot: a narrow side passage between two brick walls, a corner behind the garage or a nook under a deck. The unit ends up breathing its own discharge, which is hotter in summer and colder in winter, and on a hot northerly afternoon it can throttle back or trip out when you need it most.

Keep the front clear of fences, bins, stacked timber and plants that will grow into it. Don't box it in to hide it unless the enclosure has open louvres and gives the clearances the manufacturer asks for.

Outdoor units hum, the fan whooshes, and the compressor note carries further at night when everything else is quiet. Split systems carry an outdoor noise rating on the Zoned Energy Rating Label, which helps when comparing models, but position usually matters more than a few decibels on paper.

EPA Victoria's residential noise rules treat an air conditioner as unreasonable during prohibited times if someone in a habitable room of another home can hear it. For cooling, its guidance lists those times as before 7am and after 11pm on weekdays, and before 9am and after 11pm on weekends and public holidays, with an exception during a heat health warning. In heating mode the unit counts as a home heater, and the evening cut-off is 10pm. A unit under a neighbour's bedroom window can become a real problem on summer nights.

Hard surfaces bounce sound. A unit in a corner between two brick walls, or facing a paling fence a metre away, sounds louder than one in the open. Wall brackets on lightweight walls can carry vibration into the room behind, so a ground pad with rubber mounts is often quieter than a bracket on a bedroom wall.

In heating mode the outdoor coil runs colder than the outside air. Moisture condenses on it, and on frosty mornings it freezes, then melts off during defrost. Melbourne sits in the Cold zone of the Zoned Energy Rating Label, where frosting conditions below 5.5 °C are critical, so plenty of winter mornings produce a steady trickle from the base of the unit.

Keep the unit away from paths, steps and doorways, where drips can freeze or leave a slippery green stain, and away from timber decking. On a wall bracket, the water lands on whatever is below. A pad on gravel or beside a garden bed, or a drain fitting on the base piped to a drain point, gives it somewhere to go.

Avoid low spots that collect water or leaves, and positions under a gutter with no downpipe, where storm water pours straight onto the unit.

A unit in full western sun works harder on a summer afternoon. Laverton averages 27 days a year at or above 30 °C and 9.4 days at or above 35 °C, and those are the afternoons when a few degrees around the coil matter. A south or east wall, or the shade of the house itself, is the better choice when the layout allows.

But shade that blocks airflow is worse than sun. A shade sail well above the unit or the shadow of a wall helps; a lattice box or a hedge pressed against it doesn't. Keep the unit clear of other heat sources too, such as another unit's discharge, a heat pump water heater or a gas flue outlet.

The outdoor unit connects to the indoor head through a pair of refrigerant pipes, a drain and a cable. The shorter and more direct that run, the neater the job, and a back-to-back position through the same wall is often the tidiest of all.

Every model has a maximum pipe length and height difference, and some have a minimum. Longer runs mean more pipework and covers, and sometimes extra refrigerant, so a spot a few metres along the wall is usually fine, while one on the far side of the house may not be.

On a double storey, the choice is usually a ground unit with the pipes run up the wall in a cover duct, or a bracket high on the wall or a roof mount. Ground units are far easier to service, while high brackets and roofs need safe access for every future visit.

Whoever services or repairs the unit needs to reach its panels, the pipe connections and the isolator. The Wiring Rules require a lockable isolating switch next to the unit, not on it, so leave room for the switch and for someone to stand at it. A unit jammed behind a water tank or under a low deck turns a simple service into a difficult one.

Think about who else is around it. Children climb on units, dogs chew pipe insulation, and mowers and line trimmers nick pipe covers. A unit on a raised stand, or behind a low open fence, is safer from all three.

Near the bay, salt air wears outdoor units faster. An industry guide based on AS 4312 classes the Port Phillip Bay beaches from Altona to Portsea as an exposed marine environment, so on homes close to the water, a spot sheltered from the wind off the bay and a unit with factory corrosion protection on the coil both help.

In townhouses and apartments, the owners corporation's rules often decide where outdoor units can go, and balconies or roofs may need approval. Check before you settle on a spot.

On a heritage-listed street or in a special character area, such as parts of Williamstown or the post-war precincts in Altona, ask your council whether a unit visible from the street needs a permit. A side or rear position usually avoids the question, and looks better anyway.