Thinking of a Heat Pump Hot Water System? What It Takes to Install One in a Melbourne Home
Most of what is written about heat pump hot water is about the rebate. Very little of it tells you whether one will actually fit where your old system sat, where the condensate is going to drain, or how close it will end up to a bedroom window.
Those are the questions that decide whether you are happy with the thing in two years, and they are plumbing questions rather than sales questions. This is what the install involves in a real Melbourne house, and the situations where a heat pump is the wrong answer.
In short
- A heat pump needs clear airflow around it, so the alcove your old tank sat in may not suit one.
- It produces condensate continuously, and that has to run to a proper drain rather than onto the ground.
- It has a compressor, so siting matters. Against a bedroom wall or a neighbour’s boundary is the most common regret.
- Replacing a gas unit means the gas supply has to be properly decommissioned, which is licensed work.
- How a Heat Pump Hot Water System Works
- Will It Fit Where Your Old System Was?
- The Drainage Nobody Mentions
- Noise and Where to Put It
- The Electrical Side
- The Rest of the Plumbing Work
- When a Heat Pump Is the Wrong Choice
- Rebates, Briefly
- Talk to a Licensed Plumber in Melbourne
- Related Plumbing Services
- Frequently Asked Questions
How a Heat Pump Hot Water System Works
A heat pump does not make heat. It moves it. A compressor and a refrigerant circuit pull warmth out of the outside air and transfer it into the water in the tank, the same way a fridge moves heat out of its cabinet and dumps it out the back.
That is why they use so much less electricity than a resistive element, and it is also the source of every practical constraint in this article. Moving heat out of air means the unit has to breathe, so it needs airflow. Cooling air below its dew point produces water, so there is condensate to deal with. And running a compressor makes noise.
Two layouts exist. An all-in-one puts the compressor on top of the tank as a single unit. A split system separates them, with a compressor outside and the tank somewhere else. Which one you have changes nearly every clearance below.
Will It Fit Where Your Old System Was?
This is the question to answer before anything else, and the answer is often no. An electric or gas storage tank is happy in a tight alcove with a tank-width gap around it. A heat pump is not.
Clearance and Airflow
The manufacturer’s manual sets the minimum clearances for the specific model and that document is the authority, not a rule of thumb. The figures vary considerably between brands. As an illustration of the range, one popular compressor specifies 100 mm either side, while another all-in-one unit calls for a minimum of 300 mm from walls or barriers.
What matters more than the number is what the clearance is for. The unit pulls air through, chills it, and discharges it. Box it in and it recirculates its own cold exhaust, works harder for less result, and shortens the compressor’s life. Tight corners, fence returns and shrubs that will be twice the size in three years all cause this.
All-in-One Units
Simpler to install because there is no refrigerant line to run, but they need side access kept clear, which means the pipework cannot be routed across the service panel. They also put the compressor noise wherever the tank is, and the tank usually has to stay near the existing connections.
Split Systems
More flexible, because you can put the compressor where the noise and the airflow suit the property and keep the tank somewhere sensible. The trade-off is a refrigerant line between them, a longer install, and a higher price.
Anode Access
Storage tanks have a sacrificial anode that gets replaced periodically, and it has to come out vertically. On a split system that can mean wanting around a metre and a half of clear space above the tank. Install under a low eave with no headroom and the next person to service it has a problem, though a flexible anode can sometimes solve it.
Worth raising at quote stage. It is the sort of thing that does not matter at all on installation day and matters a great deal five years later.
The Base
The unit needs a stable, level base. A concrete slab or properly bedded pavers are the usual answer. Under the national plumbing standard a storage water heater has to be floor mounted or supported on a level stable base, or on brackets or in a wall recess, so this is a requirement rather than a preference.
A base that lets air move underneath helps, and a tank sitting on soft ground that moves over a Melbourne summer is a problem waiting to happen.
The Drainage Nobody Mentions
Two separate drain lines come off a heat pump installation, and getting either one wrong is the most common fault we see on units installed in a hurry.
Condensate
Pulling heat out of air condenses moisture out of it, and the unit produces that water whenever it runs. It is not a trickle you can ignore over a season.
It has to go to a proper drain. Not onto the ground, not into a garden bed, not down the side of a path. Draining onto soil next to a slab is how you end up with a permanently damp patch against the footings. The drain should also be left visible, so you can see that it is running and notice when it stops. Where the line connects into existing drainage it needs a proper air gap, kept away from any electrical equipment.
If you take one thing from this article, make it this. Ask your installer where the condensate is going, and get the answer before the unit is ordered. Retrofitting a drain line after the fact is far more disruptive than planning one.
The Relief Valve Drain Line
Separately, the temperature and pressure relief valve needs its own drain, and the national plumbing standard is specific about it. The line must have no taps, valves or other restrictions in it. It has to fall continuously from the valve to its discharge point. It must not discharge into a safe tray. And it has to terminate where releasing steam or hot water will not cause a nuisance, which rules out a good many convenient spots near a path, a door or a neighbour’s side of a fence.
Where discharge could reach a slab or footings, the line has to carry the water away from the building instead. Plastic drain lines need continuous support, protection from sunlight where they are exposed, and room to move as they heat and cool.
Noise and Where to Put It
A heat pump has a compressor and a fan, so it makes a sound an old electric tank never did. It is not loud in absolute terms, and most people stop noticing it. The problem is placement rather than volume.
The situations that generate complaints are consistent. Hard against a bedroom wall, where a compressor running on an overnight tariff is audible through the plaster. Directly outside a bedroom or study window. Tight against a shared boundary, close to the neighbour’s bedroom rather than yours. And in a narrow side passage or courtyard, where hard surfaces on both sides reflect the sound back and forth instead of letting it disperse.
Running the unit overnight on a cheaper tariff makes all of this more noticeable, because the house and the street are quiet. Our guide to off-peak hot water in Melbourne covers how those tariffs work and when running overnight is worth it.
Check the sound rating in the manual for the model you are considering, and walk the property before you commit to a position. Stand where the unit would go, then go and stand on the other side of each wall. It is a five minute exercise that prevents the most common regret with these systems.
The Electrical Side
Plumbing and electrical are separate trades here, and the electrical requirement depends on the model.
Some manuals require a dedicated circuit with a hardwired, lockable isolator for the compressor. Others allow certain all-in-one units to run from a standard 10 amp outlet. The practical difference matters: a unit sharing a circuit with other things means a tripped breaker takes your hot water with it, and you may not find out until the next morning.
Distance from the switchboard affects what the electrical work costs, which is another reason the siting decision and the quote are the same conversation. Get both trades looking at the position before anyone commits to it.
The Rest of the Plumbing Work
Pressure Limiting
The installer has to test the incoming water pressure and fit a pressure limiting valve where the standard requires one. Melbourne mains pressure varies a lot by suburb and elevation, and a system run at too high a pressure fails early. If your existing system has been going through relief valves, excessive pressure is a likely reason, and our page on water pressure problems explains how that gets diagnosed.
Insulation
Hot and cold pipework, relief valves and vent pipes all have to be insulated to a minimum R-value, and the insulation has to be continuous where pipes pass through walls and roof spaces. Thickness depends on climate zone, and Melbourne sits in a zone that calls for thicker foam than the warm-climate default, so this is a spot where an installer working from habit rather than the table can under-specify. Pipework in direct sun needs foil-covered insulation so it survives.
Replacing a Gas Unit
Going from gas storage or continuous flow to a heat pump leaves a redundant gas supply. That has to be properly capped and decommissioned by someone licensed for gas work, not just turned off at the appliance. An abandoned live gas point behind a removed unit is a genuine hazard and it is the sort of thing that surfaces years later during a renovation.
If the gas unit was your only gas appliance, this is also the moment to decide whether to keep the gas connection at all, since there is a standing supply charge either way. See our gas fitting and leaks page for what that work involves.
When a Heat Pump Is the Wrong Choice
Nobody selling these will tell you this part, so here it is.
- There is nowhere with clear airflow. A narrow side passage with a fence a hand’s width away, a sealed cupboard, or an alcove with no way to get air through it. Boxing one in to make it fit guarantees poor performance.
- The only viable position is against a bedroom wall. If the geometry of the property leaves no alternative and the system will run overnight, a different system type may suit you better.
- There is no practical route for condensate. Occasionally there is simply nowhere to take it without major work, and that cost belongs in the comparison rather than being discovered later.
- You need a lot of hot water very quickly. Heat pumps heat a tank gradually. A large household with a short, heavy morning peak may be better served by continuous flow, or by a larger tank.
- It is an apartment with no external wall access. Common property rules and the lack of a sensible compressor position often rule it out before anything else does.
- Your existing system is only a few years old and repairable. Replacing a working unit rarely pays back, whatever the rebate. Our hot water repair guide covers the repair against replace decision by age.
Melbourne winters are mild enough that a heat pump works through them, but efficiency does fall as the air gets colder, and most units carry an electric element that takes over when conditions call for it. Check the rated operating range for the specific model rather than assuming, particularly if you are in one of the colder outer suburbs.
Rebates, Briefly
There is a great deal of content about Victorian heat pump rebates and most of it is written by companies selling the units, so treat the numbers you read with some care.
Incentives in Victoria have come from more than one place, including Solar Victoria programs, the Victorian Energy Upgrades scheme and federal small-scale technology certificates, and the amounts and eligibility rules change. Rather than quote figures here that will be wrong within months, check Solar Victoria and the Victorian Energy Upgrades scheme directly for what applies on the day you buy.
One thing worth knowing regardless of the amount. A rebate does not change any of the physical constraints above. A unit that is wrong for your property is still wrong for your property at a discount, and the cost of a difficult condensate run or a compressor outside a bedroom lands on you rather than on the scheme.
Talk to a Licensed Plumber in Melbourne
If you are weighing up a heat pump, the useful first step is someone looking at the actual position: where it can go, where the condensate and relief lines will run, and whether your existing connections and pressure suit it. Plumb Construct is licensed, works across Melbourne, and will tell you if a heat pump is the wrong fit for your place rather than sell you one anyway.
Related Plumbing Services
Frequently Asked Questions About Heat Pump Hot Water Installation
Can a heat pump go where my old hot water tank was?
Often not without changes. An electric or gas storage tank is content in a tight alcove, but a heat pump has to move air through itself to work, so it needs clearance on the sides and a clear path for the air it discharges. The manufacturer’s manual sets the minimum for the specific model, and the figures vary widely between brands. There is also condensate drainage to route, which the old tank never needed.
Where does the condensate from a heat pump go?
To a proper drain, and this is the detail most often got wrong. The unit produces condensate continuously while it runs, and it should never discharge onto the ground or into a garden bed, particularly near a slab or footings. The drain should be left visible so you can see it operating, and where it ties into existing drainage it needs a proper air gap kept clear of electrical equipment. Ask your installer where it is going before the unit is ordered.
Are heat pump hot water systems noisy?
They have a compressor and a fan, so they are audible in a way an electric storage tank is not, but the usual problem is placement rather than volume. The complaints come from units sited against a bedroom wall, outside a bedroom window, tight against a shared boundary, or in a narrow passage where hard surfaces reflect the sound. Running overnight on a cheaper tariff makes it more noticeable. Check the model’s sound rating and stand in the proposed position before committing to it.
What happens to my gas connection if I switch from gas to a heat pump?
The redundant gas supply has to be properly capped and decommissioned by someone licensed for gas work. Turning it off at the appliance is not the same thing, and an abandoned live gas point behind a removed unit is a real hazard that tends to surface years later during renovation work. If the hot water system was your only gas appliance, it is also worth deciding whether to keep the gas connection at all, since a standing supply charge applies either way.
Do heat pumps work in Melbourne winters?
Yes. Melbourne winters are mild enough that a heat pump operates through them, but efficiency drops as the air gets colder, and most units include an electric element that takes over when conditions require it. Check the rated operating range for the specific model rather than assuming, particularly in the colder outer suburbs, and size the system for your household rather than taking the default.
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