Tldr; To plumb a hot water recirculating system, you install a circulation pump at the water heater and create a loop that returns cooled water back to the heater to be reheated, so hot water is ready almost instantly at the tap. You can do this with a dedicated return line, which is a separate pipe running from the furthest fixture back to the heater and is best for new builds, or with a retrofit pump that uses your existing cold water line as the return path and suits established homes. Either way, the loop needs a pump, a check valve, isolation valves, and proper pipe insulation, and in Australia the work generally has to be carried out by a licensed plumber.
Key Takeaways
- Keeps warm water moving through the pipes, so there’s little wait at the tap and less water wasted
- Two methods: a dedicated return line (best for new builds) or a retrofit pump using the existing cold line (best for established homes)
- Core parts: a recirculation pump, a check valve, isolation valves, and pipe insulation
- Thermostatic and smart pumps are cheaper to run than a timer on a fixed schedule
- It’s licensed work in Australia, so use a licensed plumber and a licensed gasfitter for any gas connections
This guide walks through how to plumb a hot water recirculating system from start to finish. You’ll see how it works, the parts involved, the two main layouts, and where it pays to bring in a licensed plumber.
What does a hot water recirculating system do?
A hot water recirculating system keeps a small, steady flow of hot water moving through your pipes so warm water is ready almost instantly at the tap. It does this by sending cooled water back to the heater instead of letting it sit in the line going cold.
In a standard home, hot water sits in the pipe between your heater and your tap. Once you finish using a tap, that water cools down.
The next time you want hot water, all that cooled water has to be flushed out before the warm stuff arrives. Straight down the drain it goes.
A recirculating system puts a stop to that. When the water at the far end of the loop drops below a set temperature, a circulator pump pushes it back toward the heater to be reheated and pulls fresh hot water forward in its place.
There are two broad ways to do it, and the difference matters when you’re deciding how to plumb a hot water recirculation system that suits your home:
- A dedicated return line is a separate pipe that carries cooled water from the furthest fixture back to the heater. It’s the most efficient setup and the best option for new builds or major renovations.
- A retrofit comfort system uses your existing cold water line as the return path, with a bypass valve under the furthest sink. It’s the one to reach for when you can’t easily run a new pipe through finished walls.
Both rely on a pump, and both get you to the same place. The right choice really comes down to whether you’re building from scratch or working with an existing home.
What tools and materials do you need to plumb a hot water recirculating system?
The tools and materials you need for a hot water recirculating system come down to a pump, a few valves, pipe and fittings, and insulation. It’s worth gathering everything in one place before you start.
A typical install calls for:
- A hot water recirculation pump (timer, thermostat, or smart-controlled)
- A check valve to prevent backflow
- Isolation valves either side of the pump for easy servicing
- A thermostatic bypass valve for retrofit systems using the cold line
- Copper or PEX pipe and matching fittings for any new pipework
- Pipe insulation for the hot water and return lines
- Thread tape, a pipe cutter, a deburring tool, and a spanner set
- A power point or hardwired supply near the heater for the pump
Insulation is worth a special mention here. A recirculating loop only works well if the heat actually stays in the pipe.
Uninsulated lines leak warmth into the wall cavity and make the pump work harder than it should. Insulating the loop is one of the cheapest ways to get the whole system performing better.
How to plumb a hot water recirculation loop with a dedicated return line
If you’re building new or renovating with the walls open, a dedicated return line is the way to go. It’s the purpose-built method, and it’s worth understanding even if you end up choosing a retrofit, because it shows how the ideal loop is meant to flow.
This is proper pipework, and on a new build or full renovation it’s the kind of job our team handles as part of a complete hot water installation. Here’s the process, step by step:
- Plan the loop. Map the path from your water heater out to the furthest fixture and back. The hot water line runs out to the taps as normal, while the return line picks up at the last fixture and carries cooled water back to the heater. A direct loop means less heat loss and less work for the pump.
- Run the return pipe. Run your return line from the furthest point of the hot water system back toward the heater. Plenty of installers size the return line a little smaller than the main supply, since it only carries the trickle of recirculating water rather than full demand flow.
- Install the pump. On a dedicated loop, the pump usually mounts on the return line right where it meets the heater, pushing cooled water back in to be reheated. Fit isolation valves on both sides so it can be serviced without draining the system, and add a check valve so water only ever flows the right way.
- Connect at the heater. Tie the return line into the cold inlet or a dedicated recirculation port if your heater has one. Many modern tanks and some continuous-flow units include a port for exactly this, which makes the connection a lot cleaner.
- Insulate, fill, and test. Insulate the entire loop, refill the system, bleed out any trapped air, and power up the pump. Check every joint for leaks, then run a tap at the furthest fixture and time how quickly the hot water shows up.
With a well-planned loop, that wait should drop right down. It’s the payoff for doing the groundwork properly.
How to plumb a hot water recirculating pump as a retrofit
Most existing homes don’t have a spare return pipe sitting in the walls. Chasing one in is expensive and disruptive, which is exactly where a retrofit comfort system earns its keep.
Learning how to plumb a hot water recirculating pump this way gets you most of the benefit without opening up finished walls. Instead of a dedicated return, the system borrows your existing cold water line as the return path.
The pump mounts on the hot water outlet at the top of your water heater. A built-in timer or thermostat tells it when to run, and most setups have it active during the morning and evening peaks and idle overnight.
Under the sink furthest from the heater, you fit a thermostatic bypass valve connecting the hot and cold lines. When the hot water in the line cools off, this valve opens and lets the pump push the cooled water across into the cold line, sending it back to the heater.
Once hot water arrives and the temperature climbs, the valve closes on its own. After that it’s just a matter of connecting the pump to power and setting its schedule or thermostat.
The trade-off is a brief slug of lukewarm water in the cold tap right after the pump cycles, since the two lines share a return path. For most households that’s a minor quirk and a fair swap for not having to run a new pipe. It’s the same hot-versus-cold supply question that comes up with appliances, like whether you need a plumber to install a dishwasher and which line it runs off.
Getting your head around how to plumb a hot water circulating pump this way makes instant hot water realistic in almost any existing home.
Which pump and controls should you choose?
The pump you should choose depends on how you want to balance upfront cost against running cost, but a thermostatic or smart pump suits most homes. Matching the pump to how you actually live makes a real difference to your power bill.
The main options break down like this:
- Timer-controlled pumps run on a fixed schedule. They’re simple and cheap, but they’ll run whether you need hot water or not during their active hours.
- Thermostatic pumps only run when the water in the loop drops below a set temperature, which makes them more efficient than a timer running blind.
- Smart pumps learn your habits or respond to demand and run the least amount of time necessary. They cost more upfront but they’re the kindest to your energy bill.
There’s one extra thing to watch with continuous-flow (instantaneous) hot water units. Some tankless systems need a minimum flow rate to fire up, and not every recirculation pump gets along with them.
So check compatibility carefully before you buy. A purpose-matched pump or a small buffer tank is sometimes the answer.
What mistakes should you avoid?
The mistakes you should avoid are the handful of small oversights that cause most of the disappointment people feel with these systems. Each one is easy to sidestep once you know it’s there.
Keep an eye out for these in particular:
- Skipping insulation. An uninsulated loop wastes the very heat the system is trying to hold on to.
- Oversizing the pump. A pump that’s too powerful wastes energy and can bring noise and early wear with it.
- Running the pump around the clock. Continuous running keeps water instant, but it quietly burns energy reheating water you’re not even using.
- Ignoring the check valve. Without it, water can flow backward through the loop and undo the whole thing.
- Forgetting heater compatibility. Always confirm your water heater, especially a continuous-flow unit, is rated to work with recirculation before you plumb it in.
Get these right and the system will quietly do its job for years. Get them wrong and you’ll be left wondering why the upgrade never quite delivered.
Should you call a licensed plumber?
You should call a licensed plumber for this job, because plumbing a hot water recirculating system touches the hot water service, the home’s water supply, and often the electrical or gas supply feeding the heater. That puts most of the work firmly in licensed-plumber territory.
In Australia, work on hot water systems and water supply pipework generally has to be carried out by a licensed plumber, and gas connections by a licensed gasfitter. In Victoria this is regulated, and the Victorian Building Authority sets out the licensing and registration rules for plumbing work. That’s not red tape for its own sake, it’s about safety and compliance.
A professional will also size the loop correctly and choose a pump that suits your system. They’ll connect it without voiding your heater’s warranty, and they’ll make sure the finished job is safe and signed off.
If you understand how the system works but want it done right, our team can take care of it for you as part of our general plumbing services. The comfort of instant hot water is something you’ll notice every day, so it’s worth getting right the first time.
Final thoughts on how to plumb a hot water recirculating system
A hot water recirculating system is one of those upgrades that quietly makes daily life better. Less water down the drain, no more waiting at the tap, and a more comfortable home all round.
Whether you go for a dedicated return loop in a new build or a retrofit pump in an established home, the principles don’t change. Keep hot water moving, insulate the loop, and match the pump and controls to how you live.
Thinking about adding instant hot water to your home? Get in touch with our licensed team for advice on the right system for your setup and a no-obligation quote.
