Why does one bathroom in a brand new landed home give you a steady supply of hot water, while another stubbornly stays cold? If you have a central heater, it is worth taking a closer look at those pipes.
This pipe mistake is the one we get asked about more often than any other. It is also the hardest to fix, because by the time you find it, the walls are closed and the tiles are up.
The solution? Re-run the pipes. And we know this can cost tens of thousands of dollars. This article covers what your consultant and plumber need to know when they are doing the drawings.
When do you need a circulation loop?
You need a loop when using a central heater. A central heater is a huge tank that can be 100 to over 400 litres. This tank supplies the entire household. It is fixed far away from all bathrooms, in areas like the roof top. Because of its distance, the time taken for you to get hot water can be long, up to 10 minutes.
Individual heaters are smaller and installed above false ceilings. Because these heaters are located close to the shower point, hot water gets to you fast and you don't need to run a loop.
There is no 'better' system here. It all depends on the size of your home and what you want.
What does the recirculation loop look like?
A recirculation (or circulation) loop is a pipe (red) that runs from the heater, around the house and back to the heater again, in one continuous circuit. A circulating pump (green) pushes water through that loop non-stop, so hot water is always moving somewhere in the house instead of sitting still in the heater.
Every bathroom taps into this loop through a small branch pipe called a tee-off (yellow).
With a tee-off, hot water reaches a bathroom in seconds. Without one, hot water can take 5 to 10 minutes to reach a distant bathroom in a large landed home. This is the benefit of a loop.
Rule: The loop must be continuous
It only works if the water flows in one unbroken circle. Out of the heater ➜ around the loop ➜ into the pump ➜ and back into the heater. Every bathroom tees off it along the way.
Sounds simple? It isn't. This is where most pipe work goes wrong.
Mistake 1: Pipes crossed (loop not continuous)
This mistake happens when two pipes that should remain separate are accidentally connected.
This connection creates a shortcut. Instead of going around the whole house, hot water takes the shorter route back to the heater.
As a result, the bathrooms further away may no longer get hot water fast, even though the circulation pump is running.
This simplified diagram shows how two wrong pipe connections create a shortcut for hot water. The blue arrows show the flow of hot water.
Once fixed, the water can flow around the full loop again.
In Mr. Lee's house, the plumbing drawing showed two wrong pipe connections. The main contractor followed the drawing, not knowing that it would create a shortcut for the hot water.
He was in luck, as the mistake was found before the walls were sealed. The pipes were cut and joined to the right points, restoring the full circulation loop.
Mistake 2: tee-off too far away
This problem comes up when we try to save costs on the loop. Even the loop is correct, a branch or tee-off that is too long can still cause a delay in getting hot water.
Short tee-off: short waiting time
Long tee-off: long waiting time
Our advice: keep the max length of each tee-off within 10m.
Why these mistakes are expensive
If the mistake is found after the renovation, the pipes may already be hidden behind walls or tiles. Hacking the walls to fix the pipework can cost $20,000 or more.
We have seen this happen with even the most experienced construction teams. It is the number one mistake we find in Singapore's landed homes.
A reminder is free. Fixing the mistake is not.
Below: Actual project drawings showing the wrong and corrected pipe connections. Download the full drawings for a closer look.
Wrong diagram
Correct diagram
How to get the loop right before drawings are final
Before work starts, share the correct loop diagram with your consultant and plumber. Ask them to check that hot water can flow around the whole house and back to the heater, with no shortcuts.
If you are not sure, we can help.
Things to check:
1. No two pipes join at a cross fitting.
2. The loop runs out from the heater and back in one circuit, with no dead ends.
3. Every bathroom tees off the loop.
Reviewing the plumbing drawings before installation helps prevent costly mistakes.
How to test the loop
Homeowners can do these 2 tests before the pipes are concealed:
1. Test speed. Turn on one hot water tap. You should get hot water within 15 seconds. This helps confirm that the circulation pump is working.
2. Test every tap. Check all hot water points in the house. If one stays cold or takes too long, check the diagram for wrong connections.
The water heater installer usually tests one tap to confirm that the circulation pump is working.
Testing every hot water point helps to confirm that the pipes throughout the house are connected correctly. If there is a problem, check the plumbing drawing with your consultant and plumber before making changes to the pipes.
Running cost, privacy, who uses a loop?
A central heater needs a circulating loop, and a loop needs more pipe, more fittings, and a pump that keeps running. That pump uses power around the clock, so a loop always costs more to run than the same heater without one.
So why do people use a central heater in the first place?
Maximum privacy: The central heater sits well away from any bathroom. A technician can service it without stepping into someone's ensuite. If you value privacy and personal space, that is a real benefit.
Good Class Bungalow owners tend to choose the loop because privacy matters more to them than running cost. Their homes are also large enough that instant hot water everywhere is worth it regardless of the electricity bill.
Owners of semi-detached and smaller landed homes tend to be more cost-conscious, and often prefer individual or tankless heaters instead. Neither choice is wrong.
Does a recirculation loop use more electricity?
Yes. A recirculation loop loses heat, so the water heater uses more energy.
We tested two water heating systems in a building with 25 people. These were the results:
Over 10 days:
• AOS Central Heat Pump with a loop: $58
• AOS Gen 1 Electric Heater, no loop: $123
Despite increased heat loss from the loop, the central heat pump used much less electricity overall.
Conclusion
Every central heater needs a recirculating loop. The loop only works if it is one continuous circuit with no crossed pipes. If you run a loop, use a heat pump.
Remember to check the diagrams before the drawings are final and do tests in all bathrooms before anything is tiled over.
Circulating Loop FAQ
Can the circulation pump run on a timer instead of 24 hours?
Yes. If you get the circulating pump and your heater from us, we set up a timer as part of the installation. The pump is a third-party product. If you buy it elsewhere, your contractor connects it.
Should the loop pipes be insulated?
Yes. A loop means your bathrooms are far from the heater. Insulation stops the water losing heat on the way there.
Is it normal for a circulation pump to hum?
A soft hum is normal, because the pump runs non-stop, but it should not be loud.
Brands matter here. We have dropped several suppliers and kept the few that run reliably in our climate. Their better build and materials keep the noise down.
Does a heat pump connect to the loop differently?
No. A heat pump connects to the circulation loop in the same way as other central water heaters.
If hot water takes too long to reach a bathroom, check the circulation pipes and pump before assuming the heater is the problem.
