Explaining the concept of a Hot Water Plumbing Loop

One thing that a lot of people don’t fully understand is the concept of a hot water plumbing loop (also known as a hot water return or a ring main). The reason for this is not really all that surprizing. Anyone with mains water to their house probably wouldn’t even care about the concept. Most builders won’t offer it as an option, most plumbers aren’t aware of it but the benefits of it are huge. Especially in Australia with drought conditions and water restrictions, even on mains water a hot water plumbing loop makes a lot of sense.

What is it?

Put simply, a hot water plumbing loop means that the hot water pipe from one tap to the next continues around in a loop back to some location (normally the cold water inlet to the hot water system). The picture helps to explain the concept.

In a normal plumbing setup there is normally one main hot water line. This line breaks up into branches. These branches then can further split but end up eventually at the various hot water taps.

In a hot water plumbing loop, also know as a closed loop or a sometimes a gravity loop, the line from the hot water system continues from one tap, to the next. There is no branches as the line continues until it loops back to the hot water system.

How does it work?

Now that you know what it is, your probably wondering why anyone would want it. It all comes down to water conservation. I’m sure at some point you’ve turned on your shower, felt that freezing water coming out and had to wait for it to get hot. Or you’ve run the kitchen tap until the water became hot. The hot water loop eliminates this water wastage. Instead of the cold water going down the drain, it is instead recycled back to the cold inlet of the hot water tank. The water is then reheated and reused.

There’s a number of different ways a hot water loop can be implemented. You can use a pump with a press button near each tap to start the hot water cycling in the loop. You can also setup a gravity fed system which continually recycles. Or you can use a continual pump to recycle the water. This way as soon as you turn the tap on the water is hot!

In a gravity fed system hot water is cycled from the top of the hot water tank, back down to the bottom of the hot water tank. A gravity fed system requires a lot more planning as it requires that no hot water pipe ever goes higher than the hot water system.

What type of saving is achievable?

The cost for installing a gravity feed type system is around $300 – $500 different depending on the house, how many taps it has, the distance to the hot water system, the pump used and whether it’s automatic or manually controlled (ie manual push button to start the cycle).  This is the main reason builders don’t offer it – it’s not competitive for the builders to do so. It’s also not cost effective for the average home owner due to reasons mentioned below.

The savings in water you get can be quite staggering. Take a typical shower with a water saving shower head. These typically use in the range of 9 litres of water per minute. Now if it takes 2 minutes before the water is hot enough to shower that’s 18 litres that’s normally going down the drain. Now multiply it out by a year:   18 * 365 =  6570 litres go straight down the drain! If you have 2 bathrooms this doubles! Then there’s the kitchen, laundry, etc.. it adds up very quickly.

It’s also the reason that people who have mains pressure water to their house often don’t care. What’s 6570 litres of water over a year? Just pay the water bill ( about $5 AUD at a rate of 71cents/Kl) and be done with it. However, when you don’t have mains pressure water that makes a big difference.  Our place at Gould Creek is one such example. Our total tank storage capacity is 2×23500 tanks. Hence 6570 is almost 14% of our entire storage capacity!

With drought in Australia beginning to affect South Australia and Victoria very heavily, the attitude that it’s just water, I’ll buy more needs to change. A hot water plumbing loop shifts perception back to what it should be – less about money and more about saving our precious environment!