Hot water can be a pain point in the pursuit of low carbon apartment buildings but with modern electric instantaneous hot water systems, there’s really no need for fossil fuel-intensive alternatives.

Developers have a few choices when it comes to hot water in apartments. The first is between centralised or decentralised systems, with the former storing hot water in a plant room connected to each apartment through pipes.

Then there’s the fuel source used to heat the water, with gas and electricity both common.

While it’s usually possible – but not always easy – to swap from gas to electric hot water systems, the same can’t be said for decentralised to centralised systems. The pipes and infrastructure are so different, it’s not usually viable to retrofit. 

Centralised hot water storage a relic of the past

Up until around 16 or 17  years ago, the default option for supplying hot water to apartments was a centralised hot water storage system.

That was until the industry woke up to the advantages of instantaneous (or continuous flow) hot water systems.

Compared, like-for-like, decentralised hot water systems beat the centralised alternative hands downs.

For a start, centralised systems are energy guzzlers are expensive to run. For STIEBEL ELTRON Australia national sales manager Glenn Day, it’s “simple physics”. 

That’s because when someone turns the hot water tap on in their apartment, hot water has been traveling  all the way from the centralised storage unit through a network of pipes. This is a long way for hot water to travel, and heat is lost along the way. 

Keeping the water warm 24/7 is also an inefficient use of energy, ramping up costs and the emissions created by the building.

Bulky water storage tanks also take up valuable real estate in space-constrained urban areas. Because developers are unlikely to sacrifice saleable apartment floor space, this typically means forgoing common areas.

It doesn’t help that engineers typically cater for peak demand – that is, storing hot water for worst possible peak that may never occur. when everyone hits the showers at once. 

Even though peak demand is highly unlikely in an apartment block because people have varied showering schedules, there’s a tendency to play it safe and install a hot water system big enough
to handle peak demand.

Decentralised systems put these problems to bed

Decentralised hot water systems put these concerns to rest. 

Instantaneous hot water heaters lose very little heat pumping delivering the hot water from the tank to the nearby washing machines, kitchen sink and bathroom taps and shower. 

Similarly, peak demand is no longer a concern because water is heated on demand to required flow rate and  temperature using electricity and gas, with each dwelling only paying for what they use. 

Day says that the efficiencies gleaned by a decentralised system can slash energy use by as much as 50 per cent compared to a centralised alternative.

The consumer also ends paying for exactly what they use, with centralised alternatives often billed through an end-to-end pricing system that tries to account for the energy to keep the water warm and what’s lost transporting it around. 

Instantaneous hot water cylinders  systems don’t take up much space and aren’t too obtrusive, often hidden away in laundries or beneath the kitchen sink.

Better for prefab and Legionella-free

Other lesser known benefits of decentralised hot water systems is that they work well with future building techniques such as prefabricated and modular, where building components are put together in a factory offsite and craned into place.

Decentralised hot water systems make for simplified offsite bathroom construction, with the technique used to build one of Melbourne’s tallest skyscraper, the 69-level 568 Collins Street. 

Unlike in centralised systems where warm water can be left sitting around in pipes, there’s no or little risk of a Legionella infection when using instantaneous units.

Electric is the way forward

In the wake of the horror summer bushfires, low carbon housing is top of mind in Australia. Sustainability might have been a nice-to-have before but consumers are now demanding it. 

Forward-thinking developers should be looking for opportunities to decarbonise, and this means fossil fuel-free hot water. Gas can be used for both decentralised and centralised options but when teamed with renewables, electricity is the lower carbon option. 

The trouble is, unlike in a detached home, putting renewables on the roof is not really an option. Typically, there’s only enough roof space atop an apartment block to power the common areas. Fortunately, there are other options. Residents can purchase renewable energy via Greenpower, for example.

The other point to consider is that the emissions profile of grid electricity is only going to decrease as the penetration of renewables increases, which means an all-electric home is a future proof home.

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  1. Agreed, decentralized electric HWS is the best way to go.
    Putting solar PV on a strata building is very do-able with the right developer & architect on the job.

    It is still common for building services to be haphazardly positioned on rooftops, & roof planes are poorly considered if at all.
    Build in anchor points for fastening solar racking to – with advice from solar installers at the design stage.
    consider waterproofing the roof with Colorbond or something . consider CLT / mass timber panels for roof tops which makes orientation for PV simple

    1. and – what does it cost to get 3 phase (high power) electricity wiring added to your home when most only have single phase wiring ?

      Guess a few thousand ?

      Last I enjoyed an instant heat electric heater was in Malaysia where the air temperature was maybe 30C so water heating was hardly needed at all

      In cold climates I’ve read that instant electric hot water either doesn’t heat enough quantity fast enough to have a satisfying shower flow – or if it does, can cost an arm and a leg to run.