Continuous Flow vs Storage Hot Water: Which Suits Your Home?

When a Melbourne homeowner is replacing a hot water system, the first big fork in the road is continuous flow versus storage. Both have their place. Choosing wrong locks you into 10-20 years of poor running costs or running out of hot water at the worst possible moments. Here is how to choose well.

Continuous flow (also called instantaneous)

A continuous flow unit heats water on demand. Cold water enters, passes over a gas burner or heat exchanger, and exits hot. There is no tank, so the unit never runs out. Common brands in Melbourne include Rinnai Infinity, Rheem Continuous Flow, and Bosch Highflow.

The strengths: never runs out, compact wall-mounted footprint, no standing heat loss, long service life (12-20 years).

The weaknesses: needs adequate gas pressure, can be slow to deliver hot water to distant taps, and minimum flow rates mean a barely-trickling tap may not trigger ignition.

Storage (gas, electric, or heat pump)

A storage unit heats and holds a tank of water (135L to 400L) ready to use. Common storage types in Melbourne are gas storage (Rheem, Vulcan), electric storage (Dux, Rheem Stellar), and heat pump (Reclaim, Sanden, Rheem Ambiheat).

The strengths: very high peak flow for the first 10-15 minutes, simpler retrofit when replacing like-for-like, heat pump variants are now the cheapest to run with rebates from the Victorian Energy Upgrades program (energy.vic.gov.au).

The weaknesses: can be exhausted if usage exceeds capacity, standing heat loss, larger footprint, shorter service life on the tank itself (8-15 years).

Which one for which household

For a 1-3 person household with average usage, gas continuous flow is the historical Melbourne default and still a strong choice if you have gas connected. For a 4-6 person household with morning shower peaks, a heat pump storage unit (270-315L) usually wins on running cost with rebates applied. For an all-electric new build or a home moving off gas, heat pump storage is almost always the right answer.

A quick check on whether your home will support continuous flow: existing 20mm gas line, gas meter rated for the appliance, and a wall location with adequate clearances per AS/NZS 3500 (standards.org.au).

What we usually fit in Melbourne

In Burwood, Box Hill, Blackburn, and Mount Waverley, the dominant existing install is gas continuous flow. We are now replacing about 60% of those with heat pump storage units when rebates are available, and 40% like-for-like with newer Rinnai Infinity or Rheem Metro units. All installations include a Certificate of Compliance issued via the VBA (vba.vic.gov.au).

FAQ

Does a continuous flow unit really never run out?

Almost. It can only deliver up to its rated flow rate (e.g., 26L/min).

Will a heat pump be loud near a bedroom window?

Modern units are 37-48 dB at 1m - quieter than a fridge.

Can I keep my existing gas storage tank?

If it is under 8 years old and not corroded, yes. Beyond that, replacement is usually cheaper than repair.

What is the warranty on a new install?

Manufacturer cylinder warranties are typically 7-10 years; parts and labour 1-2 years.

Phone Newton Plumbing - +61 414 951 362. Licence #107733.

Internal links: hot water Burwood, hot water Box Hill, hot water Blackburn, hot water Mount Waverley.

External links: energy.vic.gov.au, vba.vic.gov.au, standards.org.au, sustainability.vic.gov.au.