Continuous Flow vs Storage Hot Water: Understanding Your Options

Continuous Flow vs Storage Hot Water: Understanding Your Options

When you’re staring down the barrel of a cold shower or a leaking tank, the pressure to choose a new system fast is high. But here is the reality we see in Perth every day: the “standard” choice has changed. It used to be a simple toss-up between a gas tank and a gas instant unit, but in 2026, the conversation has shifted entirely.

We founded Hot Water System Perth in 2021 to help locals navigate exactly these kinds of decisions. With electricity prices changing and heat pump technology maturing, the old rules about what’s “cheapest” don’t always apply anymore. A 680 credit score might separate good loans from bad ones, but in hot water, your usage pattern is the dividing line that separates efficiency from wasted money.

Let’s look at the data, what it’s actually telling us about local running costs, and then explore which system fits your specific Perth home.

How Each System Works

Storage Hot Water

A storage system heats water and keeps it in an insulated tank, typically ranging from 125L to 400L. When you turn on the tap, hot water flows from the top of the tank while cold water enters the bottom to be heated.

The tank approach:

• Pre-heated supply: Water is ready instantly at the tap.
• Finite capacity: Once you drain the tank, you must wait for the “recovery rate” (reheating time).
• Maintenance reality: In Perth, these tanks use a “sacrificial anode” rod to prevent rust. You generally need to replace this every 3-5 years to stop the tank from corroding.

Continuous Flow Hot Water

A continuous flow system (often called “instantaneous”) heats water only when you need it. When you open a hot tap, a sensor triggers a gas burner or electric element to heat the water as it passes through a copper heat exchanger.

The on-demand approach:

• Unlimited supply: It will keep heating as long as you have gas/power and water pressure.
• Compact size: Most units are roughly the size of a carry-on suitcase.
• Hard water caution: In suburbs with high calcium levels (like Alkimos or Ellenbrook), the heat exchanger can scale up over time. We recommend flushing these units every few years to maintain efficiency.

Key Differences at a Glance

When Storage Systems Make Sense

You Have Solar Panels

This is the biggest shift we have seen in recent years. If you have a solar PV system, an electric storage unit (specifically a heat pump) acts like a “thermal battery.” You can set a timer to heat the water between 10:00 AM and 2:00 PM when your solar production is highest. This effectively gives you free hot water.

Large Families with Morning Rushes

If four people need to shower between 7:00 AM and 7:30 AM, a storage tank is often superior. It can deliver hot water to multiple showers simultaneously without the pressure drop or “cold sandwich” effect that some continuous flow units suffer from when overloaded.

Properties Without Gas Connections

Electric storage is the standard solution where gas isn’t available. While old-school electric element tanks are expensive to run, modern heat pumps (like the iStore or Reclaim models popular in WA) use 70% less energy and plug right into the storage setup.

Off-Peak Tariff Users

Synergy’s time-of-use tariffs (like the Midday Saver) allow you to heat a storage tank when electricity is cheapest (often 8 cents or less per unit during the day) and use that hot water at night. This financial arbitrage is only possible with a storage tank.

When Continuous Flow Makes Sense

Space is at a Premium

For townhouses in Subiaco or apartments in East Perth, finding square footage for a large tank is difficult. We often install continuous flow units like the Rinnai Infinity 26 recessed into a wall box. It frees up your entire outdoor walkway or laundry cupboard.

Variable Occupancy

Holiday homes and rentals benefit immensely from continuous flow. If the house sits empty for two weeks, you aren’t paying to keep 135L of water hot for no reason. You only pay when someone actually turns on a tap.

You Want “Set and Forget” Longevity

Continuous flow units have a longer expected lifespan—typically 15 to 20 years versus the 10 to 12 years of a steel tank. Since they don’t hold standing water, they are less prone to the rust and corrosion that kills storage tanks in Perth’s coastal suburbs.

Gas is Already Connected

If you have an existing gas connection, continuous flow is usually the most efficient way to use it. A 5-star or 6-star gas continuous flow unit is far cheaper to run than a standard electric storage tank and provides endless hot water.

Running Cost Comparison (Perth 2026 Estimates)

Running costs have shifted significantly with rising gas prices and the efficiency of heat pumps. Here is what we are seeing for an average family of four in WA:

Important distinction: The “cheapest” option on paper (Heat Pump) has a higher upfront cost, but federal STC incentives (Small-scale Technology Certificates) currently cover roughly $1,000 of that installation price.

Simultaneous Use Considerations

The “Bucket Test” for Capacity

Before choosing, you need to know your flow rate. Grab a standard 9L household bucket and time how long it takes to fill at your shower.

• Under 30 seconds: You have a high flow rate (>18L/min).
• Over 45 seconds: You have a low flow rate (<12L/min).

Storage Systems

Simultaneous use is limited only by your pipe size. You can run three showers at once, and they will all get hot water until the tank runs dry.

• The constraint: Recovery time. Once that 300L is gone, you might wait 45-60 minutes for the water to be hot again.

Continuous Flow Systems

Simultaneous use is limited by the unit’s heating power (measured in Litres Per Minute).

• The constraint: A 20L/min unit can comfortably run one shower (9L/min) and a kitchen tap. If you try to run two showers, the flow will drop, or the temperature will fluctuate.
• The fix: For homes with 2+ bathrooms, we always recommend a 26L/min unit or higher to handle the load.

Installation Realities in WA

Storage Systems

• Footprint: Needs a solid concrete base or reinforced roof section.
• Electrical: Heat pumps may require a dedicated circuit update.
• Valves: Must have a Temperature Pressure Relief (TPR) valve plumbed to a drain.

Continuous Flow Systems

• Gas Line Sizing: This is the most common surprise. Old gas pipes (often 15mm copper) may be too small to feed a high-powered 26L/min unit. Upgrading to 20mm pipe can add to the installation cost.
• Power Point: These are gas units, but they still need a standard power point for the electronic ignition and thermostat.
• Tempering: By law in WA, hot water to bathrooms must be tempered to a safe 50°C to prevent scalding.

Making Your Decision

Choose Storage (Heat Pump/Electric) If:

• ✅ You have solar panels (this is the #1 reason).
• ✅ You have a large family that showers at the exact same time.
• ✅ You want to disconnect from gas to save on the daily supply charge.
• ✅ You have ample outdoor space for a tank.

Choose Continuous Flow (Gas) If:

• ✅ Space is tight or you want a wall-mounted aesthetic.
• ✅ Your usage is erratic (travel frequently or varying household size).
• ✅ You want the peace of mind that hot water will literally never run out.
• ✅ You have a pre-existing, correctly sized gas connection.

Common Questions

Can I switch from storage to continuous flow?

Yes, but it isn’t always a straight swap. We check your gas pipe diameter first; if it’s too small, the cost to upgrade the pipe might outweigh the benefits.

Will hard water ruin a continuous flow unit?

It won’t ruin it immediately, but it reduces lifespan. In suburbs with hard water, scale builds up in the narrow heat exchanger pipes. Running the unit at 50°C instead of 60°C helps reduce this scaling, as does regular maintenance.

Why are heat pumps so popular right now?

It comes down to rebates and solar. Federal STC incentives can knock over $1,000 off the price, and if you have solar, running a heat pump is cheaper than even the most efficient gas system.

Our Assessment Process

We evaluate your situation considering:

1. Fuel Source: Do you have gas, solar, or just electricity?
2. Peak Demand: How many showers happen between 7:00 AM and 8:00 AM?
3. Infrastructure: Is your gas pipe 15mm or 20mm? Is your switchboard ready for a heat pump?
4. Water Quality: Do you live in a known hard water zone?

Based on this, we recommend suitable options and provide clear quotes. Sometimes storage makes sense; sometimes continuous flow is clearly better. Often both are viable, and the choice comes down to your preferences.

Contact us for a free assessment to determine whether storage or continuous flow suits your Perth home.