John Nighingale — Professional Plumber at Plumb It Right
Gas Storage vs Gas Instantaneous Hot Water: Which Is Right for Your Perth Home?
Key Takeaways
- •Gas instantaneous heats water only when a tap opens, so there is no tank to keep hot.
- •Gas storage keeps a tank of heated water ready, which suits homes where several outlets run at once.
- •Instantaneous is my pick for most Perth households, storage wins in a few specific situations.
- •Both systems involve gas, so installation and repairs must be done by a licensed gas fitter in WA.
- •Your household size and how you use hot water matter more than the brand on the box.
You are replacing a failed hot water unit, or building, and every salesperson tells you something different about gas storage versus gas instantaneous. This guide ranks the two on the criteria that actually change your daily experience, so you can decide before the plumber arrives.
What Is the Difference Between Gas Storage and Gas Instantaneous Hot Water?
One heats a tank in advance, the other heats water as you use it.
A gas storage system heats water in an insulated tank and holds it at temperature until you need it. A gas instantaneous system (also sold as continuous flow) has no tank. Gas burners heat the water as it passes through the unit, so hot water keeps coming for as long as the tap is open.
People often confuse these with heat pump, solar or electric storage systems. Those are different categories with different running costs. Our hub article, Perth Hot Water Systems Explained: Heat Pump, Solar, Gas or Electric?, covers the full field. This post compares only the two gas options.
Gas work is legally required to be done by a licensed gas fitter in Western Australia. DIY gas fixing is not permitted, including swapping a unit or touching the gas connection.
Which Gas Hot Water System Ranks Higher for Most Perth Homes?
Ranked on the criteria listed in the methodology below.
1. Gas instantaneous, best for small to mid-sized households wanting endless hot water
An instantaneous gas unit does not store water, so it never runs out while the tap is on. A long shower after three other people have showered still comes out hot. There is also no tank sitting at temperature overnight, which removes standby heat loss.
The units are compact and usually mount on an external wall, which frees up space compared with a tank. The trade-off is flow. Each unit can only heat so much water per minute, so a house running two showers and a dishwasher together can see temperature or pressure drop if the unit is undersized. Your gas fitter should size the unit to your peak demand, not your average.
Best suited for: Households that want hot water on demand without a tank taking up space, particularly couples, small families and anyone who has run out of hot water on a storage system. Choose a unit sized for your busiest morning, not a smaller one to save on the purchase.
2. Gas storage, best for busy households with several outlets running at once
A gas storage system delivers from a full tank, so two showers and a washing machine can run together without competing for heating capacity. Once the tank is used up, you wait for it to recover. That recovery wait is the main complaint from larger families.
The tank is kept hot around the clock, which means some gas is used keeping stored water warm even when nobody is home. Storage units also need floor or external space for the tank. They can be the simpler like-for-like swap where a tank, flue and pipework are already in place, which can limit the amount of alteration needed.
Best suited for: Larger households with heavy simultaneous use, and homes replacing an existing gas tank where the layout suits a like-for-like swap. Be realistic about the standby loss and the recovery time after a big evening of use.
Before you decide, count how many outlets typically run at the same time on your busiest morning. That number is the single best predictor of which system will feel right.
If your current unit is failing, see our guide on the signs your hot water system needs replacing and what to do next. If you want to compare gas against a heat pump, read how much a heat pump hot water system costs to run in Perth. For electric options, see our article on electric storage hot water pros, cons and when they still make sense, and for solar, see our guide to solar hot water in Perth and available rebates.
How Did We Rank These Two Systems?
Rankings are earned on the criteria below, and where storage wins a criterion, the table shows it. I have kept the criteria to things you can observe in your own home.
Hot water continuity
Whether hot water keeps flowing during a long or back-to-back use. It matters because running out is the top complaint with tank systems.
Simultaneous outlet performance
How the system copes with two or more outlets running together. Big households feel this first.
Standby heat loss
Whether the system uses gas to keep stored water hot when nobody is using it. This affects running cost over the year.
Space required
Whether the system needs room for a tank. Wall-mounted units free up space on a tight block.
Like-for-like replacement
How easily the system slots into an existing gas tank setup without extra alterations.
Side-by-Side Comparison
| Option | Best for | Hot water continuity | Simultaneous outlets | Standby heat loss | Space required |
|---|---|---|---|---|---|
| 1. Gas instantaneous | Households that want hot water on demand without a tank taking up space. | Continuous while the tap is open | Limited by unit flow capacity | None, no tank to keep hot | Compact, wall-mounted |
| 2. Gas storage | Larger households with heavy simultaneous use, and like-for-like tank replacements. | Runs out when the tank is used up | Strong until the tank empties | Yes, tank held at temperature | Needs room for a tank |
Which Gas Hot Water System Fits Your Situation?
Match your household to the row that sounds most like yours.
| If you are… | Look for | Best fit |
|---|---|---|
| You live as a couple or small family and sometimes run out of hot water | Hot water that does not run out and no standby loss | Gas instantaneous |
| You have a large household with several showers and appliances running at once | Strong simultaneous delivery from stored volume | Gas storage |
| You have limited outdoor space on a compact block | A small, wall-mounted footprint | Gas instantaneous |
| You are replacing an existing gas tank and want minimal alterations | Easy like-for-like fit with existing flue and pipework | Gas storage |
Gas Hot Water Questions Perth Homeowners Ask
Short answers before you call a gas fitter.
Can I swap my gas storage system for an instantaneous unit myself?
No. DIY gas work is not permitted in Western Australia, and the swap involves gas connections that must be done by a licensed gas fitter.
Will an instantaneous system really never run out of hot water?
It does not run out because there is no tank to empty. It can only heat a set amount of water per minute though, so heavy simultaneous use on an undersized unit will cool the water.
What should I do if I smell gas near my hot water unit?
Gas suppliers add a rotten-egg odorant so leaks are noticed early. Leave the area, ventilate if safe, and call a licensed gas fitter. You can call or text Plumb It Right on 0408 012 993.
Does Plumb It Right charge a callout fee for hot water jobs?
No. Plumb It Right uses fixed pricing with no callout fee, so you know the cost before work starts.
Ready to Choose the Right Gas Hot Water System?
Call or text John on 0408 012 993 for a fixed price with no callout fee. We service Perth from Mandurah up to Lancelin.
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Part of our guide: Perth Hot Water Systems Explained: Heat Pump, Solar, Gas or Electric?
John Nighingale
Professional Plumber · Plumb It Right
John Nightingale has 38+ years’ experience of working in the plumbing industry in Perth Western Australia and previously in the United Kingdom.
