Post By Admin
September 21, 2026Nothing wipes out a good morning like a cold shower kicking in halfway through, or bill shock from a tank that’s been heating way more water than your household ever uses.
Below, we’ll walk through a quick way to work it out, how that number shifts depending on the system type you choose, and what Victoria’s 2027 gas rule means if you’re due for a replacement.
Jump to the quick answer table first if you’re after a fast estimate!
Hot Water System Size by Household
The right size mostly comes down to how many people are in the house and which system type you’re after, so here’s a working range to start from.
| Household size | Electric storage (continuous tariff) | Electric storage (off-peak) | Gas storage | Gas continuous flow | Heat pump | Solar (tank + collector) |
| 1 to 2 people | 125 to 160L | 250 to 270L | 135 to 150L | 16 to 20 L/min | 170 to 220L | 200 to 270L, roughly 2 to 3 m² |
| 3 to 4 people | 160 to 200L | 250 to 315L | 135 to 170L | 20 to 26 L/min | 270 to 315L | 300 to 360L, roughly 4 m² (Melbourne homes often need a bit more collector area than this Brisbane-based figure) |
| 5+ people | 200 to 250L+ | 315L+ | 170L+ | 26 L/min+ | 315L+ | 360L+, with extra collector area |
These figures assume a Melbourne climate, average shower lengths of around 7 to 8 minutes, and typical household usage rather than heavy back-to-back demand (think teenagers home from footy training and three showers in a row).
Off-peak electric systems need a bigger tank than continuous tariff ones because they only heat water during set hours overnight.
A little note: it’s a sensible starting point rather than the final word. Actual household usage varies enough that it’s worth getting a licensed plumber to confirm the right size for your home before you buy.
What Affects Your Hot Water System Size?
Head count is only the starting point. A few other factors decide whether you should size up, size down, or stick with the average.
How Many People Live in Your Home
Plan for about 50L per person per day, with some references going up to 70L for heavier users.
Size for the home, not just who’s living there today, a three-bedroom house built for four still suits a 300L tank even if it’s currently a retired couple. Dishwashers and washing machines that heat their own water take some pressure off the system too.
Peak Demand: When Everyone Showers at Once
Peak demand is the busiest 30 to 60 minutes of your day, similar to the electricity grid’s own peak period, generally 7AM to 9AM and 5PM to 9PM. Baths add up fast, generally 100 to 210L each, so one bath can eat a big chunk of a small tank. Bathroom count matters too, especially with back-to-back showers.
Recovery Rate: Why Gas and Electric Are Sized Differently
Recovery rate is how fast a system reheats once drawn down. Gas storage recovers faster than electric, so a smaller gas tank can often cover the same household.
That comes down to how long a hot water system takes to heat up in the first place. Also worth checking is the first hour rating on spec sheets, which shows how much hot water a system delivers in its first hour of use.
Off-Peak Tariff or Continuous: Why It Changes Tank Size
Off-peak electric systems only heat overnight, so the tank needs to hold a full day’s supply, pushing tank size up. Check your bill or ask your retailer which tariff you’re on before sizing.
Melbourne’s Climate
Cold winter incoming water means your system works harder. Solar systems feel this most, so collector area and a booster matter more here than in warmer states. Some suppliers suggest stepping up to a 315L heat pump tank for inland Melbourne.
As always, confirm exact figures against the manufacturer’s spec sheet for your chosen model before buying.
How to Calculate Your Hot Water System Size
Here’s how it works in practice, using a three-bedroom, two-bathroom Melbourne home with four people as an example.
Step 1: Count the People the House Is Built For
Use bedrooms as a guide rather than just today’s headcount. A three-bedroom home is generally built to comfortably fit four people, even if fewer live there now.
Example: three bedrooms, so plan for four people.
Step 2: Multiply by 50L a Day
Take the baseline of 50L per person per day and multiply by the household size.
Example: 4 people x 50L = about 200L of hot water a day. Add a bit of buffer on top if baths, teenagers, or regular guests are part of the picture.
Step 3: Match That to a Tank Size or a Flow Rate
Source: WELS
For storage systems, a common approach is to plan for around 1.5 days of capacity: 200L x 1.5 = roughly 300L. Gas storage tanks are usually smaller than this, generally 135 to 170L, because they reheat faster and don’t need to hold as much at once.
For continuous flow systems, think about how many outlets could run at the same time. A single shower typically uses 9 to 12 L/min, so two showers running together means at least 20 to 24 L/min. Check your own showerhead’s flow rate on its WELS label rather than guessing, since flow rates vary a fair bit between models.
Step 4: Check It Against Your System Type and Tariff
Compare your result with the ranges in the quick answer table above, then adjust for your tariff type and Melbourne’s climate. If your numbers land between two sizes, that’s a good sign it’s time to ask a plumber rather than guess.
Hot Water System Sizes by System Type
The right size also depends on which types of hot water system you’re comparing, since each is sized a little differently. Here’s how each one stacks up.
Electric Storage Systems
Sized by tank volume, with tariff type having the biggest effect on the right size. Rheem lists a 250L tank for up to five people and 315L for up to six, based on 7 minute showers in a moderate climate. Electric storage tends to have a lower upfront cost, but usually higher running costs than gas or heat pump over time.
Gas Storage Systems
Smaller tanks, generally 130 to 170L, suit most families thanks to faster recovery. Worth knowing: a failed gas storage unit in an existing Victorian home can’t be replaced with another gas unit from 1 March 2027.
Gas Continuous Flow (Instantaneous) Systems
These are sized in litres per minute, not litres, so a 250L tank and a 20 L/min unit aren’t directly comparable.
As a guide: 12 L/min suits one bathroom and up to two people, 16 L/min suits around 1.5 bathrooms and up to three people, 20 L/min covers four people, and 26 L/min suits 2 to 2.5 bathrooms and up to five people.
Flow can drop if too many outlets run at once, so match the unit to your peak demand, not just headcount.
Heat Pump Hot Water Systems
Tanks of 270 to 315L are common for a family of four, though some integrated models start smaller, Rheem claims a 178L model which is enough for 1-4 people.
A smaller tank can often mean lower energy use since heat pumps heat efficiently at any time of day, but don’t go below what your household actually needs. Follow the manufacturer’s sizing guide for your specific model.
Solar Hot Water Systems
A tank plus roof collectors, working together. It’s around 4 m² of collector with a 300 to 360L tank for four people, while Rheem lists 250 to 315L systems for three to four people.
Collector numbers depend on your local climate, and Melbourne’s lower winter sun means the booster matters more here than in warmer states.
Victoria’s 2027 Gas Hot Water Rule: What It Means for Your Size Choice
What Changes From 1 March 2027
From 1 March 2027, a gas hot water appliance that breaks and can’t be repaired must be replaced with an electric alternative. A working gas system isn’t affected, it can stay and be repaired as normal.
This applies to hot water only, gas heating and cooking are untouched. Separately, new homes must be all-electric from 1 January 2027.
How This Changes the Size You Choose
Replacing a 135 to 170L gas storage unit after this date likely means moving to a heat pump, typically 270 to 315L for a family of four. Check you’ve got space for the larger tank before the old one fails, and talk to your plumber early if space or electrical capacity is tight.
Victorian Energy Upgrades discounts and the Solar Homes hot water rebate can help with costs. If your gas system’s getting on, see how long hot water systems last, typically 8 to 12 years.
If You Own a Rental Property
The same rule applies to rentals, aligning with Victoria’s rental minimum energy efficiency standards from 1 March 2027. Guidance suggests a heat pump or electric-boosted solar system would satisfy the requirement for rental hot water.
What Happens If You Get the Size Wrong?
If It’s Too Small
You’ll know quickly: cold showers, running out mid-shower, the tank never quite catching up before the next person needs it.
Sizing isn’t always the culprit though, sediment build-up and faulty heating elements can be the reasons why your hot water is running out quickly.
If It’s Too Big
Oversizing will affect how much hot water systems cost. You end up paying to heat and store water nobody uses, and bigger tanks lose more heat while they sit idle between uses. It adds up over time on your energy bill.
Should You Call a Plumber to Size Your Hot Water System?
The steps above will get you a solid working number, but a few situations are worth handing to a professional instead: replacing a failed gas unit and unsure what’s allowed, adding a bathroom or granny flat, unsure of your tariff, heavy hot water use, or switching from gas to a heat pump.
A granny flat or second dwelling should be sized as its own household, not added onto the main house’s number, since it has its own peak demand.
Neighbourhood Plumbing’s plumbers install, repair and maintain electric, gas, solar and heat pump systems across Melbourne. We’ll check your household, tariff and available space before recommending a size, so nothing’s left to guesswork.
If you’d rather have it sorted properly the first time, our hot water plumbers in Melbourne can help.
FAQs About Hot Water System Size
A few quick answers to the questions we hear most often.
What size hot water system do I need for a family of 4?
It depends on system type: 160 to 200L for electric storage, 135 to 170L for gas storage, 20 to 26 L/min for gas continuous flow, or 270 to 315L for a heat pump. See the quick answer table above for the full breakdown.
Is a 250L hot water system enough for a family of 4 or 5?
Often yes. Still, it depends on your tariff, bathroom count and morning routine.
What size hot water system do I need for 2 people?
Generally 125 to 160L for electric storage, from around 90L for gas storage, or 12 to 16 L/min for continuous flow. Consider sizing up slightly if your household might grow.
How much hot water does one person use per day?
About 50L on average, more with long showers, baths, or appliances that draw their own hot water.
What size hot water system do I need for a 3-bedroom house?
Size for the house, not just who lives there now, three bedrooms generally suits four people, so around 300L for a storage system. Gas and continuous flow systems land at different numbers, check the table above.
What size continuous flow (instantaneous) hot water system do I need?
It depends on how many outlets run at once: 12 L/min suits one bathroom and up to two people, 16 L/min around three, 20 L/min four, and 26 L/min larger households.
Does a heat pump need a bigger tank than a gas system?
Usually yes, heat pump tanks often sit at 270 to 315L against 135 to 170L for gas, since gas reheats faster. Always follow the manufacturer’s sizing guide.
How do I find out what size my current hot water system is?
Check the rating or compliance plate on the unit, it lists capacity or flow rate. A like-for-like swap isn’t always right if your household has changed.
Do I have to replace my gas hot water system with electric in Victoria?
Only once it fails and can’t be repaired, from 1 March 2027. A working system can stay and be repaired as normal. See the section above for full details.
Conclusion
The simple rule holds regardless of system type: plan for about 50L per person per day, then check that number against your peak demand and the system you’re leaning towards. Get those two things right and everything else falls into place.
If you’re a Victorian gas owner, it’s worth planning around the 2027 rule rather than being caught out by it later.
Either way, before you buy, it’s worth getting your number checked by a plumber who can weigh up your household, your tariff and your home’s setup.
Neighbourhood Plumbing’s team can help you nail down the right size and get it installed properly, so get in touch with our hot water plumbers in Melbourne before you buy!
About the Author
From unclogging the toughest drains to repairing leaking toilets, Ricky is a seasoned plumber who has brought his craftmanship to homes across Melbourne. He is passionate about sharing plumbing tips just as much as he is about fixing your plumbing issues. So, when your taps or pipes begin leaking, you know who to call.
