How much hot water capacity does a South East Melbourne house need?
Litres per person, peak hour demand and Melbourne winter mains temperature, with a working estimator that sizes the tank and then prices it.
Storage sizing for a mains-pressure system in South East Melbourne: 1 to 2 people 125 L to 170 L, 3 people 170 L to 250 L, 4 people 250 L to 315 L, 5 or more 315 L to 400 L. Heat pumps need one step more than a gas tank for the same family because recovery takes 3 to 5 hours, so four people means 280 L to 300 L. Off-peak electric needs another step again, because the whole day has to fit in the tank. Continuous flow is sized in litres per minute instead: 16 L/min for one shower, 20 L/min for two, 26 L/min for two showers in July.
Hot water capacity and cost estimator
Set the capacity you need, pick the system and the install situation, and the estimator gives you a 2026 South East Melbourne price range. It is a ballpark, not a quote: a firm price needs eyes on your switchboard, your gas run and your access.
What this estimate includes
- Assumes a standard replacement with the unit supplied by us, the old unit removed and taken away, and a compliance certificate issued.
- Includes new isolating valves and flexible connections; the tempering, PTR and expansion control set is the first tick box because it is often quoted separately elsewhere.
- Assumes reasonable access: a park within about 30 m and a side gate at least 800 mm wide.
- Excludes gas line upsizing at $300 to $900, roof access or crane hire for solar, and any repair to pipework hidden in a wall.
- The incentive tick box applies a conservative allowance only. The Solar Victoria rebate is $1,000 for eligible owner-occupiers and a Victorian Energy Upgrades discount commonly runs $800 to $2,000, but you generally cannot use both on the same unit.
- This is a 2026 guide. A firm price needs a site check. The full itemised list sits on the pricing page.
How to measure it properly, with a tape and a phone
- Measure your actual shower flow. Put a 10 L bucket under the shower on the setting you normally use, time it with your phone, then divide 600 by the seconds to get litres per minute. A water-efficient head is 7.5 to 9 L/min; an old head can be 15 L/min or more, which changes everything downstream of this calculation.
- Count the minutes honestly. Eight minutes at 9 L/min is 72 L of mixed water at about 41°C. Ask each person, do not estimate for them, and count the teenager properly.
- Convert mixed water to stored water. To make 41°C water from a 60°C tank with 12°C winter mains, roughly 60 per cent of it comes out of the tank. So a 72 L shower is about 43 L of stored hot water in July and about 38 L in January.
- Measure the space, including above. A 315 L electric cylinder is roughly 1.75 m tall and 640 mm across. Measure the alcove width, the depth and the clearance overhead, because pulling a full-length anode needs close to the tank height again above it. If it will not fit, specify a segmented anode at install time.
- Photograph the three things we will ask for. The data plate on the old unit, the switchboard, and the gas meter. Then measure the distance from the unit to each. A heat pump also needs manufacturer clearance around the air intake, commonly a few hundred millimetres each side, plus a condensate drain to a legal discharge point.
Rules of thumb and the allowance to add
Three numbers do most of the work. Usable capacity is about 70 to 80 per cent of the rated litres, because the bottom of a stratified tank is not hot enough to shower in. Winter costs you about 15 per cent more stored water for the same shower, because Melbourne mains water falls to roughly 10°C to 13°C. And the allowance to add is 10 to 20 per cent, not 50.
That last one matters because oversizing is not free. A large electric cylinder loses roughly 1.5 to 2.5 kWh a day in standing losses whether anyone showers or not, which is $160 to $270 a year of heating the laundry. Buy the size you need plus a sensible margin, and put the money you saved into the valve set instead.
Want us to size it for you?
Tell us how many people, how many bathrooms and what time the morning rush is, and we will name the capacity and the price.
The sizing mistake that costs the most here
It is undersizing a heat pump, and we see it constantly across the newer estates. A 170 L or 200 L heat pump is roughly $900 cheaper than a 280 L one on the quote, and it looks like a sensible saving on a house with a small family. Then the tank empties at 7:30am, the resistive element inside it cuts in to recover, and the electricity bill stops behaving like a heat pump. Running cost climbs from around $350 a year to closer to $700, which over ten years turns a $900 saving into a $3,500 loss. The reason it happens so often is that heat pump recovery is slow: 3 to 5 hours for a full tank against well under an hour for gas storage. Litres are how a heat pump buys itself time.
The second most expensive mistake goes the other way: a 400 L off-peak electric tank in a two-person house, quietly burning $200 a year in standing losses for capacity nobody uses. The third is sizing a continuous flow unit on the summer number. A 20 L/min unit that handles two Berwick showers comfortably in February will not do it in July, because the incoming water is 8°C to 10°C colder and the same burner has more work to do. Size up one step if two showers ever run at once.
A worked example: four people in Berwick
Two adults and two teenagers, two bathrooms, everyone out the door by 8am. We measured the shower at 9 L/min and the household admitted to 8 minute showers, so each one is 72 L of mixed water, which is about 43 L out of the tank in winter. Three of those showers back to back is 129 L, and the basins and the kitchen sink add roughly 15 L, so the morning peak is about 145 L of stored hot water inside 75 minutes.
Evening use, one more shower plus dishes plus a load of washing on warm, is about another 90 L. Total daily stored demand is roughly 235 L. Divide by 0.8 for usable capacity and you need about 294 L of rated storage, which is why we land this house on a 300 L unit rather than the 250 L one they were quoted. On gas storage you could get away with less, because gas recovers the tank in under an hour, and 170 L to 200 L would genuinely work. On a heat pump, 300 L is the honest answer.
Pricing that job through the estimator above at 300 L, heat pump with an integrated enamel tank, like-for-like position, with the tempering, PTR and expansion set replaced and the Victorian incentive applied, returns $3,100 to $5,500. On this particular house we would expect the final written quote to land near $4,200 once we had seen the switchboard and the pad. That is the number we would put in writing, and the two systems either side of it are set out on choosing a hot water system.
When you do not need a bigger tank at all
Running out of hot water is not always a capacity problem, and it is worth ruling out the cheap causes before you spend $2,000 on litres you may not need. A thermostat that has been knocked down to 50°C stores far less usable heat than one at 60°C. In a twin-element electric tank, a dead lower element leaves you with only the top third of the cylinder, which feels exactly like an undersized tank. A tempering valve that has failed part-open bleeds cold water into the hot line all day. Heavy sediment in the base of an older tank takes up volume and insulates the element from the water. Every one of those is a $180 to $420 repair, and every one of them mimics a tank that is too small.
Get the diagnosis first. We will tell you on the phone which of those it sounds like, and our repair service will confirm it on site for the cost of a callout. The symptoms and what each one means are on the warning signs page, and the realistic life expectancy of your existing unit is on how long hot water systems last. Equally, if two of you live in a house with a 400 L off-peak tank, downsizing at replacement time is a genuine saving rather than a compromise.
Once you know the capacity, the rest of the decision is money and logistics: the three price tiers are on the budget page, the day itself is on what to expect on installation day, and what happens if it ever fails is on hot water warranties in Victoria.
Sizing questions we get asked
How many litres of hot water storage does a family of four need?
How do I measure my own hot water usage?
What flow rate continuous flow unit do I need?
What is the most expensive hot water sizing mistake?
Is a bigger tank always better?
Do I need a bigger tank if I keep running out of hot water?
Have us size your tank and price it properly
Send the details below and we will come back within one business day with the capacity we would fit and a written installed price.
Sized right the first time, across the South East
Berwick, Cranbourne, Narre Warren, Hampton Park, Endeavour Hills, Officer, Beaconsfield, Pakenham and Clyde.