Electric Hot Water System Size Guide: 125L vs 160L vs 250L vs 315L vs 400L

Jun 25, 2026

Choosing the right electric hot water system size is one of the most important decisions when replacing an old tank. Too small, and the household may run out of hot water during showers. Too large, and you may pay more upfront, use more space and store more hot water than needed.

Electric storage hot water systems are commonly sized by tank capacity in litres. The right size depends on the number of people in the home, number of bathrooms, shower habits, bath use, laundry use, dishwasher use, heating tariff, recovery time, installation location and whether the old system was keeping up.

This guide compares 125L, 160L, 250L, 315L and 400L electric hot water systems so you can choose a practical replacement before ordering.

You can compare Electric Hot Water Systems, broader Hot Water Systems, Heat Pump Hot Water Systems, Instant Electric Systems, Gas Hot Water Systems, Instant Gas Hot Water Systems and Installation Add-Ons online with Installed Today.

Quick answer: which electric hot water size should you choose?

As a general starting point:

Electric hot water size	Common household fit
125L	1 to 2 people with moderate hot water use
160L	2 people or a small household with moderate use
250L	Many 3 to 4 person homes
315L	Larger families or higher-demand homes
400L	Large households, high demand or selected off-peak setups

This is only a guide. The right size depends on real usage, not just the number of people.

A two-person home with long showers and frequent guests may need more stored hot water than a three-person home with shorter showers. A four-person home with a bath may need more capacity than a four-person home with one shower and lower use.

Why electric hot water sizing matters

Electric storage systems heat water in a tank and keep it ready for use. Once the stored hot water is used, the system needs time to reheat.

If the tank is too small, you may notice:

Hot water running out during showers
Poor recovery after back-to-back use
Not enough hot water for baths
Tenants or guests complaining
More reliance on boost heating where available
Frustration during morning or evening peak times

If the tank is too large, you may notice:

Higher upfront product cost
More space required
More weight and access difficulty
More stored hot water than needed
Higher standing heat losses in some situations
Unnecessary replacement complexity

The best size is the smallest practical system that can comfortably handle the household’s real peak hot water use.

Electric hot water size is not just about people

Household size is useful, but it is not enough on its own.

Before choosing a tank size, check:

Number of people
Number of bathrooms
Number of showers per day
Shower length
Shower head flow rate
Bath use
Laundry use
Dishwasher use
Morning peak demand
Evening peak demand
Guest use
Rental or Airbnb use
Off-peak or controlled-load setup
Recovery time
Existing system performance
Available space
Installation access

If the old system ran out regularly, do not automatically replace it with the same size.

125L electric hot water systems

A 125L electric hot water system is usually considered a smaller storage option.

It may suit:

1 person
2 people with moderate use
Small units
Townhouses
Low-demand homes
Some rental properties
Properties with limited installation space
Homes without a bath
Customers replacing an existing 125L system that performed well

A 125L system may not suit:

Larger families
Long showers
Multiple bathrooms
Homes with baths
Frequent guests
Short-stay rentals
High laundry hot water use
Homes where the old 125L tank ran out

If your old 125L electric hot water system regularly ran out, upgrading to a larger size may be worth comparing.

125L electric hot water: best-fit examples

A 125L system may be a practical fit for:

A single-person apartment
A two-person unit with short showers
A small townhouse with one bathroom
A rental where hot water use is modest
A compact home where space is limited

However, it should be checked carefully where the home has a bath, high-flow shower head, long showers or frequent guests.

160L electric hot water systems

A 160L electric hot water system is often compared by smaller households that need more capacity than 125L but do not need a large family tank.

It may suit:

2 people
Small families with moderate use
Units and townhouses
One-bathroom homes
Low-to-moderate shower demand
Homes without heavy bath use
Customers replacing an existing 160L tank that worked well

A 160L system may not suit:

Larger families
Homes with multiple bathrooms
High shower use
Regular bath use
Airbnb or short-stay homes
Households that use lots of hot water at peak times

A 160L tank can be practical, but usage habits matter. Two people with long showers may use more hot water than expected.

160L electric hot water: best-fit examples

A 160L system may suit:

A couple in a one-bathroom home
A small townhouse
A low-demand rental
A unit with moderate shower use
A home where the existing 160L system has been reliable

Before choosing 160L, check whether the household ever ran out of hot water, whether guests stay often, and whether the tank will run on off-peak or controlled-load electricity.

250L electric hot water systems

A 250L electric hot water system is one of the most common family-size options.

It may suit:

3 to 4 person homes
One or two bathroom properties
Families with moderate hot water use
Standard residential replacements
Many rental properties
Homes replacing an existing 250L tank that performed well
Customers wanting a practical middle-size storage system

A 250L system may not suit:

Very large families
High bath use
Homes with frequent back-to-back showers
Short-stay properties with high guest numbers
Homes where the old 250L tank ran out often
Some off-peak setups with heavy evening use

If a 250L system has been working well, replacing with a similar size may be practical. If it has been running out, reassess before ordering.

250L electric hot water: best-fit examples

A 250L system may be suitable for:

A family of three
A family of four with moderate shower use
A two-bathroom home where showers are not always simultaneous
A rental property with average occupancy
A home replacing an old 250L electric tank

For families with teenagers, long showers or frequent guests, a 315L system or heat pump option may be worth comparing.

315L electric hot water systems

A 315L electric hot water system is often compared by larger households or homes with higher hot water demand.

It may suit:

4 to 5 people
Larger families
Homes with multiple bathrooms
Homes with back-to-back showers
Properties with bath use
Higher-demand rentals
Some off-peak electric setups
Customers who found a 250L system too small

A 315L system may not suit:

Smaller homes with low usage
Tight installation locations
Sites with poor access
Homes where a smaller heat pump may be a better long-term option
Customers focused only on lowest upfront product cost

A 315L system needs more space and may cost more than smaller tanks, but it can be useful where household demand is genuinely higher.

315L electric hot water: best-fit examples

A 315L system may suit:

A family of four with long showers
A family of five
A home with two bathrooms
A rental property with several bedrooms
A home with bath use
A household where 250L has not been enough

Before ordering, check installation space, access, base support, electrical setup and whether heat pump hot water is worth comparing.

400L electric hot water systems

A 400L electric hot water system is a large storage option for high-demand homes.

It may suit:

Large households
5 or more people with high use
Multiple bathrooms
Homes with frequent baths
Larger rental properties
Short-stay properties with high guest numbers
Some off-peak electric setups
Homes with very high peak demand

A 400L system may not suit:

Small households
Homes with limited space
Difficult access sites
Customers wanting lower upfront product cost
Properties where a heat pump may be a better efficiency upgrade
Homes that do not need that much stored hot water

Bigger is not automatically better. A 400L system should be chosen because the household genuinely needs the capacity.

400L electric hot water: best-fit examples

A 400L system may be considered for:

A large family home
A high-occupancy rental
A property with several bathrooms
A home with regular bath use
A household using off-peak electric hot water with limited reheating windows
A short-stay home where guest peak use is high

Before choosing 400L, confirm access, support, electrical setup, space and long-term running cost expectations.

125L vs 160L electric hot water

Choose 125L where:

The home has 1 to 2 people
Shower use is moderate
Space is limited
There is no regular bath use
The old 125L system worked well
Lower upfront product cost matters

Choose 160L where:

Two people need a little more storage
The home has slightly higher shower demand
Guest use is occasional
The old 125L system was borderline
There is room for a larger tank
A small upgrade makes sense

The difference between 125L and 160L can matter for two-person households, especially if showers are longer or the home has occasional guests.

160L vs 250L electric hot water

Choose 160L where:

The home has 1 to 2 people
Hot water use is modest
The property has one bathroom
There is limited space
The existing 160L system performed well

Choose 250L where:

The home has 3 to 4 people
There are more showers per day
The household has moderate family use
The property is a rental
The old smaller system ran out
More stored capacity is needed

For a growing household, 250L is often worth comparing before replacing with another 160L tank.

250L vs 315L electric hot water

Choose 250L where:

The home has 3 to 4 people
Shower use is moderate
The old 250L system worked well
There is no heavy bath use
Lower upfront cost and space matter

Choose 315L where:

The home has 4 to 5 people
The old 250L tank ran out
There are multiple bathrooms
Showers are longer or back-to-back
Bath use is common
The property is a larger rental

A 315L tank may be the better option where 250L is just not keeping up.

315L vs 400L electric hot water

Choose 315L where:

The household is large but not extreme
There are 4 to 5 people
There are multiple showers
Space is available but not unlimited
The home needs more than 250L but not maximum capacity

Choose 400L where:

The home has very high hot water demand
There are 5 or more people
Bath use is frequent
Guest use is high
Off-peak reheating windows require more storage
A large-capacity tank is justified

A 400L system should be chosen for genuine demand, not just as a “safe” oversized option.

Electric hot water sizing for 1 person

A one-person home may compare:

125L electric storage
Smaller compact electric options
Instant electric for selected point-of-use needs
Heat pump hot water where site suitability and demand justify it

For one person, a large electric tank is often unnecessary unless there are unusual usage patterns, a bath, high guest use or off-peak timing requirements.

Electric hot water sizing for 2 people

A two-person home may compare:

125L electric storage
160L electric storage
Smaller or medium heat pump options where suitable
Instant electric only for selected point-of-use needs

Choose based on shower length, bath use, guest use, tariff setup and whether the previous system ran out.

Electric hot water sizing for 3 people

A three-person household may compare:

160L electric storage for lower use
250L electric storage for more comfortable capacity
Heat pump hot water where the site suits
Gas or instant gas if the property already has suitable gas

For many three-person homes, 250L is often worth comparing if shower use is moderate to high.

Electric hot water sizing for 4 people

A four-person home may compare:

250L electric storage
315L electric storage for higher demand
Family-sized heat pump hot water
Gas or instant gas where gas supply suits

A 250L system may suit many four-person homes, but a 315L option may be better where there are long showers, teenagers, multiple bathrooms or bath use.

Electric hot water sizing for 5 people

A five-person household may compare:

315L electric storage
400L electric storage for very high use
Larger heat pump hot water where the site suits
Instant gas where gas pipe sizing and water pressure support it

Do not undersize a five-person home just to reduce upfront cost. Running out of hot water can become a daily frustration.

Electric hot water sizing for 6 or more people

Large households should be assessed carefully.

Options may include:

315L electric storage for moderate large-household use
400L electric storage for higher demand
Larger heat pump hot water
Correctly sized instant gas where gas supply supports it

Check bathrooms, simultaneous shower use, bath use, laundry use, recovery time and installation space.

Sizing for one bathroom

A one-bathroom home may not need a large tank, but usage still matters.

Check:

Number of people
Shower length
Shower head flow rate
Bath use
Laundry hot water use
Guest use
Whether showers happen back-to-back
Whether the old system ran out

A one-bathroom home with three people and long showers may need more capacity than expected.

Sizing for two bathrooms

Two-bathroom homes need more careful sizing because showers may overlap.

Check:

Whether both showers are used at the same time
Shower head flow rates
Morning peak use
Evening peak use
Bath use
Number of people
Stored capacity
Recovery rate

For two-bathroom homes, 250L, 315L or a suitable heat pump or instant gas option may be worth comparing depending on the energy source and household use.

Sizing for homes with baths

Baths can use a large amount of hot water.

If the home has a bath, consider:

Bath size
How often the bath is used
Whether showers happen after the bath
Number of people
Tank capacity
Recovery rate
Off-peak or timer setup
Whether the old system ran out

A small tank may be frustrating in homes where baths are used regularly.

Sizing for high-flow shower heads

High-flow shower heads can drain a tank faster.

Before upsizing the hot water system, check:

Shower head flow rate
Shower length
Number of showers per day
Whether multiple showers run back-to-back
Whether a lower-flow shower head would help
Whether the existing system is undersized or just being overused

Sometimes the issue is not only tank size. Usage and fixture flow can be part of the problem.

Sizing for off-peak or controlled-load electricity

Off-peak or controlled-load electric hot water can affect sizing because the system may only reheat during certain times.

A home on restricted reheating may need more stored capacity than a similar home with more flexible heating.

Before choosing a size, check:

Heating window
Tank capacity
Household demand
Morning and evening peak use
Boost heating availability
Whether the old system ran out before reheating
Tariff setup
Installer advice

This is one reason two homes with the same number of people may need different tank sizes.

Sizing for rooftop solar homes

Electric hot water can sometimes be timed to run during solar generation hours where the setup allows.

Before sizing around solar, check:

Solar system size
Daytime electricity generation
Household daytime usage
Timer setup
Tank capacity
Electrical configuration
Controlled-load arrangement
Installer advice

If rooftop solar is part of the plan, Heat Pump Hot Water Systems may also be worth comparing where the site suits.

Electric storage vs heat pump sizing

Electric storage and heat pump hot water are both tank-based, but they are not identical.

Electric storage sizing focuses on:

Tank capacity
Element size
Recovery time
Tariff setup
Household demand

Heat pump sizing also considers:

Tank capacity
Recovery rate
Outdoor airflow
Condensate drainage
Timer settings
Boost mode
Climate
Noise placement

If you are replacing an old electric tank, heat pump hot water may be worth comparing, but only where the installation location is suitable.

Electric storage vs instant electric sizing

Electric storage and instant electric sizing are completely different.

Electric storage uses tank capacity.

Instant electric uses flow rate, temperature rise and electrical capacity.

Instant Electric Systems may suit:

Hand basins
Small sinks
Kitchenettes
Point-of-use applications
Remote fixtures
Low-demand areas

For most whole-home replacements, electric storage is more common than instant electric.

Electric storage vs gas hot water sizing

Electric storage uses tank capacity.

Gas hot water may use tank capacity or flow rate depending on whether it is gas storage or instant gas.

Gas Hot Water Systems may suit homes already using natural gas or LPG.

Instant Gas Hot Water Systems are sized by flow rate in L/min and depend heavily on gas pipe sizing and water pressure.

Natural gas and LPG are not interchangeable. Any gas system must match the property gas type.

Sizing for rentals

Rental properties should be sized for likely occupancy, not just the current tenant.

Check:

Number of bedrooms
Number of bathrooms
Likely tenant count
Past hot water complaints
Maintenance access
Existing system performance
Energy source
Simplicity for tenants
Replacement budget

A rental system that is too small can create repeat complaints.

Sizing for Airbnb and short-stay homes

Short-stay homes should be sized for peak guest use.

Check:

Maximum guest count
Number of bathrooms
Back-to-back showers
Bath use
Laundry between bookings
Recovery time
Guest expectations
Maintenance access
Installation location

A short-stay property may need more capacity than a normal owner-occupied home with the same number of bedrooms.

Sizing for renovations

A renovation is a good time to reassess electric hot water sizing.

Before ordering, confirm:

Final number of bathrooms
Shower locations
Bath use
Kitchen and laundry locations
System location
Pipe runs
Electrical setup
Future solar plans
Access after renovation
Whether heat pump hot water is being considered

Do not lock in a hot water system size before the final plumbing and electrical plan is clear.

Sizing for units and townhouses

Units and townhouses may have limited space and access.

Before choosing a size, check:

Existing system location
Cupboard dimensions
Indoor drainage
Body corporate or strata rules
Electrical supply
Access for removal
New system dimensions
Whether larger tanks can physically fit
Whether heat pump airflow is possible

In many units, a practical replacement size is limited by the existing cupboard or plant area.

Brand options for electric hot water sizing

Installed Today lists multiple homepage-linked brands that customers commonly compare for electric hot water, heat pump, gas and broader hot water replacement.

Brands worth comparing include:

Choose by system type, capacity, dimensions, warranty, installation requirements and household demand.

Rheem electric hot water sizing

Rheem Hot Water Systems are commonly compared by customers wanting a major hot water brand.

When sizing Rheem systems, check:

Tank capacity
Household size
Number of bathrooms
Existing system size
Whether the old system ran out
Dimensions
Installation location
Warranty terms

A Rheem replacement should be chosen around household demand, not just brand familiarity.

Rinnai electric hot water sizing

Rinnai Hot Water Systems are commonly compared across electric, gas and heat pump categories.

When sizing Rinnai systems, check:

Electric storage capacity where relevant
Heat pump capacity where relevant
Household demand
Number of bathrooms
Installation space
Electrical setup
Warranty terms
Whether gas or heat pump options may suit better

Rinnai can be compared across multiple hot water pathways, so make sure the system type is clear before ordering.

Dux electric hot water sizing

Dux Hot Water Systems are commonly compared for electric storage replacement.

When sizing Dux systems, check:

Tank size
Existing system performance
Shower demand
Bath use
Household size
Installation dimensions
Access
Warranty terms

A Dux tank may suit simple replacement where the size and site requirements match.

Vulcan electric hot water sizing

Vulcan Hot Water Systems may suit customers comparing value-focused storage hot water options.

When sizing Vulcan systems, check:

Tank capacity
Number of people
Shower habits
Existing system size
Installation space
Access
Total replacement pathway

A value-focused system still needs to be correctly sized.

Stiebel Eltron electric hot water sizing

Stiebel Eltron Hot Water Systems are commonly compared for compact electric, instant electric and premium electric options.

When sizing Stiebel Eltron systems, check:

Point-of-use or whole-home application
Flow rate
Temperature rise
Electrical capacity
Switchboard suitability
Fixture type
Water pressure
Installation location

Instant electric sizing is not the same as storage tank sizing.

Heat pump brands to compare when upsizing or upgrading

If you are replacing electric storage and considering a more efficient electric pathway, compare heat pump brands where the site suits.

Common homepage-linked heat pump brands include:

Heat pump sizing depends on tank size, recovery, airflow, drainage, electrical setup and household use.

Installation Add-Ons and electric hot water sizing

Installation Add-Ons may be relevant if the replacement needs extra selected components or work.

Add-ons may relate to:

Valves
Disposal
Electrical work
Pipework changes
Drainage requirements
Access issues
Other installation-related needs where available

The right tank size still needs the right installation pathway.

Supply-only electric hot water sizing checks

Supply-only ordering can suit customers who already have their own licensed installer arranged.

Before ordering supply only, confirm:

Correct tank size
Correct product dimensions
Suitable installation location
Suitable electrical supply
Suitable valve setup
Suitable drainage
Access for delivery
Access for old unit removal
Whether disposal is arranged
Whether extra parts or add-ons are needed
Whether the old system size was adequate

Supply-only product pricing generally does not include installation, valves, old unit removal, disposal, electrical work, pipework changes, drainage, access upgrades or compliance upgrades unless clearly selected or included.

Supplied-and-installed electric hot water sizing checks

Supplied-and-installed options may be available on selected products in eligible Brisbane and Gold Coast service areas where shown.

Before ordering supplied and installed, check:

Service area eligibility
Existing system type
Current tank size
Household demand
Product suitability
Installation inclusions
Electrical work
Valve requirements
Pipework changes
Drainage
Old unit removal
Disposal
Access
Compliance upgrades

Do not assume every site requirement is included. Check the selected product and installation options carefully.

Common mistake: choosing by household size only

People count is only a starting point.

A household’s actual hot water use depends on shower length, bath use, laundry, guests, flow rates and peak demand.

Common mistake: replacing the old tank size without checking performance

If the old system worked well, the same size may be suitable.

If the old system regularly ran out, replacing it with the same size may repeat the problem.

Common mistake: choosing the biggest tank available

A bigger tank can help high-demand homes, but it can also increase product cost, space requirements and installation complexity.

Do not oversize without a reason.

Common mistake: ignoring off-peak reheating

Off-peak or controlled-load systems may need more stored capacity because reheating may only occur during certain times.

Check tariff setup before choosing size.

Common mistake: ignoring access

A larger tank may not fit through the available access path or into the existing location.

Check dimensions, stairs, side access, cupboard size and base support.

Common mistake: ignoring heat pump alternatives

If you are replacing a larger electric storage tank and want to reduce electricity use, heat pump hot water may be worth comparing where the site has suitable airflow, drainage and noise placement.

Common mistake: assuming instant electric is a simple whole-home replacement

Instant electric can be useful for point-of-use applications, but whole-home use needs careful electrical and flow-rate checks.

Common mistake: DIY hot water replacement

Electric hot water replacement can involve plumbing, electrical work, pressure control, drainage, scalding safety and compliance.

DIY work can create:

Water leaks
Electrical risks
Scalding risks
Poor performance
Warranty issues
Insurance problems
Non-compliant work
Property damage

Use licensed professionals for installation and technical checks.

Final verdict: 125L, 160L, 250L, 315L or 400L?

Choose a 125L electric hot water system for low-demand 1 to 2 person homes where the old system performed well and space is limited.

Choose a 160L electric hot water system for 2-person homes or small households that need more capacity than 125L but do not need a full family tank.

Choose a 250L electric hot water system for many 3 to 4 person homes with moderate shower use.

Choose a 315L electric hot water system for larger families, higher-demand homes, multiple bathrooms or households where 250L has not been enough.

Choose a 400L electric hot water system only where high demand, large occupancy, bath use, short-stay use or off-peak storage requirements justify the larger capacity.

Start by comparing Electric Hot Water Systems, broader Hot Water Systems, Heat Pump Hot Water Systems, Instant Electric Systems, Gas Hot Water Systems, Instant Gas Hot Water Systems and Installation Add-Ons.

The right electric hot water size is not the smallest, largest or cheapest option. It is the tank that matches the household’s real hot water use and suits the installation site.

Long-tail FAQs

Is 125L enough for 2 people?

A 125L electric hot water system may suit two people with moderate shower use, no regular bath use and limited guest demand. If showers are long or the old system ran out, 160L or larger may be worth comparing.

Is 160L enough for a family?

A 160L system may suit a small family with moderate use, but it may be too small for larger families, long showers, baths or multiple bathrooms.

Is 250L enough for 4 people?

A 250L electric hot water system can suit many four-person homes with moderate use, but a 315L system may be better where showers are long, bathrooms are used back-to-back, or bath use is common.

Should I choose 250L or 315L electric hot water?

Choose 250L for moderate 3 to 4 person use where the old system worked well. Choose 315L where the household is larger, demand is higher or the old 250L system ran out.

Is 400L electric hot water too big?

A 400L system may be too large for small or moderate-use households. It is generally better suited to large families, high-demand homes, short-stay properties or selected off-peak setups.

What size electric hot water system do I need for 3 people?

A three-person household may compare 160L and 250L electric storage depending on shower habits, bath use, tariff setup and whether the previous system ran out.

What size electric hot water system do I need for 5 people?

A five-person household may compare 315L and 400L electric storage, or a suitable heat pump or gas option depending on the property setup.

Does off-peak electricity change hot water sizing?

Yes. Off-peak or controlled-load electric hot water may need more stored capacity because reheating may only happen during certain times.

Should I upgrade from electric storage to heat pump?

Heat pump hot water may be worth comparing if the home has suitable outdoor airflow, condensate drainage, electrical setup and noise placement.

Can I install an electric hot water system myself?

No. Electric hot water installation should be completed by licensed professionals. Plumbing, electrical work, pressure control and compliance requirements can create safety, warranty and insurance issues if handled incorrectly.

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