Instant Electric Hot Water Size Guide: Point-of-Use vs Shower vs Whole Home

Jun 26, 2026

Choosing the right instant electric hot water system size is very different from choosing a storage tank size. Electric storage systems are usually sized by litres of stored hot water, while instant electric systems are sized around flow rate, temperature rise, electrical capacity and the fixture being supplied.

Instant electric hot water can be useful for hand basins, small sinks, kitchenettes, remote fixtures and selected low-demand applications. However, it should not be treated as a simple replacement for every full-size electric storage, heat pump or gas hot water system. Electrical requirements can be significant, especially for shower or whole-home use.

This guide explains how to size instant electric hot water systems, when they make sense, when storage or heat pump hot water may be better, and what to check before ordering.

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

Quick answer: what size instant electric hot water system do I need?

The right instant electric hot water size depends on what the unit needs to supply.

As a general starting point:

Application	Sizing consideration
Hand basin	Low flow, low demand, point-of-use system may suit
Small sink	Point-of-use system may suit depending on flow and temperature rise
Kitchenette	Depends on sink use, flow rate and electrical supply
Remote fixture	Point-of-use instant electric may reduce long pipe runs
Shower	Needs careful flow rate, temperature rise and electrical checks
Granny flat	Depends on fixtures, occupancy and electrical capacity
Whole home	Needs major assessment; storage or heat pump may be better
Commercial hand wash	Depends on usage, compliance and electrical capacity

Instant electric sizing is not only about the unit size. The electrical supply must support the unit, and the unit must suit the intended fixture.

What is an instant electric hot water system?

An instant electric hot water system heats water as it flows through the unit.

It does not store hot water in a tank.

Instant electric systems are also called:

Tankless electric hot water systems
Continuous flow electric hot water systems
Instantaneous electric hot water systems
Point-of-use electric water heaters
Under-sink electric water heaters in some applications

They can be compact and convenient, but they need the right electrical supply, water pressure, flow rate and installation setup.

How instant electric sizing works

Instant electric sizing depends on how much water the unit needs to heat and how much the water temperature needs to rise.

Important sizing factors include:

Fixture type
Required flow rate
Incoming water temperature
Desired outlet temperature
Temperature rise
Electrical capacity
Circuit requirements
Switchboard capacity
Cable size
Water pressure
Pipework route
Usage frequency
Whether multiple outlets run at once

A small hand basin and a shower have completely different hot water requirements.

Flow rate matters

Flow rate is the amount of water moving through the unit.

A hand basin may need much less flow than a shower.

Flow rate depends on:

Tap type
Shower head type
Restrictors
Water pressure
Pipework
Fixture demand
Whether more than one outlet runs at once

If the flow rate is too high for the unit, the water may not heat enough.

If the flow rate is too low, some units may not activate properly.

Temperature rise matters

Temperature rise means how much the unit must increase the water temperature.

For example, water entering the unit at a lower temperature needs more heating to reach a comfortable outlet temperature.

Temperature rise affects:

Available flow rate
Electrical demand
Unit suitability
Shower comfort
Sink performance
Whether the system can serve the intended fixture

A unit that works well for hand washing may not be suitable for showering.

Electrical capacity matters most

Electrical capacity is one of the biggest instant electric sizing factors.

Instant electric systems can require significant electrical power because they heat water quickly as it flows through the unit.

Before ordering, check:

Existing circuit
Switchboard capacity
Cable size
Safety switch requirements
Isolation requirements
Available electrical load
Whether a new circuit is needed
Whether the property can support the unit
Whether a licensed electrician is required

Do not choose instant electric until electrical suitability is confirmed.

Point-of-use instant electric sizing

Point-of-use instant electric systems are installed close to the fixture they supply.

They may suit:

Hand basins
Small sinks
Office kitchenettes
Remote fixtures
Utility sinks
Workshops
Sheds
Small wash areas
Selected commercial hand wash points

Point-of-use sizing should be based on the exact fixture.

Before choosing a point-of-use unit, check:

Fixture type
Flow rate
Desired water temperature
Usage frequency
Power availability
Electrical circuit requirements
Water pressure
Installation space
Access for maintenance
Compliance requirements

Point-of-use instant electric can be useful, but the product still needs to match the fixture and electrical setup.

Instant electric for hand basins

A hand basin is one of the most common use cases for small instant electric hot water.

It may suit:

Bathrooms far from the main hot water system
Powder rooms
Office wash areas
Small commercial hand wash points
Workshops
Sheds
Low-demand fixtures

Before choosing a hand basin unit, check:

Tap flow rate
Required temperature
Space under the basin
Power supply
Electrical requirements
Water pressure
Whether warm hand-wash water is enough
Whether higher-temperature water is needed for the application

A small instant electric unit may suit hand washing, but it should not be assumed suitable for showers or kitchens.

Instant electric for kitchen sinks

Kitchen sinks usually need more careful sizing than hand basins.

Kitchen use may include:

Washing dishes
Rinsing cookware
Filling containers
Regular tap use
Higher flow demand
Higher temperature expectations

Before choosing instant electric for a kitchen sink, check:

Flow rate
Desired outlet temperature
Usage frequency
Electrical capacity
Space under the sink
Water pressure
Whether a small storage system may be more practical
Whether the main hot water system can be improved instead

Instant electric may suit some kitchenettes or low-use sinks, but it may not suit heavy kitchen demand.

Instant electric for kitchenettes

Kitchenettes can be a good use case for point-of-use hot water where demand is low.

This may include:

Office kitchenettes
Small studios
Staff rooms
Granny flat kitchenettes
Workshop sinks
Low-use utility areas

Before choosing a unit, check:

How often the sink is used
Whether hot water is used for washing dishes
Flow rate expectations
Electrical capacity
Cabinet space
Compliance requirements
Whether a small storage system is more suitable

A kitchenette with light hand-wash and rinse use has different needs from a full kitchen.

Instant electric for showers

Instant electric for showers needs careful assessment.

Shower use requires higher flow and comfortable temperature rise.

Before choosing instant electric for a shower, check:

Shower head flow rate
Incoming water temperature
Desired shower temperature
Required temperature rise
Electrical capacity
Switchboard capacity
Circuit requirements
Cable size
Water pressure
Whether the unit is approved and suitable for shower use
Whether a storage or heat pump system would be better

Do not assume any instant electric unit can run a shower.

A shower-capable instant electric system may require much more electrical capacity than a small hand basin unit.

Instant electric for whole-home hot water

Whole-home instant electric hot water should be assessed very carefully.

It may not be suitable for many homes because whole-home demand can be high.

Before considering whole-home instant electric, check:

Number of bathrooms
Number of showers
Whether showers run at the same time
Shower flow rates
Bath use
Kitchen use
Laundry use
Electrical capacity
Switchboard capacity
Circuit requirements
Water pressure
Temperature rise
Installer advice

For many full-home replacements, Electric Hot Water Systems or Heat Pump Hot Water Systems may be more practical.

Instant electric for granny flats

Instant electric may suit some granny flats, but only where demand is low and electrical capacity supports the system.

Before choosing instant electric for a granny flat, check:

Number of occupants
Number of fixtures
Shower use
Kitchen use
Laundry use
Electrical supply
Switchboard capacity
Water pressure
Pipework route
Whether storage hot water is more suitable
Whether heat pump hot water is practical

A granny flat with one basin is very different from a self-contained dwelling with a shower and kitchen.

Instant electric for sheds and workshops

Instant electric may suit sheds and workshops where hot water demand is limited.

It may be considered for:

Hand washing
Utility sinks
Small wash stations
Light-use kitchenettes
Remote fixtures

Before ordering, check:

Electrical supply to the shed
Available circuit capacity
Water pressure
Fixture type
Installation location
Weather protection
Usage frequency
Compliance requirements

Many sheds have limited electrical capacity, so this should be checked early.

Instant electric for commercial hand wash

Some small commercial or workplace applications may consider instant electric hot water for hand washing.

This may include:

Staff bathrooms
Office wash points
Utility areas
Small treatment rooms where suitable
Light commercial hand wash fixtures

Before choosing a system, check:

Compliance requirements
Required temperature
Usage frequency
Fixture flow rate
Electrical capacity
Installation space
Maintenance access
Whether a commercial-grade solution is needed

Commercial applications should be assessed properly before ordering.

Instant electric vs electric storage sizing

Instant electric and electric storage systems are sized differently.

Instant Electric Systems are sized by flow rate, temperature rise and electrical capacity.

Electric Hot Water Systems are usually sized by tank capacity in litres.

Electric storage may suit:

Whole-home hot water
Families
Rentals
Units and townhouses
Homes wanting stored hot water
Simple like-for-like replacement

Instant electric may suit:

Point-of-use applications
Small fixtures
Low-demand spaces
Remote sinks
Compact areas where electrical supply supports it

For many homes, electric storage is more practical than whole-home instant electric.

Instant electric vs heat pump sizing

Instant electric and heat pump hot water are both electric, but they work differently.

Heat Pump Hot Water Systems store hot water in a tank and use electricity to transfer heat from surrounding air into the water.

Instant electric heats water as it flows through the unit.

Heat pump may suit:

Whole-home hot water
Families
Homes replacing electric storage
Rooftop solar homes
Customers wanting efficient electric hot water
Properties with suitable outdoor airflow and drainage

Instant electric may suit:

Hand basins
Small sinks
Low-demand fixtures
Compact point-of-use applications
Selected small spaces where electrical capacity suits

If the goal is whole-home efficient electric hot water, heat pump hot water may be worth comparing where the site suits.

Instant electric vs instant gas sizing

Instant electric and instant gas both heat water on demand, but they use different energy sources.

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

Instant electric may suit homes or fixtures without gas where electrical capacity supports the application.

Instant gas sizing depends on:

Flow rate
Natural gas or LPG
Gas pipe sizing
Water pressure
Power point availability
Household demand

Instant electric sizing depends on:

Flow rate
Temperature rise
Electrical capacity
Circuit requirements
Switchboard capacity
Fixture demand

For whole-home hot water, instant gas is often more commonly compared than instant electric, but only where gas supply suits.

Instant electric vs gas storage sizing

Gas storage and instant electric solve different problems.

Gas Hot Water Systems may suit homes already using natural gas or LPG and wanting stored hot water.

Instant electric may suit selected point-of-use electric applications.

Gas storage sizing depends on:

Tank capacity
Gas type
Recovery
Household demand
Existing gas setup

Instant electric sizing depends on:

Fixture flow
Temperature rise
Electrical capacity
Installation location

Natural gas and LPG are not interchangeable. Gas work must be completed by a licensed gas fitter.

Instant electric for 1 person

A one-person home may use instant electric in selected situations.

It may suit:

A hand basin
A remote sink
A kitchenette
A small low-use area
A compact space without gas

For whole-home hot water, one person may still be better served by:

Small electric storage
Suitable heat pump hot water
Existing gas hot water where already installed
Another system type confirmed by a licensed installer

Do not choose instant electric for the whole home unless the electrical and flow requirements are confirmed.

Instant electric for 2 people

A two-person household may use instant electric for selected fixtures, but whole-home use needs careful checks.

Before choosing instant electric for a two-person home, check:

Shower use
Kitchen use
Number of outlets
Whether more than one outlet runs at once
Electrical capacity
Switchboard capacity
Water pressure
Whether electric storage or heat pump hot water is more practical

Instant electric may suit a point-of-use fixture, but it may not be the best whole-home system.

Instant electric for families

Families usually have higher hot water demand.

Instant electric may suit:

A remote hand basin
A kitchenette
A workshop sink
A small additional fixture
Selected low-demand point-of-use needs

For family whole-home hot water, compare:

A family home should not rely on instant electric unless the system is properly assessed for demand and electrical capacity.

Instant electric for one bathroom

One-bathroom homes may still need careful assessment.

Check:

Shower flow rate
Number of people
Bath use
Kitchen hot water use
Laundry use
Electrical capacity
Whether a storage system is more suitable
Whether heat pump hot water is practical
Whether gas is available

A one-bathroom home does not automatically suit instant electric.

Instant electric for two bathrooms

Two-bathroom homes are usually more demanding.

Before considering instant electric, check:

Whether two showers run at once
Shower flow rates
Number of people
Electrical capacity
Switchboard capacity
Multiple circuit requirements
Water pressure
Temperature rise
Whether storage or gas options are more practical

For many two-bathroom homes, instant electric may not be the best whole-home pathway.

Instant electric for homes with baths

Baths usually need a significant volume of hot water.

Before choosing instant electric for a home with a bath, check:

Bath size
Fill rate expectations
Desired temperature
Electrical capacity
Flow rate
Whether the unit can meet demand
Whether storage hot water is more practical
Whether heat pump hot water is suitable

Homes with baths often suit stored hot water better than small instant electric systems.

Instant electric for high-flow fixtures

High-flow fixtures can quickly exceed the practical capacity of smaller instant electric systems.

Before choosing a unit, check:

Fixture flow rate
Water pressure
Temperature rise
Electrical capacity
Whether flow restriction is needed
Whether the fixture demand is realistic
Whether a storage system is more suitable

A higher-flow fixture may require a system with much higher electrical demand.

Instant electric and incoming water temperature

Incoming water temperature affects instant electric performance.

Cooler incoming water needs more heating to reach the same outlet temperature.

This matters for:

Shower use
Kitchen use
Winter performance
Higher-flow fixtures
Homes in cooler climates
Systems expected to supply multiple outlets

A unit that performs acceptably in one location may not perform the same in another.

Instant electric and switchboard capacity

Switchboard capacity can determine whether instant electric is practical.

Before ordering, check:

Existing switchboard age
Available capacity
Existing electrical loads
Spare circuit space
Safety switch requirements
Metering setup
Cable routes
Whether upgrades are needed

A small wall-mounted unit can still require major electrical work.

Instant electric and circuit requirements

Instant electric systems often require dedicated electrical circuits.

Before choosing a system, confirm:

Required circuit size
Cable size
Isolation requirements
Safety switch requirements
Distance from switchboard
Whether a new circuit is needed
Whether the existing circuit can be reused
Whether the installation location is practical

Electrical requirements should be confirmed by a licensed electrician.

Instant electric and water pressure

Water pressure affects instant electric performance.

Issues can include:

Unit not activating properly
Reduced flow
Inconsistent temperature
Poor shower performance
Poor user experience
Incorrect sizing assumptions

If water pressure is poor, diagnose it before ordering an instant electric system.

Instant electric and pipe length

One benefit of point-of-use instant electric is that it can reduce the wait time caused by long pipe runs from a distant main hot water system.

This may help where:

A basin is far from the main hot water system
A kitchenette is remote
A shed or workshop needs limited hot water
A small fixture is added during renovation

However, the electrical and plumbing requirements still need to be checked.

Instant electric and renovations

A renovation is a good time to decide whether instant electric makes sense.

It may suit:

A new powder room basin
A remote vanity
A compact kitchenette
A utility sink
A workshop area
A low-use hand wash point

Before rough-in, confirm:

Fixture demand
Power supply
Circuit route
Switchboard capacity
Pipework route
Cabinet space
Access for servicing
Compliance requirements

Do not leave instant electric selection until after cabinetry and electrical locations are fixed.

Instant electric for units and townhouses

Units and townhouses may have limited space, but instant electric still needs proper assessment.

Before choosing, check:

Body corporate or strata rules
Existing hot water system type
Electrical capacity
Switchboard location
Cabinet space
Water pressure
Drainage
Access
Whether a storage system is more practical
Whether gas is available

Compact does not always mean suitable.

Instant electric for rentals

Rental properties need reliable hot water that suits likely occupancy.

Instant electric may suit a rental for:

A remote hand basin
A small kitchenette
A low-use wash point
Selected point-of-use applications

For whole-home rental hot water, compare storage, heat pump or gas options where suitable.

Before choosing instant electric for a rental, check:

Likely tenant use
Fixture demand
Electrical capacity
Maintenance access
User simplicity
Warranty terms
Total replacement pathway

A rental system should be easy for tenants to use and hard to misuse.

Instant electric for Airbnb and short-stay homes

Short-stay properties can have unpredictable demand.

Instant electric may suit:

A small hand basin
A kitchenette
A remote fixture
A low-use utility area

For showers or whole-home use, be careful.

Check:

Maximum guest count
Number of showers
Bath use
Guest expectations
Electrical capacity
Flow rate
Recovery alternative
Maintenance access
Simplicity

Guest complaints can occur if the system cannot meet peak use.

Instant electric brands to compare

Installed Today lists homepage-linked hot water brands customers may compare across electric, instant, gas and heat pump categories.

Brands worth comparing include:

Compare by application, flow rate, electrical requirements, warranty, dimensions and installation suitability.

Stiebel Eltron instant electric sizing

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

When sizing Stiebel Eltron instant electric options, check:

Fixture type
Flow rate
Temperature rise
Electrical capacity
Switchboard suitability
Circuit requirements
Water pressure
Installation location
Whether the product suits the intended use

Stiebel Eltron may be worth comparing where instant electric or compact electric hot water suits the application.

Rheem electric sizing

Rheem Hot Water Systems are commonly compared across electric storage, gas and heat pump hot water.

Rheem may be worth comparing where:

Whole-home electric storage is preferred
Heat pump hot water is being considered
A recognised hot water brand is preferred
Instant electric is not suitable for the demand

When sizing Rheem systems, check tank capacity, household demand, installation location, warranty and electrical setup.

Rinnai electric sizing

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

Rinnai may be worth comparing where:

The customer is comparing electric and gas pathways
Instant gas may suit the home
Electric storage or heat pump options are being considered
A recognised brand is preferred

Check the exact system type before ordering because Rinnai electric, gas and heat pump systems have different sizing and installation requirements.

Dux electric sizing

Dux Hot Water Systems are commonly compared for electric storage and broader hot water replacement.

Dux may suit:

Electric storage replacement
Whole-home stored hot water
Rentals
Family homes
Customers comparing mainstream hot water brands

Dux electric storage sizing is based on tank capacity, not instant flow rate.

Vulcan electric sizing

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

Vulcan may suit:

Budget-conscious storage replacements
Rental properties
Simple electric hot water needs
Like-for-like storage replacement where suitable

If instant electric is not suitable for the application, a storage system may be worth comparing.

Installation Add-Ons and instant electric sizing

Installation Add-Ons may be relevant where a hot water replacement needs extra selected work or components.

Add-ons may relate to:

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

The right instant electric unit still needs the right installation pathway.

Supply-only instant electric sizing checks

Supply-only ordering can suit customers who already have their own licensed plumber or electrician arranged.

Before ordering supply only, confirm:

Correct application
Correct flow rate
Correct electrical requirements
Suitable switchboard capacity
Suitable circuit pathway
Suitable water pressure
Suitable installation location
Correct product dimensions
Whether electrical work is arranged
Whether plumbing work is arranged
Whether old unit removal is arranged
Whether disposal is required

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

Supplied-and-installed instant electric 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
Application
Product suitability
Installation inclusions
Electrical work
Switchboard requirements
Circuit requirements
Plumbing changes
Valve requirements
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: sizing instant electric like a storage tank

Instant electric systems are not sized by stored litres.

They are sized by flow rate, temperature rise and electrical capacity.

Common mistake: choosing instant electric because it is compact

A compact unit can still require significant electrical work.

Always check switchboard capacity and circuit requirements before ordering.

Common mistake: assuming instant electric suits every shower

Not every instant electric system is suitable for shower use.

Shower demand must be assessed carefully.

Common mistake: using point-of-use logic for whole-home hot water

A unit that suits a hand basin may not suit a bathroom, kitchen or whole home.

Match the system to the application.

Common mistake: ignoring temperature rise

Temperature rise affects how much hot water the unit can deliver.

A system may perform differently depending on incoming water temperature and required outlet temperature.

Common mistake: ignoring water pressure

Poor water pressure can affect activation, flow and user experience.

Check pressure issues before selecting a system.

Common mistake: ignoring electrical upgrade costs

Electrical work can change the total cost significantly.

The product price is not the full project cost.

Common mistake: choosing instant electric when storage or heat pump is better

Instant electric may be useful for small point-of-use needs, but whole-home hot water may be better served by electric storage, heat pump or gas where suitable.

Common mistake: DIY instant electric installation

Instant electric installation can involve plumbing, electrical work, pressure control, scalding safety and compliance.

DIY installation can create:

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

Use licensed professionals for installation and technical checks.

Final verdict: what size instant electric hot water system should you choose?

Choose a small point-of-use instant electric system for low-demand hand basins, small sinks, remote fixtures or kitchenettes where the electrical and plumbing setup suits.

Choose a larger instant electric option only where the required flow rate, temperature rise, electrical capacity, switchboard capacity and water pressure have been confirmed.

Be very cautious with instant electric for showers or whole-home hot water. In many homes, Electric Hot Water Systems, Heat Pump Hot Water Systems, Gas Hot Water Systems or Instant Gas Hot Water Systems may be better suited depending on the property.

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

The best instant electric size is not the smallest, largest or cheapest model. It is the system that matches the exact fixture, flow rate, temperature rise, electrical setup, water pressure and long-term hot water need.

Long-tail FAQs

What size instant electric hot water system do I need?

The right size depends on the fixture, flow rate, temperature rise, water pressure, electrical capacity, switchboard capacity and whether the unit is point-of-use, shower-only or whole-home.

Is instant electric good for a hand basin?

Instant electric can suit some hand basins and point-of-use applications where flow demand is low and electrical supply supports the unit.

Is instant electric good for a kitchen sink?

It can suit some low-use kitchenettes or small sinks, but full kitchen demand may need careful sizing or a different hot water system.

Can instant electric run a shower?

Some systems may suit shower applications, but shower use needs careful flow rate, temperature rise and electrical checks before ordering.

Can instant electric run a whole house?

Whole-home instant electric can be difficult because electrical demand can be high. Electric storage, heat pump or gas options may be more practical for many homes.

Does instant electric need special wiring?

Many instant electric systems require dedicated circuits or specific electrical capacity. A licensed electrician should confirm requirements before ordering.

Is instant electric cheaper than electric storage?

Not always. The product may be compact, but electrical work, switchboard upgrades and installation requirements can affect total cost.

Is instant electric better than heat pump hot water?

Instant electric may suit point-of-use applications. Heat pump hot water may be better for whole-home efficient electric hot water where the property has suitable airflow, drainage and space.

Is instant electric better than instant gas?

It depends on the property. Instant electric may suit small fixtures without gas. Instant gas may suit whole-home continuous flow where natural gas or LPG supply supports it.

Can I install instant electric hot water myself?

No. Instant electric installation should be completed by licensed professionals. Plumbing, electrical work and compliance requirements can create safety, warranty and insurance issues if handled incorrectly.

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