Best Hot Water System for a Granny Flat

Jun 6, 2026

Choosing the best hot water system for a granny flat depends on the number of occupants, bathroom layout, kitchen use, laundry use, available space, energy source and whether the granny flat will share services with the main home. A granny flat usually has lower hot water demand than a full-sized family home, but the system still needs to be correctly sized and suitable for the property.

At Hot Water Outlet, you can compare hot water systems online, including electric hot water systems, heat pump hot water systems, gas hot water systems, instant gas hot water systems, instant electric hot water systems and common valves, pipework and fittings.

Quick Answer: What Is the Best Hot Water System for a Granny Flat?

The best hot water system for a granny flat is usually a compact electric storage system, a suitable instant gas unit where gas is available, or a point-of-use instant electric system for very specific applications. The right choice depends on the granny flat’s layout, number of occupants, available space and energy source.

As a general guide:

Choose an electric hot water system if the granny flat needs a simple tank-style hot water system and has suitable electrical supply and space.
Choose a heat pump hot water system if the granny flat has enough outdoor space, airflow and hot water demand to justify an efficient electric storage option.
Choose a gas hot water system if the property already has natural gas or LPG and a small gas storage system suits the layout.
Choose an instant gas hot water system if natural gas or LPG is available and a compact continuous flow system suits the granny flat.
Choose an instant electric hot water system only where the electrical requirements and intended point-of-use demand match the product.

For most granny flats, the best starting point is to work out whether the dwelling needs its own independent hot water system or whether it will share hot water from the main house.

Does a Granny Flat Need Its Own Hot Water System?

A granny flat may need its own hot water system if it has a separate bathroom, kitchen, laundry or independent living area. In many cases, a dedicated system is more practical than running hot water long distances from the main home.

A separate hot water system may be worth comparing when:

The granny flat is detached from the main house
The bathroom or kitchen is far from the main hot water system
The granny flat will be rented or used independently
The main house hot water system is already close to capacity
Separate metering or service separation is preferred
Long pipe runs would cause delays or heat loss
The main system is old or undersized
A compact system can be placed close to the granny flat fixtures

Sharing the main house system may work in some layouts, but it needs to be assessed carefully. If the main system is already sized for the main home only, adding a granny flat may create hot water performance issues.

Hot Water System Options for Granny Flats

System Type	Good For	Main Benefit	Main Thing to Check
Electric storage	Simple independent granny flat hot water	Familiar tank-style option	Tank size, space and power requirements
Heat pump	Efficient electric storage where demand and space suit	Energy-efficient option	Outdoor space, airflow, noise and tank size
Gas storage	Properties already using gas	Traditional gas tank option	Natural gas or LPG, tank size and recovery
Instant gas	Granny flats with gas access	Compact continuous flow hot water	Flow rate in L/min and correct gas type
Instant electric	Specific point-of-use applications	Compact local hot water where suitable	Electrical requirements and intended use

The best system depends on the granny flat’s layout, services, access and daily hot water needs.

What Size Hot Water System Does a Granny Flat Need?

The right size depends on how the granny flat will be used.

A granny flat used by one person may need much less hot water than a two-bedroom secondary dwelling used by a couple or small family. A granny flat with a bathroom only may need a different setup from one with a bathroom, kitchen and laundry.

When sizing a granny flat hot water system, consider:

Number of occupants
Number of bathrooms
Shower frequency
Shower length
Bath use if included
Kitchen sink use
Dishwasher use where relevant
Laundry use
Whether hot water is used in multiple areas at once
Whether the unit is occupied full-time or occasionally
Available space
Distance from fixtures
Energy source
Product dimensions
Required valves and fittings

Storage hot water systems are measured by tank capacity in litres. Instant gas systems are measured by flow rate in L/min. Instant electric systems are selected by intended use, flow demand and electrical requirements.

Best Electric Hot Water System for a Granny Flat

An electric hot water system is often a practical option for granny flats because electricity is commonly available and storage tanks come in a range of sizes.

Electric storage may suit a granny flat when:

The granny flat needs its own independent system
Natural gas or LPG is not available
A simple tank-style system is preferred
There is suitable space for a compact tank
Daily hot water demand is moderate
The electrical supply suits the selected product
A like-for-like electric replacement is needed

Electric storage systems are usually compared by tank capacity, recovery rate, pressure rating, dimensions, connection positions and power requirements.

For a granny flat, the key is not choosing a system that is too large or too small. A compact tank may suit one person, but a larger system may be needed if the granny flat has two occupants, a full kitchen and laundry use.

Electric Hot Water for Granny Flats: What to Check

Before choosing electric storage, check:

Number of occupants
Bathroom layout
Kitchen and laundry use
Available tank location
Tank capacity
Recovery rate
Power requirements
Product dimensions
Connection positions
Indoor or outdoor suitability
Delivery access
Required valves and fittings

An electric storage system can be a straightforward choice, but it still needs to suit the actual demand of the granny flat.

Best Heat Pump Hot Water System for a Granny Flat

A heat pump hot water system may suit some granny flats, especially where the dwelling has regular daily hot water use and enough outdoor space.

Heat pump hot water may suit a granny flat when:

An efficient electric storage option is preferred
Outdoor space is available
Airflow is suitable
Noise can be managed
The tank size suits the occupants
The granny flat is occupied regularly
The system location can be planned properly

Heat pumps need more space and airflow than many standard electric storage systems. For a small granny flat, a heat pump may not always be the most practical option, especially if hot water demand is low or outdoor space is limited.

However, for a larger or regularly occupied secondary dwelling, a heat pump may be worth comparing.

Heat Pump Hot Water for Granny Flats: What to Check

Before choosing a heat pump, check:

Outdoor location
Airflow around the unit
Noise rating
Distance from bedrooms, windows and neighbours
Tank capacity
Household demand
Product dimensions
Electrical requirements
Connection positions
Delivery access
Required valves and fittings

A heat pump should be chosen by suitability, not just energy efficiency. The granny flat must have the right space and usage pattern.

Best Gas Hot Water System for a Granny Flat

A gas hot water system may suit a granny flat if the property already has natural gas or LPG available and a gas storage system is preferred.

Gas storage may suit a granny flat when:

Natural gas or LPG is already available
A small gas storage system suits the layout
A traditional tank-style system is preferred
The selected tank size suits demand
The recovery rate is suitable
The system location works for the dwelling

Gas hot water systems are usually compared by tank capacity, recovery rate, gas type, pressure rating, dimensions and connection positions.

For granny flats, gas type is essential. Natural gas and LPG systems are not interchangeable.

Gas Hot Water for Granny Flats: What to Check

Before choosing gas storage, check:

Natural gas or LPG
Existing gas availability
Tank capacity
Recovery rate
Number of occupants
Bathroom and kitchen demand
Product dimensions
Connection positions
Indoor or outdoor suitability
Required valves and fittings

If the property does not already have gas near the granny flat, compare electric options as well, because extending gas services may require extra planning.

Best Instant Gas Hot Water System for a Granny Flat

An instant gas hot water system can be a strong option for granny flats where natural gas or LPG is available and a compact wall-mounted system is preferred.

Instant gas, also called continuous flow gas hot water, heats water as it passes through the unit instead of storing it in a tank.

Instant gas may suit a granny flat when:

Natural gas or LPG is available
A compact external wall-mounted unit is preferred
A large storage tank is not ideal
The selected flow rate suits the number of fixtures
The correct gas type is chosen
The granny flat has regular shower and kitchen use
A suitable external location is available

Instant gas systems are usually compared by flow rate in L/min. For many granny flats, a lower to medium flow rate may be suitable, but this depends on the number of fixtures and how the dwelling is used.

Instant Gas Hot Water for Granny Flats: What to Check

Before choosing instant gas, check:

Natural gas or LPG
Required flow rate in L/min
Number of bathrooms
Shower demand
Kitchen use
Laundry use
Whether outlets may run at the same time
Controller compatibility
Outdoor wall location
Product dimensions
Connection positions
Gas supply suitability
Required valves and fittings

A compact instant gas unit may be a good fit for some granny flats, but only where gas type, gas supply and flow rate are suitable.

Best Instant Electric Hot Water System for a Granny Flat

An instant electric hot water system may suit specific granny flat applications, especially where a small point-of-use hot water supply is needed.

Instant electric may suit:

A compact kitchenette
A hand basin
A small point-of-use application
A remote fixture where storage is not practical
A low-flow application where the electrical requirements match

Instant electric systems should be selected carefully. They are not automatically suitable for a full bathroom, kitchen and laundry setup. Electrical requirements can vary, and the product must match the intended use.

Instant Electric Hot Water for Granny Flats: What to Check

Before choosing instant electric, check:

Intended use
Number of fixtures
Flow demand
Electrical requirements
Product suitability
Connection requirements
Product dimensions
Warranty information
Whether the unit is for point-of-use or broader demand

A small instant electric system can be useful in the right application, but it should not be chosen as a whole-granny-flat solution unless the product is suitable.

Independent Hot Water vs Shared Hot Water From the Main House

One of the biggest decisions for a granny flat is whether to install a dedicated hot water system or share the main house system.

Independent Hot Water System

An independent system may be better when:

The granny flat is detached
The fixtures are far from the main hot water unit
Separate use is preferred
The main house system is already near capacity
The granny flat may be rented
Hot water delay from long pipe runs would be inconvenient
The granny flat has its own kitchen, bathroom and laundry

A dedicated system can allow the granny flat to be sized properly for its own use.

Shared Main House Hot Water

Sharing the main house hot water system may be possible when:

The granny flat is attached or very close
Pipe runs are short
The main system has enough capacity
Occupancy is light or occasional
The layout allows practical connection
Licensed tradespeople confirm suitability

Sharing may sound simpler, but it can create performance issues if the main system is not sized for the extra demand.

Best Hot Water System for a One-Person Granny Flat

A one-person granny flat usually has lower hot water demand, especially if there is one bathroom and a small kitchenette.

For one occupant, compare:

Compact electric storage systems
Instant gas where gas is already available
Instant electric for suitable point-of-use applications
Small heat pump options only where space and demand suit

The best option depends on whether the granny flat is occupied full-time, how often the shower is used and whether the kitchen or laundry needs regular hot water.

Best Hot Water System for a Two-Person Granny Flat

A two-person granny flat may need more capacity than a one-person setup, especially if both occupants shower daily or use the kitchen and laundry regularly.

For two occupants, compare:

Small to medium electric storage
Suitable heat pump systems where space allows
Gas storage where gas is available
Instant gas with a flow rate matched to demand

If two people shower back-to-back, tank capacity or flow rate becomes more important. Do not choose the smallest system automatically.

Best Hot Water System for a Granny Flat With One Bathroom

Most granny flats have one bathroom, so shower demand is often the main sizing factor.

For one-bathroom granny flats, compare:

Electric storage tank size
Instant gas flow rate
Heat pump tank capacity where suitable
Kitchen and laundry demand
Whether hot water is used in more than one place at once

If the granny flat has a shower only, demand may be lower. If it has a bath, larger storage or stronger system performance may be needed.

Best Hot Water System for a Granny Flat With a Kitchen

A granny flat with a kitchen needs hot water for more than showers. Kitchen sink use, cleaning and dishwasher connections can affect demand.

For granny flats with kitchens, check:

Kitchen sink hot water use
Dishwasher connection requirements where relevant
Distance from the hot water system to the kitchen
Whether kitchen and bathroom hot water may be used at the same time
Pipework and fittings
System location

A system placed closer to the granny flat fixtures may reduce hot water delay compared with sharing a distant main-house system.

Best Hot Water System for a Granny Flat With Laundry

A granny flat with its own laundry may need more hot water than a bathroom-only setup.

For granny flats with laundry, consider:

Washing machine hot water use
Laundry tub use
Shower demand
Whether laundry and bathroom use may overlap
Tank size or flow rate
Pipework requirements
Available space

A compact system may still be suitable, but laundry use should be included in the sizing decision.

Best Hot Water System for a Detached Granny Flat

A detached granny flat often benefits from a dedicated hot water system because it may be too far from the main house system for practical shared hot water.

For detached granny flats, compare:

Dedicated electric storage
Instant gas where gas is available
Heat pump where space and airflow suit
Instant electric for specific point-of-use needs
Pipework distance
Delivery access
Location near bathroom, kitchen and laundry fixtures

A dedicated system can help avoid long hot water wait times and reduce reliance on the main house unit.

Best Hot Water System for an Attached Granny Flat

An attached granny flat may be able to share hot water with the main house in some layouts, but this depends on distance, pipework and main system capacity.

For attached granny flats, compare:

Whether the main system has enough capacity
Distance to fixtures
Hot water delay
Whether a dedicated compact system would be better
Available space for a separate unit
Energy source
Plumbing layout

Even when attached, a separate system may still be worth comparing if the main house hot water system is already heavily used.

Best Hot Water System for a Granny Flat Rental

If the granny flat will be rented, hot water reliability and correct sizing become especially important.

For rental granny flats, compare:

Independent hot water system options
Expected number of occupants
Bathroom, kitchen and laundry demand
Electric or gas availability
Warranty information
Product availability
Required valves and fittings
Delivery access

A separate hot water system may also make the dwelling easier to manage, depending on the property setup and local requirements.

Best Hot Water System for a Granny Flat Renovation

If you are converting a shed, garage or existing space into a granny flat, hot water planning should happen early.

For granny flat renovations, consider:

Future bathroom location
Kitchenette location
Laundry location
Distance from existing services
Whether the main system will be shared
Whether the granny flat needs a dedicated system
Available electrical supply
Gas availability
Space for a tank or wall-mounted unit
Required valves, pipework and fittings

Planning early can help avoid choosing a system that is difficult to place or poorly matched to the final layout.

Best Hot Water System for a Granny Flat on a Budget

If budget is important, compare systems that suit the property first, then choose the most affordable suitable option.

Budget-friendly tips:

Start with the available energy source
Avoid oversizing the system
Do not undersize the system
Compare compact electric storage options
Compare instant gas only if gas is available
Use instant electric only where the application suits
Check required valves and fittings
Check delivery costs
Confirm licensed trade costs separately

The cheapest system is only good value if it suits the granny flat’s actual use.

Best Hot Water Brands for Granny Flats

Hot Water Outlet lists recognised hot water brands across electric, gas, heat pump and instant gas categories.

Depending on the system type, you may want to compare:

Brand can help narrow the search, but the final decision should be based on system type, size, gas type, dimensions, energy source, warranty information and granny flat suitability.

Valves, Fittings and Accessories for Granny Flat Hot Water Systems

A granny flat hot water system may need valves, fittings, pipework or connection accessories as well as the main unit.

Common items include:

Tempering valves
Pressure relief valves
Duo valves
Non-return valves
Isolation valves
Copper pipework
Fittings
Controller accessories
Thermostats
Elements
Connection parts

Hot Water Outlet has a dedicated range of valves, pipework and fittings to help customers compare common hot water accessories.

Always confirm compatibility before ordering.

Common Mistakes When Choosing Hot Water for a Granny Flat

Sharing the Main System Without Checking Capacity

The main house hot water system may not be sized for an extra dwelling. Adding a granny flat can create performance issues.

Choosing the Smallest System Automatically

A granny flat may be small, but it still needs enough hot water for showers, kitchen use and laundry use where relevant.

Ignoring Pipe Run Distance

Long pipe runs from the main house can create hot water delays and may not be practical.

Choosing Instant Electric Without Checking Electrical Requirements

Instant electric systems can have specific electrical requirements and are not always suitable for whole-dwelling demand.

Choosing Gas Without Confirming Gas Type

Natural gas and LPG systems are not interchangeable. Always confirm the correct gas type.

Choosing Heat Pump Without Checking Airflow

Heat pumps need outdoor space, airflow and noise consideration. They may not suit every granny flat.

Forgetting Valves and Fittings

The main hot water system may not be the full order. Valves, pipework and fittings may also be required.

Assuming DIY Is Suitable

Hot water systems involve plumbing, gas and electrical work. These tasks should be completed by licensed tradespeople.

Granny Flat Hot Water Buyer Checklist

Before ordering a hot water system for a granny flat, check:

Whether the system will be dedicated or shared
Number of occupants
Number of bathrooms
Shower demand
Bath use
Kitchen hot water use
Laundry hot water use
Whether fixtures may be used at the same time
Available energy source
Electricity, natural gas or LPG
Available system location
Distance from fixtures
Tank capacity if storage
Flow rate in L/min if instant gas
Electrical requirements if instant electric
Heat pump airflow if relevant
Heat pump noise rating if relevant
Gas type if choosing gas
Product dimensions
Connection positions
Required valves and fittings
Delivery access
Warranty information
Product specifications

Compare Hot Water Systems for Granny Flats Online

Hot Water Outlet makes it easier to compare hot water systems for granny flats by type, brand, size, energy source and product specifications.

Start with:

FAQs About Hot Water Systems for Granny Flats

What is the best hot water system for a granny flat?

The best hot water system for a granny flat depends on the number of occupants, bathroom and kitchen layout, available space and energy source. Compact electric storage, instant gas, suitable heat pump and point-of-use instant electric options may all suit different granny flats.

Does a granny flat need its own hot water system?

A granny flat may need its own hot water system if it is detached, has its own bathroom and kitchen, is far from the main house system, or will be used independently. Sharing the main system may work in some layouts, but capacity and pipe distance need to be checked.

What size hot water system does a granny flat need?

The right size depends on occupants, showers, kitchen use, laundry use and whether the system is storage or instant. Storage systems are measured in litres, while instant gas systems are measured by flow rate in L/min.

Is electric hot water good for a granny flat?

Electric storage hot water can be a practical choice for granny flats because it is familiar, available in compact sizes and does not require gas. The tank size, power requirements and available space need to suit the dwelling.

Is instant gas hot water good for a granny flat?

Instant gas can suit granny flats where natural gas or LPG is available and a compact continuous flow system is preferred. The flow rate and gas type must match the property.

Is instant electric hot water good for a granny flat?

Instant electric hot water may suit specific point-of-use applications, but it is not automatically suitable for a full granny flat with bathroom, kitchen and laundry demand. Check the intended use and electrical requirements carefully.

Is a heat pump suitable for a granny flat?

A heat pump may suit a granny flat with regular hot water use, suitable outdoor space, airflow and noise conditions. It may not be practical for very small or low-demand setups.

Can a granny flat share hot water with the main house?

A granny flat may be able to share hot water with the main house if the system has enough capacity and the pipe run is practical. If the granny flat is detached or far away, a dedicated system may be better.

Do granny flat hot water systems need valves and fittings?

Some granny flat hot water systems require valves, pipework or fittings depending on the system type, pressure rating and connection layout. Browse valves, pipework and fittings and confirm compatibility before ordering.

Can I install a granny flat hot water system myself?

No. Hot water systems involve plumbing, gas and electrical work that should be completed by appropriately licensed tradespeople. Hot Water Outlet sells supply-only hot water systems and accessories online, and may help organise quotes from reputable installers where appropriate.

Find the Best Hot Water System for Your Granny Flat

The best hot water system for a granny flat is the one that suits the dwelling’s layout, occupants, energy source, available space and hot water demand. Before ordering, compare tank capacity, flow rate, gas type, electrical requirements, dimensions, connection positions, warranty information and required accessories.

Browse hot water systems online with Hot Water Outlet to compare electric, heat pump, gas, instant gas, instant electric and hot water accessories by brand, size and product specifications.

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