Best Hot Water System for Dual Occupancy Homes

Choosing the best hot water system for a dual occupancy home depends on whether the dwellings share one hot water system or need separate systems. A duplex, granny flat setup, secondary dwelling, dual-key property or two-family home can have very different hot water needs. At Hot Water Outlet, you can compare supply-only hot water systems online, including electric hot water systems, gas hot water systems, instant gas hot water systems, heat pump hot water systems and compatible valves, pipework and fittings.

Quick Answer

For most dual occupancy homes, the best hot water system is usually either:

• One correctly sized shared system, if both dwellings are designed to run from one unit

• Two separate hot water systems, if each dwelling needs independent control, billing, servicing and reliability

For simple electric setups, separate electric hot water systems may suit each dwelling.

For properties with natural gas or LPG, separate or shared instant gas hot water systems may suit, provided the gas supply, pipe sizing, location and flow rate are correct.

For energy-conscious properties with suitable outdoor space, heat pump hot water systems may be worth comparing, especially where each dwelling has enough space, airflow, drainage and electrical capacity.

The main decision is not just electric vs gas vs heat pump. It is whether the property should use one system or separate systems.

Best Hot Water Options for Dual Occupancy Homes

What Counts as a Dual Occupancy Home?

A dual occupancy home can include several property layouts, such as:

• Duplex

• Granny flat plus main house

• Secondary dwelling

• Dual-key property

• Two homes on one lot

• Converted home with separate living areas

• Rental property with two separate households

• Multi-generational home with separate zones

The best hot water setup depends on how independent the dwellings are. A main house and granny flat may need separate systems, while a family home with a self-contained downstairs area may be fine with one larger system.

Shared System vs Separate Systems

This is the most important question for dual occupancy homes.

One Shared Hot Water System May Suit When

• Both dwellings are part of one household

• Hot water use is predictable

• The existing plumbing already runs from one system

• Billing does not need to be separated

• The system can be sized for total demand

• Pipe runs are not too long

• A single point of maintenance is preferred

Separate Hot Water Systems May Suit When

• Each dwelling is rented separately

• Each household wants independent use

• Billing needs to be separated

• One dwelling should not affect the other

• The property has two kitchens or two laundries

• The dwellings are far apart

• The occupants have different hot water habits

• Access for servicing should be independent

For rental-style dual occupancy homes, separate systems are often easier to manage because one tenant’s hot water use does not affect the other.

Key Buyer Checks Before Ordering Online

Before buying a supply-only hot water system for a dual occupancy home, check:

• Whether the dwellings share plumbing

• Whether one or two systems are needed

• Number of people in each dwelling

• Number of bathrooms

• Number of kitchens

• Number of laundries

• Whether showers may run at the same time

• Existing system type

• Existing tank size or gas flow rate

• Natural gas or LPG if applicable

• Electrical supply

• Switchboard capacity

• Outdoor airflow if considering heat pump

• Drainage options

• Noise placement

• Pipe run distances

• Metering and billing needs

• Access for delivery and future servicing

• Required valves and fittings

Supply-only pricing usually does not include installation, plumbing labour, electrical work, gas fitting, old unit removal, disposal, valves, fittings, pipework changes, drainage work, switchboard upgrades, gas upgrades, regulator changes, LPG bottle work, controller wiring, compliance upgrades, concrete bases, platforms or delivery beyond what is shown at checkout.

Plumbing, gas fitting and electrical work must be completed by appropriately licensed tradespeople.

Electric Hot Water Systems for Dual Occupancy Homes

Electric hot water systems are a common option for dual occupancy homes, especially where gas is not available or where each dwelling needs a simple independent hot water supply.

Electric storage can be suitable for duplexes, granny flats and secondary dwellings because it is familiar, available in many sizes and can be matched to each household’s demand.

Electric Storage May Suit When

• The property already has electric storage

• There is no gas connection

• Each dwelling needs a separate system

• The electrical supply is suitable

• Noise needs to be minimal

• A straightforward replacement is preferred

• The system location has enough space

Electric Storage Buyer Checks

Check:

• Tank capacity

• Element size

• Recovery rate

• Indoor or outdoor rating

• Connection locations

• Physical dimensions

• Electrical supply

• Switchboard capacity

• Safe tray requirements

• Tempering valve requirements

• Drainage and discharge points

For a dual occupancy property, one large electric tank may not always be better than two smaller systems. If both dwellings use hot water at the same time, a shared tank can run out quickly unless it is sized correctly.

Heat Pump Hot Water Systems for Dual Occupancy Homes

Heat pump hot water systems may suit dual occupancy homes where energy efficiency is important and the site has suitable outdoor space.

Heat pumps are often compared when replacing electric storage, especially in homes with solar power or higher regular hot water use.

Brands commonly compared include iStore hot water systems, Stiebel Eltron hot water systems, Envirosun hot water systems and Emerald Energy.

Heat Pumps May Suit When

• There is suitable outdoor airflow

• Condensate drainage can be managed

• Noise placement is acceptable

• Each dwelling has enough space for its own system

• A shared system has enough capacity for both dwellings

• The electrical setup is suitable

• Solar power is available

• Energy efficiency is a priority

Heat Pumps May Not Suit When

• The only location is a tight cupboard

• Outdoor space is limited

• The system would be too close to bedrooms or neighbours

• Condensate drainage is difficult

• Noise could affect either dwelling

• The system cannot recover fast enough for shared demand

• Body corporate or planning rules restrict the location

Heat pump rebates, STCs and incentives can change and depend on the product, installer, property, purchase type and program rules. Do not assume a rebate applies without checking current eligibility.

Instant Gas Hot Water Systems for Dual Occupancy Homes

Instant gas hot water systems, also called continuous flow gas systems, can be useful for dual occupancy properties where natural gas or LPG is available.

Instant gas systems heat water as it is used, which can suit homes where storage space is limited or where strong recovery is needed. However, gas supply and flow rate are critical.

Common brands include Rinnai hot water systems, Bosch hot water systems and Rheem hot water systems.

Instant Gas May Suit When

• The property already has gas

• Natural gas or LPG is available

• The correct gas type is selected

• The gas pipe sizing is suitable

• Storage space is limited

• Separate systems are wanted for each dwelling

• The system location is external or correctly flued

• Flow rate suits the number of bathrooms

Natural gas and LPG are not interchangeable. A natural gas unit must not be connected to LPG unless it is specifically converted and approved by a licensed gas fitter, and an LPG unit must not be connected to natural gas unless the same applies.

External gas hot water units are outdoor/external only unless the product is specifically designed and approved for internal or flued installation.

Instant Gas Buyer Checks

Check:

• Natural gas or LPG

• Existing gas meter capacity

• LPG bottle and regulator setup if applicable

• Gas pipe sizing

• Required flow rate

• Number of bathrooms

• Whether showers may run at the same time

• Minimum flow rate

• Water pressure

• Controller compatibility

• Flue requirements

• Clearances to windows, doors and openings

• Whether one or two units are needed

For dual occupancy homes, one instant gas system may not suit both dwellings if multiple showers, kitchens or laundries run at once. Separate systems may provide better independence.

Gas Storage Hot Water Systems for Dual Occupancy Homes

Gas hot water systems may suit dual occupancy properties where gas storage already exists or where a like-for-like replacement is preferred.

Gas storage can provide stored hot water with gas recovery, but it still needs correct gas type, ventilation, flue setup and compliance checks.

Brands commonly compared for storage-style replacements include Rheem hot water systems, Dux hot water systems and Vulcan hot water systems.

Gas Storage Buyer Checks

Check:

• Natural gas or LPG

• Tank capacity

• Recovery rate

• Indoor or outdoor rating

• Flue and ventilation requirements

• Gas pipe sizing

• Safe discharge location

• Drainage

• Tempering valve requirements

• Access for servicing

Gas storage may be practical where the existing setup already uses gas storage and the replacement matches the approved location and services.

Instant Electric Hot Water Systems for Dual Occupancy Homes

Instant electric hot water systems may suit small point-of-use applications, but they are not always suitable for whole-dwelling hot water.

Instant electric systems can need significant electrical capacity, especially for showers and high-flow fixtures.

Instant Electric May Suit

• Small studios

• Kitchenettes

• Hand basins

• Small granny flats with low demand

• Point-of-use hot water

• Compact areas where storage is difficult

Instant Electric May Not Suit

• Multiple bathrooms

• Whole-home high-flow use

• Back-to-back showers

• Homes with limited electrical capacity

• Shared dual occupancy hot water demand

Before buying instant electric, confirm the required electrical supply with a licensed electrician.

One Hot Water System for Both Dwellings

A shared hot water system can work in some dual occupancy homes, but it needs to be sized carefully.

A shared system may be considered when:

• Both dwellings are occupied by one family

• There is one electricity or gas account

• Hot water usage is predictable

• Bathrooms are not used heavily at the same time

• Pipe runs are practical

• There is enough space for a larger system

• The existing plumbing is already shared

The main risk with one shared system is that one household can run down the hot water supply for the other. This is especially important with storage systems.

Shared System Buyer Checks

Check:

• Total number of people

• Total number of bathrooms

• Whether both dwellings may shower at once

• Total kitchen and laundry demand

• Pipe run length

• Heat loss through pipework

• Recovery rate

• Energy source capacity

• Access for servicing

• How billing will be handled

Separate Hot Water Systems for Each Dwelling

Separate hot water systems often make sense for dual occupancy homes where each dwelling operates independently.

Separate systems may be better when:

• The dwellings are rented separately

• Each household pays its own utilities

• One household should not affect the other

• The systems are in separate locations

• Access should be independent

• The property may be sold or managed separately later

• Demand is too high for one shared system

For example, the main house might use a larger heat pump or electric storage system, while the granny flat may use a smaller electric storage unit or compact instant gas unit if gas is already available and suitable.

What Size Hot Water System Does a Dual Occupancy Home Need?

Sizing depends on whether the systems are shared or separate.

As a guide, each dwelling should be sized based on its own number of occupants, bathrooms and usage pattern if separate systems are used.

Common Dual Occupancy Sizing Examples

Main House With 3–4 People

Common options to compare may include:

• 250L to 315L electric storage

• Suitable heat pump

• 20L to 26L instant gas if gas supply suits

Granny Flat With 1–2 People

Common options to compare may include:

• 50L to 125L electric storage

• Compact instant gas if gas already exists

• Point-of-use electric for very small applications

• Small heat pump only if location and airflow suit

Duplex With 2–4 People Per Side

Each side may need its own correctly sized system, such as:

• 125L to 250L electric storage

• Separate heat pumps where space allows

• Separate instant gas systems if gas supply and clearances suit

Large Shared Dual Occupancy

A larger shared system may need:

• Larger storage capacity

• Faster recovery

• Higher-flow gas

• Multiple units

• Site-specific design

If both dwellings have multiple bathrooms, do not guess the size. Hot water demand should be checked before ordering.

Valves and Fittings for Dual Occupancy Hot Water

Dual occupancy properties may need more careful valve and pipework planning than a standard single home.

Depending on the setup, you may need compatible valves, pipework and fittings, such as:

• Tempering valve

• Pressure limiting valve

• Duo valve

• Expansion control valve

• Isolation valves

• Non-return valves

• Relief drain materials

• Connection fittings

• Pipework changes

• Separate isolation for each dwelling

The correct parts depend on the system, property layout, water pressure, hot water temperature and local compliance requirements.

Best Brands for Dual Occupancy Hot Water Systems

The best brand depends on the system type, demand and property layout.

Rheem

Rheem hot water systems are commonly compared across electric storage, gas storage, instant gas and heat pump categories. Rheem may suit buyers wanting a broad range of common replacement sizes.

Rinnai

Rinnai hot water systems are commonly compared for instant gas and continuous flow systems, especially where natural gas or LPG is available.

Dux

Dux hot water systems are often compared for practical electric and gas storage replacements.

Bosch

Bosch hot water systems are commonly compared for instant gas applications and compact continuous flow replacements.

Vulcan

Vulcan hot water systems are often considered for budget-conscious electric and gas storage replacements.

iStore

iStore hot water systems are commonly compared in the heat pump category, especially for homes moving away from standard electric storage.

Stiebel Eltron

Stiebel Eltron hot water systems may suit buyers comparing electric, instant electric and heat pump options.

Envirosun and Emerald Energy

Envirosun hot water systems and Emerald Energy are often compared for heat pump hot water systems where outdoor space and airflow suit.

Common Mistakes When Buying Hot Water for Dual Occupancy Homes

Assuming One System Will Suit Both Dwellings

One system may work, but it must be sized for total peak demand. If both dwellings shower at the same time, a shared system can struggle.

Forgetting About Billing

If the dwellings are rented separately, separate systems may make billing and responsibility easier.

Buying the Same Size for Both Dwellings

The main house and secondary dwelling may have very different hot water demand. Each should be sized based on actual use.

Choosing Heat Pump Without Checking Location

Heat pumps need airflow, drainage and sensible noise placement. They are not suitable for tight enclosed spaces.

Buying the Wrong Gas Type

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

Using an External Gas Unit Indoors

External gas hot water units are outdoor units unless specifically designed and approved for internal or flued installation.

Ignoring Simultaneous Use

Dual occupancy homes can have two households using showers, kitchens and laundries at the same time.

Forgetting Valves and Compliance Parts

Supply-only system pricing is not the same as total installed cost. Replacement work may require valves, fittings, plumbing, electrical, gas fitting or compliance upgrades.

Buyer Checklist Before Ordering Online

Before ordering a supply-only hot water system for a dual occupancy home, confirm:

• Whether you need one system or two

• Number of occupants in each dwelling

• Number of bathrooms in each dwelling

• Number of kitchens and laundries

• Whether showers may run at the same time

• Existing system type

• Existing tank size or flow rate

• Natural gas or LPG if applicable

• Gas meter or LPG regulator capacity

• Electrical supply

• Switchboard capacity

• Outdoor airflow for heat pumps

• Drainage requirements

• Noise placement

• Pipe run distances

• Access for delivery

• Access for future servicing

• Required valves and fittings

• Whether billing needs to be separated

• Licensed plumbing, electrical and gas fitting requirements

Supply-Only vs Installed Cost

Hot Water Outlet sells supply-only hot water systems and accessories online. Supply-only pricing is useful for comparing product costs, but it is not the same as total installed cost.

The final installed cost may depend on:

• Licensed plumbing labour

• Licensed electrical work

• Licensed gas fitting

• Valve replacement

• Pipework changes

• Drainage work

• Old unit removal

• Disposal

• Access difficulty

• Compliance upgrades

• Switchboard capacity

• Gas pipe sizing

• LPG regulator upgrades

• Separate metering requirements

• Concrete bases or platforms

• Delivery access

Where appropriate, Hot Water Outlet may help organise quotes from reputable installers.

FAQ: Best Hot Water System for Dual Occupancy Homes

What is the best hot water system for a dual occupancy home?

The best hot water system for a dual occupancy home depends on whether the dwellings share services or need separate systems. Separate electric, heat pump or instant gas systems may suit independent dwellings, while one larger shared system may suit a single-family dual occupancy layout.

Should a duplex have one hot water system or two?

Many duplexes are better suited to two separate hot water systems because each dwelling can operate independently. However, the right setup depends on plumbing layout, billing, usage and available space.

What hot water system is best for a granny flat?

A small electric storage system is often compared for granny flats, especially where gas is not available. Instant gas may suit if the property already has suitable gas, and heat pump may suit only where outdoor airflow, drainage and space are suitable.

Can one heat pump supply two dwellings?

Sometimes, but it depends on tank size, recovery rate, pipe runs, number of occupants, bathrooms and simultaneous use. A shared heat pump must be sized for total demand and installed in a suitable location.

Can one instant gas system supply a dual occupancy home?

Sometimes, but the flow rate, gas supply and pipe sizing must be suitable. If both dwellings may use hot water at once, one unit may not be enough.

Is electric hot water good for dual occupancy homes?

Electric hot water can be a practical option, especially where each dwelling has its own system. The correct tank size, recovery rate and electrical supply need to be checked.

Do dual occupancy hot water systems need separate meters?

That depends on the property setup, rental arrangement and local requirements. If each dwelling is rented separately, separate systems and separate utility arrangements may make management easier.

Does supply-only pricing include installation?

No. Supply-only pricing generally does not include installation, plumbing labour, electrical work, gas fitting, valves, fittings, pipework changes, old unit removal, disposal or compliance upgrades.

Can Hot Water Outlet install the system?

Hot Water Outlet sells supply-only hot water systems and accessories online. Plumbing, gas fitting and electrical work must be completed by appropriately licensed tradespeople. Where appropriate, Hot Water Outlet may help organise quotes from reputable installers.

Final Thoughts

For dual occupancy homes, the best hot water system depends on whether the property should operate as one household or two independent dwellings. A shared system may suit some family homes, but separate systems often make more sense for duplexes, granny flats and rental-style layouts.

Browse hot water systems, compare electric hot water systems, heat pump hot water systems, gas hot water systems, instant gas hot water systems and compatible valves, pipework and fittings online at Hot Water Outlet.