Hot Water System Replacement Guide: What to Check Before You Buy Online

Buying a replacement hot water system online can save time and make product comparison easier, but the wrong system can create extra costs, delays or compliance issues. Before ordering, you need to check the existing system type, size, energy source, installation location, access, valves, fittings and licensed trade requirements. 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, instant electric hot water systems and compatible valves, pipework and fittings.

Quick Answer

Before buying a replacement hot water system online, check:

• Existing system type

• Existing tank size or flow rate

• Electric, gas, heat pump, instant gas or solar setup

• Natural gas or LPG if applicable

• Indoor or outdoor location

• Physical dimensions

• Access for delivery

• Electrical supply

• Gas pipe sizing if applicable

• Drainage and relief valve discharge

• Heat pump airflow if applicable

• Required valves and fittings

• Whether licensed plumbing, electrical or gas fitting work is needed

The safest online purchase is usually a system that matches the existing setup unless a licensed trade confirms the property is suitable for a system change.

Supply-only pricing is not the same as total installed cost. Installation, valves, fittings, pipework changes, electrical work, gas fitting, disposal and compliance upgrades may all be separate.

Replacement Hot Water System Checklist

Step 1: Identify Your Existing Hot Water System

Before choosing a replacement, identify what type of hot water system you currently have.

Common systems include:

• Electric storage

• Gas storage

• Instant gas

• Heat pump

• Instant electric

• Solar hot water

• Gas boosted solar

• Electric boosted solar

This matters because a like-for-like replacement is often simpler than changing system type.

For example, replacing an old electric storage tank with another electric hot water system may be more straightforward than changing to gas, instant electric or heat pump.

Replacing an old instant gas unit with another instant gas hot water system may suit if the gas type, location, pipe sizing and clearances are still suitable.

Changing from gas to electric, electric to heat pump, solar to heat pump or storage to instant can involve extra work.

Step 2: Check the Existing Size

The existing size gives you a starting point, but it should not be the only thing you rely on.

For storage systems, check the tank size in litres. Common sizes include:

For instant gas systems, check the flow rate. Common sizes may include:

Do not assume the same litre size or flow rate will always perform the same way across different system types. Electric storage, gas storage, instant gas and heat pumps all recover and operate differently.

Step 3: Check the Energy Source

The replacement system must suit the energy available at the property.

Electric

If the existing system is electric storage, compare electric hot water systems by tank size, dimensions, element rating and indoor or outdoor suitability.

Heat Pump

If you are considering a heat pump hot water system, check outdoor airflow, drainage, noise placement, electrical supply and available space.

Gas

If replacing gas, compare gas hot water systems or instant gas hot water systems, depending on the current setup.

Instant Electric

Instant electric hot water systems may suit small point-of-use applications, but they are not always suitable for whole-home replacements because they can require significant electrical capacity.

Step 4: Confirm Natural Gas or LPG

If the existing system is gas, you must confirm whether it is natural gas or LPG.

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

Check:

• Existing appliance label

• Gas bottle setup

• Gas meter

• Property gas supply

• Existing paperwork if available

• Licensed gas fitter confirmation

Ordering the wrong gas type can delay the job and may make the system unsuitable.

Step 5: Check Indoor vs Outdoor Suitability

Not every hot water system can be installed in every location.

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

Heat pumps need suitable airflow and should not be placed in tight enclosed cupboards unless the product and site are specifically suitable.

Electric storage systems may be available in indoor or outdoor versions, but safe tray, drainage and access requirements still matter.

Check:

• Current system location

• Indoor or outdoor rating

• Cupboard size

• Ventilation

• Flue requirements for gas

• Heat pump airflow

• Clearance around the unit

• Drainage and discharge points

Step 6: Measure the Existing Unit

Before ordering online, measure the existing hot water system carefully.

Measure:

• Height

• Width

• Diameter

• Depth

• Clearance above the unit

• Clearance around valves

• Doorway access

• Side access

• Cupboard opening

• Base or slab size

• Safe tray size if installed indoors

The new unit may have the same litre capacity but different dimensions. A 250L replacement tank from one brand may not have the same height, diameter or connection positions as another.

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

Step 7: Check Access for Delivery and Replacement

A replacement hot water system needs to physically reach the installation location.

Check:

• Driveway access

• Side access

• Gates

• Stairs

• Retaining walls

• Steep blocks

• Tight pathways

• Unit weight

• Lift access for apartments

• Balcony access

• Garage clearance

• Distance from delivery point to system location

A system may be suitable on paper but difficult to move into position. Larger electric tanks, heat pumps and commercial-style systems can be heavy and may need extra labour or lifting equipment.

Supply-only pricing does not include specialist access, lifting, crane work, difficult removal or additional trade labour.

Step 8: Check Electrical Requirements

Electric, heat pump and instant electric systems need suitable electrical supply.

Electrical checks may include:

• Existing circuit size

• Element rating

• Switchboard capacity

• Isolator requirements

• Timer or tariff setup

• Heat pump electrical connection

• Instant electric power demand

• Circuit protection

• Compliance testing

A standard electric storage replacement may be simpler if the existing circuit is suitable. A heat pump may have different electrical requirements. Instant electric may require significant electrical capacity.

Electrical work must be completed by a licensed electrician.

Step 9: Check Gas Requirements

Gas hot water replacement needs more than matching the brand.

Check:

• Natural gas or LPG

• Gas pipe sizing

• Gas meter capacity

• LPG bottle setup

• LPG regulator capacity

• Appliance location

• Flue requirements

• Clearances to windows, doors and openings

• Controller wiring

• Existing compliance

• Whether other appliances share the gas supply

If changing from gas storage to instant gas, or from a smaller instant gas unit to a larger one, the gas supply may need to be checked carefully.

Gas fitting work must be completed by a licensed gas fitter.

Step 10: Check Heat Pump Placement

Heat pump hot water systems can be a strong option for many replacements, but only where the site suits.

Check:

• Outdoor airflow

• Space around the unit

• Condensate drainage

• Relief valve drainage

• Noise placement

• Distance to bedrooms

• Distance to neighbours

• Electrical supply

• Base or platform

• Access for servicing

• Local rules or body corporate requirements if applicable

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

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.

Step 11: Check Drainage and Discharge

Hot water systems need safe drainage for valve discharge. Heat pumps also produce condensate.

Check:

• Existing relief drain

• Safe discharge point

• Drainage location

• Safe tray if indoors

• Condensate drain for heat pump

• Whether pipework changes are needed

• Whether discharge could cause nuisance or damage

Poor drainage planning can cause water damage, unsafe discharge or compliance issues.

Step 12: Check Valves and Fittings

Replacement hot water systems often need new valves and fittings. The old parts may not be suitable, compliant or reusable.

You may need compatible valves, pipework and fittings, such as:

• Tempering valve

• Pressure limiting valve

• Duo valve

• Expansion control valve

• Isolation valve

• Non-return valve

• Relief valve drain materials

• Connection fittings

• Pipework materials

• Safe tray parts

• Heat pump condensate drain materials

The correct parts depend on the system type, water pressure, temperature, location and local compliance requirements.

Step 13: Understand Supply-Only Pricing

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

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 or platforms

• Delivery beyond what is shown at checkout

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

Step 14: Check Warranty Conditions

Warranty can vary by brand, model, component and conditions.

Before buying, check:

• Product warranty period

• Tank warranty

• Parts warranty

• Labour warranty, if any

• Domestic or commercial use conditions

• Installation requirements

• Water quality requirements

• Maintenance requirements

• Location requirements

• Proof of purchase requirements

• Licensed installation requirements

Do not assume every part of the system has the same warranty period. Tanks, compressors, controllers, valves and labour may have different warranty terms.

Step 15: Check Rebates, STCs and Incentives

Rebates, STCs and incentives may be available for some hot water systems, especially heat pumps, but they can change.

Eligibility may depend on:

• Product model

• Installer

• Property type

• State or territory

• Existing system type

• Purchase type

• Installation date

• Program rules

• Whether the buyer or installer claims the incentive

Do not rely on old rebate information. Always check current eligibility before buying.

Like-for-Like Replacement vs Changing System Type

A like-for-like replacement means the new system is similar to the old system.

Examples:

• Electric storage to electric storage

• Gas storage to gas storage

• Instant gas to instant gas

• Heat pump to heat pump

Changing system type means moving to a different style of hot water system.

Examples:

• Gas to electric

• Electric to heat pump

• Solar to heat pump

• Storage to instant gas

• Gas storage to instant gas

• Electric storage to instant electric

Changing system type can be worthwhile, but it usually needs more checking.

When Like-for-Like May Be Better

Like-for-like may suit when:

• You want a simpler replacement

• The existing setup worked well

• The location is compliant

• The energy source is staying the same

• You want fewer service changes

• Access and pipework are already suitable

• You want to reduce installation complexity

When Changing System Type May Be Worth Comparing

Changing system type may suit when:

• The old system was expensive to run

• You are moving away from gas

• You have solar power

• You want a heat pump

• The old solar system is failing

• The current system is undersized

• The home has changed usage

• The old location is no longer suitable

• You are renovating

Before changing system type, check the full cost and service requirements.

Common Mistakes When Buying a Replacement Online

Buying Only by Litres

Tank size matters, but recovery rate, element size, heat pump performance, flow rate and household demand also matter.

Not Checking Dimensions

A new system can have the same capacity but different dimensions and connection positions.

Ordering the Wrong Gas Type

Natural gas and LPG are not interchangeable.

Choosing Heat Pump Without Checking Airflow

Heat pumps need suitable airflow, drainage and noise placement.

Assuming Instant Electric Can Replace Instant Gas

Instant electric may require significant electrical capacity and may not suit whole-home use.

Forgetting Valves and Fittings

Replacement systems often need new valves, fittings and compliance parts.

Ignoring Drainage

Relief valve discharge and heat pump condensate need to be managed correctly.

Comparing Supply-Only Price to Installed Cost

Supply-only pricing does not include all installation-related work.

Not Checking Access

Tight access, stairs, apartments and difficult locations can affect delivery and replacement.

Assuming Rebates Always Apply

Rebates and STCs depend on current rules and eligibility.

Best Brands to Compare for Replacement Hot Water

The best brand depends on system type, budget, household size and site requirements.

Rheem

Rheem hot water systems are commonly compared across electric storage, gas storage, instant gas and heat pump categories.

Rinnai

Rinnai hot water systems are commonly compared for instant gas and continuous flow hot water systems.

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 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.

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 site conditions suit.

Buyer Checklist Before Ordering Online

Before ordering a supply-only replacement hot water system, confirm:

• Existing system type

• Existing tank size or flow rate

• Household size

• Number of bathrooms

• Whether showers run at the same time

• Whether the home has a bath or spa

• Electric, gas, heat pump or solar setup

• Natural gas or LPG if applicable

• Indoor or outdoor location

• Dimensions of the existing unit

• Dimensions of the new unit

• Access for delivery and replacement

• Electrical supply

• Switchboard capacity

• Gas pipe sizing if applicable

• Heat pump airflow if applicable

• Drainage and discharge location

• Noise placement

• Required valves and fittings

• Warranty conditions

• Rebate or STC eligibility if applicable

• Licensed plumbing, electrical and gas fitting requirements

FAQ: Hot Water System Replacement Guide

What should I check before buying a hot water system online?

Check your existing system type, tank size or flow rate, energy source, gas type if applicable, electrical supply, dimensions, access, drainage, valves, fittings and licensed trade requirements.

Is it better to replace like-for-like?

A like-for-like replacement is often simpler if the existing setup is suitable and compliant. Changing system type may be worthwhile, but it usually needs more plumbing, electrical, gas or drainage checks.

Can I replace electric storage with a heat pump?

Yes, if the site has suitable outdoor airflow, drainage, noise placement, electrical supply and enough space. The heat pump also needs to be sized correctly for the household.

Can I replace gas hot water with electric?

Yes, but it is not always a direct swap. You may need gas disconnection, electrical work, plumbing changes, drainage changes and a suitable electric or heat pump system.

Can I replace instant gas with instant electric?

Sometimes for small applications, but instant electric is not always suitable for whole-home hot water because it can require significant electrical capacity.

How do I know if I have natural gas or LPG?

Check whether the property has gas bottles or a gas meter, and check the appliance label if accessible. A licensed gas fitter should confirm before replacement.

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.

Do I need new valves when replacing a hot water system?

Often, yes. The required valves depend on water pressure, system type, temperature control, location and compliance requirements. A licensed plumber should confirm what is needed.

What size replacement hot water system do I need?

Sizing depends on household size, bathrooms, showers, baths, usage habits and system type. Do not choose based only on the old tank size.

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

Buying a replacement hot water system online is easier when you know what to check first. Start with the existing system type, size, energy source and location. Then check dimensions, access, drainage, electrical supply, gas type, valves, fittings and licensed trade requirements.

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