RANGE OF AVAILABLE REPLACEMENT SYSTEMS
Rheem MPi-325 Series II Heat Pump Hot Water System – 551325
The Rheem MPi-325 Series II Heat Pump Hot Water System is a 325 litre air-source heat pump designed primarily as an energy-efficient replacement for small to medium electric storage water heaters.
Model 551325 combines a 325L storage cylinder, separate heat-pump module and 180L electric boost capacity. Rheem specifies an 800W rated heat-pump power input, a 3.6kW backup element and suitability for approximately 2–5 people under its published usage assumptions.
Installed Today offers the Rheem MPi-325 as a supply-only system or with supply and installation across eligible Brisbane and Gold Coast service areas.
How Does the Rheem MPi-325 Work?
The MPi-325 absorbs thermal energy from the surrounding outdoor air and transfers that energy into the stored water using a refrigeration circuit.
Instead of relying solely on a resistive electric element, the heat pump moves heat from the air into the water. Rheem describes the system as using approximately one third of the energy of a conventional electric water heater under suitable operating conditions.
The system uses multi-pass heating, where water circulates through the heat exchanger multiple times during the heating cycle, together with a constant-recovery control strategy designed to optimise heat-pump operation.
Who Is the Rheem MPi-325 Best For?
2–5 Person Homes
Rheem's current plumbers' information lists the MPi-325 for approximately 2–5 people, while the product datasheet states up to five people under its published usage assumptions.
Electric Storage Replacements
Rheem recommends the MPi-325 for replacement of small to medium electric water heaters across Australian climate Zones 1 to 4.
Outdoor Heat Pump Upgrades
The 551325 is specifically designed for outdoor installation and needs adequate airflow, drainage, electrical provision and servicing access.
Rheem MPi-325 Key Details
*Rheem bases its household guide on seven-minute showers at 42°C and counts appliances using hot water as an additional person. Actual suitability depends on household usage.
The MPi-325 Is an Outdoor-Only Heat Pump
Rheem's current Owner's Guide states that the 551325 is designed for outdoor installation only.
The water heater should be positioned with noise, airflow, safety and servicing in mind. Rheem recommends avoiding locations close to bedroom or living-room windows and considering neighbouring windows because operating noise can reflect from nearby structures.
The system must be installed at ground or floor level, vertically upright, on a stable supporting base.
Rheem MPi-325 Installation Clearances
A heat pump needs unrestricted airflow through the evaporator. Installing it in a tight enclosure or immediately against walls can reduce performance and create servicing problems.
- At least 100mm clearance from the storage tank to a wall
- At least 300mm perpendicular clearance from the front air inlet
- At least 300mm clearance from the air outlet to a wall or obstruction
- Stable supporting base approximately 900mm wide × 650mm deep minimum
- Service access without requiring a ladder or scaffold
- Access to TPR valve, controls, thermostat and covers
- Headroom for anode inspection or replacement where practical
- Location clear of shrubs and other airflow obstructions
Separate Tank & Heat Pump Module
The MPi-325 consists of two main components: the storage tank and the heat-pump module.
Rheem ships the two sections separately for transport and handling and they are assembled together at the installation site. Rheem describes the design as allowing a one-person plumbing installation without a refrigeration mechanic.
That does not remove normal trade requirements. The complete system still needs to be installed by a qualified person and all fixed electrical work must be completed in accordance with applicable electrical requirements.
3.6kW Backup Element & 180L Boost Capacity
The MPi-325 includes a 3.6kW electric booster element with a published 180L boost capacity.
The booster provides heating support when ambient conditions are outside the heat pump's operating range and forms part of the system's frost-protection strategy.
During normal favourable conditions, the heat-pump refrigeration system provides the primary heating. The electric element is not intended to operate continuously as the main heating source.
Rheem MPi-325 Heat Pump Performance
Heat-pump performance varies with ambient temperature, humidity and incoming cold-water temperature. Rheem publishes the following laboratory figures for model 551325.
| Ambient Air | Relative Humidity | Average Heating Capacity | Recovery @ 45°C Rise | Average COP |
|---|---|---|---|---|
| 7°C | 86% | 1.5kW | 28 L/hr | 2.8 |
| 19°C | 65% | 1.9kW | 36 L/hr | 3.6 |
| 33°C | 35% | 2.5kW | 47 L/hr | 4.2 |
| 33°C | 59% | 2.6kW | 50 L/hr | 4.5 |
COP is the ratio of useful heat delivered to electrical energy consumed. Installed performance varies with weather, inlet-water temperature, hot-water usage and site conditions.
How Much Energy Can the MPi-325 Save?
Rheem states that the MPi-325 can provide up to 65% water-heating energy savings in Zone 3 when replacing a similar-sized electric storage water heater under Australian Government-approved TRNSYS modelling conditions.
This is a modelled comparison rather than a guaranteed household saving. Actual energy use depends on climate, water consumption, electricity tariff, installation conditions and the water heater being replaced.
Heat pumps typically use less electrical energy because most of the heat transferred into the water comes from ambient air rather than being created directly by a resistive heating element.
How Loud Is the Rheem MPi-325?
Rheem publishes a noise level of 52 dB(A) at one metre under its specified laboratory test conditions.
Installed noise can be higher because sound reflects from walls, fences and other nearby structures. Rheem therefore recommends considering bedrooms, living areas and neighbouring properties when selecting the installation position.
Rheem MPi-325 Specifications
| Specification | Rheem MPi-325 Series II |
|---|---|
| Brand | Rheem |
| Model | 551325 |
| System Type | Air-source heat pump water heater |
| Installation | Outdoor only |
| Storage Capacity | 325L |
| Boost Capacity | 180L |
| Rated Heat Pump Power Input | 800W |
| Backup Element | 3.6kW |
| Recommended Electrical Circuit | Minimum 15A supply |
| Electrical Supply | 220–240V AC, 50Hz |
| COP @ 19°C | 3.6 under Rheem's stated test conditions |
| Noise Level | 52 dB(A) at 1m under laboratory test conditions |
| Household Guide | 2–5 people / up to 5 under stated assumptions |
| Water Connections | Rp 3/4 / 20mm |
| TPR Valve Setting | 1000 kPa |
| Expansion Control Valve | 850 kPa |
| Maximum Mains Pressure With ECV | 680 kPa |
| Maximum Mains Pressure Without ECV | 800 kPa |
| Minimum Water Supply Pressure | 200 kPa |
| Approx. Complete System Empty Weight | 130kg |
| Heat Pump Module Weight | Approx. 42kg |
| Storage Tank Weight | Approx. 88kg |
| Certification | WaterMark and applicable Australian Standard certification as published by Rheem |
Rheem MPi-325 Dimensions
Rheem's newer plumbers' handbook drawing shows an overall installation width of approximately 894mm, a tank diameter of approximately 619mm, a depth of approximately 638mm and a total height of 1631mm.
*An earlier Rheem MPi-325 datasheet publishes an 863mm width with the same 638mm depth and 1631mm height. Because official Rheem publications show a dimensional revision, use the current plumbers' drawing and confirm the supplied unit where site clearance is tight.
Which Refrigerant Does the MPi-325 Use?
Rheem's official documentation currently shows a production-revision difference for model 551325.
The MPi-325 technical datasheet and Owner's Guide identify R134a, while a newer Rheem heat-pump range brochure identifies the MPi-325 as using low-GWP R513a.
Because the same 551325 model designation appears across these publications, the refrigerant should be confirmed from the compliance or rating plate on the actual unit being supplied where this detail is important.
What Electrical Supply Does the MPi-325 Need?
Rheem specifies direct connection to a 220–240V AC, 50Hz mains supply capable of supplying at least 15 amps.
The water heater must have its own electrical circuit. Rheem's installation instructions also require appropriate isolation and an RCD in accordance with the applicable Wiring Rules.
All permanent electrical wiring must be completed by a qualified person. The system should not be energised until the storage tank is completely filled and commissioning checks have been completed.
Continuous or Extended Off-Peak?
Rheem recommends the 551325 for connection to either a 24-hour continuous tariff or an extended off-peak tariff providing at least 16 hours of power per day, subject to climate and the system being replaced.
Rheem's MPi-325 datasheet recommends a 24-hour continuous tariff when replacing an electric water heater greater than 160L, while its Owner's Guide contains a later threshold reference of greater than 250L.
Because Rheem publications differ on that replacement-size threshold, a 24-hour continuous supply is the more conservative choice for larger-system replacements. Tariff suitability should be confirmed with the energy provider and installer before ordering.
The Heat Pump Requires a Condensate Drain
Unlike a standard electric storage water heater, the MPi-325 produces condensate while extracting heat from the outdoor air.
Rheem requires a drain line from the heat-pump module's condensate connection. The condensate pipe should fall continuously away from the unit, remain as short and unrestricted as practical and discharge where the flow can be seen without creating damage or nuisance.
The condensate drain must not be connected directly into the relief-valve drain lines, although Rheem permits them to terminate at the same discharge location where correctly installed.
Rheem MPi-325 Water Pressure Requirements
Rheem specifies a 1000 kPa temperature-pressure relief valve and an 850 kPa expansion control valve where an ECV is required.
The maximum mains supply pressure is 680 kPa with an ECV and 800 kPa without an ECV. Where supply pressure exceeds the applicable limit, an approved pressure-limiting valve is required.
Rheem specifies a minimum supply pressure of 200 kPa. Where a tank-fed water supply cannot maintain that pressure, a suitable pressure-pump system is required so the heat-pump circulator can operate correctly.
What Is Required to Install the Rheem MPi-325?
The system must be installed by qualified trades and in accordance with Rheem's installation instructions, the Plumbing Code of Australia, AS/NZS 3500.4, AS/NZS 3000 and applicable local requirements.
- Outdoor installation location
- Stable ground or floor-level base
- Approx. 900mm × 650mm minimum supporting base
- 100mm minimum wall clearance
- 300mm minimum air inlet and outlet ventilation clearance
- Rp 3/4 compatible water pipework
- Suitable water-pressure control valves
- Compliant TPR and ECV drainage
- Separate condensate drain
- Minimum 15A electrical supply
- Dedicated electrical circuit and required isolators
- RCD protection where required by applicable Wiring Rules
- Suitable temperature-limiting device for relevant fixtures
- Service access to covers, controls, valves and anodes
- Location selected with operating noise in mind
Is the Rheem MPi-325 Eligible for STCs?
Rheem identifies the MPi-325 as eligible for Small-scale Technology Certificates where the installation meets the applicable scheme requirements.
The number and value of certificates depend on the approved product registration, installation date, climate zone and current government scheme rules.
Other state-based incentives may also be available from time to time. Any rebate, certificate value or discount should be confirmed for the specific installation before relying on it in the purchase decision.
Rheem MPi-325 Warranty
For qualifying single-family domestic installations, Rheem publishes the following MPi-325 warranty structure.
| Component | Coverage |
|---|---|
| All Components | Year 1 – repair or replacement including labour |
| Sealed Refrigeration System | Year 2 – repair or replacement including labour for qualifying single-family domestic installations |
| Cylinder | Years 2–3 – repair or replacement including labour for qualifying single-family domestic installations |
| Cylinder | Years 4–5 – replacement cylinder supplied; installation and repair labour is owner's responsibility |
| Non-Single-Family Application Cylinder | Years 2–3 – replacement cylinder supplied; labour is owner's responsibility |
Rheem's marketing summary describes this as 5 years cylinder supply, 3 years cylinder labour, 2 years sealed-system supply and labour and 1 year supply and labour on other parts. Full warranty conditions apply.
Buy the Rheem MPi-325 Supply Only
Choose supply only if you require the Rheem MPi-325 and already have appropriately qualified plumbing and electrical installation arranged.
The supply-only price covers the water-heating equipment itself. Installation, valves, electrical work, pipework alterations, condensate drainage, supporting bases, old-system removal, disposal and other site-specific work are separate unless specifically included in the order.
Before ordering, confirm the available outdoor space, airflow clearances, power supply, water pressure, drainage and electricity tariff.
Rheem MPi-325 Supplied & Installed
Supply Only
Order the MPi-325 by itself where suitably qualified plumbing and electrical installation are already arranged.
Brisbane Installation
Eligible Brisbane customers can check available supply-and-install options for replacing a compatible electric storage water heater with the MPi-325.
Gold Coast Installation
Eligible Gold Coast customers can also check available installation options, including electrical, drainage, valve and site-clearance requirements.
Buy the Rheem MPi-325 Across Australia
Installed Today offers supply-only ordering across supported Australian delivery areas, subject to product availability, with local supply-and-install options available in eligible Brisbane and Gold Coast locations.
Customers elsewhere can arrange compliant installation with appropriately qualified local trades after delivery.
Rheem MPi-325 Installation Brisbane
Eligible Brisbane customers can order the Rheem MPi-325 with a local installation option where available. The warm South East Queensland climate can provide favourable ambient conditions for heat-pump operation, but final performance still depends on installation location and household use.
Before installation, check outdoor airflow, the approximately 894mm × 638mm equipment footprint, condensate drainage, 15A electrical provision, water pressure, valves, access and the condition of the existing hot-water installation.
Rheem MPi-325 Installation Gold Coast
Eligible Gold Coast customers can also check supplied-and-installed options for the MPi-325.
The installation site should provide unrestricted outdoor airflow, adequate distance from bedrooms and neighbouring living areas, drainage for condensate and relief valves, a stable base and suitable fixed electrical supply.
Check These Items Before Ordering Installation
- Moving the water heater to a new outdoor position
- Constructing or upgrading the supporting base
- Old, missing or non-compliant valves
- Additional hot or cold water pipework
- New condensate drainage
- Relief-valve drainage alterations
- Electrical circuit or switchboard modifications
- New adjacent isolation switch or RCD requirements
- Restricted access for the tank and heat-pump module
- Insufficient air inlet or outlet clearance
- Noise-sensitive installation locations
- Tempering or delivery-temperature compliance work
- Removal and disposal of the existing water heater
Questions About the Rheem MPi-325
What is the Rheem MPi-325 model number?
The model number is 551325.
How much water does the MPi-325 store?
Rheem specifies a 325 litre storage capacity.
What is the boost capacity?
The 3.6kW booster has a published 180 litre boost capacity.
How many people is the Rheem MPi-325 suitable for?
Rheem's current plumber guide lists approximately 2–5 people. Its datasheet describes the unit as suitable for up to five people under its stated assumptions.
Can the MPi-325 be installed indoors?
No. Rheem's current Owner's Guide specifically states that the 551325 is designed for outdoor installation only.
Does the Rheem MPi-325 need direct sunlight?
No. It extracts heat from ambient air and can operate day or night without roof-mounted solar collectors.
Does it need a refrigeration mechanic for installation?
Rheem describes the two-piece design as allowing plumbing assembly without a refrigeration mechanic. Plumbing and electrical work must still be performed by appropriately qualified people.
What electrical circuit is required?
Rheem specifies a 220–240V AC supply capable of at least 15A, with a dedicated circuit and required electrical isolation and protection.
What is the COP?
Rheem publishes an average COP of 3.6 at 19°C ambient temperature under its specified performance test.
What is the noise level?
The published laboratory figure is 52 dB(A) at one metre. Installed noise can be higher due to reflections from nearby walls and structures.
How much energy can it save?
Rheem publishes potential water-heating energy savings of up to 65% in Zone 3 compared with a similar-sized electric water heater under its stated modelling conditions. Actual savings vary.
What water pressure does it require?
Rheem specifies a minimum water supply pressure of 200 kPa, with maximum mains pressure of 680 kPa when an ECV is fitted and 800 kPa without an ECV.
What water connections does it use?
The hot and cold connections are Rp 3/4 / 20mm.
Does it produce condensate?
Yes. A separate condensate drain must be provided from the heat-pump module.
What are the MPi-325 dimensions?
Rheem's newer plumbers' drawing shows approximately 1631mm high × 894mm overall width × 638mm deep. An earlier datasheet shows an 863mm width, so confirm the supplied unit where space is restricted.
How much does it weigh?
The current Rheem plumber guide lists approximately 130kg empty for the complete system. The earlier detailed datasheet separates this into approximately 88kg for the tank and 42kg for the heat-pump module.
What refrigerant does the MPi-325 use?
Rheem publications show a revision difference. The MPi-325 datasheet and Owner's Guide list R134a, while a newer official heat-pump range brochure states low-GWP R513a. Confirm the refrigerant from the rating plate on the actual 551325 unit being supplied.
Is the MPi-325 suitable for off-peak power?
Rheem permits connection to an extended off-peak supply of at least 16 hours per day where appropriate. A 24-hour continuous tariff is recommended for many larger electric-storage replacements.
Is the Rheem MPi-325 eligible for STCs?
Rheem identifies the model as STC eligible where all current scheme and installation requirements are met.
What warranty does the MPi-325 have?
For qualifying single-family domestic installations, Rheem publishes 5 years cylinder supply coverage, 3 years cylinder labour, 2 years sealed-system supply and labour and 1 year supply and labour on other components, subject to full warranty terms.
Can I buy the Rheem MPi-325 supply only?
Yes. Installed Today offers a supply-only pathway where compliant installation is being arranged separately.
Can Installed Today install the MPi-325?
Supply-and-install options are available in selected Brisbane and Gold Coast service areas. Final requirements depend on outdoor space, airflow, drainage, plumbing, water pressure, electrical provision and site access.
Why Order the Rheem MPi-325 From Installed Today?
Installed Today provides a clear pathway to order the Rheem MPi-325 as a product-only purchase or combine it with an eligible local installation option. Check outdoor space, airflow, drainage, electrical supply, tariff, valves, water pressure and old-system removal requirements before checkout.
Is the Rheem MPi-325 Right for You?
The Rheem MPi-325 Series II 551325 is suited to households wanting to replace a small-to-medium electric storage water heater with a 325L air-source heat pump. It combines a large storage cylinder with multi-pass heat-pump heating and a 3.6kW electric booster for additional support when operating conditions require it.
Before ordering, confirm that the household's hot-water demand suits the system, that a compliant outdoor-only installation position is available and that the property has the required airflow, condensate drainage, 15A electrical supply, water pressure and service access. Choose supply only where compliant installation is already arranged, or check Installed Today's Brisbane and Gold Coast installation options.
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DELIVERY TIMES WITH INSTALLATION - HOT WATER SYSTEMS EXC. HEAT PUMPS
Greater Brisbane and Gold Coast (EXCLUDING BAY ISLANDS) - up to 2 business days
Toowoomba, Tweed Heads and Sunshine Coast - up to 3 business days
DELIVERY TIMES WITHOUT INSTALLATION - HOT WATER SYSTEMS EXC. HEAT PUMPS
Greater Brisbane and Gold Coast (EXCLUDING BAY ISLANDS) - up to 3 business days
Toowoomba, Tweed Heads and Sunshine Coast - up to 5 business days
Harvey Bay, Cairns and Townsville - up to 5 business days
Metropolitan Cities - up to 5 Business Days
Listed Metropolitan Centers - up to 10 Business Days
DELIVERY TIMES WITH INSTALLATION - HEAT PUMPS
Greater Brisbane and Gold Coast (EXCLUDING BAY ISLANDS) - up to 2 business days
Toowoomba, Tweed Heads and Sunshine Coast - up to 5 business days
DELIVERY TIMES WITHOUT INSTALLATION - HEAT PUMPS
Greater Brisbane and Gold Coast (EXCLUDING BAY ISLANDS) - up to 5 business days
Toowoomba, Tweed Heads and Sunshine Coast - up to 5 business days
Metropolitan Cities - up to 5 Business Days
Listed Metropolitan Centers - up to 10 Business Days
DELIVERY TIMES WITH/WITHOUT INSTALLATION - PUMPS AND WATER FILTERS
Greater Brisbane and Gold Coast - up to 5 business days
Toowoomba, Tweed Heads and Sunshine Coast - up to 5 business days
Harvey Bay, Cairns and Townsville - up to 10 business days
**PLEASE NOTE ORDERS OUTSIDE OF THESE AREAS WILL BE REFUNDED AS SOON AS POSSIBLE**
SERVICED METROPOLITIAN CENTRES & CITIES
-Brisbane (EXCLUDING BAY ISLANDS)
-Gold Coast
-Sunshine Coast
-Toowoomba
-Coffs Harbour
-Tamworth
-Canberra
-Sydney (EXCLUDING ISLANDS)
-Bathurst
-Melbourne
-Ballarat
-Geelong
-Adelaide
-Perth
-Darwin
-Cairns
-Townsville
-Harvey Bay
-Rockhampton
-Bundaberg
-Tweed Heads
-Wollongong