How a heat pump water heater works
Rheem describes its heat pump water heaters as absorbing warmth from the surrounding air and transferring it into a home's water. There's still a storage tank, much like an electric cylinder, plus an electric back-up element for times when the weather gets really cold.
Layouts vary by maker. Rinnai sells integrated and split models (HydraHeat Integrated, HydraHeat Split) and an Enviroflo GR Series; Rheem's range includes the AmbiPower and Ambiheat models. Our independent brand guides say what each maker offers, and the wider hot water cylinders section covers every type.
When a heat pump is worth a look
- Your electric cylinder is due for replacement and you want to compare options.
- There's outdoor space close to where the hot water is used.
- There's no piped gas and you'd rather not rely on bottles.
- You're renovating and can plan the position now.
- The roof doesn't suit solar.
What changes the job
Space comes first. Rheem notes that a heat pump will need outdoor space, and that switching can mean relocating the cylinder. That brings new pipe runs, a new electrical connection and a base or wall fixing, all of which a plumber will plan with you.
Rinnai's installation guide boils it down to three things: a licensed plumber, an electrician and a suitable installation site. Ask the installer how close the unit will sit to bedrooms and neighbours, and how the back-up element is set up for your local winters.
Heat pump against the usual alternatives
| Heat pump | Electric cylinder | Gas continuous flow | |
|---|---|---|---|
| Heat source | Warmth from the air, plus a back-up element | An element inside the tank | A gas burner that fires when a hot tap opens |
| Stored hot water | Yes, in a tank | Yes, in a tank | No tank |
| Space | Needs outdoor space | Indoors, or an outdoor model | No tank to house; Rheem says it needs a larger gas pipe from the meter |
| Who connects it | Plumber and electrician | Plumber and electrician | Authorised gasfitter |
Consent and who does the work
A heat pump water heater is still a water heater under the Building Act. Replacing one, or repositioning an existing one, is exempt from building consent under Schedule 1 clause 38 when the replacement is connected to, or incorporates, a controlled heat source, and an authorised person does the work. The Act text doesn't define 'controlled heat source', so your installer or council confirms whether your model qualifies.
The plumbing has to be done by someone authorised under the Plumbers, Gasfitters, and Drainlayers Act 2006, and an electrician does the electrical connection. Exempt or not, the result must meet the Building Code.
Prices, savings and subsidies
We don't print prices or savings figures. The percentages in advertising are the makers' own claims. We couldn't confirm any current national or council scheme that funds heat pump water heaters, and a bank's green home loan is a bank product, not government support. No scheme makes hot water cost nothing.
Homework before a site visit
You can
- Photograph the current cylinder and the outdoor spots you have in mind.
- Note where the switchboard is compared with those spots.
- Work out when the household uses the most hot water.
- Talk to neighbours if the unit will sit near their windows.
Leave to an authorised tradie
- Choosing the model and capacity.
- Pipework, valves and the tank itself.
- The electrical connection (an electrician).
- Moving the cylinder if it has to go outside.
Questions for the installer
- Is there a suitable outdoor spot, and how far is it from where we use hot water?
- Integrated or split model, and why for us?
- How does the back-up element work in a cold snap here?
- Does our job fit the clause 38 consent exemption?
- Who does the electrical work?
- What does the warranty cover, and from what date?
What we would do
Get the site checked before comparing models. A heat pump that suits the space, the household and the electrical supply matters more than the badge on it. Ask a heat pump water heater installer to visit, confirm the consent position, and quote the plumbing and electrical sides together.