Check these at home first
- What you have now: an electric cylinder, gas storage, a califont, a heat pump, a wetback or solar.
- Whether it still works, or has already given up.
- Whether the house has piped natural gas, uses bottled LPG, or has no gas at all.
- Whether there's outdoor space near the house where a unit could sit.
- Whether the hot water is low pressure or mains pressure, if you know.
The main kinds, in plain terms
| How it works | What it needs | |
|---|---|---|
| Electric cylinder | An element heats the water and the cylinder stores it | A plumber, an electrician for the wiring, and room for the cylinder |
| Califont (gas continuous flow) | Heats water only as you use it, with nothing stored | A gasfitter, and in Rheem's words a larger gas pipe from the meter than most gas storage heaters |
| Gas storage | Gas heats the water, which is stored and supplied at mains pressure | A gasfitter, and natural gas or bottled LPG where there's no piped supply |
| Heat pump | Moves warmth from the surrounding air into the water, with a storage tank and an electric back-up element | Outdoor space, plus a licensed plumber and an electrician (Rinnai) |
| Solar | Roof collectors heat the water, with a gas or electric boost for cloudy days | An unshaded patch of roof, ideally facing north (Rheem) |
| Wetback | Pipework in a wood or pellet fire heats water that rises to the cylinder | A plumber to judge it, because where the fire sits relative to the cylinder is crucial (Rheem) |
Who does the work, and the paperwork after
Anything on the gas side is for a gasfitter. The Act also lets a licensed gasfitter the Board accepts as competent fit the water pipes to and from a gas water heater.
A brand-new gas installation is general gasfitting, which needs a gas certificate of compliance. Swapping a gas appliance for an equivalent one, with no change to pipework, flue, pressure, gas type, ventilation or energy use, is low-risk, and that certificate is optional. Either way, a Gas Safety Certificate is needed once the work is connected.
Replacing a water heater is exempt from building consent when the new one is connected to, or includes, a controlled heat source and an authorised person does the work. It still has to meet the Building Code, so ask whether your choice changes anything.
Taking it to a tradie
Take the kinds that fit your home to a tradie who specialises in hot water cylinders. Ask where each option would go, what else would have to change, such as the gas pipe, the wiring or the cylinder's spot, and what paperwork you'll get at the end. Cylinder, califont or heat pump compared goes into more detail.