Last updated October 2026
A heat pump hot water cylinder is one of the most common upgrades Nelson homeowners ask about when an old cylinder starts to fail. It heats the same water using a fraction of the electricity, but it costs more to buy, it needs a spot outside, and it does not suit every house. This guide covers how they work, the two main types, the trade-offs, and what to check before you switch in Nelson or Tasman.
★View the Best Plumbers in Nelson→How a heat pump hot water cylinder works
A standard electric cylinder heats water with an element, a bit like a jug. A heat pump works more like a fridge in reverse. A fan draws in outside air, a refrigerant absorbs heat from it, and a compressor concentrates that heat and passes it into the stored water.
Because most of the energy comes from the air rather than the power point, the savings are large. The Energy Efficiency and Conservation Authority’s guide to hot water heat pumps puts it at around 60 to 75 percent less electricity than a conventional electric hot water system, and notes they are cheaper to run than piped gas or LPG as well.
Integrated or split: the two main types
What it is
- Integrated unit
- Heat pump and cylinder in one outdoor unit
- Split system
- Outdoor heat pump unit piped to a separate cylinder
Where it goes
- Integrated unit
- Outside, on a level pad
- Split system
- Heat pump outside, cylinder inside or out
Best for
- Integrated unit
- Freeing up an indoor cylinder cupboard
- Split system
- Keeping the cylinder indoors, or reusing a suitable existing cylinder
Things to check
- Integrated unit
- Space and access outside
- Split system
- Pipe run between the two units
An integrated unit is the simpler install and gives you back the cupboard the old cylinder lived in. A split system suits houses where the cylinder needs to stay inside, or where there is no good outdoor spot right beside the bathroom and kitchen.
Is a heat pump hot water cylinder worth it?
For most households that use a fair amount of hot water, the answer is yes over the life of the unit. EECA describes the expected lifespan as around 15 years, which is long enough for the lower running costs to matter.
It is a weaker case if:
- only one or two people live in the house and hot water use is low
- you are likely to sell in the next few years
- the only outdoor space is right under a bedroom window
- your existing cylinder is nearly new and working well
If you have rooftop solar, the case gets stronger, because the unit can be timed to run during the day when your own panels are generating.
The downsides people ask about
Upfront cost. A heat pump unit costs more to buy and install than a like-for-like electric cylinder. Get the full installed price, including the electrician, before comparing.
Noise. The outdoor unit has a fan and compressor. It is roughly as audible as an air-conditioning heat pump, so think about where it will sit relative to bedrooms, decks and the neighbours.
Cold mornings. A heat pump draws heat from the air, so it works harder when the air is cold. Nelson’s sunny, mild climate suits them well, but frosty nights are common inland in places like Richmond, Brightwater and Wakefield. Check the model’s rated operating range and ask how it behaves on a frosty morning.
Recovery time. A heat pump heats water more gently than an element. Sizing the cylinder properly for the household matters more than it does with a standard cylinder.
Local things to check in Nelson and Tasman
- Coastal sites. Homes close to the water at Tāhunanui, Monaco, Ruby Bay or Māpua get salt air. Ask about the outdoor unit’s corrosion protection and where it can sit out of the direct sea breeze.
- Older homes on low pressure. Many older Nelson villas and bungalows still run a low pressure cylinder. Most heat pump cylinders are mains pressure, so a switch is often also a pressure upgrade. Older pipework and tapware should be checked before full mains pressure goes through them.
- Placement and drainage. The outdoor unit needs a level base, airflow around it, and somewhere for condensate water to drain.
- Power supply. The unit needs its own electrical connection, which means an electrician as well as a plumber.
Do you need building consent?
Usually not, if you are replacing a storage cylinder. Schedule 1 of the Building Act allows a water heater to be replaced or repositioned without consent in many cases, including swapping a storage cylinder for a heat pump water heater. The government guide to replacing a water heater without consent sets out what is covered. Adding a new split heat pump to an existing cylinder is treated differently and usually does need consent, so check that first.
Whatever the consent position, the plumbing is restricted work and must be done by an authorised plumber, and the electrical connection by a registered electrician.
Questions to ask before you book
- Which type suits this house, integrated or split, and why?
- What size cylinder do you recommend for the number of people here?
- Where would the outdoor unit go, and how noisy will it be there?
- Will the existing pipework cope with mains pressure?
- Does the price include the electrician, valves, removal of the old cylinder and the paperwork?
Getting started with a heat pump cylinder in Nelson
Plumbing and More is a family-run plumbing, gasfitting and drainlaying business in Nelson and Tasman. Its hot water branch, Cylinders and More, handles cylinder repairs, replacements and upgrades, including low-pressure to mains-pressure changes and electric to heat pump cylinders, and will assess an existing system before recommending repair or replacement. The team’s wider plumbing, gas fitting and drainlaying services cover the pipework that often comes with an older setup. You can get in touch through their contact page or call 021 758 651.
