Your Guide to Hot Water Heat Pump Installation

A hot water heat pump can cut the energy you use to heat water by half or more. But that number assumes one thing: the system was chosen and installed well. In practice, the difference between a great result and a disappointing is often one that comes down to the installation - rather than the brand you choose.

EECA’s own research bears this out. When it put over 75 systems into real New Zealand homes, the units that under performed almost always traced back to something fixable in the install: a system sized wrong for the climate, a commissioning step skipped, or a handover that never happened.

The good news is that a good installation follows a pattern you can recognise - even if you’re not a plumber.

This guide draws on EECA’s published research, view the source documents for full details. A final project report will be issued by EECA in late 2026, I’ll update this page with any new findings then.

• EECA: Heat Pump Water Heater: Good Practice Installation Guide (Oct 2025)
• EECA: Heat Pump Water Heater Project: Interim Findings Report (Jan 2026)
• EECA: Heat Pump Water Heater Project: Market Insights Report (May 2025)
• Goes Electric: Compare hot water heat pumps

1. A site visit before the quote

Your water pressure, where the cylinder sits, outdoor space, climate and how your household uses hot water all change which system is right. A good installer sees your home before pricing the job. A quote with no site visit is guessing — and guesses get corrected later, at your cost.

2. The right system & tank size for your household and climate

System type and sizing can cause problems if you get it wrong.

• Too small and it runs out. Heating capacity and reheat speed matter as much as tank litres. Capacity falls as the air gets colder, so cold-region homes need more margin. Make sure the system you are being recommended is designed for the temperature range you live in and ensure the tank size reflects this too. EECA had to replace one undersized cold-zone system with a bigger tank.
• Too big and you pay twice. Oversizing costs more upfront and then wastes energy for years keeping unused water hot. Many systems on the NZ market are too big for a smaller household. Check our sizing guide.

3. Where the outdoor unit goes

The units do make some noise - products range from 32-55 dB and integrated units tend to be slightly noisier than split. Not loud, but where you put it matters. Placement is also important to ensure the unit operates well.

• Space required: check the products installation manual to ensure the required clearances are able to be met.
• Sunny side: It’s tempting to hide your unit away in a shady area, but the efficiency of the unit will be slightly better if placed in a warmer area. Remember it draws warmth from the air to transfer to your water.
• Distance: ideally at least 2m from a bedroom and 3m from a neighbour’s bedroom window. My old gas califont was super noisy so I think my neighbours will be relieved with my quieter heat pump unit, even though it is closer than this.
• Airflow: clear air in and out, not boxed in a corner, not hard against fences or buried under a hedge, and away from leaf traps.
• Base: needs to be level, stable and water-shedding, secured so it doesn’t rattle, with room to service it. I went with a concrete pad poured a couple of weeks ahead of my install so the concrete had time to cure. But if this is an emergency replacement talk to your installer, a compacted gravel base with a larger concrete paver can be a good alternative.

4. The plumbing that protects you

A few fittings are mandatory for safety and longevity. You don’t need to inspect them, your plumber should handle this. Your install will include:

• Tempering valve: delivers water at a safe temperature (set ~45–50°C).
• Pressure-reducing valve + TPR valve: protecting the cylinder, draining to an approved point.
• Condensate to a drain or garden: never across a path or driveway. EECA flagged condensate dripping onto a lawn as an unacceptable result.
• Insulation:

The low-pressure trap: switching from low pressure to mains pressure raises the flow, which can expose old tapware and pipework. Some EECA trial homes leaked soon after install. A good installer checks your pipes and fittings first and tells you honestly if any need replacing.

5. The electrical side

Done by a registered electrician, on the right circuit, and signed off:

• A dedicated, protected, labelled circuit back to the switchboard.
• Ripple control only if the manufacturer allows it — cutting power to the compressor that way can damage some units.
• A Certificate of Compliance handed to you — your proof the wiring was tested. Keep it.

6. Commissioning

Commissioning is where the installer turns the system on properly: filling and bleeding it, leak-testing, setting the temperature, running diagnostics, confirming quiet running, and setting the heating schedule to your routine. In EECA’s trial, several early faults — running out of hot water, wrong run-times, odd element behaviour — traced back to skipped commissioning and callbacks. A properly commissioned system works from day one.

On the schedule: these systems heat gradually, often off-peak — that’s how they save you money. It only works if the run times match when your household needs hot water, so a good installer sets this with you and shows you how to change it.

7. The handover

Before the installer leaves — and this is part of a compliant install — you should have:

• A demonstration of how to run and adjust the system
• The operating manual
• Warranties for each part (cylinders are often warranted far longer than the heat-pump components)
• The electrical Certificate of Compliance
• Clear servicing advice — what to do, and when

No demonstration and no documents means the job isn’t finished.