Your Guide to Hot Water Heat Pump Installation

A hot water heat pump can more than halve your water heating energy bill when it’s chosen and installed well. The difference between a great result and a disappointing one can come down to the installation - rather than the brand you choose.

EECA’s own research, when it put over 75 systems into New Zealand homes, often traced under performing units back to something fixable in the install: a system sized wrong for the climate, a commissioning step skipped, or a poor handover.

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

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

NZ hot water heat pump tank sizes range from 190L to 400L.

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.

• 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 meet clearances and service it. If this is an emergency replacement talk to your installer, a compacted gravel base with a larger concrete paver can be a good alternative. Remember tanks are often 600mm in diameter and are extremely heavy when filled with water. Your base is important.

I went with a concrete pad poured a week ahead of my install so the concrete had time to cure.

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: high quality UV resistant pipe insulation should cover all hot water pipes. In frost prone areas insulate your cold water pipes too.

• 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 will avoid disasters by identifying any that 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.
• Replacing an instant gas califont? The weatherproof outdoor socket that ran the califont will usually run an iStore too — it plugs directly into a standard 230V 10A outlet, so no new circuit is required. Meaning you only need a plumber.

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, the homes that ran out of hot water or got an inconsistent supply usually traced back to one thing: setup steps missed at installation. Run times and heating schedules were left unadjusted, and installers had to come back and fine-tune them. A system commissioned properly 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.
• Off-peak power, or daytime warmth and sunshine? Most systems have timer and efficiency settings, and some adjust themselves. Used well, they heat your water when it's cheapest and most efficient: during free or off-peak power windows, in the warmer part of the day (heat pumps work better in warmer air), or while your solar panels are generating.

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 (or one by email soon after)
• Clear servicing advice — what to do, and when

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

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