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Hamilton, Waikato

Heat pumps in HamiltonReady for a foggy, frosty July morning.

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Heat pumps are already Hamilton's main heater: 77.62% of Hamilton City homes listed one in the 2023 Census. The ones that cope best were sized for a frosty July morning rather than a mild afternoon, and given an outdoor spot where fog and frost can clear. Here's what the city's climate asks of a heat pump.

Hamilton's winter, by the numbers

Cold mornings

Wikipedia's climate table for Hamilton, built on NIWA's 1991 to 2020 normals, gives a July mean daily minimum of 3.8 degrees. NIWA's Ruakura station averages 21.0 air frosts and 62.9 ground frosts a year, most from May to September, with 7.2 air frosts in July alone.

Fog and humidity

Ruakura averages 38 foggy days a year, and NIWA says Waikato fog turns up most between March and August. Mean 9 am relative humidity at Hamilton AWS is 84% across the year and 88% in June.

Heating need

NIWA's degree-day table gives Ruakura 1,780 heating degree-days a year and only 94 for cooling. MBIE's H1/AS1 places Hamilton City in climate zone 2 of six.

Damp

In the 2023 Census, 20.8% of people in the Waikato health district lived in homes that were sometimes or always damp, a touch above the 20.6% national figure (EHINZ).

Other heating

27.8% of homes in the Waikato health district used a wood burner as a main heater in 2023. Firstgas says its networks serve parts of Waikato, so mains gas is a street-by-street question.

What a Hamilton winter asks of a heat pump

A heat pump gives out less heat as the air outside gets colder, so the label's 7 degree figure flatters it on a frosty morning. EECA says that where nights get down to 2 degrees or below, the heating capacity at 2 degrees should match or beat the 7 degree figure. With 21.0 air frosts a year at Ruakura, that test is real here, not a technicality.

Hamilton's damp, foggy air adds a second one. Mitsubishi Electric NZ says the more moisture in the air, the more freezes on the outdoor coil, so expect defrost pauses on still, foggy mornings. Consumer NZ describes outdoor units needing a few minutes to defrost before they can work again. A unit boxed in under a deck makes it worse: Mitsubishi warns that units with impeded airflow can create their own microclimate.

Summer is the easy part. With 94 cooling degree-days a year, a heat pump bought for winter will handle a February heatwave in the room it's in.

The jobs that come up most in Hamilton

A first heat pump, or a bigger one. If your unit runs flat out on frosty mornings and still can't hold the room, it may be undersized. BRANZ says an undersized heat pump runs continuously and defrosts often. Our size calculator is a good first check.

Heating the rest of the house. One high-wall unit warms the lounge, not the bedrooms down the hall. A multi-room heat pump or a ducted heat pump is the usual next step, and a ducted heat pump specialist will want to see the ceiling space before quoting.

Servicing before the frosts. A unit that runs every winter morning collects dust fast. Our Hamilton servicing page covers timing and what to ask.

Damp that heating alone doesn't fix. If the windows still stream on June mornings with the heat pump running, the house needs moisture taken out as well. That's a job for a home ventilation specialist, once the bathroom and kitchen extractor fans are sorted.

Worth asking any Hamilton installer

  • What's this unit's heating capacity at 2 degrees, not just at 7?
  • Where will the outdoor unit go, and will it get sun and open air on a foggy morning?
  • Where does the condensate drain end up?
  • Who does the electrical connection, and when will I get the Certificate of Compliance?
  • Is this a quote or an estimate?

What we'd do

If it were our home

We'd pick the unit on its 2 degree heating figure, because that's the number a Hamilton July actually tests. We'd keep the outdoor unit out from under the deck and on the warmest wall available, such as a north or west facing one, as BRANZ suggests. And we'd want a specialist who installs heat pumps every week to size it, so it holds the room on a frosty morning instead of defrosting its way through it.

Heat pump and heating jobs in Hamilton

Areas around Hamilton

Questions people ask

Why does my heat pump stop blowing warm air on frosty Hamilton mornings?
It's probably defrosting. Mitsubishi Electric NZ says heat pumps stop heating for short periods in cold weather to clear ice off the outdoor unit, and damp air makes that happen more often. If it never seems to catch up, the unit may be too small for the room.
Is a heat pump better than a wood burner in Hamilton?
On efficiency, BRANZ calls heat pumps the most efficient form of purchased space heating commonly available. Plenty of Waikato homes run both. Our heat pump against other heating page compares them.
Can I get a Warmer Kiwi Homes grant in Hamilton?
Warmer Kiwi Homes is EECA's programme, and EECA says it makes no exceptions to its criteria. Check with EECA before you sign anything with an installer. Our Warmer Kiwi Homes guide explains how it works.
How do I find a heat pump installer in Hamilton?
Tell us the job and your postcode. Registration-checked local installers who specialise in that work can see it, and only the one who takes it gets your contact details. If none of them takes it within 48 hours, heat pump installers elsewhere in Waikato may see it as well.

Ready for the right installer to take a look in Hamilton?

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Read next

  1. 01Heat pump servicing in HamiltonWhen and how often to service a Hamilton heat pump, and what the visit should cover.
  2. 02What size heat pump do I need?How to work out the kW for a room, and why the 2 degree figure on the label matters.
  3. 03Heat pump size calculatorRoom size and insulation in, a rough heating size in kW out, using BRANZ's rule of thumb.
  4. 04Heat pump not heatingDefrost pauses, the wrong mode, dirty filters and the other reasons a heat pump blows cool air.
  5. 05Multi-room heat pumpsOne outdoor unit, several rooms: when a multi-split heat pump makes sense and what to ask first.
  6. 06Heat pump installers in WaikatoHow Hamilton's and Taupō's different winters change the heat pump a Waikato home needs.

Where this information comes from

We don't publish prices. Every home is different, so an installer's written quote is the only real number. How we write and check these pages.

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