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Blenheim, Marlborough

Heat pumps in BlenheimClear, frosty winter nights and properly warm summers.

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Blenheim gets more sunshine than any other New Zealand town or city on NIWA's figures, and those same clear skies bring frost: Blenheim Research averages 59 ground frosts a year. A heat pump here heats through still, cold winter nights and cools on summer afternoons, so size it for both and put the outdoor unit where cold air can't settle around it.

What Blenheim's climate means for your heat pump

Sun and frost together

NIWA says Blenheim's 2,475 sunshine hours a year are the most of any New Zealand town or city, and that 59 ground frosts and 22 air frosts a year at Blenheim Research give residents a large number of fine, frosty winter days. On the 1991 to 2020 normals, July's mean daily minimum is 2.9 degrees.

Still, cold valley air

Blenheim Aero's mean wind speed of 13.5 km/h is the lowest of Marlborough's NIWA stations, thanks to its sheltered spot in the Wairau Valley. Cold air draining down the valley makes a light westerly the usual winter wind. Mitsubishi Electric NZ says the outdoor unit's location is essential for performance in the cold, so keep it out of hollows and out from under decks.

A real cooling season

NIWA gives Blenheim Research 104 cooling degree-days a year against 1,938 for heating, and Blenheim averages 34 days above 25 degrees, with January's mean daily high at 23.4. Heating still leads, but cooling counts for more here than in Nelson or Christchurch. MBIE's H1/AS1 places Marlborough District in climate zone 3 of six.

Winter wood smoke

Marlborough District Council reported that Blenheim's PM10 readings went over the limit on 16 days in 2021, the most since monitoring began in 2006, and that 90% of human-caused PM10 emissions come from home heating, mainly wood smoke. In the 2023 Census, 54.88% of Marlborough Region homes used a wood burner and 66.73% a heat pump, up from 56.59% in 2018.

Low damp, bottled gas

EHINZ puts the Nelson Marlborough health district's damp-home rate at 14.1% in 2023, the lowest in its chart. And with no natural gas reticulation in the South Island (Te Waihanga), gas heating means LPG.

The jobs Blenheim homes are likely to need

A heat pump instead of a burner. With home heating behind 90% of Blenheim's human-caused PM10, a heat pump in the lounge takes the smoke out of the equation. A replacement burner would need a building consent, and burner grants are off the table: Warmer Kiwi Homes stopped accepting them on 9 January 2026. Our heat pump and other heating comparison sets out the trade-offs.

Sizing for both seasons. EECA says that where winter nights get down to 2 degrees or less, check the heating capacity at 2 degrees is at least the figure at 7. BRANZ adds that cooling capacity is generally about 10 to 20% below heating. In Blenheim, both checks matter. See our sizing guide.

Servicing a unit that works year-round. A heat pump that heats in winter and cools in summer gets no quiet season, so stick to the brand's service interval, yearly for many. See heat pump servicing.

HRV, DVS and ventilation in a sunny town

If you searched for an HRV in Blenheim, you're after a home ventilation system. HRV and DVS are companies that sell them. The types are positive pressure, which usually blows filtered roof space air into the house, and balanced heat recovery, which swaps stale air for outside air through a heat exchanger.

Blenheim's sun warms roof spaces, and roof space systems lean on that. BRANZ is cautious, citing EECA and University of Otago research that found pumping roof space air into a house provided no heating or cooling benefit the majority of the time. On a frosty night, BRANZ says, the roof space can be colder than your rooms. With damp low here, heat the house well first, then ventilate where moisture is still a problem. Our ventilation comparison explains the types.

What we'd do

If it were our Blenheim home

We'd size the lounge heat pump on its 2 degree heating figure for those frosty valley nights, then check its cooling capacity covers a hot January afternoon. We'd keep the outdoor unit out in open air, not tucked under a deck where the cold settles. If a burner is still doing the heating, we'd get a heat pump quoted before replacing it. And before any ventilation system, we'd ask what it does at night when the roof space is cold. Send us the job when it suits you. If no Blenheim installer takes it within 48 hours, heat pump installers elsewhere in Marlborough may see it too.

Questions people ask

Is HRV the only home ventilation option in Blenheim?
HRV is one company, and DVS is another. What you're really choosing is the type: positive pressure or balanced heat recovery. A ventilation specialist will say which suits your house after looking at the joinery and the roof space.
Can I put in a new wood burner in Blenheim?
Ask Marlborough District Council first. We don't hold its current burner rules, and the council counted 15 breaches of the national PM10 standard in Blenheim in 2021. A new burner needs a building consent either way.
Will a heat pump cool my Blenheim house in summer?
It will cool the room it's in. Check the 35 degree cooling capacity for the room that overheats, because cooling usually runs below the heating figure. To cool the bedrooms as well, you'd be looking at a ducted heat pump or a multi-room heat pump.
Do heat pumps cope with Blenheim's frosty mornings?
Yes, but they pause to defrost. EECA says frosting conditions start below 5.5 degrees outside, and some units hold their output in the cold better than others, so compare the 2 and 7 degree heating figures on the label.

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Read next

  1. 01Heat pump installers in MarlboroughHeating and cooling across Marlborough: frosty valley nights, wood smoke, sea air and the national rules.
  2. 02Heat pumps compared with other heatingHow a heat pump stacks up against a wood burner, gas, electric heaters and central heating.
  3. 03What 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.
  4. 04Home ventilation systems comparedPositive pressure, balanced heat recovery and heat transfer systems, and why HRV and DVS are company names.
  5. 05Home ventilation systemsWhat a home ventilation system does, the two main types, and how to tell which one suits your house.
  6. 06Air conditioning with a heat pumpCooling with a heat pump: sizing for summer, the label's cooling figures, and night-time noise.

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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