Why standard heat pump advice doesn’t apply to older homes

Thursday, 9 July 2026

Apparently, I’ve been showering wrong for years. I’ve also been expecting too much of the heat pump in my home, and sometimes I’ve even committed the crime of drying clothes inside.

All these issues were raised with me in discussion with Julie Villard, who works for the Christchurch City Council as part of the Eco Design Adviser service, an advisory available through some councils that aims to improve the “comfort, health and performance of New Zealand homes”.

I’ve used the service in a previous house, at which time I learned I’d been directing the heat pump vanes incorrectly (up instead of down), but this time Villard is harsher about the system’s effectiveness at all in a 100-year-old house.

The house is far from airtight, she says. She likens trying to heat it with a heat pump, as we do in the kitchen/dining area, to going to some trouble preparing a meal, and then throwing half of it straight in the bin before serving it.

“Heating your house with a heat pump is the worst thing you can do for an old villa,” she says, “because your house is a sieve. It probably has between 18 and 20 air exchanges an hour.

“New build? No problem. Old villa, forget about it.”

Radiant heating is what she recommends for a house like this, and our best bet would be a pellet fire, ideally with a heat transfer system to share that with the rest of the house.

Moisture management is a big issue for many of the houses that Villard analyses, and she has many tips and tricks for managing it.

If you have crying windows in the mornings, this is a big problem, she says. “Usually we blame the windows, but that’s not the problem. When you buy them, they don’t come with condensation. Cooking, breathing, taking showers, boiling the jug… We are creating 80% of the condensation in the house.”

Drying laundry inside is the worst, she says, quoting 5L per load of moisture released into the air.

However, she’s a realist. She recognises that people are going to do it. “If you do, do it in a north-facing room, with the window open on a sunny day. And, use a dehumidifier with it. Even the little ones from Bunnings or Mitre 10 are good.“

Her surprising bathroom advice is to use a fan heater to pre-heat the room for five minutes before taking a shower.

This is not about comfort. “You can raise the temperature from 12 to 18 degrees very quickly, and at 18 degrees, the air has a huge capacity to hold moisture. You take your shower. You put the extractor on, and the air goes out.”

Villard says this has been calculated to cost $13 per person a year to do.

She also recommends shower domes, which typically cost about $500 to $600 installed.

The wooden shutters in my home may look beautiful, but they are not doing much for insulation.

“They are good for one thing,” she says; “privacy.”

She says if we use radiant energy to heat the house, they will retain some warmth. “They have a thermal mass capacity, and so will be a little bit effective reducing condensation on the windows but there are air gaps everywhere. The hot air can go behind [the shutters]. At least double-layered curtains are recommended.

Villard answered specific ways to improve this home’s liveability depending on budget:

If we wanted to spend $10,000 or less, what should we do?

She recommends more insulation in the ceiling because this is where much of the heat is lost. Aim for 400mm of insulation to get it to R5 or R6, she says.

“After that try to make the house a bit more airtight. Deal with window seals.”

And with the money left, spend $5,000 to $8,000 on a solar system. She says that even a 2.5kW system would allow for the heat pump - and many other electrical devices - to be run during the day 'for free'.

Otherwise, she says to check if the heat pump needs replacing (about every 15 years), or to consider installing small radiators.

What about spending $50,000?

I was surprised that she didn’t recommend retrofitting double glazing at this price point. “It will make the house warmer,” Villard says, “but it won’t deal with the draught issues.”

She says once again to add more ceiling insulation, deal with the draughts, and put insulation in the walls. Next on the list is a more comprehensive solar panel system, spending about $15,000 on that.

“Only after, if I have a little money left, would I deal with the windows. You don’t want to spend your whole budget on that and find ‘I’m half a degree warmer.’”

And if the budget is $100,000 or more?

Surprisingly, Villard does not recommend knocking the house down and starting again. She says houses this age have lots of charm, and BRANZ, New Zealand’s building research body, has good information about how to do a deep retrofit on older villas and bungalows.

Overcladding is one route. “That’s like putting a jacket on,” she says. “You can keep the character.”

Also recommended would be all of the above cheaper steps, including double glazing, and adding an extensive solar panel array.

Recommendations that are free or very low cost:

• Dry clothes outside, or use a vented dryer

• Clean heat pump filters (inside unit) and get them checked two yearly

• Check eligibility for a Warmer Kiwi Homes grant for insulation and heating

• Use lined curtains (even triple-lined) that go to the floor

• Always use extraction fans when cooking, showering, boiling jug

• Open bedroom windows for five minutes each morning