Category Archives: General

Ducted Heat Pumps

Or, “Why the Government should subsidise central heating“.

New Zealand houses are poorly heated, by and large. Through the work of Housing New Zealand, rental standards and the upgrades initiated by homeowners of their own volition, we have made major improvements to many of them. But the standard to meet in these upgrades seems to be adding some insulation and a heat pump.

The heat pump usually goes in the living area, which if you’re lucky is open-plan and includes the kitchen and dining area, and if the doors are left open it will try to heat the rest of the house a bit – but it is not enough. Electric heaters will be used in other rooms. They don’t tend to regulate the room temperature as well as a heat pump, and they cost more to run. Unless a ventilation system is used as well, even with judicious opening of windows the home is likely to be at least a bit damp.

Our personal case study: Before

This was our experience for many years. We tried our best to keep warm because we know that a warm, dry house is healthier for us and our children. The WHO recommends rooms be heated to at least 18 degrees to maintain good health outcomes.

As for humidity, BRANZ on their website recommend an indoor humidity level of 40-60% for comfort, and on the same page references standard NZS 4303:1990 Ventilation for acceptable indoor air quality, from a health perspective.

Being a bit of a geek, I can actually look back at some data and see how we’d been doing:

Temperature, before

Humidity, before

Not that well. Over the two week period shown above, the temperature in the master bedroom is 18 degrees or greater only 56% of the time, while the humidity was 60% or less only 17% of the time, despite considerable use of electric heating and a dehumidifier.

Really, unless everyone is spending all their time in the lounge, this kind of setup is just not going to achieve the minimum recommended temperatures to say nothing of humidity, at least not without an unaffordable level of supplementary electric heating.

After installing a central heating system

We recently had a ducted heat pump central heating system installed, at a cost of just under $10,000. Within a few days, I was thinking, “every house in New Zealand should have one of these, starting with state homes”.

Let’s start with the data:

Temperature, after

Humidity, after

Now, the temperature of the master bedroom (the coldest bedroom) is above 18 degrees 98% of the time without any effort required on our part to manage this (we do turn the temperature setpoint down from 19 to 16 at night time, which we find comfortable, and that is the cause of the small oscillation seen in the temperature graph).

The humidity remains below the 60% mark 80% of the time despite no use of the dehumidifier. It seems it is very easy to keep the house dry through ventilation (opening a window occasionally) when it is well heated, even though previously this was not effective for us.

Subjectively, we noticed that the house was more comfortable due to the lack of draughts from the heat pump (which has to blow a lot more air around to do its job), and (we think) the fact that the air was kept fresher. Previously, heating the master bedroom to even 16 degrees using an electric heater made it uncomfortably stuffy, but now at 18 degrees overnight the air is pleasant.

Our electricity usage appears to have dropped slightly despite the constant whole-house heating we now enjoy. In the “before” two-week period, we used 463kWh (excluding hot water which is metered separately), while in the “after” period we used 393kWh – 15% less. This is despite the “after” period having a colder average outdoor temperature of 10.8 degrees compared to 11.6 in the “before” period. It’s worth noting that various confounding factors such as which days we happened to work from home in those periods, and our usage of our electric car, mean that this “15% reduction” is not very precise – but it probably at least rules out a significant increase.

Policy Suggestions

Although I am not under a great illusion that Ministers are reading this blog post and forming policy based on it, I just could not leave these thoughts unpublished. I can see several opportunities to steer the country in a really helpful direction through some policy tweaks.

State Homes

There are about 66,000 state homes in New Zealand managed by Kāinga Ora. For various good reasons, successive governments have sought to progressively upgrade this housing stock, for example by adding insulation.

I suggest that it is worth considering the health benefits that could be achieved, over and above existing planned upgrades, by installing ducted heat pump systems in state homes. This would be effective at keeping vulnerable kids warm at night to a far greater extent than a heat pump in the living room and good insulation (which is great, but inadequate by itself if there is not sufficient heating on a cold night).

It would also be a great “shovel ready project”, with several days worth of work required for each installation.

Rental Homes

The Government has also recently introduced the Healthy Home Standards, which landlords will soon have to comply with. Many will be installing heat pumps and ventilation systems, when for a few thousand dollars more a vastly superior option could be achieved.

This is the prime opportunity for the Government to help by subsidising central heating systems (particularly favouring systems such as ducted heat pumps which do not rely on fossil fuels). That will create a far better outcome for tenants, improve the housing stock dramatically, and the subsidy will also help to soothe landlords who feel attacked by these standards.

Private Homes

Even in private homes there is merit in subsidising this option to promote it. This is a time where many homeowners are installing heat pumps and ventilation systems. Some people install more than one heat pump, and spend more than $5,000 on a ventilation system when they could, for the same or only a slightly greater amount of money, achieve far greater comfort and health benefits.

A small subsidy of even $1,000 would help to tip the scales a little in favour of an option that is better for the homeowner and for future occupants.

Gas vs Electricity

For those who do choose to install central heating today, gas central heating seems to be a popular option. Given the government’s commitment to getting New Zealand to a carbon neutral position by 2050, and our decision to cease offshore gas exploration, it seems to me that energy-intensive, long-term gas appliances such as central heating systems and instant hot water heaters should be discouraged in favour of electric or other options that can be carbon-neutral.

About Me

I’m a software engineer with a passion for making cool stuff that solves problems. Cool stuff doesn’t necessarily mean software.

Sometimes it’s software, sometimes it’s hardware, sometimes it’s a bit of both and sometimes it’s made of wood.

I’ve decided to start writing this in case some of my projects are interesting to people. Coming up will be write-ups on my in-dash Nexus 7 installation, my home automation system (it controls our heat pump and a few other things), and maybe a few little apps…