Future living: Reduce your power bill

This article will be most helpful for people living in Aotearoa New Zealand, or areas with similar climatic conditions.

By Camilla Carty-Melis

If you live in Aotearoa New Zealand, you can have an Eco Design Advisor come to your home and carry out a free and impartial Home Performance Assessment. It supports people reduce their resource use (energy, water and waste) and improve their home's performance.

Bigger Picture

In Aotearoa New Zealand, the majority of homes perform to a very poor standard. They are cold, damp, expensive to run, and making us sick. Each year there are 1600 deaths caused or contributed to by poor housing conditions.

According to the World Health Organisation, the following temperatures lead to health implications:

  • Less than 16 degrees C affects respiratory system
  • Less than 12 degrees C affects cardiovascular system.
    (These values are for healthy adults. Children, elderly and people with illness or disabilities require at least 2 degrees warmer than these values.) 

Living areas should not fall below 18 degrees and bedrooms should not fall below 16 degrees. Yet in New Zealand, 17.9% of living rooms are colder than 18 degrees during winter months (despite active heating), and 13.6% of bedrooms are colder than 12 degrees. In addition, 55% of our homes have visible mould.

This is making people sick, but we can do a lot to avoid it. For example, it has been calculated that for every $1 you invest into insulating your home, you save $6-10 through direct cost savings (e.g. power bill) and indirect savings (e.g. lower medical bills, better school attendance and education, etc.).When designing or retrofitting a home, it is important to consider 3 factors:


If you try to cut on one, you will end up cutting on the others as well. We spend 55% of our lives in our home, so it is important to make sure we make it good.

Our energy use is divided roughly equally into

  • Spatial heating
  • Lights and appliances
  • Water heating

If we can reduce the cost involved in any of these, we simultaneously reduce our energy bill and impact on the planet.

Lowering energy needed for spatial heating?

There are two ways to go about reducing energy needs for heating:

  1. Heat the home more efficiently,
  2. Make sure heat is not lost

Heat the home efficiently

There are many different ways to heat homes. Below are some common home-heating methods ranked according to cost effectiveness. Cost effectiveness refers to how much warmth you get for how much money it costs to run.


  1. Heat pump (converts 1kW of electricity into 5kW of heat)
  2. Wood burners (they emit a lot of heat and are relatively cheap to fuel. They are even cheaper to run if you collect some of the fuel yourself)
  3. Gas heaters (flued!)
  4. Electric heaters (ones you plug into the wall, such as fan heaters, oil column, panel/ecopanel, etc.)
  5. Unflued gas heaters – these should be avoided, as they burn oxygen, release toxic gases (including carbon monoxide) and emit moisture (which makes homes damper). They have been banned in most Western countries, though unfortunately not yet in New Zealand.


Make sure heat is not lost – Insulation

Insulation slows down the movement of heat. Good materials to use for insulating have low conductivity and air pockets (as still air is highly insulating). 

R values  are used to reflect the thermal resistance of different materials. Thermal resistance is the ability of a material to keep cold things cold and hot things hot.Heat loss is motivated by temperature differentials. The larger the difference in heat, the faster the heat will move. In an uninsulated house, heat can be expected to be lost in roughly the following ways:

Insulating different places (e.g. ceiling, underfloor, etc.), reduces the overall heat loss speed. However, it is important to think about the whole thermal envelope of the house. It does not make sense to just insulate one area of the house as the heat will then just escape somewhere else. It can be likened to being naked in the cold: it helps if you put on a jacket, but to get truly warm you will also need trousers, socks, hat, etc. 3 jackets but no trousers/socks/hat is not as useful as one of each.Below are R values according to the Building Code and as recommended by Ian Mayes:

Make sure heat is not lost – Curtaining

Curtaining windows is important because windows allow a lot of heat loss. There are 4 rules to good curtaining:

  1. Curtain all glass (or cover it in some way if it is not possible to put a curtain on)
  2. Have 2 (or more) layers
  3. Stop convection currents through pelmets and having curtains to the floor
  4. Good curtain behaviour – close curtains before heat is lost, around 4pm.

The diagram below illustrates the difference between a well and poorly performing curtain: 

Lowering energy needs for lights and appliances

The way we use appliances majorly affects their energy performance, and the average household can save several hundred dollars each year by taking the following steps:

  • Switching off appliances at the wall. Appliances that use a remote or are programmable each use $20 of electricity a year by being in standby mode (this includes TVs, DVD players, internet modems, game consoles, microwaves, dishwashers, washing machines, and more). multiplug/powerstrip Each appliance that gets switched off at the wall when not in use will save $20 of electricity. TIP: Organise the appliances you want to keep on vs the ones you would like to switch off using a multiplug/powerstrip.
  • Switch to LED lightbulbs. These are more expensive to buy, but they pay for themselves within the first year and lead to hundreds of dollars worth of savings in their lifetime. TIP: You don't have to replace all bulbs in one go. Switch the bulbs you use most often first of all(kitchen and living room, then bedroom). You might want to check out this tool to calculate your savings when you replace different light bulbs, created by the EECA.

Lowering energy needs for hot water

  • If you have a hot water cylinder, insulate it with a cylinder jacket.
  • Insulate the hot water pipes leading out of the hot water cylinder as well.
  • Reduce the amount of water used in showers (as showers use the bulk of a household's hot water). This can be done by: 
    • Shortening shower length. Depending on how long your household currently showers for, and how long shower time is reduced by, there is potential for hot water usage to halve (or more) by shortening shower time. Each minute added to a person's daily shower adds up to about $70/yr. TIP: Put a 3 or 4 timer in the shower to help keep track of shower lengths. Even switching off the water while lathering and/or shaving helps reduce hot water usage.
    • Reducing water flow. You can check the flow rate of your shower head. If it is greater than 9 litres per minute, it may be good to reduce the flow rate. The video below shows how to do this with a flow restrictor, or you may wish to replace the showerhead to a more water-efficient one.

The Energywise website has many useful resources and tips to making your home energy efficient: www.energywise.govt.nz/at-home

[All statistics from BRANZ and EECA.]


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