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Be passive

15 June 2021
view of living room in home
View of living room in home

Harnessing the warmth from the sun to heat your home can have a positive effect in that it reduces dampness and condensation while also reducing heating costs. The key to passive heating is two-fold. First, you need to capture the right amount of sunlight through your windows, and then you need to manage that source of free heat within your home so it is kept at a pleasant temperature. This is achieved by using a combination of smart design and good insulation, which in turn reduces overheating.

storage decking on top of fiberglass roof insulating material in attic

New & old

With a new build, one of the key factors is the orientation of the home to maximise efficiency for heating in winter and cooling in summer. You need to make sure you get plenty of sun streaming in during winter, for instance. To do this, you need to make sure your home is designed to maximise the sun’s warmth by having north-facing windows. You also need to look at the natural environment. Are there neighbouring trees or buildings that could block the sun?
Passive heating can be improved in an existing home without making major alterations. The most common way is to insulate the roof cavity. I’m a fan of doing double or triple layers in this area, up to 30cm, because it makes a major difference. Make sure you insulate under the floor too. If you are relining walls, do consider double insulating these – it makes a tremendous difference to the amount of heat you lose from the home.

Transfer it

If you are renovating, consider installing a heat transfer system. These are specifically designed to use excess heat and send it around the home to make it a cosy temperature throughout. This means that when the sun is warming up your north-facing room, you can send that heat to the cooler rooms. It is also good for those who have heating in a main room, like a gas or wood fire.An underutilised source of heating is a home’s roof cavity – particularly if it’s an older home where the building’s orientation to the sun wasn’t always a consideration. Transferring the heat from the roof cavity into a living area or such is a wonderful way to use this heat, especially on a frosty day when the sky is blue and sunny.

empty window sill

Get glazed

Double glazing is two panes of glass with an insulating layer of inert gas or air between them. Installing double glazing can help reduce heat loss through glass by about 70 per cent, which means that the sun’s warmth stays around in your home instead of disappearing through the window. It also means you have less condensation on your window panes because the seal stops it from building up.
Framing is important – plastic or wood are less likely to attract condensation than aluminium frames. If you have an older home, you can get double glazing retrofitted.

pouf and tent in bright kid's bedroom interior with drapes at window and blanket on blue bed. real photo

Trap it in

Trap in the heat of the sun with good curtains or blinds. If you do it right, you can stop nearly two-thirds of your heat from disappearing out the window. Keep your curtains open during the day to make the most of the sun and close them as soon as the sun sets to trap that heat in.
It is best to opt for well-interlined drapes, shutters or honeycomb blinds (they have fabric cells that trap air, acting like insulation) over a Venetian or roller blind. According to a Consumer NZ test, honeycomb blinds are a ‘star performer’ because they retain more than 60 per cent of the heat lost through a window.


  • Make sure your curtains are lined for extra insulation. The extra layer acts as an air trap. It has been reported that lined curtains are more effective than thermal-backed curtains.
  • Make sure your curtains are floor-length and wider than your window frame. Curtains that are not sealed at the top or bottom create a ‘reverse chimney’. When it is cold outside, the air by the window pane cools and goes to the bottom of the window, where it gets replaced by warmer air from the room – creating an air current that chills the room.
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